Repairing Electrostatic Filters in AC Systems

Repairing Electrostatic Filters in AC Systems

heating

Common Issues with Electrostatic Filters in HVAC Systems



Electrostatic filters in HVAC systems are a popular choice for many homeowners and businesses due to their ability to effectively capture dust, pollen, and other airborne particles. A sudden rise in your energy bills could mean it’s time for HVAC Repair Air conditioning service to enhance your air cooling efficiency and comfort. These filters work by using an electrostatic charge to attract and trap particles, preventing them from recirculating through the air. However, like any component of an HVAC system, electrostatic filters can encounter issues that may require repair or maintenance.


Repairing Electrostatic Filters in AC Systems - Bayou La Batre

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One common issue with electrostatic filters is reduced efficiency over time. As these filters accumulate dirt and debris, their ability to generate an effective electrostatic charge diminishes. This reduction in performance can lead to poorer air quality within the space being serviced. To address this problem, regular cleaning is essential. Most manufacturers recommend washing the filter every one to three months, depending on usage and environmental conditions. Proper cleaning involves removing the filter from the unit and rinsing it thoroughly with water before allowing it to dry completely.

Another frequent problem is physical damage to the filter itself. The delicate nature of some electrostatic filter materials means they can be easily damaged during handling or cleaning. Tears or punctures in the filter material compromise its ability to capture particles effectively. If damage occurs, it's often necessary to replace the entire filter rather than attempting repairs that could further reduce its effectiveness.

In addition to mechanical issues, electrical problems can also arise with electrostatic filters. Since these devices rely on an electrical charge for operation, any failure in their power supply or internal electronics can render them ineffective. Troubleshooting electrical issues typically requires checking connections for signs of corrosion or disconnection and ensuring that all components receive adequate power.

Moreover, improper installation of electrostatic filters may lead to inefficiencies in airflow and particle capture capabilities. Ensuring correct placement within the HVAC system's ductwork is crucial for optimal performance; even minor misalignments can significantly impact overall efficiency.

Finally, compatibility issues between older HVAC systems and modern electrostatic filters might pose challenges during replacement or upgrade processes. It's important to ensure that any new filter fits properly within existing equipment specifications without causing undue strain on motors or other components.

In conclusion, while electrostatic filters offer several advantages regarding indoor air quality improvement compared with traditional filtration methods-such as enhanced particle retention capabilities-they do come with certain maintenance requirements critical for sustained functionality over time: routine cleaning schedules need adherence alongside prompt attention towards potential damages (both physical/electrical). Additionally addressing compatibility concerns ensures long-term cost-effectiveness when integrating updated technologies into pre-existing infrastructure setups thereby maximizing return-on-investment outcomes associated across broad-spectrum applications involving residential/commercial settings alike!

Diagnosing Problems with Electrostatic Filters



Diagnosing problems with electrostatic filters in air conditioning (AC) systems is a crucial task for ensuring optimal performance and maintaining indoor air quality. These filters are specifically designed to capture small particles such as dust, pollen, and smoke by using an electric charge. However, like any component of an AC system, they can encounter issues that necessitate careful diagnosis and repair.

The first step in diagnosing problems with electrostatic filters is understanding the symptoms indicating that something might be amiss. Common signs include reduced airflow through the AC system, unusual noises during operation, increased energy consumption, or diminished effectiveness at removing airborne contaminants. If any of these symptoms are present, it may indicate that the filter requires attention.

One possible issue could be clogging due to excessive accumulation of dirt and debris on the filter plates. Although electrostatic filters are efficient at attracting particles, over time they can become saturated if not cleaned regularly. This buildup restricts airflow and reduces the efficiency of both the filter and the overall AC system. Regular maintenance checks should involve inspecting these plates for visible dirt or residue and cleaning them as necessary according to manufacturer instructions.

Another potential problem could lie within the power supply to the filters themselves. Electrostatic filters require a continuous electrical charge to function effectively; hence any disruption in this supply can lead to malfunctioning. Technicians should ensure that all electrical connections are secure and inspect components such as transformers or capacitors for signs of wear or failure.

Furthermore, physical damage to filter components can also impact performance. The delicate nature of some parts means they can be easily damaged during handling or routine maintenance tasks. Bent plates or broken frames compromise their ability to generate an effective electrostatic field needed for particle attraction.

Additionally, diagnosing problems often involves assessing external factors affecting filter performance-such as humidity levels within indoor environments-which directly impacts how well particulates adhere onto charged surfaces inside these devices.

In conclusion, diagnosing issues with electrostatic filters in AC systems demands a thorough understanding of both mechanical operations involved as well its interaction with environmental conditions surrounding them too! Identifying common symptoms early on allows timely intervention preventing more significant failures while preserving comfortable living spaces free from pollutants alike! Regular inspections combined knowledgeable troubleshooting techniques will ultimately extend lifespan promote healthier outcomes across board!

Citations and other links

Steps for Repairing Damaged or Malfunctioning Filters

Steps for Repairing Damaged or Malfunctioning Filters



Repairing damaged or malfunctioning electrostatic filters in air conditioning (AC) systems is a crucial task that ensures efficient airflow and maintains indoor air quality. These filters play a vital role in trapping airborne particles, dust, and pollutants, thereby improving the overall performance of AC units. When these filters become damaged or malfunction, it can lead to decreased efficiency and potential health risks. To address these issues effectively, one must follow a systematic approach.

The first step in repairing electrostatic filters is diagnosis. Identifying the problem accurately is essential before proceeding with any repair work. This involves inspecting the filter for visible damage such as tears, holes, or warping. It is also important to check for signs of reduced effectiveness like increased dust accumulation on surfaces or unusual noises from the AC system. If the filter appears clogged or excessively dirty despite regular cleaning, this could indicate a deeper issue requiring attention.

Once the problem has been identified, the next step is cleaning and maintenance. Electrostatic filters are reusable and designed to be cleaned rather than replaced frequently. Begin by turning off the AC unit to ensure safety during maintenance work. Carefully remove the filter following manufacturer instructions to avoid causing further damage. Use a vacuum cleaner with a soft brush attachment to gently remove loose dirt and debris from both sides of the filter.

For more thorough cleaning, rinse the filter under running water using mild soap if necessary. It's important not to use harsh chemicals or abrasive materials that could damage the delicate components of the electrostatic filter. Allow it to dry completely before reinstalling it back into the AC unit; moisture can promote mold growth and reduce filtration effectiveness.

In cases where cleaning does not resolve issues such as physical damage or persistent malfunctions, repairs might be needed. Repairing minor tears or holes can often be done using adhesive patches specifically designed for this purpose-available at most hardware stores-or applying silicone sealant for small perforations.

However, if major structural damage exists or if previous repairs have failed repeatedly, replacement may be necessary despite initial reluctance due to cost considerations involved with purchasing new parts versus maintaining existing ones over time through regular upkeep practices alone being insufficient long term solution viability wise speaking from practical standpoint logically furthermore always considering environmental impact factor too whenever possible opting sustainable choices wherever feasible within budget constraints imposed upon project scope limitations duly noted accordingly so forth thus ensuring optimal outcomes achieved consistently across board holistically addressing myriad concerns simultaneously thereby maximizing efficiency ultimately achieving desired results satisfactorily fulfilling objectives set forth originally intended goals strategically aligned mission vision values organizational context terms reference agreed stipulated therein aforementioned documentation guidelines policies procedures standardized best practice protocols industry benchmarks standards compliance regulatory requirements statutory obligations mandated relevant authorities governing jurisdiction applicable thereto subject matter area expertise domain specialization knowledge competence proficiency skillset acquired developed honed cultivated nurtured refined enhanced continuously lifelong learning journey pursuit excellence mastery craft art science technology innovation advancement progress evolution transformation future readiness preparedness adaptability resilience agility flexibility dynamism responsiveness proactive anticipatory foresight insight wisdom pragmatism realism practicality commonsense sound judgement discernment astuteness acumen savvy shrewdness perceptiveness awareness understanding comprehension grasp cognition intelligence aptitude capability capacity potential talent knack flair genius brilliance ingenuity creativity imagination originality inventiveness resourcefulness cleverness wit humor charm charisma personality character integrity honesty trustworthiness reliability dependability responsibility accountability transparency openness sincerity authenticity genuineness empathy compassion kindness generosity altruism benevolence goodwill cooperation collaboration teamwork partnership synergy mutual benefit reciprocity win-win scenario situation environment ecosystem habitat niche biome biosphere planet earth universe cosmos existence life itself precious sacred invaluable cherished beloved treasure gift blessing miracle wonder mystery awe inspiration aspiration ambition

Steps for Repairing Damaged or Malfunctioning Filters
Tools and Materials Needed for Filter Repair

Tools and Materials Needed for Filter Repair

Tools and Materials Needed for Filter Repair



Repairing electrostatic filters in AC systems is a crucial maintenance task that ensures the efficiency and longevity of air conditioning units. These filters play an essential role in purifying the air by using static electricity to trap dust and other airborne particles, thereby improving indoor air quality. To effectively repair and maintain these filters, specific tools and materials are required.

Firstly, one must have a basic set of hand tools at their disposal. This includes screwdrivers, pliers, and wrenches, which are necessary for disassembling parts of the AC unit to access the filter. A screwdriver set with various types and sizes is particularly useful since different models may use different screws. Pliers are helpful for gripping and pulling out components safely without causing damage.

Next on the list of essentials is a multimeter or a voltage tester. These devices are crucial for ensuring that power to the AC system has been completely shut off before any repair work begins. Safety cannot be overemphasized when dealing with electrical appliances; thus, confirming there is no live current prevents potential electric shock.

Cleaning materials are also vital when repairing electrostatic filters. Since these filters rely on an electrical charge to capture particles, they can become less effective as they accumulate dust over time. A soft brush or vacuum cleaner can be used to remove loose dirt from the filter surface gently. For a more thorough clean, mild detergent mixed with warm water can help remove stubborn grime without damaging the filter's delicate structure.

Replacement parts may also be needed depending on the state of the filter being repaired. Sometimes it might be more cost-effective to replace certain components rather than attempt to fix them. Having spare parts such as new filter media or ionizing wires can expedite repairs if these elements are worn out beyond repair.

In addition to physical tools and replacement parts, having access to technical manuals or manufacturer guides specific to your AC system model is invaluable. These documents provide detailed instructions on how to safely dismantle units, identify issues within electrostatic filters, and correctly reassemble everything post-repair.

Lastly, proper personal protective equipment (PPE) should never be overlooked when performing any repair work on electrostatic filters in AC systems. Gloves protect hands from sharp edges and components while safety goggles prevent debris from entering eyes during cleaning processes.

In conclusion, repairing electrostatic filters requires not just technical know-how but also an array of specialized tools and materials designed for both efficiency and safety.

Repairing Electrostatic Filters in AC Systems - heating

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By equipping oneself with appropriate hand tools, cleaning supplies, spare parts, technical documentation, and PPE gear - one ensures that maintenance tasks are performed effectively while extending both filter life span and overall performance of AC systems.

Safety Precautions During Repair Processes

Safety Precautions During Repair Processes



Repairing electrostatic filters in air conditioning systems requires meticulous attention to safety precautions to ensure the wellbeing of technicians and the efficient functioning of the equipment. Electrostatic filters are critical components that help maintain indoor air quality by removing dust, pollen, and other airborne particles. However, they can pose certain risks during repair processes if proper safety measures are not followed.

Firstly, one of the primary safety precautions is ensuring that the power supply to the AC system is completely turned off before beginning any repair work. This prevents accidental electric shocks which can occur due to residual charges in electrostatic filters. It's advisable for technicians to use a voltage tester to confirm that there is no live electricity flowing before proceeding with repairs.

Wearing appropriate personal protective equipment (PPE) such as insulated gloves and safety goggles is another essential precaution. Insulated gloves protect against potential electrical hazards, while safety goggles shield eyes from dust or debris dislodged during cleaning or dismantling processes. Additionally, wearing long sleeves and pants can further reduce exposure to any sharp edges or sudden sparks.

Proper ventilation in the workspace is crucial when repairing electrostatic filters. Although most modern AC units are designed with user-friendly features, older models might release harmful particles when opened for maintenance. Ensuring adequate ventilation helps disperse these particles and reduces inhalation risks.

Using tools specifically designed for electrical work can also enhance safety levels during repairs. Non-conductive screwdrivers and pliers prevent accidental short circuits when handling filter components. Moreover, keeping tools organized and within easy reach minimizes distractions and allows technicians to focus on their tasks without unnecessary interruptions.

Another significant precaution involves understanding the technical specifications of each electrostatic filter model being repaired. Technicians should familiarize themselves with manufacturer guidelines regarding disassembly procedures and component compatibility to avoid damaging sensitive parts or voiding warranties unintentionally.

Training plays a vital role in maintaining high safety standards during repair processes involving electrostatic filters in AC systems. Regular workshops and certification programs keep technicians updated on best practices and emerging technologies related to HVAC systems' maintenance and repair.

In conclusion, prioritizing safety precautions when repairing electrostatic filters is paramount for safeguarding both personnel involved in maintenance activities as well as preserving optimal performance levels within AC units themselves. By adhering strictly to recommended guidelines-such as ensuring power shutdowns prior commencing work; wearing suitable PPE; utilizing correct tools; ventilating workspaces adequately-and staying informed through ongoing education programs-technicians create safer environments conducive successful repair outcomes every time they engage such tasks professionally responsibly diligently consistently across all scenarios encountered fieldwork assignments alike worldwide today tomorrow beyond!

Maintenance Tips to Prevent Future Issues
Maintenance Tips to Prevent Future Issues

Maintenance Tips to Prevent Future Issues



Maintaining electrostatic filters in air conditioning (AC) systems is crucial for ensuring optimal performance, enhancing indoor air quality, and extending the lifespan of the system. These filters are designed to capture dust, pollen, and other airborne particles using an electric charge, making them highly efficient compared to traditional filters. However, like any component of an AC system, they require regular maintenance to function effectively and prevent potential issues down the line.

One of the fundamental tips for maintaining electrostatic filters is regular cleaning. Unlike disposable filters that need replacement every few months, electrostatic filters are reusable but must be cleaned consistently. It's recommended to clean them at least once a month during peak usage seasons such as summer or winter when the AC system operates more frequently. To clean these filters, gently remove them from the unit and rinse with lukewarm water. Avoid using high-pressure sprays or harsh chemicals as these can damage the delicate components of the filter. Allowing them to dry completely before reinserting them into the AC unit is essential to avoid mold growth or damage.

Inspecting the condition of electrostatic filters periodically is another important step in their maintenance routine. Over time, wear and tear might occur due to constant exposure to airflow and particles. Look for signs of physical damage such as tears or bends in the mesh material. If any damage is evident, replacing rather than attempting repairs may be necessary since compromised filters can lead to reduced efficiency and potentially harm other parts of your HVAC system.

Keeping a close eye on airflow efficiency can also indicate when maintenance is needed. A decrease in airflow could signify that your filter is clogged with debris even if it appears clean upon inspection; this could happen if particles have accumulated deeply within its layers over time without adequate cleaning.



Repairing Electrostatic Filters in AC Systems - heating

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Additionally, maintaining overall cleanliness around your AC unit contributes significantly to preventing issues with electrostatic filters. Ensure that there are no obstacles blocking vents or ducts which could cause excessive strain on your system's operation leading up towards filter congestion faster than usual intervals would suggest otherwise necessary actions take place promptly avoiding unnecessary complications later stages arise unexpectedly causing further inconveniences not initially anticipated beforehand properly addressed earlier stages instead proactive measures implemented timely manner accordingly results more favorable outcomes achieved ultimately longer-term perspectives considered appropriately taken account right outset itself proactively managed throughout duration continued use engagement involved all stakeholders concerned interested parties alike benefit mutually cooperative efforts combined collectively contribute shared objectives common goals unified vision success sustainability future endeavors pursued wholeheartedly sincere commitment dedication determination unwavering resolve achieve desired results fully realized comprehensive manner possible fullest extent capabilities resources available hand disposal efficiently effectively maximized optimized meet exceed expectations set forth originally intended purpose design meeting needs demands requirements evolving circumstances changing conditions environmental factors external influences internal dynamics affect impact processes procedures operations functioning ongoing basis continuously monitored evaluated assessed adjusted revised improved refined betterment improvement progressive advancement development transformation evolution innovation adaptation change progress forward momentum drive initiative leadership guidance support collaboration teamwork partnership cooperation communication coordination integration harmonization alignment synergy positive outcome realization manifestation expression final form completion fruition attainment fulfillment satisfaction accomplishment achievement excellence superiority distinction prestige honor recognition respect admiration esteem appreciation gratitude acknowledgment worth value significance importance relevance necessity urgency priority emphasis focus concentration attention devotion passion enthusiasm vigor vitality energy effort investment input contribution participation involvement dedication loyalty allegiance fidelity faith trust confidence assurance certainty guarantee reliability dependability consistency stability security predictability continuity permanence durability resilience robustness strength fortitude endurance perseverance persistence tenacity steadfastness resolution firmness commitment obligation responsibility duty accountability charge custody guardianship stewardship care protection safeguarding defense preservation conservation survival thriving flourishing prospering succeeding prevailing excelling outstanding surpassing exceeding outperforming outshining eclipsing transcending elevating uplifting inspiring motivating encouraging

 

An air filter being cleaned

Indoor air quality (IAQ) is the air quality within buildings and structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also been linked to sick building syndrome, respiratory issues, reduced productivity, and impaired learning in schools. Common pollutants of indoor air include: secondhand tobacco smoke, air pollutants from indoor combustion, radon, molds and other allergens, carbon monoxide, volatile organic compounds, legionella and other bacteria, asbestos fibers, carbon dioxide,[1] ozone and particulates.

Source control, filtration, and the use of ventilation to dilute contaminants are the primary methods for improving indoor air quality. Although ventilation is an integral component of maintaining good indoor air quality, it may not be satisfactory alone.[2] In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary.[3]

IAQ is evaluated through collection of air samples, monitoring human exposure to pollutants, analysis of building surfaces, and computer modeling of air flow inside buildings. IAQ is part of indoor environmental quality (IEQ), along with other factors that exert an influence on physical and psychological aspects of life indoors (e.g., lighting, visual quality, acoustics, and thermal comfort).[4]

Indoor air pollution is a major health hazard in developing countries and is commonly referred to as "household air pollution" in that context.[5] It is mostly relating to cooking and heating methods by burning biomass fuel, in the form of wood, charcoal, dung, and crop residue, in indoor environments that lack proper ventilation. Millions of people, primarily women and children, face serious health risks. In total, about three billion people in developing countries are affected by this problem. The World Health Organization (WHO) estimates that cooking-related indoor air pollution causes 3.8 million annual deaths.[6] The Global Burden of Disease study estimated the number of deaths in 2017 at 1.6 million.[7]

Definition

[edit]

For health reasons it is crucial to breathe clean air, free from chemicals and toxicants as much as possible. It is estimated that humans spend approximately 90% of their lifetime indoors[8] and that indoor air pollution in some places can be much worse than that of the ambient air.[9][10]

Various factors contribute to high concentrations of pollutants indoors, ranging from influx of pollutants from external sources, off-gassing by furniture, furnishings including carpets, indoor activities (cooking, cleaning, painting, smoking, etc. in homes to using office equipment in offices), thermal comfort parameters such as temperature, humidity, airflow and physio-chemical properties of the indoor air.[citation needed] Air pollutants can enter a building in many ways, including through open doors or windows. Poorly maintained air conditioners/ventilation systems can harbor mold, bacteria, and other contaminants, which are then circulated throughout indoor spaces, contributing to respiratory problems and allergies.

There have been many debates among indoor air quality specialists about the proper definition of indoor air quality and specifically what constitutes "acceptable" indoor air quality.

Health effects

[edit]
Share of deaths from indoor air pollution. Darker colors mean higher numbers.

IAQ is significant for human health as humans spend a large proportion of their time in indoor environments. Americans and Europeans on average spend approximately 90% of their time indoors.[11][12]

The World Health Organization (WHO) estimates that 3.2 million people die prematurely every year from illnesses attributed to indoor air pollution caused by indoor cooking, with over 237 thousand of these being children under 5. These include around an eighth of all global ischaemic heart disease, stroke, and lung cancer deaths. Overall the WHO estimated that poor indoor air quality resulted in the loss of 86 million healthy life years in 2019.[13]

Studies in the UK and Europe show exposure to indoor air pollutants, chemicals and biological contamination can irritate the upper airway system, trigger or exacerbate asthma and other respiratory or cardiovascular conditions, and may even have carcinogenic effects.[14][15][16][17][18][19]

Poor indoor air quality can cause sick building syndrome. Symptoms include burning of the eyes, scratchy throat, blocked nose, and headaches.[20]

Common pollutants

[edit]

Generated by indoor combustion

[edit]
a 3-stone stove
A traditional wood-fired 3-stone stove in Guatemala, which causes indoor air pollution

Indoor combustion, such as for cooking or heating, is a major cause of indoor air pollution and causes significant health harms and premature deaths. Hydrocarbon fires cause air pollution. Pollution is caused by both biomass and fossil fuels of various types, but some forms of fuels are more harmful than others.

Indoor fire can produce black carbon particles, nitrogen oxides, sulfur oxides, and mercury compounds, among other emissions.[21] Around 3 billion people cook over open fires or on rudimentary cook stoves. Cooking fuels are coal, wood, animal dung, and crop residues.[22] IAQ is a particular concern in low and middle-income countries where such practices are common.[23]

Cooking using natural gas (also called fossil gas, methane gas or simply gas) is associated with poorer indoor air quality. Combustion of gas produces nitrogen dioxide and carbon monixide, and can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases.[24][25]

Carbon monoxide

[edit]

One of the most acutely toxic indoor air contaminants is carbon monoxide (CO), a colourless and odourless gas that is a by-product of incomplete combustion. Carbon monoxide may be emitted from tobacco smoke and generated from malfunctioning fuel burning stoves (wood, kerosene, natural gas, propane) and fuel burning heating systems (wood, oil, natural gas) and from blocked flues connected to these appliances.[26] In developed countries the main sources of indoor CO emission come from cooking and heating devices that burn fossil fuels and are faulty, incorrectly installed or poorly maintained.[27] Appliance malfunction may be due to faulty installation or lack of maintenance and proper use.[26] In low- and middle-income countries the most common sources of CO in homes are burning biomass fuels and cigarette smoke.[27]

Health effects of CO poisoning may be acute or chronic and can occur unintentionally or intentionally (self-harm). By depriving the brain of oxygen, acute exposure to carbon monoxide may have effects on the neurological system (headache, nausea, dizziness, alteration in consciousness and subjective weakness), the cardiovascular and respiratory systems (myocardial infarction, shortness of breath, or rapid breathing, respiratory failure). Acute exposure can also lead to long-term neurological effects such as cognitive and behavioural changes. Severe CO poisoning may lead to unconsciousness, coma and death. Chronic exposure to low concentrations of carbon monoxide may lead to lethargy, headaches, nausea, flu-like symptoms and neuropsychological and cardiovascular issues.[28][26]

The WHO recommended levels of indoor CO exposure in 24 hours is 4 mg/m3.[29] Acute exposure should not exceed 10 mg/m3 in 8 hours, 35 mg/m3 in one hour and 100 mg/m3 in 15 minutes.[27]

Secondhand tobacco smoke

[edit]

Secondhand smoke is tobacco smoke which affects people other than the 'active' smoker. It is made up of the exhaled smoke (15%) and mostly of smoke coming from the burning end of the cigarette, known as sidestream smoke (85%).[30]

Secondhand smoke contains more than 7000 chemicals, of which hundreds are harmful to health.[30] Secondhand tobacco smoke includes both a gaseous and a particulate materials which, with particular hazards arising from levels of carbon monoxide and very small particulates (fine particulate matter, especially PM2.5 and PM10) which get into the bronchioles and alveoles in the lung.[31] Inhaling secondhand smoke on multiple occasions can cause asthma, pneumonia, lung cancer, and sudden infant death syndrome, among other conditions.[32]

Thirdhand smoke (THS) refers to chemicals that settle on objects and bodies indoors after smoking. Exposure to thirdhand smoke can happen even after the actual cigarette smoke is not present anymore and affect those entering the indoor environment much later. Toxic substances of THS can react with other chemicals in the air and produce new toxic chemicals that are otherwise not present in cigarettes.[33]

The only certain method to improve indoor air quality as regards secondhand smoke is to eliminate smoking indoors.[34] Indoor e-cigarette use also increases home particulate matter concentrations.[35]

Particulates

[edit]

Atmospheric particulate matter, also known as particulates, can be found indoors and can affect the health of occupants. Indoor particulate matter can come from different indoor sources or be created as secondary aerosols through indoor gas-to-particle reactions. They can also be outdoor particles that enter indoors. These indoor particles vary widely in size, ranging from nanomet (nanoparticles/ultrafine particles emitted from combustion sources) to micromet (resuspensed dust).[36] Particulate matter can also be produced through cooking activities. Frying produces higher concentrations than boiling or grilling and cooking meat produces higher concentrations than cooking vegetables.[37] Preparing a Thanksgiving dinner can produce very high concentrations of particulate matter, exceeding 300 μg/m3.[38]

Particulates can penetrate deep into the lungs and brain from blood streams, causing health problems such as heart disease, lung disease, cancer and preterm birth.[39]

Generated from building materials, furnishing and consumer products

[edit]

Volatile organic compounds

[edit]

Volatile organic compounds (VOCs) include a variety of chemicals, some of which may have short- and long-term adverse health effects. There are numerous sources of VOCs indoors, which means that their concentrations are consistently higher indoors (up to ten times higher) than outdoors.[40] Some VOCs are emitted directly indoors, and some are formed through the subsequent chemical reactions that can occur in the gas-phase, or on surfaces.[41][42] VOCs presenting health hazards include benzene, formaldehyde, tetrachloroethylene and trichloroethylene.[43]

VOCs are emitted by thousands of indoor products. Examples include: paints, varnishes, waxes and lacquers, paint strippers, cleaning and personal care products, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.[44] Chlorinated drinking water releases chloroform when hot water is used in the home. Benzene is emitted from fuel stored in attached garages.

Human activities such as cooking and cleaning can also emit VOCs.[45][46] Cooking can release long-chain aldehydes and alkanes when oil is heated and terpenes can be released when spices are prepared and/or cooked.[45] Leaks of natural gas from cooking appliances have been linked to elevated levels of VOCs including benzene in homes in the USA.[47] Cleaning products contain a range of VOCs, including monoterpenes, sesquiterpenes, alcohols and esters. Once released into the air, VOCs can undergo reactions with ozone and hydroxyl radicals to produce other VOCs, such as formaldehyde.[46]

Health effects include eye, nose, and throat irritation; headaches, loss of coordination, nausea; and damage to the liver, kidney, and central nervous system.[48]

Testing emissions from building materials used indoors has become increasingly common for floor coverings, paints, and many other important indoor building materials and finishes.[49] Indoor materials such as gypsum boards or carpet act as VOC 'sinks', by trapping VOC vapors for extended periods of time, and releasing them by outgassing. The VOCs can also undergo transformation at the surface through interaction with ozone.[42] In both cases, these delayed emissions can result in chronic and low-level exposures to VOCs.[50]

Several initiatives aim to reduce indoor air contamination by limiting VOC emissions from products. There are regulations in France and in Germany, and numerous voluntary ecolabels and rating systems containing low VOC emissions criteria such as EMICODE,[51] M1,[52] Blue Angel[53] and Indoor Air Comfort[54] in Europe, as well as California Standard CDPH Section 01350[55] and several others in the US. Due to these initiatives an increasing number of low-emitting products became available to purchase.

At least 18 microbial VOCs (MVOCs) have been characterised[56][57] including 1-octen-3-ol (mushroom alcohol), 3-Methylfuran, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone, 3-octanol, 2-octen-1-ol, 1-octene, 2-pentanone, 2-nonanone, borneol, geosmin, 1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, and thujopsene. The last four are products of Stachybotrys chartarum, which has been linked with sick building syndrome.[56]

Asbestos fibers

[edit]

Many common building materials used before 1975 contain asbestos, such as some floor tiles, ceiling tiles, shingles, fireproofing, heating systems, pipe wrap, taping muds, mastics, and other insulation materials. Normally, significant releases of asbestos fiber do not occur unless the building materials are disturbed, such as by cutting, sanding, drilling, or building remodelling. Removal of asbestos-containing materials is not always optimal because the fibers can be spread into the air during the removal process. A management program for intact asbestos-containing materials is often recommended instead.

When asbestos-containing material is damaged or disintegrates, microscopic fibers are dispersed into the air. Inhalation of asbestos fibers over long exposure times is associated with increased incidence of lung cancer, mesothelioma, and asbestosis. The risk of lung cancer from inhaling asbestos fibers is significantly greater for smokers. The symptoms of disease do not usually appear until about 20 to 30 years after the first exposure to asbestos.

Although all asbestos is hazardous, products that are friable, e.g. sprayed coatings and insulation, pose a significantly higher hazard as they are more likely to release fibers to the air.[58]

Microplastics

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Microplastic is a type of airborne particulates and is found to prevail in air.[59][60][61][62] A 2017 study found indoor airborne microfiber concentrations between 1.0 and 60.0 microfibers per cubic meter (33% of which were found to be microplastics).[63] Airborne microplastic dust can be produced during renovation, building, bridge and road reconstruction projects[64] and the use of power tools.[65]

Ozone

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Indoors ozone (O3) is produced by certain high-voltage electric devices (such as air ionizers), and as a by-product of other types of pollution. It appears in lower concentrations indoors than outdoors, usually at 0.2-0.7 of the outdoor concentration.[66] Typically, most ozone is lost to surface reactions indoors, rather than to reactions in air, due to the large surface to volume ratios found indoors.[67]

Outdoor air used for ventilation may have sufficient ozone to react with common indoor pollutants as well as skin oils and other common indoor air chemicals or surfaces. Particular concern is warranted when using "green" cleaning products based on citrus or terpene extracts, because these chemicals react very quickly with ozone to form toxic and irritating chemicals[46] as well as fine and ultrafine particles.[68] Ventilation with outdoor air containing elevated ozone concentrations may complicate remediation attempts.[69]

The WHO standard for ozone concentration is 60 μg/m3 for long-term exposure and 100 μg/m3 as the maximum average over an 8-hour period.[29] The EPA standard for ozone concentration is 0.07 ppm average over an 8-hour period.[70]

Biological agents

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Mold and other allergens

[edit]

Occupants in buildings can be exposed to fungal spores, cell fragments, or mycotoxins which can arise from a host of means, but there are two common classes: (a) excess moisture induced growth of mold colonies and (b) natural substances released into the air such as animal dander and plant pollen.[71]

While mold growth is associated with high moisture levels,[72] it is likely to grow when a combination of favorable conditions arises. As well as high moisture levels, these conditions include suitable temperatures, pH and nutrient sources.[73] Mold grows primarily on surfaces, and it reproduces by releasing spores, which can travel and settle in different locations. When these spores experience appropriate conditions, they can germinate and lead to mycelium growth.[74] Different mold species favor different environmental conditions to germinate and grow, some being more hydrophilic (growing at higher levels of relative humidity) and other more xerophilic (growing at levels of relative humidity as low as 75–80%).[74][75]

Mold growth can be inhibited by keeping surfaces at conditions that are further from condensation, with relative humidity levels below 75%. This usually translates to a relative humidity of indoor air below 60%, in agreement with the guidelines for thermal comfort that recommend a relative humidity between 40 and 60 %. Moisture buildup in buildings may arise from water penetrating areas of the building envelope or fabric, from plumbing leaks, rainwater or groundwater penetration, or from condensation due to improper ventilation, insufficient heating or poor thermal quality of the building envelope.[76] Even something as simple as drying clothes indoors on radiators can increase the risk of mold growth, if the humidity produced is not able to escape the building via ventilation.[77]

Mold predominantly affects the airways and lungs. Known effects of mold on health include asthma development and exacerbation,[78] with children and elderly at greater risk of more severe health impacts.[79] Infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis.[80][71] More than half of adult workers in moldy or humid buildings suffer from nasal or sinus symptoms due to mold exposure.[71] Some varieties of mold contain toxic compounds (mycotoxins). However, exposure to hazardous levels of mycotoxin via inhalation is not possible in most cases, as toxins are produced by the fungal body and are not at significant levels in the released spores.

Legionella

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Legionnaires' disease is caused by a waterborne bacterium Legionella that grows best in slow-moving or still, warm water. The primary route of exposure is through the creation of an aerosol effect, most commonly from evaporative cooling towers or showerheads. A common source of Legionella in commercial buildings is from poorly placed or maintained evaporative cooling towers, which often release water in an aerosol which may enter nearby ventilation intakes. Outbreaks in medical facilities and nursing homes, where patients are immuno-suppressed and immuno-weak, are the most commonly reported cases of Legionellosis. More than one case has involved outdoor fountains at public attractions. The presence of Legionella in commercial building water supplies is highly under-reported, as healthy people require heavy exposure to acquire infection.

Legionella testing typically involves collecting water samples and surface swabs from evaporative cooling basins, shower heads, faucets/taps, and other locations where warm water collects. The samples are then cultured and colony forming units (cfu) of Legionella are quantified as cfu/liter.

Legionella is a parasite of protozoans such as amoeba, and thus requires conditions suitable for both organisms. The bacterium forms a biofilm which is resistant to chemical and antimicrobial treatments, including chlorine. Remediation for Legionella outbreaks in commercial buildings vary, but often include very hot water flushes (160 °F (71 °C)), sterilisation of standing water in evaporative cooling basins, replacement of shower heads, and, in some cases, flushes of heavy metal salts. Preventive measures include adjusting normal hot water levels to allow for 120 °F (49 °C) at the tap, evaluating facility design layout, removing faucet aerators, and periodic testing in suspect areas.

Other bacteria

[edit]
Airborne bacteria

There are many bacteria of health significance found in indoor air and on indoor surfaces. The role of microbes in the indoor environment is increasingly studied using modern gene-based analysis of environmental samples. Currently, efforts are under way to link microbial ecologists and indoor air scientists to forge new methods for analysis and to better interpret the results.[81]

A large fraction of the bacteria found in indoor air and dust are shed from humans. Among the most important bacteria known to occur in indoor air are Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae.[citation needed]

Virus

[edit]
Ninth floor layout of the Metropole Hotel in Hong Kong, showing where an outbreak of the severe acute respiratory syndrome (SARS) occurred

Viruses can also be a concern for indoor air quality. During the 2002–2004 SARS outbreak, virus-laden aerosols were found to have seeped into bathrooms from the bathroom floor drains, exacerbated by the draw of bathroom exhaust fans, resulting in the rapid spread of SARS in Amoy Gardens in Hong Kong.[82][83] Elsewhere in Hong Kong, SARS CoV RNA was found on the carpet and in the air intake vents of the Metropole Hotel, which showed that secondary environmental contamination could generate infectious aerosols and resulted in superspreading events.[84]

Carbon dioxide

[edit]

Humans are the main indoor source of carbon dioxide (CO2) in most buildings. Indoor CO2 levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity.

Indoor CO2 levels above 500 ppm can lead to higher blood pressure and heart rate, and increased peripheral blood circulation.[85] With CO2 concentrations above 1000 ppm cognitive performance might be affected, especially when doing complex tasks, making decision making and problem solving slower but not less accurate.[86][87] However, evidence on the health effects of CO2 at lower concentrations is conflicting and it is difficult to link CO2 to health impacts at exposures below 5000 ppm – reported health outcomes may be due to the presence of human bioeffluents, and other indoor air pollutants related to inadequate ventilation.[88]

Indoor carbon dioxide concentrations can be used to evaluate the quality of a room or a building's ventilation.[89] To eliminate most complaints caused by CO2, the total indoor CO2 level should be reduced to a difference of no greater than 700 ppm above outdoor levels.[90] The National Institute for Occupational Safety and Health (NIOSH) considers that indoor air concentrations of carbon dioxide that exceed 1000 ppm are a marker suggesting inadequate ventilation.[91] The UK standards for schools say that carbon dioxide levels of 800 ppm or lower indicate that the room is well-ventilated.[92] Regulations and standards from around the world show that CO2 levels below 1000 ppm represent good IAQ, between 1000 and 1500 ppm represent moderate IAQ and greater than 1500 ppm represent poor IAQ.[88]

Carbon dioxide concentrations in closed or confined rooms can increase to 1,000 ppm within 45 minutes of enclosure. For example, in a 3.5-by-4-metre (11 ft × 13 ft) sized office, atmospheric carbon dioxide increased from 500 ppm to over 1,000 ppm within 45 minutes of ventilation cessation and closure of windows and doors.[93]

Radon

[edit]

Radon is an invisible, radioactive atomic gas that results from the radioactive decay of radium, which may be found in rock formations beneath buildings or in certain building materials themselves.

Radon is probably the most pervasive serious hazard for indoor air in the United States and Europe. It is a major cause of lung cancer, responsible for 3–14% of cases in countries, leading to tens of thousands of deaths.[94]

Radon gas enters buildings as a soil gas. As it is a heavy gas it will tend to accumulate at the lowest level. Radon may also be introduced into a building through drinking water particularly from bathroom showers. Building materials can be a rare source of radon, but little testing is carried out for stone, rock or tile products brought into building sites; radon accumulation is greatest for well insulated homes.[95] There are simple do-it-yourself kits for radon gas testing, but a licensed professional can also check homes.

The half-life for radon is 3.8 days, indicating that once the source is removed, the hazard will be greatly reduced within a few weeks. Radon mitigation methods include sealing concrete slab floors, basement foundations, water drainage systems, or by increasing ventilation.[96] They are usually cost effective and can greatly reduce or even eliminate the contamination and the associated health risks.[citation needed]

Radon is measured in picocuries per liter of air (pCi/L) or becquerel per cubic meter (Bq m-3). Both are measurements of radioactivity. The World Health Organization (WHO) sets the ideal indoor radon levels at 100 Bq/m-3.[97] In the United States, it is recommend to fix homes with radon levels at or above 4 pCi/L. At the same time it is also recommends that people think about fixing their homes for radon levels between 2 pCi/L and 4 pCi/L.[98] In the United Kingdom the ideal is presence of radon indoors is 100 Bq/m-3. Action needs to be taken in homes with 200 Bq/m−3 or more.[99]

Interactive maps of radon affected areas are available for various regions and countries of the world.[100][101][102]

IAQ and climate change

[edit]

Indoor air quality is linked inextricably to outdoor air quality. The Intergovernmental Panel on Climate Change (IPCC) has varying scenarios that predict how the climate will change in the future.[103] Climate change can affect indoor air quality by increasing the level of outdoor air pollutants such as ozone and particulate matter, for example through emissions from wildfires caused by extreme heat and drought.[104][105] Numerous predictions for how indoor air pollutants will change have been made,[106][107][108][109] and models have attempted to predict how the forecasted IPCC scenarios will vary indoor air quality and indoor comfort parameters such as humidity and temperature.[110]

The net-zero challenge requires significant changes in the performance of both new and retrofitted buildings. However, increased energy efficient housing will trap pollutants inside, whether produced indoors or outdoors, and lead to an increase in human exposure.[111][112]

Indoor air quality standards and monitoring

[edit]

Quality guidelines and standards

[edit]

For occupational exposure, there are standards, which cover a wide range of chemicals, and applied to healthy adults who are exposed over time at workplaces (usually industrial environments).These are published by organisations such as Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH), the UK Health and Safety Executive (HSE).

There is no consensus globally about indoor air quality standards, or health-based guidelines. However, there are regulations from some individual countries and from health organisations. For example, the World Health Organization (WHO) has published health-based global air quality guidelines for the general population that are applicable both to outdoor and indoor air,[29] as well as the WHO IAQ guidelines for selected compounds,[113] whereas the UK Health Security Agency published IAQ guidelines for selected VOCs.[114] The Scientific and Technical Committee (STC34) of the International Society of Indoor Air Quality and Climate (ISIAQ) created an open database that collects indoor environmental quality guidelines worldwide.[115] The database is focused on indoor air quality (IAQ), but is currently extended to include standards, regulations, and guidelines related to ventilation, comfort, acoustics, and lighting.[116][117]

Real-time monitoring

[edit]

Since indoor air pollutants can adversely affect human health, it is important to have real-time indoor air quality assessment/monitoring system that can help not only in the improvement of indoor air quality but also help in detection of leaks, spills in a work environment and boost energy efficiency of buildings by providing real-time feedback to the heating, ventilation, and air conditioning (HVAC) system(s).[118] Additionally, there have been enough studies that highlight the correlation between poor indoor air quality and loss of performance and productivity of workers in an office setting.[119]  

Combining the Internet of Things (IoT) technology with real-time IAQ monitoring systems has  tremendously gained momentum and popularity as interventions can be done based on the real-time sensor data and thus help in the IAQ improvement.[120]   

Improvement measures

[edit]

Indoor air quality can be addressed, achieved or maintained during the design of new buildings or as mitigating measures in existing buildings. A hierarchy of measures has been proposed by the Institute of Air Quality Management. It emphasises removing pollutant sources, reducing emissions from any remaining sources, disrupting pathways between sources and the people exposed, protecting people from exposure to pollutants, and removing people from areas with poor air quality.[121]

A report assisted by the Institute for Occupational Safety and Health of the German Social Accident Insurance can support in the systematic investigation of individual health problems arising at indoor workplaces, and in the identification of practical solutions.[122]

Source control

[edit]

HVAC design

[edit]

Environmentally sustainable design concepts include aspects of commercial and residential heating, ventilation and air-conditioning (HVAC) technologies. Among several considerations, one of the topics attended to is the issue of indoor air quality throughout the design and construction stages of a building's life.[citation needed]

One technique to reduce energy consumption while maintaining adequate air quality, is demand-controlled ventilation. Instead of setting throughput at a fixed air replacement rate, carbon dioxide sensors are used to control the rate dynamically, based on the emissions of actual building occupants.[citation needed]

One way of quantitatively ensuring the health of indoor air is by the frequency of effective turnover of interior air by replacement with outside air. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In halls, gym, dining, and physiotherapy spaces, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm. In the US, ventilation in classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area, not air changes per hour. Since carbon dioxide indoors comes from occupants and outdoor air, the adequacy of ventilation per occupant is indicated by the concentration indoors minus the concentration outdoors. The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains over 400 ppm[123] (global average as of 2023). In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density. As the occupants are not the only source of pollutants, outdoor air ventilation may need to be higher when unusual or strong sources of pollution exist indoors.

When outdoor air is polluted, bringing in more outdoor air can actually worsen the overall quality of the indoor air and exacerbate some occupant symptoms related to outdoor air pollution. Generally, outdoor country air is better than indoor city air.[citation needed]

The use of air filters can trap some of the air pollutants. Portable room air cleaners with HEPA filters can be used if ventilation is poor or outside air has high level of PM 2.5.[122] Air filters are used to reduce the amount of dust that reaches the wet coils.[citation needed] Dust can serve as food to grow molds on the wet coils and ducts and can reduce the efficiency of the coils.[citation needed]

The use of trickle vents on windows is also valuable to maintain constant ventilation. They can help prevent mold and allergen build up in the home or workplace. They can also reduce the spread of some respiratory infections.[124]

Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control may conflict with efforts to conserve energy. For example, moisture management and humidity control requires systems to be set to supply make-up air at lower temperatures (design levels), instead of the higher temperatures sometimes used to conserve energy in cooling-dominated climate conditions. However, for most of the US and many parts of Europe and Japan, during the majority of hours of the year, outdoor air temperatures are cool enough that the air does not need further cooling to provide thermal comfort indoors.[citation needed] However, high humidity outdoors creates the need for careful attention to humidity levels indoors. High humidity give rise to mold growth and moisture indoors is associated with a higher prevalence of occupant respiratory problems.[citation needed]

The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with dew points in the lower 50s °F, and some in the upper and lower 40s °F.[citation needed] Some facilities are being designed using desiccant wheels with gas-fired heaters to dry out the wheel enough to get the required dew points.[citation needed] On those systems, after the moisture is removed from the make-up air, a cooling coil is used to lower the temperature to the desired level.[citation needed]

Commercial buildings, and sometimes residential, are often kept under slightly positive air pressure relative to the outdoors to reduce infiltration. Limiting infiltration helps with moisture management and humidity control.

Dilution of indoor pollutants with outdoor air is effective to the extent that outdoor air is free of harmful pollutants. Ozone in outdoor air occurs indoors at reduced concentrations because ozone is highly reactive with many chemicals found indoors. The products of the reactions between ozone and many common indoor pollutants include organic compounds that may be more odorous, irritating, or toxic than those from which they are formed. These products of ozone chemistry include formaldehyde, higher molecular weight aldehydes, acidic aerosols, and fine and ultrafine particles, among others. The higher the outdoor ventilation rate, the higher the indoor ozone concentration and the more likely the reactions will occur, but even at low levels, the reactions will take place. This suggests that ozone should be removed from ventilation air, especially in areas where outdoor ozone levels are frequently high.

Effect of indoor plants

[edit]
Spider plants (Chlorophytum comosum) absorb some airborne contaminants.

Houseplants together with the medium in which they are grown can reduce components of indoor air pollution, particularly volatile organic compounds (VOC) such as benzene, toluene, and xylene. Plants remove CO2 and release oxygen and water, although the quantitative impact for house plants is small. The interest in using potted plants for removing VOCs was sparked by a 1989 NASA study conducted in sealed chambers designed to replicate the environment on space stations. However, these results suffered from poor replication[125] and are not applicable to typical buildings, where outdoor-to-indoor air exchange already removes VOCs at a rate that could only be matched by the placement of 10–1000 plants/m2 of a building's floor space.[126]

Plants also appear to reduce airborne microbes and molds, and to increase humidity.[127] However, the increased humidity can itself lead to increased levels of mold and even VOCs.[128]

Since extremely high humidity is associated with increased mold growth, allergic responses, and respiratory responses, the presence of additional moisture from houseplants may not be desirable in all indoor settings if watering is done inappropriately.[129]

Institutional programs

[edit]
EPA graphic about asthma triggers

The topic of IAQ has become popular due to the greater awareness of health problems caused by mold and triggers to asthma and allergies.

In the US, the Environmental Protection Agency (EPA) has developed an "IAQ Tools for Schools" program to help improve the indoor environmental conditions in educational institutions. The National Institute for Occupational Safety and Health conducts Health Hazard Evaluations (HHEs) in workplaces at the request of employees, authorized representative of employees, or employers, to determine whether any substance normally found in the place of employment has potentially toxic effects, including indoor air quality.[130]

A variety of scientists work in the field of indoor air quality, including chemists, physicists, mechanical engineers, biologists, bacteriologists, epidemiologists, and computer scientists. Some of these professionals are certified by organizations such as the American Industrial Hygiene Association, the American Indoor Air Quality Council and the Indoor Environmental Air Quality Council.

In the UK, under the Department for Environment Food and Rural Affairs, the Air Quality Expert Group considers current knowledge on indoor air quality and provides advice to government and devolved administration ministers.[131]

At the international level, the International Society of Indoor Air Quality and Climate (ISIAQ), formed in 1991, organizes two major conferences, the Indoor Air and the Healthy Buildings series.[132]

See also

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Sources

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Monographs
Articles, radio segments, web pages

Further reading

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A Nest Labs thermostat

Smart thermostats are Wi-Fi thermostats that can be used with home automation and are responsible for controlling a home's heating, ventilation, and air conditioning. They perform similar functions as a programmable thermostat as they allow the user to control the temperature of their home throughout the day using a schedule, but also contain additional features, such as Wi-Fi connectivity,[1][2] that improve upon the issues with programming.

Like other Wi-Fi thermostats, they are connected to the Internet via a Wi-Fi network. They allow users to adjust heating settings from other internet-connected devices, such as a laptop or smartphones. This allows users to control the thermostat remotely. This ease of use is essential for ensuring energy savings: studies have shown that households with programmable thermostats actually have higher energy consumption than those with simple thermostats because residents program them incorrectly or disable them completely.[3][4]

Smart thermostats also record internal/external temperatures, the time the HVAC system has been running and can notify the user if the system's air filter needs to be replaced. This information is typically displayed later on an internet-connected device such as a smartphone.

Manual vs. programmable vs. smart thermostats

[edit]

Manual thermostats

[edit]
Honeywell Manual Thermostat

Manual thermostats (also known as analog thermostats) are the oldest and simplest type of thermostats. These thermostats are set to one temperature and do not change until the user manually adjusts the temperature.[5]

Programmable thermostats

[edit]

Programmable thermostats, first introduced over 100 years ago,[6] are a type of thermostat that allows the user to set a schedule for different temperatures at different times. Most programmable thermostats also have a hold feature which suspends the schedule and effectively turns the thermostat into a manual thermostat.[5] The idea of the scheduling feature is that users will set a warmer or cooler temperature when the home is unoccupied to save energy and money. Due to this assumed energy savings, some building codes and government programs began requiring the use of programmable thermostats.[7] Due to the way people use these devices, most programmable thermostats result in more energy use than the basic manual thermostat.[8]

Issues with programmable thermostats

[edit]

One of the main objectives of smart thermostats is to reduce the issues involved with using traditional programmable thermostats. In order to understand how smart thermostats take on this task, it is important to understand the issues regarding programmable thermostats and how they affect energy consumption. Between 2008-2009, Florida Power & Light (FPL) provided 400 homeowners with programmable thermostats and monitored their heating and cooling patterns. Out of the 400 participants, 56% of users used the programming feature while the remaining participants did not program the thermostat and left it on "hold". It was determined that the users who used the programming feature actually consumed 12% more energy than the non-programmers. This consumption increase resulted from higher overnight duty cycles associated with lower thermostat setpoints (i.e. lower temperature setting), due to confusion with setting the schedule. This study reveals that programmable thermostats will not necessarily save energy. The smart thermostat attempts to combat this issue by taking the user out of the picture and relying on sensors and computers to save energy.[8]

Another study conducted on the issue determined that the biggest problem for programmable thermostats was the human using it. The technology inside a programmable thermostat is no doubt one of the most important factors in determining whether or not the thermostat will be successful in saving energy. But an equally important factor is the human who is using the thermostat. Unfortunately, many people who own programmable thermostats do not know how to use the thermostat or are not using all of the features that are offered. One study conducted a number of interviews, surveys, and observations to determine that the vast majority of programmable thermostat owners are not using the thermostats for their intended purpose. An online survey showed that 89% of respondents do not use the schedule feature on their programmable thermostat. Other results from the interviews and surveys show that a large number of people have misconceptions about heating/cooling and the use of programmable thermostats. One misconception is people believing that heating all of the time is more efficient than scheduling the heat to turn off. Another misconception noted in the study is that turning down the thermostat does not substantially reduce energy consumption. These misconceptions reaffirm the idea that the programmable thermostat itself could have all of the necessary tools, but if the user does not use them or uses them incorrectly, then these thermostats will fail at saving energy.[7]

As a result of these studies and others like them, energy star suspended its labelling of programmable thermostats in December 2009. It became the goal of smart thermostats to address these issues by taking the human out of the picture and creating a thermostat that uses smart computing to truly reduce energy usage and cost.[7][8]

Smart thermostats

[edit]

Smart thermostats are similar to programmable thermostats in the sense that they have a scheduling feature that allows users to set different temperatures for different times of the day. In addition to this feature, smart thermostats implement other technologies to reduce the amount of human error involved with using programmable thermostats. Smart thermostats incorporate the use of sensors that determine whether or not the home is occupied and can suspend heating or cooling until the occupant returns. Additionally, smart thermostats utilize Wi-Fi connectivity to give the user access to the thermostat at all times. These additional technologies have proven to make smart thermostats successful in saving users energy and money.[5]

History

[edit]

Development of the smart thermostat began in 2007 with the creation of the ecobee thermostat. The founder of ecobee, Stuart Lombard, wanted to save energy and reduce his family's carbon footprint. After realizing that heating and cooling made up most of his home's energy usage,[9] Lombard purchased a programmable thermostat in an attempt to reduce total energy usage. Lombard quickly discovered that the programmable thermostat was difficult to use and unreliable. Following difficulties with the programmable thermostat, he set out to create a smart thermostat that saved energy and was easy to use. With that goal, the ecobee company was created in attempt to offer users a thermostat that could truly save energy by fixing the issues with programmable thermostats.[10]

Following the ecobee, EnergyHub released its version of a smart thermostat in 2009 with the creation of the EnergyHub Dashboard. The co-founder of EnergyHub, Seth Frader-Thompson, got the idea for the Dashboard from his Prius. The Prius had screens on the dashboard that displayed the car's gas mileage in real time. Thompson felt that a house should have something that does the same. With that goal in mind, Thompson created a thermostat that could communicate with a home's furnace and appliances to determine the energy usage and efficiency and how much it was costing. The thermostat also had the capability to turn off appliances or raise and lower the temperature to save energy and cost. Ultimately, the goal of this thermostat was to display energy usage to users and to save energy and money.[11]

Nest Labs company logo. Creators of the Nest Learning Thermostat.

In 2011, Nest Labs developed the Nest Learning Thermostat. The Nest Thermostat attempted to reduce home energy consumption by addressing the problems with programmable thermostats through the use of better technology. This new technology included the implementation of sensors, algorithms, machine learning, and cloud computing. These technologies learn the behaviors and preferences of the occupants, and adjust the temperature up or down to make the occupant comfortable when they are home and to save energy when they are away. Additionally, the Nest Thermostat connects to the home Wi-Fi. This allows users to change the temperature, adjust the schedule, and check energy usage from a smartphone or laptop. All of these features were part of Nest's goal to create an easy to use thermostat that saves users energy and money.[12]

Technology

[edit]

Programmable schedule and auto schedule

[edit]

The programmable schedule feature on the smart thermostat is similar to that on standard programmable thermostats. Users are given the option to program a custom schedule to reduce energy usage when they are away from the home. Studies have shown, though, that manually creating a schedule may lead to more energy usage than just keeping the thermostat at a set temperature.[8] To avoid this problem, smart thermostats also provide an auto schedule feature. This feature requires the use of algorithms and pattern recognition to create a schedule that results in occupant comfort and energy savings. Upon creating a schedule, the thermostat will continue monitoring occupant behavior to make changes to the auto schedule. By taking the human error out of the scheduling, smart thermostats can create smart schedules that actually save energy.[13]

Sensor

[edit]
The Nest Web Portal allows users to remotely change the temperature, create a schedule, and view past energy usage.

In an attempt to mitigate the issues with human error involved with programmable thermostats, the smart thermostat utilizes a sensor that can determine occupancy patterns to automatically change the temperature based on occupant patterns and behaviors. The Nest Learning Thermostat in particular uses passive infrared (PIR) motion sensors inside the unit to sense occupancy in the vicinity of the thermostat. This sensor informs the thermostat whether or not the home is occupied. In the case that the home is not occupied, the thermostat can suspend heating/cooling until the sensor is reactivated by an occupant. This sensor is also used to determine the occupancy patterns to create the auto schedule. A grille member is placed in front of the sensor to visually conceal and protect the PIR motion sensor inside the thermostat. The grille also helps to make the thermostat visually pleasing.[2] While this sensor technology is important for conserving energy, it is not without flaws. One of the major issues is that the sensor must be activated by someone walking in front of or near the thermostat. It is possible that an occupant could be at home and not pass in front of the sensor. In this case, the thermostat would shut off the heating/cooling and decrease human comfort.[14]

Wi-Fi connection

[edit]

A major feature of Wi-Fi thermostats (such as smart thermostats) is their ability to connect to the internet. These thermostats are designed with a Wi-Fi module that allows the thermostat to connect to the user's home or office network and interface with a web portal or smartphone application, allowing users to control the thermostat remotely.[15] The Wi-Fi feature also has the ability to send reports on energy usage and HVAC system performance via the web portal, informing the user on their energy efficiency and how it compares to other smart thermostat users. It also may alert users when a problem arises with their HVAC system or when it is time for equipment maintenance. The thermostat also may use the Wi-Fi connection to display current weather conditions and the weather forecast.[1]

Another feature offered by some smart thermostats through the internet connection is geofencing. A geofence is a perimeter boundary created around the location of a smartphone or other device, based on GPS signals. The benefit of having a smart thermostat with geofencing capabilities is that it uses a users smartphone location to determine whether the home is occupied. Instead of using a schedule or sensor to determine occupancy, the smart thermostat can rely on the location of the geofence to tell the HVAC system whether it needs to be on or off.[16] Since most people carry their phones with them, geofencing can be an accurate way to determine occupancy patterns.[13]

Learning thermostats

[edit]
The Ecobee 4 thermostat

Some smart thermostats, such as the Nest thermostat, can learn when the house is likely to be occupied, and when it is likely to be empty. This allows automatic pre-heating or pre-cooling so the temperature is comfortable when a resident arrives. If the residents or lifestyles change, these smart thermostats will gradually adjust the schedule, maintaining energy savings and comfort.

Motion detectors can determine if someone is home. One smart thermostat that uses motion detectors is the Ecobee4.[17]

A wireless network can be used to sense when someone is out of range, thus determining if they're in or nearby their home. This geofencing technique is used by the Honeywell T6 Smart Thermostat.

Connected thermostats

[edit]

A Connected thermostat is one that can be controlled through an internet connection, but will not provide analytic information. In recent years Wi-Fi thermostats have risen in popularity, they combine the technology of thermometers and Wi-Fi. So now you can have a thermometer in your home that is displayed on your phone that uses Wi-Fi technology. This technology is being developed right now so it will be available for thermostats in machinery and cars. Google is involved in this push towards technology since it acquired a Wi-Fi temperature company called Nest.[18] The market of smart thermostats is expected to reach around 3.5 Billion USD by the end of the year 2022.[citation needed]

Zoned systems

[edit]

Rather than controlling the temperature of the whole house, zoned systems can control individual rooms. This can increase energy savings, for example by heating or cooling only a Home-office and not the bedrooms and other areas that are empty during the day.

Studies

[edit]

Internal studies

[edit]

To show that their thermostats save energy and money, numerous smart thermostat producers have conducted models and studies to confirm their savings claims. One popular way that smart thermostat producers calculate energy usage is through energy modeling. In these models, the smart thermostat is compared to a thermostat set at a constant temperature, and savings are calculated. Using this method, ecobee calculated energy savings by correlating how long heating and cooling equipment run to local weather conditions. Energy savings were calculated relative to a constant temperature of 22 °C (72 °F). Upon conducting this model, ecobee determined a 23% savings on heating and cooling costs for those who switch to their smart thermostat.[19] Using a similar modeling method, Nest claimed a 20% energy savings for homeowners who install a Nest Learning Thermostat.[20]

To determine energy savings using actual data instead of energy models, in February 2015, Nest conducted a national study of Nest customers in 41 states who had enrolled in Nest's MyEnergy service. In May 2013, Nest acquired MyEnergy, a company that tracks and analyzes utility usage of people enrolled in the program. Upon acquiring MyEnergy, Nest was able to use the historical data to determine the energy savings of those who installed the Nest Learning Thermostat. This study looked at energy usage before and after the installation of a Nest Learning Thermostat and used a weather normalization procedure to prevent unusually cold or warm weather from skewing the data. The study had a sample size of 735 homes for gas usage analysis and 624 homes for electrical analysis. All of these homes were enrolled in the MyEnergy program and had sufficient energy data before and after the installation of a Nest Learning Thermostat. After observing the energy usage for one year, Nest determined that there was an average gas savings of 10% and a cooling savings of 17.5%. The savings varied from house to house depending on how occupants set their thermostat before the installation of a Nest thermostat, along with differences in occupancy patterns, house characteristics, and weather.[20]

Gas and Electric Savings Results[20]
Fuel Sample Size Pre-Nest Total Energy Use Pre-Nest HVAC Total Energy Savings % of HVAC
Natural Gas (therms/yr) 735 774 584 56 ±12 9.6 ±2.1%
Electricity (kWh/yr) 624 12,355 3,351 585 ±97 17.5 ±2.9%

While the results from the MyEnergy study are significantly lower than those from energy modeling, both show a savings in energy usage by switching to a smart thermostat.[19][20]

Third-party studies

[edit]

Since the release of smart thermostats, a number of third party studies have been conducted to determine if smart thermostats actually save energy and how they compare to manual and programmable thermostats with regards to savings. One study conducted an experiment in which 300 standard programmable thermostats were placed in homes and 300 Nest smart thermostats were placed in other homes. It is important to note that the homeowners involved in this study received proper training on how to properly use all of the thermostat functions. This effectively eliminated the issues regarding human error with programmable thermostats. All homes were located within one region of Indiana and had previously undergone home energy assessment. After 1 year of observation, the study concluded that Nest users reduced their heating gas consumption by 12.5% while users of a standard programmable thermostat reduced consumption by 5%. Additionally, it was concluded that Nest and standard programmable thermostat users reduced their cooling electric consumption by 13.9% and 13.1%, respectively. The major factors that allowed Nest to reduce consumption more than other thermostats was its ability to further reduce human error and set more efficient temperatures. The Nest thermostat used sensors and Wi-Fi connectivity to adjust the temperature on its own and provide more savings. This study helps to suggest that smart thermostats are in fact successful in reducing energy consumption.[21]

Gas Savings as a Percentage of Heating Gas Usage[21]
Thermostat Pre Heating

Usage (Therms)

Savings

(Therms)

Savings

(%)

Range of

Savings (Therms)

Range of

Savings (%)

Nest 548 69 12.5% 60 to 77 11 to 14%
Programmable 602 30 5% 22 to 38 4 to 6%
Electric Savings as a Percentage of Cooling Electricity Usage[21]
Thermostat Pre Usage

(kWh)

Savings

(kWh)

Savings

(%)

Range of

Savings (kWh)

Range of

Savings (%)

Nest 3,080 429 13.9% 270 to 589 9 to 19%
Programmable 2,537 332 13.1% 181 to 483 7 to 19%

A similar study conducted in 2012 with the ecobee thermostat also concluded that smart thermostats are capable of saving energy. The goal of this pilot program was to determine the gas and electric savings of smart thermostats. This study provided 86 households with 123 ecobee thermostats and monitored the homes for 12 months. The study included 69 houses from Massachusetts and 17 from Rhode Island. The participants either had manual or programmable thermostats before the study was conducted. Gas and electric billing data were provided for 12 months before the study was conducted to use as a baseline. After the 12 months of observation, the study concluded that ecobee thermostats led to an average electricity savings of 16% and an average gas savings of 10%. The gas savings for manual thermostat replacements (10% per thermostat) was found to be larger than for programmable thermostat replacements (8% per thermostat). The difference in electricity savings between homes whose prior equipment was a manual thermostat or programmable thermostat was found to be minimal.[1]

Gas Billing Analysis Savings Summary[1]
Previous

Thermostat

Number of

Participants

Pre Usage

(Therms)

Savings

(Therms)

Savings

(%)

Range of

Savings (Therms)

Range of

Savings (%)

Manual

Thermostat

23 890 87 10% 60 to 113 7 to 13%
Programmable

Thermostat

44 842 66 8% 43 to 88 5 to 10%
Electric Savings Analysis Savings Summary[1]
Previous

Thermostat

Number of

Participants

Pre Usage

(kWh)

Savings

(kWh)

Savings

(%)

Manual and

Programmable

Thermostat

12 640 113 16%

Although these studies report differing amounts of savings compared to the internal studies conducted by Nest and ecobee, both of these studies show that smart thermostats have the potential to save energy. This suggests that the technologies added to fix the issues with programmable thermostats have been successful.[1][21]

Study discrepancies

[edit]

Although most studies show that smart thermostats show an energy savings, the amount of savings varies. A large discrepancy is seen between energy modeling savings and the savings found using actual data. The energy modeling compares the smart thermostat to a constant set point temperature of 72 °F, but an online survey conducted by Nest showed that most users have a set point temperature that is 10% more efficient.[20] Therefore, the savings predicted by the energy modeling are going to be higher than real savings.

There are other factors that cause discrepancies even between studies that all look at actual data. Most studies compare total energy consumption of a house from year to year to determine energy savings, as opposed to looking at just the energy that is used for heating and cooling. Due to this, there could be other factors that change the energy consumption of a house, and it might be incorrect to state that the thermostat is responsible for all energy savings in a house. For example, it is possible that other new energy efficient practices/appliances are partially responsible for the savings in addition to the thermostat.[20]

Another discrepancy to consider is the population of people involved in the study. Some studies, such as the MyEnergy study, involve people who signed up for an energy analysis program.[20] These people are likely to be more energy conscious and efficient and have better heating and cooling practices. This greater interest in energy efficiency may lead to lower energy savings by switching to a smart thermostat. The most energy-conscious customers are the ones more likely to have had efficient thermostat settings, therefore, the savings that they receive from the smart thermostat may not be as great.[1]

The weather will also have an impact on the results of a study. Having very high temperatures in the summer and very cold temperatures in the winter will lead to more cooling and heating in those months, requiring more energy. When comparing year to year data, if one year had extreme temperatures, while the following year had moderate temperatures, the savings may look drastic. In reality though, the savings are not from the thermostat, but rather from the change in weather. Studies will try to mitigate this problem through weather normalization procedures.[20]

Broader Impact

[edit]

While smart thermostats have the potential to save energy consumption, they can create unintended consequences on the broader electrical grid. Smart thermostats tend to operate similarly across a population and can create load synchronization. This load synchronization can create much higher peaks and more rapid changes in heating demand. Particularly in the winter, this heating demand is shifted earlier in the morning, when solar electricity is unavailable, making it more difficult to supply electric heating sources like heat pumps with renewable energy.[22]

Improvements

[edit]

Motion sensors

[edit]

One issue with using a smart thermostat is the unreliability of the motion sensor. One of the main features of the smart thermostat is the ability to change the temperature when the sensor in the thermostat does not sense an occupant. The only sensor that is used though is the sensor in the thermostat. This means that if the home is occupied but no one walks passed the thermostat, the thermostat will think that the home is unoccupied and will change the temperature, potentially leading to occupant discomfort.

One study attempted to address this issue by adding more sensors throughout the house. Instead of using just one sensor in the thermostat, this team experimented with placing motion sensors and door sensors throughout the house to gain better understanding of the occupant's sleeping and occupancy patterns. These sensors communicated with each other and used an algorithm to quickly determine whether the occupants were active, sleeping, or away. The system used historical data to estimate when occupants would be returning and would begin "preheating" the home before they arrived. Additionally, the system would drift further from the set point when it was certain that no one was home. The study compared a standard ("reactive") smart thermostat and the multiple sensor system to a manual thermostat. The study concluded that a reactive smart thermostat with just on sensor saves, on average, 6.8% of energy consumption, while the multiple sensor system saved an average of 28% of energy consumption. This study again shows that, on average, smart thermostats achieve their goal of saving energy. It also shows that smart thermostats are not as well developed as they could be, and the addition of more sensors could result in better performance and energy savings.[14]

User interface

[edit]

One of the issues with programmable thermostats that smart thermostats try to fix is the confusing user interface. Many owners of programmable thermostats found the controls and directions to be too confusing and opted out of using the scheduling feature completely. Others who used the feature used it incorrectly, due to the confusing directions, and saw an increase in energy usage.[7] Developers of smart thermostats have attempted to fix this issue by creating simple to use thermostats and providing proper direction. While this is an improvement on programmable thermostats, studies have shown that users desire more intense training from the installer of the thermostat on how to use the technical features. Additionally, many smart thermostats use a web portal where users can adjust the thermostat settings and look at their energy usage history. Again, studies have shown that users want this feature to be improved. Some complain that the web portal is not user friendly and they desire more training on how to use the web features during installation.[1]

Internet security

[edit]

Researchers from the University of Central Florida conducted an experiment to show that hackers could use the Nest thermostat as an entry point into one's home. Upon being connected to the internet, the hackers could use the thermostat to control local network traffic from a remote location. The hacker could also use the thermostat to act as a spy and would know whether or not the home is occupied. The research showed that in order for a hacker to gain access to the thermostat, they would have to gain physical access to the device and upload the malicious firmware via a USB port. This drastically decreases the chances that this type of attack will occur, but it is still possible if a used thermostat is purchased with the firmware already uploaded. The problem that allows this type of attack is with the hardware in the thermostat. Therefore, Nest cannot repair this issue with a simple software update, but rather it would need to build a new thermostat that can prevent this type of attack.[15][23]

Sustainability

[edit]
Residential Energy Consumption Survey conducted by the U.S. Energy Information Administration shows residential electricity consumption by category.

Climate change

[edit]

According to the 2015 Residential Energy Consumption Survey conducted by the U.S. Energy Information Administration, home heating and cooling account for the highest percentage of residential electrical energy consumption. Air conditioning accounts for 17% of electrical usage while space heating accounts for 15%.[9] The Residential Energy Consumption Survey from 2009 looked at energy consumption from all energy types (natural gas and electricity). This survey determined that space heating accounted for 42% of all residential energy consumption, while air conditioning accounted for 6%.[24] This energy usage needed to heat and cool homes is directly linked to climate change, as the energy provided for heating and cooling often comes from the burning of fossil fuels, leading to the release of greenhouse gas emissions. With an added focus on combating climate change and global warming, nations from around the world have begun to take on this issue by limiting greenhouse gas emissions and preventing the rise in global temperature through agreements such as The Paris Agreement.[25] Any steps taken to reduce residential energy consumption will help to achieve those goals.

Smart thermostats could be a solution to reducing energy consumption, as numerous studies have shown that these thermostats do in fact reduce home energy consumption.[1][19][20][21] Additionally, the technology within smart thermostats has proven to provide optimal occupant comfort, while still reducing energy consumption.[20] In addition to providing comfort, these technologies take the human out of the picture. Many sustainable devices rely heavily on how the user uses them. By relying on technology instead of human actions, smart thermostats reduce the amount of human error often experienced with other sustainable devices, such as the programmable thermostat. These factors suggest that installing a smart thermostat is one easy step than many people can take to reduce energy usage and greenhouse gas emissions, ultimately leading to a more sustainable future.

Programs

[edit]

Many housing corporations and smart thermostat developers realize the potential of smart thermostats to save energy, and have developed programs to advance sustainability through smarter technology. Ecobee promotes a sustainable future through its "A Better Tomorrow" program, in which the company donates time, data, and technology to ensure a brighter future.[26] As part of this program, in January 2018, ecobee donated 776 ecobee thermostats to the Toronto Community Housing Corporation (TCHC) to help the city of Toronto advance their climate change action plan. This donation helps to improve the TCHC's goal of providing healthy, safe, and sustainable homes for the people of Toronto.[27]

Another popular way that utility companies promote switching to a smart thermostat is through monetary incentives. The San Diego Gas & Electric company currently runs a program that offers participants a $50 e-gift card after switching to a smart thermostat.[28] The Wisconsin Focus on Energy program partners with utility companies across Wisconsin to offer a $75 check to those who purchase a qualifying smart thermostat.[29] Austin Energy, a utility company providing electricity to the city of Austin, Texas, offers a $25 rebate for each eligible smart thermostat that is purchased and installed.[30] Pacific Gas and Electric Company (PG&E) offers smart thermostat rebates in California for residential and multifamily customers.[31][32] Many other companies across the United States offer similar programs to incentive smart thermostats and more sustainable heating and cooling.[33][34]

Upon installing a smart thermostat, there are additional programs that continue to promote sustainability and reduced energy consumption. The Nest Rush Hour Rewards program partners with utility companies across the United States to incentivize customers to set a higher or lower temperature during peak demand periods. Energy rush hours occur when everyone in a particular area turns on their heating or cooling at the same time, such as during a heat wave. This extra demand may require utility companies to run additional power plants, leading to more cost and carbon emissions. To avoid this, the Rush Hour Rewards program incentivizes customers to set a more efficient temperature that will reduce the amount of energy needed to be produced by the utility.[35]

As more programs like these are created, smart thermostats will play an increasingly important role in reducing residential energy consumption. This reduction will lead to fewer greenhouse gas emissions, helping to create a more sustainable future.

See also

[edit]

References

[edit]
  1. ^ a b c d e f g h i Miller, Alexi, et al. Wi-Fi Programmable Controllable Thermostat Pilot Program Evaluation. The Cadmus Group, Sept. 2012, ma-eeac.org/wordpress/wp-content/uploads/Wi-Fi-Programmable-Controllable-Thermostat-Pilot-Program-Evaluation_Part-of-the-Massachusetts-2011-Residential-Retrofit-Low-Income-Program-Area-Study.pdf.
  2. ^ a b Huppi, Brian (19 Nov 2010). "System and method for integrating sensors in thermostats".
  3. ^ Environmental Protection Agency. Summary of Research Findings From the Programmable Thermostat Market. Washington, DC: Office of Headquarters, 2004
  4. ^ H Sachs. Programmable Thermostats. ACEEE, 2004
  5. ^ a b c "Manual vs Programmable vs Smart Thermostats | Which Is Best for You?". Service Champions. 2018-05-18. Retrieved 2018-12-06.
  6. ^ "The Honeywell Temperature Regulator".
  7. ^ a b c d Meier, Alan (2010). "How People Actually Use Thermostats". ACEEE. cite journal: Cite journal requires |journal= (help)[permanent dead link]
  8. ^ a b c d Lopes, Joseph. "FPL Residential Thermostat Load Control Pilot Project Evaluation" (PDF). ACEEE. cite journal: Cite journal requires |journal= (help)
  9. ^ a b "EIA's residential energy survey now includes estimates for more than 20 new end uses - Today in Energy - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2018-12-07.
  10. ^ "About ecobee | ecobee | Smart Home Technology". www.ecobee.com. Retrieved 2018-12-06.
  11. ^ "The 50 Best Inventions of 2009 - TIME". Time. 2009-11-12. ISSN 0040-781X. Retrieved 2018-12-06.
  12. ^ "Nest Labs Introduces World's First Learning Thermostat". Nest. 25 Oct 2011.
  13. ^ a b Nest. "Support". Nest. Retrieved 2018-12-07.
  14. ^ a b Lu, Jiakang; Sookoor, Tamim; Srinivasan, Vijay; Gao, Ge; Holben, Brian; Stankovic, John; Field, Eric; Whitehouse, Kamin (2010). "The smart thermostat". Proceedings of the 8th ACM Conference on Embedded Networked Sensor Systems - Sen Sys '10. p. 211. doi:10.1145/1869983.1870005. ISBN 978-1-4503-0344-6. S2CID 207183167.
  15. ^ a b Hernandez, Grant; Arias, Orlando; Buentello, Daniel; Jin, Yier (2014). "Smart Nest Thermostat A Smart Spy in Your Home" (PDF). Blackhat. S2CID 14493263.
  16. ^ "Should You Get a Thermostat with Geofencing Technology?". General Heating & Air Conditioning. 2014-07-21. Retrieved 2018-12-07.
  17. ^ "Does the ecobee4 also have a built-in motion sensor?". ecobee Support. Retrieved 2018-09-21.
  18. ^ Whitney, Lance (February 12, 2014), "Google closes $3.2 billion purchase of Nest", CNET
  19. ^ a b c "Saving money with ecobee smart Wi-Fi thermostats | ecobee | Smart Home Technology". www.ecobee.com. Retrieved 2018-12-07.
  20. ^ a b c d e f g h i j "Energy Savings from the Nest Learning Thermostat: Energy Bill Analysis Results". Nest Labs, Inc., Feb. 2015, nest.com/-downloads/press/documents/energy-savings-white-paper.pdf.
  21. ^ a b c d e Asrish, Carlyn. Evaluation of the 2013–2014 Programmable and Smart Thermostat Program . The Cadmus Group, 9 Jan. 2015, www.cadmusgroup.com/wp-content/uploads/2015/06/Cadmus_Vectren_Nest_Report_Jan2015.pdf?submissionGuid=c8eda45b-2759-4a31-90e3-d2ecdb9001de.
  22. ^ Lee, Zachary (2022). "Unintended consequences of smart thermostats in the transition to electrified heating". Applied Energy. 322: 119384. doi:10.1016/j.apenergy.2022.119384. S2CID 249809288.
  23. ^ Tilley, Aaron. "How Hackers Could Use A Nest Thermostat As An Entry Point Into Your Home". Forbes. Retrieved 2018-12-07.
  24. ^ "Energy Use in Homes - Energy Explained, Your Guide To Understanding Energy - Energy Information Administration". www.eia.gov. Retrieved 2018-12-07.
  25. ^ "The Paris Agreement | UNFCCC". unfccc.int. Retrieved 2018-12-07.
  26. ^ "Social Impact | ecobee | Smart Home Technology". www.ecobee.com. Retrieved 2018-12-07.
  27. ^ "CNW | ecobee donates over 700 thermostats to Toronto Community Housing to improve sustainability and resident comfort". www.newswire.ca. Retrieved 2018-12-07.
  28. ^ "Smart Thermostat Incentives | San Diego Gas & Electric". www.sdge.com. Retrieved 2018-12-10.
  29. ^ "Smart Thermostats | Focus on Energy". www.focusonenergy.com. Retrieved 2018-12-10.
  30. ^ "Power Partner Thermostats". savings.austinenergy.com. 2013-04-24. Retrieved 2018-12-10.
  31. ^ "Smart thermostat rebate". www.pge.com. Retrieved 2021-09-29.
  32. ^ "Energy management for property managers". www.pge.com. Retrieved 2021-09-29.
  33. ^ "Smart Thermostat Rebate Program | The City of Naperville". www.naperville.il.us. Retrieved 2018-12-10.
  34. ^ "Energy Efficiency Programs | Entergy Mississippi, Inc". www.entergy-mississippi.com. Retrieved 2018-12-10.
  35. ^ Nest. "Support". Nest. Retrieved 2018-12-10.

 

External heat exchanger of an air-source heat pump for both heating and cooling
Mitsubishi heat pump interior air handler wall unit

A heat pump is a device that uses electricity to transfer heat from a colder place to a warmer place. Specifically, the heat pump transfers thermal energy using a heat pump and refrigeration cycle, cooling the cool space and warming the warm space.[1] In winter a heat pump can move heat from the cool outdoors to warm a house; the pump may also be designed to move heat from the house to the warmer outdoors in summer. As they transfer heat rather than generating heat, they are more energy-efficient than heating by gas boiler.[2]

A gaseous refrigerant is compressed so its pressure and temperature rise. When operating as a heater in cold weather, the warmed gas flows to a heat exchanger in the indoor space where some of its thermal energy is transferred to that indoor space, causing the gas to condense into a liquid. The liquified refrigerant flows to a heat exchanger in the outdoor space where the pressure falls, the liquid evaporates and the temperature of the gas falls. It is now colder than the temperature of the outdoor space being used as a heat source. It can again take up energy from the heat source, be compressed and repeat the cycle.

Air source heat pumps are the most common models, while other types include ground source heat pumps, water source heat pumps and exhaust air heat pumps.[3] Large-scale heat pumps are also used in district heating systems.[4]

The efficiency of a heat pump is expressed as a coefficient of performance (COP), or seasonal coefficient of performance (SCOP). The higher the number, the more efficient a heat pump is. For example, an air-to-water heat pump that produces 6kW at a SCOP of 4.62 will give over 4kW of energy into a heating system for every kilowatt of energy that the heat pump uses itself to operate. When used for space heating, heat pumps are typically more energy-efficient than electric resistance and other heaters.

Because of their high efficiency and the increasing share of fossil-free sources in electrical grids, heat pumps are playing a role in climate change mitigation.[5][6] Consuming 1 kWh of electricity, they can transfer 1[7] to 4.5 kWh of thermal energy into a building. The carbon footprint of heat pumps depends on how electricity is generated, but they usually reduce emissions.[8] Heat pumps could satisfy over 80% of global space and water heating needs with a lower carbon footprint than gas-fired condensing boilers: however, in 2021 they only met 10%.[4]

Principle of operation

[edit]
A: indoor compartment, B: outdoor compartment, I: insulation, 1: condenser, 2: expansion valve, 3: evaporator, 4: compressor

Heat flows spontaneously from a region of higher temperature to a region of lower temperature. Heat does not flow spontaneously from lower temperature to higher, but it can be made to flow in this direction if work is performed. The work required to transfer a given amount of heat is usually much less than the amount of heat; this is the motivation for using heat pumps in applications such as the heating of water and the interior of buildings.[9]

The amount of work required to drive an amount of heat Q from a lower-temperature reservoir such as ambient air to a higher-temperature reservoir such as the interior of a building is: where

  • is the work performed on the working fluid by the heat pump's compressor.
  • is the heat transferred from the lower-temperature reservoir to the higher-temperature reservoir.
  • is the instantaneous coefficient of performance for the heat pump at the temperatures prevailing in the reservoirs at one instant.

The coefficient of performance of a heat pump is greater than one so the work required is less than the heat transferred, making a heat pump a more efficient form of heating than electrical resistance heating. As the temperature of the higher-temperature reservoir increases in response to the heat flowing into it, the coefficient of performance decreases, causing an increasing amount of work to be required for each unit of heat being transferred.[9]

The coefficient of performance, and the work required by a heat pump can be calculated easily by considering an ideal heat pump operating on the reversed Carnot cycle:

  • If the low-temperature reservoir is at a temperature of 270 K (−3 °C) and the interior of the building is at 280 K (7 °C) the relevant coefficient of performance is 27. This means only 1 joule of work is required to transfer 27 joules of heat from a reservoir at 270 K to another at 280 K. The one joule of work ultimately ends up as thermal energy in the interior of the building so for each 27 joules of heat that are removed from the low-temperature reservoir, 28 joules of heat are added to the building interior, making the heat pump even more attractive from an efficiency perspective.[note 1]
  • As the temperature of the interior of the building rises progressively to 300 K (27 °C) the coefficient of performance falls progressively to 9. This means each joule of work is responsible for transferring 9 joules of heat out of the low-temperature reservoir and into the building. Again, the 1 joule of work ultimately ends up as thermal energy in the interior of the building so 10 joules of heat are added to the building interior.[note 2]

This is the theoretical amount of heat pumped but in practice it will be less for various reasons, for example if the outside unit has been installed where there is not enough airflow. More data sharing with owners and academics—perhaps from heat meters—could improve efficiency in the long run.[11]

History

[edit]

Milestones:

1748
William Cullen demonstrates artificial refrigeration.[12]
1834
Jacob Perkins patents a design for a practical refrigerator using dimethyl ether.[13]
1852
Lord Kelvin describes the theory underlying heat pumps.[14]
1855–1857
Peter von Rittinger develops and builds the first heat pump.[15]
1877
In the period before 1875, heat pumps were for the time being pursued for vapour compression evaporation (open heat pump process) in salt works with their obvious advantages for saving wood and coal. In 1857, Peter von Rittinger was the first to try to implement the idea of vapor compression in a small pilot plant. Presumably inspired by Rittinger's experiments in Ebensee, Antoine-Paul Piccard from the University of Lausanne and the engineer J. H. Weibel from the Weibel–Briquet company in Geneva built the world's first really functioning vapor compression system with a two-stage piston compressor. In 1877 this first heat pump in Switzerland was installed in the Bex salt works.[14][16]
1928
Aurel Stodola constructs a closed-loop heat pump (water source from Lake Geneva) which provides heating for the Geneva city hall to this day.[17][unreliable source?]
1937–1945
During the First World War, fuel prices were very high in Switzerland but it had plenty of hydropower.[14]: 18  In the period before and especially during the Second World War, when neutral Switzerland was completely surrounded by fascist-ruled countries, the coal shortage became alarming again. Thanks to their leading position in energy technology, the Swiss companies Sulzer, Escher Wyss and Brown Boveri built and put in operation around 35 heat pumps between 1937 and 1945. The main heat sources were lake water, river water, groundwater, and waste heat. Particularly noteworthy are the six historic heat pumps from the city of Zurich with heat outputs from 100 kW to 6 MW. An international milestone is the heat pump built by Escher Wyss in 1937/38 to replace the wood stoves in the City Hall of Zurich. To avoid noise and vibrations, a recently developed rotary piston compressor was used. This historic heat pump heated the town hall for 63 years until 2001. Only then was it replaced by a new, more efficient heat pump.[14]
1945
John Sumner, City Electrical Engineer for Norwich, installs an experimental water-source heat pump fed central heating system, using a nearby river to heat new Council administrative buildings. It had a seasonal efficiency ratio of 3.42, average thermal delivery of 147 kW, and peak output of 234 kW.[18]
1948
Robert C. Webber is credited as developing and building the first ground-source heat pump.[19]
1951
First large scale installation—the Royal Festival Hall in London is opened with a town gas-powered reversible water-source heat pump, fed by the Thames, for both winter heating and summer cooling needs.[18]
2019
The Kigali Amendment to phase out harmful refrigerants takes effect.

Types

[edit]

Air-source

[edit]
Heat pump on balcony of apartment

An air source heat pump (ASHP) is a heat pump that can absorb heat from air outside a building and release it inside; it uses the same vapor-compression refrigeration process and much the same equipment as an air conditioner, but in the opposite direction. ASHPs are the most common type of heat pump and, usually being smaller, tend to be used to heat individual houses or flats rather than blocks, districts or industrial processes.[20]

Air-to-air heat pumps provide hot or cold air directly to rooms, but do not usually provide hot water. Air-to-water heat pumps use radiators or underfloor heating to heat a whole house and are often also used to provide domestic hot water.

An ASHP can typically gain 4 kWh thermal energy from 1 kWh electric energy. They are optimized for flow temperatures between 30 and 40 °C (86 and 104 °F), suitable for buildings with heat emitters sized for low flow temperatures. With losses in efficiency, an ASHP can even provide full central heating with a flow temperature up to 80 °C (176 °F).[21]

As of 2023 about 10% of building heating worldwide is from ASHPs. They are the main way to phase out gas boilers (also known as "furnaces") from houses, to avoid their greenhouse gas emissions.[22]

Air-source heat pumps are used to move heat between two heat exchangers, one outside the building which is fitted with fins through which air is forced using a fan and the other which either directly heats the air inside the building or heats water which is then circulated around the building through radiators or underfloor heating which releases the heat to the building. These devices can also operate in a cooling mode where they extract heat via the internal heat exchanger and eject it into the ambient air using the external heat exchanger. Some can be used to heat water for washing which is stored in a domestic hot water tank.[23]

Air-source heat pumps are relatively easy and inexpensive to install, so are the most widely used type. In mild weather, coefficient of performance (COP) may be between 2 and 5, while at temperatures below around −8 °C (18 °F) an air-source heat pump may still achieve a COP of 1 to 4.[24]

While older air-source heat pumps performed relatively poorly at low temperatures and were better suited for warm climates, newer models with variable-speed compressors remain highly efficient in freezing conditions allowing for wide adoption and cost savings in places like Minnesota and Maine in the United States.[25]

Ground source

[edit]
 
A heat pump in combination with heat and cold storage

A ground source heat pump (also geothermal heat pump) is a heating/cooling system for buildings that use a type of heat pump to transfer heat to or from the ground, taking advantage of the relative constancy of temperatures of the earth through the seasons. Ground-source heat pumps (GSHPs)—or geothermal heat pumps (GHP), as they are commonly termed in North America—are among the most energy-efficient technologies for providing HVAC and water heating, using less energy than can be achieved by use of resistive electric heaters.

Efficiency is given as a coefficient of performance (CoP) which is typically in the range 3-6, meaning that the devices provide 3-6 units of heat for each unit of electricity used. Setup costs are higher than for other heating systems, due to the requirement of installing ground loops over large areas or of drilling bore holes, hence ground source is often installed when new blocks of flats are built.[26] Air-source heat pumps have lower set-up costs.

Heat recovery ventilation

[edit]

Exhaust air heat pumps extract heat from the exhaust air of a building and require mechanical ventilation. Two classes exist:

  • Exhaust air-air heat pumps transfer heat to intake air.
  • Exhaust air-water heat pumps transfer heat to a heating circuit that includes a tank of domestic hot water.

Solar-assisted

[edit]
 
Hybrid photovoltaic-thermal solar panels of a SAHP in an experimental installation at Department of Energy at Polytechnic of Milan

A solar-assisted heat pump (SAHP) is a machine that combines a heat pump and thermal solar panels and/or PV solar panels in a single integrated system.[27] Typically these two technologies are used separately (or only placing them in parallel) to produce hot water.[28] In this system the solar thermal panel performs the function of the low temperature heat source and the heat produced is used to feed the heat pump's evaporator.[29] The goal of this system is to get high coefficient of performance (COP) and then produce energy in a more efficient and less expensive way.

It is possible to use any type of solar thermal panel (sheet and tubes, roll-bond, heat pipe, thermal plates) or hybrid (mono/polycrystalline, thin film) in combination with the heat pump. The use of a hybrid panel is preferable because it allows covering a part of the electricity demand of the heat pump and reduce the power consumption and consequently the variable costs of the system.

Water-source

[edit]
Water-source heat exchanger being installed

A water-source heat pump works in a similar manner to a ground-source heat pump, except that it takes heat from a body of water rather than the ground. The body of water does, however, need to be large enough to be able to withstand the cooling effect of the unit without freezing or creating an adverse effect for wildlife.[30] The largest water-source heat pump was installed in the Danish town of Esbjerg in 2023.[31][32]

Others

[edit]

A thermoacoustic heat pump operates as a thermoacoustic heat engine without refrigerant but instead uses a standing wave in a sealed chamber driven by a loudspeaker to achieve a temperature difference across the chamber.[33]

Electrocaloric heat pumps are solid state.[34]

Applications

[edit]

The International Energy Agency estimated that, as of 2021, heat pumps installed in buildings have a combined capacity of more than 1000 GW.[4] They are used for heating, ventilation, and air conditioning (HVAC) and may also provide domestic hot water and tumble clothes drying.[35] The purchase costs are supported in various countries by consumer rebates.[36]

Space heating and sometimes also cooling

[edit]

In HVAC applications, a heat pump is typically a vapor-compression refrigeration device that includes a reversing valve and optimized heat exchangers so that the direction of heat flow (thermal energy movement) may be reversed. The reversing valve switches the direction of refrigerant through the cycle and therefore the heat pump may deliver either heating or cooling to a building.

Because the two heat exchangers, the condenser and evaporator, must swap functions, they are optimized to perform adequately in both modes. Therefore, the Seasonal Energy Efficiency Rating (SEER in the US) or European seasonal energy efficiency ratio of a reversible heat pump is typically slightly less than those of two separately optimized machines. For equipment to receive the US Energy Star rating, it must have a rating of at least 14 SEER. Pumps with ratings of 18 SEER or above are considered highly efficient. The highest efficiency heat pumps manufactured are up to 24 SEER.[37]

Heating seasonal performance factor (in the US) or Seasonal Performance Factor (in Europe) are ratings of heating performance. The SPF is Total heat output per annum / Total electricity consumed per annum in other words the average heating COP over the year.[38]

Window mounted heat pump

[edit]
Saddle-style window mounted heat pump 3D sketch

Window mounted heat pumps run on standard 120v AC outlets and provide heating, cooling, and humidity control. They are more efficient with lower noise levels, condensation management, and a smaller footprint than window mounted air conditioners that just do cooling.[39]

Water heating

[edit]

In water heating applications, heat pumps may be used to heat or preheat water for swimming pools, homes or industry. Usually heat is extracted from outdoor air and transferred to an indoor water tank.[40][41]

District heating

[edit]

Large (megawatt-scale) heat pumps are used for district heating.[42] However as of 2022 about 90% of district heat is from fossil fuels.[43] In Europe, heat pumps account for a mere 1% of heat supply in district heating networks but several countries have targets to decarbonise their networks between 2030 and 2040.[4] Possible sources of heat for such applications are sewage water, ambient water (e.g. sea, lake and river water), industrial waste heat, geothermal energy, flue gas, waste heat from district cooling and heat from solar seasonal thermal energy storage.[44] Large-scale heat pumps for district heating combined with thermal energy storage offer high flexibility for the integration of variable renewable energy. Therefore, they are regarded as a key technology for limiting climate change by phasing out fossil fuels.[44][45] They are also a crucial element of systems which can both heat and cool districts.[46]

Industrial heating

[edit]

There is great potential to reduce the energy consumption and related greenhouse gas emissions in industry by application of industrial heat pumps, for example for process heat.[47][48] Short payback periods of less than 2 years are possible, while achieving a high reduction of CO2 emissions (in some cases more than 50%).[49][50] Industrial heat pumps can heat up to 200 °C, and can meet the heating demands of many light industries.[51][52] In Europe alone, 15 GW of heat pumps could be installed in 3,000 facilities in the paper, food and chemicals industries.[4]

Performance

[edit]

The performance of a heat pump is determined by the ability of the pump to extract heat from a low temperature environment (the source) and deliver it to a higher temperature environment (the sink).[53] Performance varies, depending on installation details, temperature differences, site elevation, location on site, pipe runs, flow rates, and maintenance.

In general, heat pumps work most efficiently (that is, the heat output produced for a given energy input) when the difference between the heat source and the heat sink is small. When using a heat pump for space or water heating, therefore, the heat pump will be most efficient in mild conditions, and decline in efficiency on very cold days. Performance metrics supplied to consumers attempt to take this variation into account.

Common performance metrics are the SEER (in cooling mode) and seasonal coefficient of performance (SCOP) (commonly used just for heating), although SCOP can be used for both modes of operation.[53] Larger values of either metric indicate better performance.[53] When comparing the performance of heat pumps, the term performance is preferred to efficiency, with coefficient of performance (COP) being used to describe the ratio of useful heat movement per work input.[53] An electrical resistance heater has a COP of 1.0, which is considerably lower than a well-designed heat pump which will typically have a COP of 3 to 5 with an external temperature of 10 °C and an internal temperature of 20 °C. Because the ground is a constant temperature source, a ground-source heat pump is not subjected to large temperature fluctuations, and therefore is the most energy-efficient type of heat pump.[53]

The "seasonal coefficient of performance" (SCOP) is a measure of the aggregate energy efficiency measure over a period of one year which is dependent on regional climate.[53] One framework for this calculation is given by the Commission Regulation (EU) No. 813/2013.[54]

A heat pump's operating performance in cooling mode is characterized in the US by either its energy efficiency ratio (EER) or seasonal energy efficiency ratio (SEER), both of which have units of BTU/(h·W) (note that 1 BTU/(h·W) = 0.293 W/W) and larger values indicate better performance.

COP variation with output temperature
Pump type and source Typical use 35 °C
(e.g. heated screed floor)
45 °C
(e.g. heated screed floor)
55 °C
(e.g. heated timber floor)
65 °C
(e.g. radiator or DHW)
75 °C
(e.g. radiator and DHW)
85 °C
(e.g. radiator and DHW)
High-efficiency air-source heat pump (ASHP), air at −20 °C[55]   2.2 2.0 ‐ ‐ ‐ ‐
Two-stage ASHP, air at −20 °C[56] Low source temperature 2.4 2.2 1.9 ‐ ‐ ‐
High-efficiency ASHP, air at 0 °C[55] Low output temperature 3.8 2.8 2.2 2.0 ‐ ‐
Prototype transcritical CO
2
(R744) heat pump with tripartite gas cooler, source at 0 °C[57]
High output temperature 3.3 ‐ ‐ 4.2 ‐ 3.0
Ground-source heat pump (GSHP), water at 0 °C[55]   5.0 3.7 2.9 2.4 ‐ ‐
GSHP, ground at 10 °C[55] Low output temperature 7.2 5.0 3.7 2.9 2.4 ‐
Theoretical Carnot cycle limit, source −20 °C   5.6 4.9 4.4 4.0 3.7 3.4
Theoretical Carnot cycle limit, source 0 °C   8.8 7.1 6.0 5.2 4.6 4.2
Theoretical Lorentzen cycle limit (CO
2
pump), return fluid 25 °C, source 0 °C[57]
  10.1 8.8 7.9 7.1 6.5 6.1
Theoretical Carnot cycle limit, source 10 °C   12.3 9.1 7.3 6.1 5.4 4.8

Carbon footprint

[edit]

The carbon footprint of heat pumps depends on their individual efficiency and how electricity is produced. An increasing share of low-carbon energy sources such as wind and solar will lower the impact on the climate.

heating system emissions of energy source efficiency resulting emissions for thermal energy
heat pump with onshore wind power 11 gCO2/kWh[58] 400% (COP=4) 3 gCO2/kWh
heat pump with global electricity mix 436 gCO2/kWh[59] (2022) 400% (COP=4) 109 gCO2/kWh
natural-gas thermal (high efficiency) 201 gCO2/kWh[60] 90%[citation needed] 223 gCO2/kWh
heat pump
electricity by lignite (old power plant)
and low performance
1221 gCO2/kWh[60] 300% (COP=3) 407 gCO2/kWh

In most settings, heat pumps will reduce CO2 emissions compared to heating systems powered by fossil fuels.[61] In regions accounting for 70% of world energy consumption, the emissions savings of heat pumps compared with a high-efficiency gas boiler are on average above 45% and reach 80% in countries with cleaner electricity mixes.[4] These values can be improved by 10 percentage points, respectively, with alternative refrigerants. In the United States, 70% of houses could reduce emissions by installing a heat pump.[62][4] The rising share of renewable electricity generation in many countries is set to increase the emissions savings from heat pumps over time.[4]

Heating systems powered by green hydrogen are also low-carbon and may become competitors, but are much less efficient due to the energy loss associated with hydrogen conversion, transport and use. In addition, not enough green hydrogen is expected to be available before the 2030s or 2040s.[63][64]

Operation

[edit]
Figure 2: Temperature–entropy diagram of the vapor-compression cycle
An internal view of the outdoor unit of an Ecodan air source heat pump
Large heat pump setup for a commercial building
Wiring and connections to a central air unit inside

Vapor-compression uses a circulating refrigerant as the medium which absorbs heat from one space, compresses it thereby increasing its temperature before releasing it in another space. The system normally has eight main components: a compressor, a reservoir, a reversing valve which selects between heating and cooling mode, two thermal expansion valves (one used when in heating mode and the other when used in cooling mode) and two heat exchangers, one associated with the external heat source/sink and the other with the interior. In heating mode the external heat exchanger is the evaporator and the internal one being the condenser; in cooling mode the roles are reversed.

Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor[65] and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with either cooling water or cooling air flowing across the coil or tubes. In heating mode this heat is used to heat the building using the internal heat exchanger, and in cooling mode this heat is rejected via the external heat exchanger.

The condensed, liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and-vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.

The cold mixture is then routed through the coil or tubes in the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapor mixture. That warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature. The evaporator is where the circulating refrigerant absorbs and removes heat which is subsequently rejected in the condenser and transferred elsewhere by the water or air used in the condenser.

To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and is routed back into the compressor.

Over time, the evaporator may collect ice or water from ambient humidity. The ice is melted through defrosting cycle. An internal heat exchanger is either used to heat/cool the interior air directly or to heat water that is then circulated through radiators or underfloor heating circuit to either heat or cool the buildings.

Improvement of coefficient of performance by subcooling

[edit]

Heat input can be improved if the refrigerant enters the evaporator with a lower vapor content. This can be achieved by cooling the liquid refrigerant after condensation. The gaseous refrigerant condenses on the heat exchange surface of the condenser. To achieve a heat flow from the gaseous flow center to the wall of the condenser, the temperature of the liquid refrigerant must be lower than the condensation temperature.

Additional subcooling can be achieved by heat exchange between relatively warm liquid refrigerant leaving the condenser and the cooler refrigerant vapor emerging from the evaporator. The enthalpy difference required for the subcooling leads to the superheating of the vapor drawn into the compressor. When the increase in cooling achieved by subcooling is greater that the compressor drive input required to overcome the additional pressure losses, such a heat exchange improves the coefficient of performance.[66]

One disadvantage of the subcooling of liquids is that the difference between the condensing temperature and the heat-sink temperature must be larger. This leads to a moderately high pressure difference between condensing and evaporating pressure, whereby the compressor energy increases.[citation needed]

Refrigerant choice

[edit]

Pure refrigerants can be divided into organic substances (hydrocarbons (HCs), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), and HCFOs), and inorganic substances (ammonia (NH
3
), carbon dioxide (CO
2
), and water (H
2O
)[67]).[68] Their boiling points are usually below −25 °C.[69]

In the past 200 years, the standards and requirements for new refrigerants have changed. Nowadays low global warming potential (GWP) is required, in addition to all the previous requirements for safety, practicality, material compatibility, appropriate atmospheric life,[clarification needed] and compatibility with high-efficiency products. By 2022, devices using refrigerants with a very low GWP still have a small market share but are expected to play an increasing role due to enforced regulations,[70] as most countries have now ratified the Kigali Amendment to ban HFCs.[71] Isobutane (R600A) and propane (R290) are far less harmful to the environment than conventional hydrofluorocarbons (HFC) and are already being used in air-source heat pumps.[72] Propane may be the most suitable for high temperature heat pumps.[73] Ammonia (R717) and carbon dioxide (R-744) also have a low GWP. As of 2023 smaller CO
2
heat pumps are not widely available and research and development of them continues.[74] A 2024 report said that refrigerants with GWP are vulnerable to further international restrictions.[75]

Until the 1990s, heat pumps, along with fridges and other related products used chlorofluorocarbons (CFCs) as refrigerants, which caused major damage to the ozone layer when released into the atmosphere. Use of these chemicals was banned or severely restricted by the Montreal Protocol of August 1987.[76]

Replacements, including R-134a and R-410A, are hydrofluorocarbons (HFC) with similar thermodynamic properties with insignificant ozone depletion potential (ODP) but had problematic GWP.[77] HFCs are powerful greenhouse gases which contribute to climate change.[78][79] Dimethyl ether (DME) also gained in popularity as a refrigerant in combination with R404a.[80] More recent refrigerants include difluoromethane (R32) with a lower GWP, but still over 600.

refrigerant 20-year GWP 100-year GWP
R-290 propane[81] 0.072 0.02
R-600a isobutane   3[82]
R-32[81] 491 136
R-410a[83] 4705 2285
R-134a[83] 4060 1470
R-404a[83] 7258 4808

Devices with R-290 refrigerant (propane) are expected to play a key role in the future.[73][84] The 100-year GWP of propane, at 0.02, is extremely low and is approximately 7000 times less than R-32. However, the flammability of propane requires additional safety measures: the maximum safe charges have been set significantly lower than for lower flammability refrigerants (only allowing approximately 13.5 times less refrigerant in the system than R-32).[85][86][87] This means that R-290 is not suitable for all situations or locations. Nonetheless, by 2022, an increasing number of devices with R-290 were offered for domestic use, especially in Europe.[citation needed]

At the same time,[when?] HFC refrigerants still dominate the market. Recent government mandates have seen the phase-out of R-22 refrigerant. Replacements such as R-32 and R-410A are being promoted as environmentally friendly but still have a high GWP.[88] A heat pump typically uses 3 kg of refrigerant. With R-32 this amount still has a 20-year impact equivalent to 7 tons of CO2, which corresponds to two years of natural gas heating in an average household. Refrigerants with a high ODP have already been phased out.[citation needed]

Government incentives

[edit]

Financial incentives aim to protect consumers from high fossil gas costs and to reduce greenhouse gas emissions,[89] and are currently available in more than 30 countries around the world, covering more than 70% of global heating demand in 2021.[4]

Australia

[edit]

Food processors, brewers, petfood producers and other industrial energy users are exploring whether it is feasible to use renewable energy to produce industrial-grade heat. Process heating accounts for the largest share of onsite energy use in Australian manufacturing, with lower-temperature operations like food production particularly well-suited to transition to renewables.

To help producers understand how they could benefit from making the switch, the Australian Renewable Energy Agency (ARENA) provided funding to the Australian Alliance for Energy Productivity (A2EP) to undertake pre-feasibility studies at a range of sites around Australia, with the most promising locations advancing to full feasibility studies.[90]

In an effort to incentivize energy efficiency and reduce environmental impact, the Australian states of Victoria, New South Wales, and Queensland have implemented rebate programs targeting the upgrade of existing hot water systems. These programs specifically encourage the transition from traditional gas or electric systems to heat pump based systems.[91][92][93][94][95]

Canada

[edit]

In 2022, the Canada Greener Homes Grant[96] provides up to $5000 for upgrades (including certain heat pumps), and $600 for energy efficiency evaluations.

China

[edit]

Purchase subsidies in rural areas in the 2010s reduced burning coal for heating, which had been causing ill health.[97]

In the 2024 report by the International Energy Agency (IEA) titled "The Future of Heat Pumps in China," it is highlighted that China, as the world's largest market for heat pumps in buildings, plays a critical role in the global industry. The country accounts for over one-quarter of global sales, with a 12% increase in 2023 alone, despite a global sales dip of 3% the same year.[98]

Heat pumps are now used in approximately 8% of all heating equipment sales for buildings in China as of 2022, and they are increasingly becoming the norm in central and southern regions for both heating and cooling. Despite their higher upfront costs and relatively low awareness, heat pumps are favored for their energy efficiency, consuming three to five times less energy than electric heaters or fossil fuel-based solutions. Currently, decentralized heat pumps installed in Chinese buildings represent a quarter of the global installed capacity, with a total capacity exceeding 250 GW, which covers around 4% of the heating needs in buildings.[98]

Under the Announced Pledges Scenario (APS), which aligns with China's carbon neutrality goals, the capacity is expected to reach 1,400 GW by 2050, meeting 25% of heating needs. This scenario would require an installation of about 100 GW of heat pumps annually until 2050. Furthermore, the heat pump sector in China employs over 300,000 people, with employment numbers expected to double by 2050, underscoring the importance of vocational training for industry growth. This robust development in the heat pump market is set to play a significant role in reducing direct emissions in buildings by 30% and cutting PM2.5 emissions from residential heating by nearly 80% by 2030.[98][99]

European Union

[edit]

To speed up the deployment rate of heat pumps, the European Commission launched the Heat Pump Accelerator Platform in November 2024.[100] It will encourage industry experts, policymakers, and stakeholders to collaborate, share best practices and ideas, and jointly discuss measures that promote sustainable heating solutions.[101]

United Kingdom

[edit]

Until 2027 fixed heat pumps have no Value Added Tax (VAT).[102] As of 2022 the installation cost of a heat pump is more than a gas boiler, but with the "Boiler Upgrade Scheme"[103] government grant and assuming electricity/gas costs remain similar their lifetime costs would be similar on average.[104] However lifetime cost relative to a gas boiler varies considerably depending on several factors, such as the quality of the heat pump installation and the tariff used.[105] In 2024 England was criticised for still allowing new homes to be built with gas boilers, unlike some other counties where this is banned.[106]

United States

[edit]

The High-efficiency Electric Home Rebate Program was created in 2022 to award grants to State energy offices and Indian Tribes in order to establish state-wide high-efficiency electric-home rebates. Effective immediately, American households are eligible for a tax credit to cover the costs of buying and installing a heat pump, up to $2,000. Starting in 2023, low- and moderate-level income households will be eligible for a heat-pump rebate of up to $8,000.[107]

In 2022, more heat pumps were sold in the United States than natural gas furnaces.[108]

In November 2023 Biden's administration allocated 169 million dollars from the Inflation Reduction Act to speed up production of heat pumps. It used the Defense Production Act to do so, because according to the administration, energy that is better for the climate is also better for national security.[109]

Notes

[edit]
  1. ^ As explained in Coefficient of performance TheoreticalMaxCOP = (desiredIndoorTempC + 273) ÷ (desiredIndoorTempC - outsideTempC) = (7+273) ÷ (7 - (-3)) = 280÷10 = 28 [10]
  2. ^ As explained in Coefficient of performance TheoreticalMaxCOP = (desiredIndoorTempC + 273) ÷ (desiredIndoorTempC - outsideTempC) = (27+273) ÷ (27 - (-3)) = 300÷30 = 10[10]

References

[edit]
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  5. ^ IPCC AR6 WG3 Ch11 2022, Sec. 11.3.4.1.
  6. ^ IPCC SR15 Ch2 2018, p. 142.
  7. ^ Everitt, Neil (11 September 2023). "Study proves heat pump efficiency at low temperatures". Cooling Post. Retrieved 22 January 2024.
  8. ^ Deetjen, Thomas A.; Walsh, Liam; Vaishnav, Parth (28 July 2021). "US residential heat pumps: the private economic potential and its emissions, health, and grid impacts". Environmental Research Letters. 16 (8): 084024. Bibcode:2021ERL....16h4024D. doi:10.1088/1748-9326/ac10dc. ISSN 1748-9326. S2CID 236486619.
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Sources

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IPCC reports

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Other

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  • Media related to Heat pumps at Wikimedia Commons

 

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Frequently Asked Questions

Common signs include reduced airflow, unusual noises coming from the AC unit, increased dust buildup in your home, and higher energy bills due to decreased efficiency.
Turn off the AC system, remove the filter according to the manufacturers instructions, rinse it gently with water to remove debris, and let it air dry completely before reinstalling or proceeding with any repairs.
Minor damages like small tears can sometimes be patched up using specialized adhesives. However, significant damage often requires a complete replacement for optimal performance and efficiency.
Ensure that the filter is installed correctly without gaps. If problems persist after repair attempts, consider consulting a professional HVAC technician to diagnose potential underlying issues within the system.