Air source heat pump

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This article is about details of the most common type of heat pump. For more general information, see heat pump.

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.<ref name=":9">"Why Britain's homes will need different types of heat pump". The Economist. ISSN 0013-0613. Retrieved 19 February 2024.</ref>

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 (86–104 °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).<ref>Le, Khoa; Huang, M.J.; Hewitt, Neil (2018). "Domestic High Temperature Air Source Heat Pump: Performance Analysis Using TRNSYS Simulations". International High Performance Buildings Conference. West Lafayette, IN, USA: 5th International High Performance Buildings Conference at Purdue University: 1. Retrieved 20 February 2022.</ref>

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.<ref name=":0" />

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.<ref>Lawrence, Karen. "Air source heat pumps explained". Which?. Archived from the original on 4 October 2022. Retrieved 4 October 2022.</ref>

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.<ref>Canada, Natural Resources (22 April 2009). "Heating and Cooling With a Heat Pump". natural-resources.canada.ca. Retrieved 22 February 2024.</ref>

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.<ref>"Heat pumps do work in the cold – Americans just don't know it yet". Grist. 9 May 2022. Archived from the original on 9 May 2022. Retrieved 9 May 2022.</ref>

Technology

Air source heat pump

Air at any natural temperature contains some heat. An air source heat pump transfers some of this from one place to another, for example between the outside and inside of a building.

An air-to air system can be designed to transfer heat in either direction, to heat or cool the interior of the building in winter and summer respectively. Internal ducting may be used to distribute the air.<ref name=":1">"The 9 Types of Heat Pumps". ACHR News. Retrieved 15 September 2023.</ref> An air-to-water system only pumps heat inwards, and can provide space heating and hot water.<ref>Lawrence, Karen; Massey, Jake (14 July 2023). "Air source heat pumps explained". Which?.</ref> For simplicity, the description below focuses on use for interior heating.

The technology is similar to a refrigerator or freezer or air conditioning unit: the different effect is due to the location of the different system components. Just as the pipes on the back of a refrigerator become warm as the interior cools, so an ASHP warms the inside of a building whilst cooling the outside air.

The main components of a split-system (called split as there are both inside and outside coils) air source heat pump are:

  • An outdoor evaporator heat exchanger coil, which extracts heat from ambient air
  • One or more<ref>"Ductless Mini-Split Heat Pumps". Energy.gov. Retrieved 14 September 2023.</ref> indoor condenser heat exchanger coils. They transfer the heat into the indoor air, or an indoor heating system such as water-filled radiators or underfloor circuits and a domestic hot water tank.

Less commonly a packaged ASHP has everything outside, with hot (or cold) air sent inside through a duct.<ref>"Air-Source Heat Pumps". Energy.gov. Retrieved 14 September 2023.</ref>

These are also called monobloc and are useful for keeping flammable propane outside the house.<ref name=":0" />

An ASHP can provide three or four times as much heat as an electric resistance heater using the same amount of electricity.<ref name=":5" /> Burning gas or oil will emit carbon dioxide and also NOx, which can be harmful to health.<ref name=GBN_1>"Gas boilers and NOx: the hidden emitter" (PDF). Energy & Climate Intelligence Unit. October 2020. Retrieved 20 January 2024.</ref> An air source heat pump issues no carbon dioxide, nitrogen oxide or any other kind of gas. It uses a small amount of electricity to transfer a large amount of heat.

Unlike an air conditioning unit, most ASHPs are reversible and are able to either warm or cool buildings<ref>The Contribution of Reversible Air-to-Air Heat Pumps to the UK's Obligation under the Renewable Energy Directive (2009/28/EC) - A Delta-ee Report for the Department for Business, Energy and Industrial Strategy (PDF) (Report). Delta Energy & Environment. 2017. virtually all air-air heat pumps sold today are reversible (p.7)</ref> and in some cases also provide domestic hot water. The use of an air-to-water heat pump for house cooling has been criticised.<ref>Hendra, Graham (5 May 2021). "Four reasons not cool your house using a heat pump". Renewable Heating Hub. Retrieved 23 December 2023.</ref>

An internal view of the outdoor unit of an air source heat pump
A: indoor compartment, B: outdoor compartment, I: insulation, 1: condenser, 2: expansion valve, 3: evaporator, 4: compressor

Heating and cooling is accomplished by pumping a refrigerant through the heat pump's indoor and outdoor coils. Like in a refrigerator, a compressor, condenser, expansion valve and evaporator are used to change states of the refrigerant between colder liquid and hotter gas states.

When the liquid refrigerant at a low temperature and low pressure passes through the outdoor heat exchanger coils, ambient heat causes the liquid to boil (change to gas or vapor). Heat energy from the outside air has been absorbed and stored in the refrigerant as latent heat. The gas is then compressed using an electric pump; the compression increases the temperature of the gas.

Inside the building, the gas passes through a pressure valve into heat exchanger coils. There, the hot refrigerant gas condenses back to a liquid and transfers the stored latent heat to the indoor air, water heating or hot water system. The indoor air or heating water is pumped across the heat exchanger by an electric pump or fan.

The cool liquid refrigerant then re-enters the outdoor heat exchanger coils to begin a new cycle. Each cycle usually takes a few minutes.<ref name=":5">"Everything you need to know about the wild world of heat pumps". MIT Technology Review. Retrieved 19 September 2023.</ref>

Most heat pumps can also operate in a cooling mode where the cold refrigerant is moved through the indoor coils to cool the room air.

As of 2024 tech other than vapour compression is insignificant in the market.<ref>"Annex 53 Advanced Cooling/Refrigeration Technologies 2 page summary". HPT - Heat Pumping Technologies. Retrieved 19 February 2024.</ref>

Usage

ASHPs are the most common type of heat pump and, usually being smaller, are generally more suitable to heat individual houses rather than blocks of flats, compact urban districts or industrial processes.<ref name=":9" /> In dense city centres heat networks may be better than ASHP.<ref name=":9" /> Air source heat pumps are used to provide interior space heating and cooling even in colder climates, and can be used efficiently for water heating in milder climates. A major advantage of some ASHPs is that the same system may be used for heating in winter and cooling in summer. Though the cost of installation is generally high, it is less than the cost of a ground source heat pump, because a ground source heat pump requires excavation to install its ground loop. The advantage of a ground source heat pump is that it has access to the thermal storage capacity of the ground which allows it to produce more heat for less electricity in cold conditions.

Home batteries can mitigate the risk of power cuts and like ASHPs are becoming more popular.<ref>Ambrose, Jillian (14 August 2023). "UK homes install 'record number' of solar panels and heat pumps". The Guardian. ISSN 0261-3077. Retrieved 16 September 2023.</ref> Some ASHPs can be coupled to solar panels as primary energy source, with a conventional electric grid as backup source.[citation needed]

Thermal storage solutions incorporating resistance heating can be used in conjunction with ASHPs. Storage may be more cost-effective if time of use electricity rates are available. Heat is stored in high density ceramic bricks contained within a thermally-insulated enclosure;<ref>Franklin Energy Services, LLC (2011). "Air Source Heat Pump Efficiency Gains from Low Ambient Temperature Operation Using Supplemental Electric Heating: Thermal Storage Supplemental Heating Systems" (PDF). Minnesota Division of Energy Resources; Minnesota Department of Commerce. p. 9. Archived from the original (PDF) on 11 June 2014. Retrieved 15 October 2014.</ref> storage heaters are an example. ASHPs may also be paired with passive solar heating. Thermal mass (such as concrete or rocks) heated by passive solar heat can help stabilize indoor temperatures, absorbing heat during the day and releasing heat at night, when outdoor temperatures are colder and heat pump efficiency is lower.

Replacing gas heating in existing houses

Good home insulation is important.<ref name=":10" /> As of 2023 ASHPs are bigger than gas boilers and need more space outside, so the process is more complex and can be more expensive than if it was possible to just remove a gas boiler and install an ASHP in its place.<ref name=":0">"Heat pumps show how hard decarbonisation will be". The Economist. ISSN 0013-0613. Retrieved 14 September 2023.</ref><ref name=":4">Harris, B. (14 July 2023). "Heat pumps" (PDF). UK Parliament . Retrieved 20 January 2024.</ref> If running costs are important choosing the right size is important because an ASHP which is too large will be more expensive to run.<ref>"Here's How to Pick the Right Size Heat Pump for Your Home". CNET. Retrieved 18 September 2023.</ref>

It can be more complicated to retrofit conventional heating systems that use radiators/radiant panels, hot water baseboard heaters, or even smaller diameter ducting, with ASHP-sourced heat. The lower heat pump output temperatures means radiators (and possibly pipes) may have to be replaced with larger sizes, or a low temperature underfloor heating system installed instead.<ref>"Do Heat Pumps Work with Radiators? | Heat Pump House". heatpumphouse.com. Retrieved 19 February 2024.</ref>

Alternatively, a high temperature heat pump can be installed and existing heat emitters can be retained, however as of 2023 these heat pumps are more expensive to buy and run so may only be suitable for buildings which are hard to alter or insulate, such as some large historic houses.<ref>Jackman, Josh (28 January 2022). "High Temperature Heat Pumps | Are They Worth It?". The Eco Experts. Retrieved 17 September 2023.</ref>

ASHP are claimed to be healthier than fossil-fuelled heating such as gas heaters by maintaining a more even temperature and avoiding harmful fumes risk.<ref name=":10">"Advice | I tried, and failed, to install a heat pump. Here's how to do it right". Washington Post. 28 February 2023. Retrieved 19 February 2024.</ref> Also by filtering the air and reducing humidity in hot humid summer climates they are said to reduce dust and allergens and mould health risk.<ref name=":11" />

In cold climates

The outdoor unit of an air source heat pump operating in freezing conditions

Operation of normal ASHPs is generally not recommended below −10 °C.<ref name=":3" /> However ASHPs designed specifically for very cold climates (in the US these are certified under Energy Star<ref name=":2">"Can Heat Pumps Actually Work in Cold Climates?". Consumer Reports. 2 August 2022. Retrieved 15 September 2023.</ref>) can extract useful heat from ambient air as cold as −30 °C (−22 °F), however below −25 °C electric resistance heating may be more efficient.<ref name=":3">"Cold climate air source heat pumps". www.hydro.mb.ca. Retrieved 15 September 2023.</ref> This is made possible by the use of variable-speed compressors, powered by inverters.<ref name=":2" /> Although air source heat pumps are less efficient than well-installed ground source heat pumps in cold conditions, air source heat pumps have lower initial costs and may be the most economic or practical choice.<ref>"Are Air Source Heat Pumps A Threat To Geothermal Heat Pump Suppliers?". Forbes. Retrieved 15 October 2014.</ref> A hybrid system, with both a heat pump and an alternative source of heat such as a fossil fuel boiler, may be suitable if it is impractical to properly insulate a large house.<ref name=":8">"Hybrid heat pumps". Energy Saving Trust. Retrieved 30 September 2023.</ref> Alternatively multiple heat pumps or a high temperature heat pump may be considered.<ref name=":8" />

In some weather conditions condensation will form and then freeze onto the coils of the heat exchanger of the outdoor unit, reducing air flow through the coils. To clear this the unit operates a defrost cycle, switching to cooling mode for a few minutes, heating the coils until the ice melts. Air-to-water heat pumps use heat from the circulating water for this purpose, which results in a small and probably undetectable drop in water temperature;<ref>"How to defrost a heat pump in winter". Evergreen Energy. February 2018. Retrieved 14 September 2021.</ref> for air-to-air systems heat is either taken from the air in the building or using an electrical heater.<ref>"Defrost Cycle of a Heat Pump". International Association of Home Inspectors. Retrieved 14 September 2021.</ref> Some air-to-air systems simply stop the operation of the fans of both units and switch to cooling mode, so that the outdoor unit returns to being the condenser such that it heats up and defrosts.

Noise

An air source heat pump requires an outdoor unit containing moving mechanical components including fans which produce noise. Modern devices offer schedules for silent mode operation with reduced fan speed. This will reduce the maximum heating power but can be applied at mild outdoor temperatures without efficiency loss. Acoustic enclosures are another approach to reduce the noise in a sensitive neighbourhood. In insulated buildings, operation can be paused at night without significant temperature loss. Only at low temperatures, frost protection forces operation after a few hours. Proper siting is also important.<ref>"HEAT PUMPS & NOISE: A NEIGHBOURLY INSTALLATION GUIDE" (PDF).</ref>

In the United States, the allowed nighttime noise level is 45 A-weighted decibels (dBA),<ref>"Monica S. Hammer, Tracy K. Swinburn, and Richard L. Neitzel "Environmental Noise Pollution in the United States: Developing an Effective Public Health Response" Environmental Health Perspectives V122,I2,2014". Archived from the original on 2 July 2016. Retrieved 25 January 2016.</ref> and in the UK 42 measured from the nearest neighbour.<ref>"How Noisy Are Heat Pumps?". Heat Pumps UK. 11 April 2022. Retrieved 14 September 2023.</ref> In Germany the limit in residential areas is 35, which is usually measured by European Standard EN 12102.<ref>"Petition No 0922/2020 by F.B. (German) on low-frequency noise limit values" (PDF).</ref> In the United Kingdom, the adoption of Absorptive Acoustic fencing has become increasingly prevalent, especially in commercial properties utilising Air Source Heat Pumps.<ref>"Acoustic Enclosures For Air Source Heat Pumps".</ref>

Another feature of air source heat pumps (ASHPs) external heat exchangers is their need to stop the fan from time to time for a period of several minutes in order to get rid of frost that accumulates in the outdoor unit in the heating mode. After that, the heat pump starts to work again. This part of the work cycle results in two sudden changes of the noise made by the fan. The acoustic effect of such disruption is especially powerful in quiet environments where background nighttime noise may be as low as 0 to 10dBA. This is included in legislation in France. According to the French concept of noise nuisance, "noise emergence" is the difference between ambient noise including the disturbing noise, and ambient noise without the disturbing noise.<ref>"Hiil innovating Justice "How to determine acceptable levels of noise nuisance (France)". Archived from the original on 12 February 2017. Retrieved 25 January 2016.</ref><ref>"Code de la santé publique – Article R1334-33 (in French)". Retrieved 8 February 2016.</ref>

By contrast a ground source heat pump has no need for an outdoor unit with moving mechanical components.

Efficiency ratings

The efficiency of air source heat pumps is measured by the coefficient of performance (COP). A COP of 4 means the heat pump produces 4 units of heat energy for every 1 unit of electricity it consumes. Within temperature ranges of −3 °C (27 °F) to 10 °C (50 °F), the COP for many machines is fairly stable. Approximately TheoreticalMaxCOP = (desiredIndoorTempC + 273) ÷ (desiredIndoorTempC - outsideTempC).[citation needed]<ref>"Is there some theoretical maximum coefficient of performance (COP) for heat pumps and chillers?". Physics Stack Exchange. Retrieved 19 February 2024.</ref>Template:Better cite

In mild weather with an outside temperature of 10 °C (50 °F), the COP of efficient air source heat pumps ranges from 4 to 6.<ref>"Wärmepumpen mit Prüf- / Effizienznachweis (heat pumps with efficiency validation)". BAFA (Federal Office for Economic Affairs and Export Control in Germany). Retrieved 20 February 2022.</ref> However, on a cold winter day, it takes more work to move the same amount of heat indoors than on a mild day.<ref name=EH_1>"Air Source Heat Pumps". ICAX. Retrieved 20 January 2024.</ref> The heat pump's performance is limited by the Carnot cycle and will approach 1.0 as the outdoor-to-indoor temperature difference increases, which for most air source heat pumps happens as outdoor temperatures approach −18 °C (0 °F).[citation needed]Heat pump construction that enables carbon dioxide as a refrigerant may have a COP of greater than 2 even down to −20 °C, pushing the break-even figure downward to −30 °C (−22 °F).[citation needed] A ground source heat pump has comparatively less of a change in COP as outdoor temperatures change, because the ground from which they extract heat has a more constant temperature than outdoor air.

The design of a heat pump has a considerable impact on its efficiency. Many air source heat pumps are designed primarily as air conditioning units, mainly for use in summer temperatures. Designing a heat pump specifically for the purpose of heat exchange can attain greater COP and an extended life cycle. The principal changes are in the scale and type of compressor and evaporator.

Seasonally adjusted heating and cooling efficiencies are given by the heating seasonal performance factor (HSPF) and seasonal energy efficiency ratio (SEER) respectively. In the US the legal minimum efficiency is 14 or 15 SEER and 8.8 HSPF.<ref name=":2" />

Variable speed compressors are more efficient because they can often run more slowly and because the air passes through more slowly giving its water more time to condense, thus more efficient as drier air is easier to cool. However they are more expensive and more likely to need maintenance or replacement.<ref name=":11">"Single Stage vs. Two Stage vs. Variable Speed For Heat Pump/Air Conditioner". How to Choose Best HVAC Systems. 4 April 2018. Retrieved 19 February 2024.</ref> Maintenance such as changing filters can improve performance by 10% to 25%.<ref>"Operating and Maintaining Your Heat Pump". Energy.gov. Retrieved 19 February 2024.</ref>

Refrigerant types

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Impact on decarbonization and electricity supply

Heat pumps are key to decarbonizing home energy use by phasing out gas boilers.<ref name=":4" /><ref name=":5" /> As of 2024 the IEA says that 500 million tonnes of CO2 emissions could be cut by 2030.<ref>"Heat Pumps - Energy System". IEA. Retrieved 19 February 2024.</ref>

While heat pumps with backup systems other than electrical resistance heating are often encouraged by electric utilities, air source heat pumps are a concern for winter-peaking utilities if electrical resistance heating is used as the supplemental or replacement heat source when the temperature drops below the point that the heat pump can meet all of the home's heat requirement. Even if there is a non-electric backup system, the fact that efficiencies of ASHPs decrease with outside temperatures is a concern to electric utilities. The drop in efficiency means their electrical load increases steeply as temperatures drop.[citation needed]

As wind farms are increasingly used to supply electricity to some grids, such as Canada's Yukon Territory, the increased winter load matches well with the increased winter generation from wind turbines, and calmer days result in decreased heating load for most houses even if the air temperature is low.<ref>"An Evaluation of Air Source Heat Pump Technology in Yukon" (PDF). Government of Yukon's Energy Solution Centre and Yukon Energy, Mines and Resources. 31 May 2013. Retrieved 15 October 2014.</ref>

Heat pumps could help stabilize grids through demand response.<ref>"The added value of heatpumps for grid stability via demand response". HPT - Heat Pumping Technologies. Retrieved 15 September 2023.</ref> As heat pump penetration increases some countries, such as the UK, may need to encourage households to use thermal energy storage, such as very well insulated water tanks.<ref>"How heat pumps can keep homes warm without frying the power grid". eng.ox.ac.uk. Retrieved 15 September 2023.</ref> In some countries, such as Australia, integration of this thermal storage with rooftop solar would also help.<ref>Li, Yuanyuan; Rosengarten, Gary; Stanley, Cameron; Mojiri, Ahmad (10 December 2022). "Electrification of residential heating, cooling and hot water: Load smoothing using onsite photovoltaics, heat pump and thermal batteries". Journal of Energy Storage. 56: 105873. doi:10.1016/j.est.2022.105873. ISSN 2352-152X. S2CID 253858807.</ref>

Although higher cost heat pumps can be more efficient a 2024 study concluded that for the UK "from an energy system perspective, it is overall cost-optimal to design heat pumps with nominal COP in the range of 2.8–3.2, which typically has a specific cost lower than 650 £/kWth, and simultaneously to invest in increased capacities of renewable energy generation technologies and batteries, in the first instance, followed by OCGT and CCGT with CCS."<ref>Olympios, Andreas V.; Hoseinpoori, Pooya; Markides, Christos N. (14 February 2024). "Toward optimal designs of domestic air-to-water heat pumps for a net-zero carbon energy system in the UK". Cell Reports Sustainability: 100021. doi:10.1016/j.crsus.2024.100021. ISSN 2949-7906.</ref>

Economics

Cost

As of 2023 buying and installing an ASHP in an existing house is expensive if there is no government subsidy, but the lifetime cost will likely be less than or similar to a gas boiler and air conditioner.<ref name=":7">"How Much Does Heat Pump Installation Cost? (2023 Guide)". ASHI. Retrieved 30 September 2023.</ref><ref name=WS_1>Chung, E. (26 September 2023). "Will switching to a heat pump save you money? Here's how to find out". CBC/Radio-Canada. Retrieved 20 January 2024.</ref> This is generally also true if cooling is not required, as the ASHP will likely last longer if only heating.<ref>"Heat pumps vs. AC — Why Upfront Costs Can Be Misleading". carbonswitch.com. Retrieved 30 September 2023.</ref> The lifetime cost of an air source heat pump will be affected by the price of electricity compared to gas (where available), and may take two to ten years to break even.<ref name=":7" /> The IEA recommends governments subsidize the purchase price of residential heat pumps, and some countries do so.<ref name=":6" />

Market

In Norway,<ref>Rosenow, Jan; Gibb, Duncan; Nowak, Thomas; Lowes, Richard (October 2022). "Heating up the global heat pump market". Nature Energy. 7 (10): 901–904. doi:10.1038/s41560-022-01104-8. ISSN 2058-7546. S2CID 252141783.</ref> Australia and New Zealand most heating is from heat pumps. In 2022 heat pumps outsold fossil fuel based heating in the US and France.<ref name=":6">"Global heat pump sales continue double-digit growth – Analysis". IEA. Retrieved 15 September 2023.</ref> ASHPs can be helped to compete by increasing the price of fossil gas compared to that of electricity and using suitable flexible electricity pricing.<ref name=":4" /> In the US air-to-air is the most common type.<ref>"A Heat Pump Might Be Right for Your Home. Here's Everything to Know". The New York Times. 6 June 2023. ISSN 0362-4331. Retrieved 18 September 2023.</ref> As of 2023 over 80% of heat pumps are air source.<ref name=":5" /> In 2023 the IEA appealed for better data - especially on air-to-air.<ref name=":6" />

Maintenance and reliability

It is thought that ASHP need less maintenance than fossil fuelled heating, and some say that ASHPs are easier to maintain than ground source heat pumps due to the difficulty of finding and fixing underground leaks. Installing too small an ASHP could shorten its lifetime (but one which is too large will be less efficient).<ref>"Which Heat Pump is the Best for Reliability & Efficiency 2023?". www.ecohome.net. Retrieved 18 September 2023.</ref> However others say that boilers require less maintenance than ASHPs.<ref>"Heat Pump vs. Furnace: Which Heat Source Is Right for Your Home?". CNET. Retrieved 18 September 2023.</ref> A Consumer Reports survey found that "on average, around half of heat pumps are likely to experience problems by the end of the eighth year of ownership".<ref>"Most and Least Reliable Heat Pump Brands". Consumer Reports. 7 April 2023. Retrieved 18 September 2023.</ref>

History

Modern chemical refrigeration techniques developed after the proposal of the Carnot cycle in 1824. Jacob Perkins invented an ice-making machine that used ether in 1843, and Edmond Carré built a refrigerator that used water and sulfuric acid in 1850. In Japan, Fusanosuke Kuhara, founder of Hitachi, Ltd., made an air conditioner for his own home use using compressed CO2 as a refrigerant.

In 1930 Thomas Midgley Jr. discovered dichlorodifluoromethane, a chlorinated fluorocarbon (CFC) known as freon. CFCs rapidly replaced traditional refrigerant substances, including CO2 (which proved hard to compress for domestic use<ref name=discoverCO2>The rediscovery of CO2 Archived 2007-10-07 at the Wayback Machine SHECCO</ref>), for use in heat pumps and refrigerators. But from the 1980s CFCs began to lose favor as refrigerant when their damaging effects on the ozone layer were discovered. Two alternative types of refrigerant, hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), also lost favor when they were identified as greenhouse gases (additionally, HCFCs were found to be more damaging to the ozone layer than originally thought). The Vienna Convention for the Protection of the Ozone Layer, the Montreal Protocol and the Kyoto Protocol call for the complete abandonment of such refrigerants by 2030.

In 1989, amid international concern about the effects of chlorofluorocarbons and hydrochlorofluorocarbons on the ozone layer, scientist Gustav Lorentzen and SINTEF patented a method for using CO2 as a refrigerant in heating and cooling. Further research into CO2 refrigeration was then conducted at Shecco<ref>shecco Archived 2005-02-07 at the Wayback Machine shecco.com</ref> (Sustainable Heating and Cooling with CO2) in Brussels, Belgium, leading to increasing use of CO2 refrigerant technology in Europe.<ref name=discoverCO2 />

In 1993 the Japanese company Denso, in collaboration with Gustav Lorentzen, developed an automobile air conditioner using CO2 as a refrigerant. They demonstrated the invention at the June 1998 International Institute of Refrigeration/Gustav Lorentzen Conference.<ref name=sheeco-japan-1> Shecco, Nikkan Kogyo ShimbunArchived 2004-10-20 at the Wayback Machine</ref><ref>Natural Working Fluids '98, IIR - Gustav Lorentzen Conference: CiNii</ref>After the conference, CRIEPI (Central Research Institute of Electric Power Industry) and TEPCO (The Tokyo Electric Power Company) approached Denso about developing a prototype air conditioner using natural refrigerant materials instead of freon. Together they produced 30 prototype EcoCute units for a year-long experimental installation at locations throughout Japan, from the cold climate of Hokkaidō to hotter Okinawa. After this successful feasibility study, Denso obtained a patent to compress CO2 refrigerant for use in a heat pump from SINTEF in September 2000.<ref>Archived 2007-10-07 at the Wayback Machine What is Shecco?, EcoCute: The first commercial success</ref><ref>Archived 2004-10-20 at the Wayback Machine, Topic with Nikkan Kogyo Shimbun: Since 1995, SINTEF and Denso had been developing....</ref>

The first commercial domestic EcoCute was marketed in Japan by Corona Corporation [ja] in May 2001, and several manufacturers sold 1.74 million units there by 2008.<ref name=EcoCuteShipments >EcoCute: number of units , cumulative transition, shipments, 9.01 million by August 2023Archived 2023-06-05 at the Wayback Machine Archived: Bar graph describes: EcoCute, number of units in transition, cumulative shipments (エコキュート累積出荷台数の推移), Horizontal axis represents year (Japanese fiscal year Apr.-Mar.) 2001- 2021. Vertical axis depicts shipment units in Myriad 10,000 units. 1.74 million by 2008 and 8.06 million by 2021 for example. Heat Pump & Thermal Storage Technology center of Japan (HPTCJ)</ref><ref>Announcement Archived 2004-06-09 at the Wayback Machine, CORONA Corp., Japanese edition: コロナ (in Japanese) Page 2, section 2. Growth Strategy (コロナの成長戦略): World first household use EcoCute developed, shipment and on sale in 2001 (2001年に世界で初めて家庭用「エコキュート」」の開発に成功し、発売以来)</ref>

Manufacturing

Demand for heat pumps increased in the first quarter of the 21st century in the US and Europe, with governments subsidizing them to increase energy security and decarbonisation. Europeans tend to use air-to-water (also called hydronic) systems such as to radiators, rather than air-to-air systems more common elsewhere. This may help European manufacturers to defend their home market. However as they are not high-tech and are similar to aircon Asian countries such as China made three-quarters of heat pumps in 2021.<ref>"Who Wants to Become a Heat-Pump Billionaire?".</ref>

EcoCute

Domestic EcoCute outdoor unit (front) and hot water storage tank (back)

The Template:Nihongo is an energy-efficient electric air source heat pump, water heating and supply system that uses heat extracted from the air to heat water for domestic, industrial and commercial use. Instead of the more conventional ammonia or haloalkane gases, EcoCute uses supercritical carbon dioxide as a refrigerant. The technology offers a means of energy conservation and reduces the emission of greenhouse gas. It is a registered trademark of Kansai Electric Power Company.<ref>Patents application on Heating and cooling by natural refrigerant Archived 2006-12-08 at the Wayback Machine Trademark No. 4575216 – Japan, third line 10. from bottom on page 3/24, May 15, 2003, Japan Patent Office (in Japanese)</ref>

Etymology

The name of the EcoCute comes from the Japanese phrase Template:Nihongo, which literally means "natural refrigerant heat pump water heater". <ref>"Fiscal year 2001, 12th Energy Conservation Award of Minister of Economy, Trade and Industry" (in 日本語). The Energy Conservation Center, Japan (ECCJ). Archived from the original on 20 October 2002. Retrieved 10 July 2008.(in Japanese) The Energy Conservation Center, Japan (ECCJ) (in Japanese) Fiscal year 2001 (Heisei 13), 12th Energy Conservation Award from Ministry of Economy, Trade and Industry. 5 companies with product named EcoCute and other 4 not named but conforming EcoCute requirement and performance, total 9 companies awarded (Denso, CORONA, Mitsubishi Electric, Sekisui Chemical, 四変テック, キューヘン, Former 日立空調システム, Tokyo Electric Power Company, Central Research Institute of Electric Power Industry).</ref> Eco is a contraction of either ecology or economical and Cute is a near homonym to Template:Nihongo; literally "supply hot water". <ref name="CRIEPI-1">"Making hot water by CO2" (in 日本語). Central Research Institute of Electrical Power Industry. Archived from the original on 10 August 2009. Retrieved 10 July 2008. Archive indicates: Go to page 1-3, by bottom right selector ← Back [1] [2] [3] Next → Page 1: Naming. Page 2: illustrated EcoCute compositions and function. Page 3 shows, 2nd sentence from bottom in 2nd paragraph indicates 5.2 million (*3) unit diffusion by 2010. Back to page 2, top left illustration is detail of EcoCute closed refrigerant loop circuit, from left, the heat of outside air is taken into (pumping into) refrigerant gas CO2 via evaporation type heat exchanger (Electricity fan used for smooth air flow in/out for outdoor unit with negligible electricity cost in this stage). This is first stage in four stages. Step forward next stage in clockwise, compressor (electricity is mostly consumed here) compressing gas CO2 to higher heat temperature. Heated up CO2 circulates to another heat exchanger, hot refrigerant CO2 to hot water, then step to expansion valve (no electricity) and refrigerant back to gas CO2 as last stage, then step back to first stage. Noted that as EcoCute principle (<エコキュートの原理>), CO2 is state of matter of supercritical between compressor - heat exchanger (producing hot water) - expansion valve in sealed manner circulation. </ref>

Features and demand

In Japan in 1998, water heating (Template:Nihongo) accounted for 33.8% of typical domestic energy consumption, with air conditioner and kerosene heater heating accounting for another 26.9% and cooling by air conditioner another 2.3%. Most of the remaining 37% was spent on electrical home appliances, a field where 21st-century innovations in energy conservation began to make considerable energy savings.<ref>2.2 (2) Yearly home energy consumption by usage category Archived 2007-06-11 at the Wayback Machine Bar graph: Section (2) Energy consumption by purpose of usage per household、bottom, year '98 ((2)　世帯当たり用途別エネルギー消費量) The Energy Conservation Center, Japan (ECCJ) (in Japanese)</ref> This left hot water supply as the most difficult area for energy conservation, leaving a gap in the market for the EcoCute. By January 2005, 26 Japanese companies were producing more than 450 models of EcoCute machines, and sales of domestic units increased 130–150% each year between 2001 and 2005.<ref>TOKUGIKON (特許庁技術懇話会) Archived 2005-05-12 at the Wayback Machine, Organized current and retired officers, with Japan Patent Office, technical discussion association (特許庁技術懇話会) since 1934 (in Japanese). Archive indicates: To select page 1-3, by bottom right selector ← Back [1] [2] [3] Next →. First page with page number 122: Context/content line 10-11. EcoCute put on market in 2001, approx. 450 types produced by 26 Mfg. as of now/today (2005.1.28. shown at bottom line, this pdf file/document issued date) and 130 - 150% annual increased in 2001 – 2005. (エコキュートは、2 0 0 1年に発売されて以来年成長率 1 3 0～1 5 0％と好調な売れ行きを見せており、今では2 6 社から約4 5 0種類の製品が販売されています)</ref>

Denso first introduced the EcoCute outside Japan at the COP9 Milan, Italy on December 9, 2003. From 2007, Denso began concentrating on marketing the EcoCute in the EU.<ref name=discoverCO2 /><ref>EcoCute demand surges in Europe Archived 2008-10-19 at the Wayback Machine, European Heat pump network</ref><ref>Heat pumps offer huge potential Archived 2009-08-13 at the Wayback Machine, IEA Conference</ref> In Japan, the Japanese government incorporated the EcoCute into its CO2 reduction program under the Kyoto Protocol, mandating the installation of 5.2 million units in commercial and domestic properties by 2010.<ref name="CRIEPI-1" /> <ref>26 pages of the plan for energy saving and CO2 emission reduction: Page 16/26, the second block from left of bottom layer frame: Promote CO2 refrigerant heat pump for hot water supply 5.2 million unit by 2010. (CO２冷媒ヒートポンプ給湯器の普及台数<約520万台>) Official issue from Kantei (in Japanese)</ref>

EcoCute machine basics

An EcoCute machine or system consists of a heat pump and hot water storage unit. The sealed components are serially connected with refrigerant CO2 gas in circulation.<ref>ITOMIC Industrial use Eco-cute, Features, WorkflowArchived 2023-12-09 at the Wayback Machine</ref><ref name="CRIEPI-1" />

  1. At the first stage, a heat exchanger collects heat from the air outside to use as energy for the refrigerant. Air flow is usually obtained using a centrifugal fan; in cold areas with ambient temperatures around −20 to −25 °C an auxiliary fan heater is attached.
  2. A gas compressor is used to increase the temperature of the gaseous CO2 refrigerant to around 100 °C under pressure of 10MPa via adiabatic compression. The carbon dioxide becomes a supercritical fluid.<ref name="CRIEPI-1"/>Several types of compressors can be used, including dual layer cylindrical compressors, scroll compressors, and dual stage rotary compressors.<ref>Cooling System Composed with Rolling Piston Type 2-Stage CO2 Compressor Archived 2006-02-19 at the Wayback Machine, Sanyo</ref>
  3. At the third stage a heat exchanger transfers energy from the hot refrigerant into water to produce hot water. Water temperatures around 50 °C and up are suitable at this stage.<ref>Output of hot water supply temperature is preference of individual or family user, and EcoCute manufacture set temperature range by model for market, not industrial specific value.</ref><ref>EcoCuteArchived 2005-11-07 at the Wayback Machine, Japan Patent Office Society (in Japanese). Page 127, 2005.1.28. no.236 tokugikon, Fig 7 Heat pump configuration illustration: At top right, Output of hot water is possible to rise up to 90 °C. Under the condition of outside air temperature -10 °C, EcoCute can produce 90 °C hot water that could not obtain by chlorofluorocarbon refrigerant (5 °C water inlet at bottom right). Website is organized current and retired officers from Japan Patent Office technical discussion association (特許庁技術懇話会) since 1934. Accessed on 2024-02-06.</ref><ref>Referenced web site (in Japanese) of Sakaguchi Boiler ServiceArchived 2023-06-06 at the Wayback Machine, sakabo.com (in Japanese) Referenced web site of Sakaguchi Boiler Service in Kumamoto, Japan (坂口ボイラーサービス). Recommending temperature setting is boiling the hot water tank to be 65 to 80 °C, hot water supply is recommended to 50 to 60 °C then mixed with cool water suitable for human body. Avoid growth range of legionella in 20 to 45 °C, also under 40 °C tend to make the trouble on thermostatic mixing valve with hot and cool water. Temperature more than 90 °C is wasting heat energy and cost of electric cost. Accessed on 2024-02-06.</ref>
  4. Finally, ejector or expansion valvesreduce pressure on the refrigerant, letting it cool via adiabatic expansion and revert to CO2 gas from supercritical fluid, then circulation back to the first stage.<ref name="CRIEPI-1"/>

Refrigerant carbon dioxide (CO2) is numbered or coded as R-744 by ASHRAE standard 34. The EcoCute can derive two to five unit ratio of COP (Coefficient Of Performance) to heated hot water energy from outdoor air with single unit input of electrical energy, resulting in reduced CO2 emissions compared to water heating via electricity or natural gas.<ref>Japan Atomic Energy Relations Organization Template:Nihongo Archived 2023-10-05 at the Wayback Machine (in Japanese) Energy Encyclopedia (エネ百科), website supported by JAERO, describing: Mechanism of CO2 refrigerant heat pump, titled EcoCute (エコキュート), for hot water supply Electric energy (1) + Outdoor air energy (2 or more) = Obtained hot water energy (3 or more) (CO₂冷媒ヒートポンプ給湯器のしくみ): Three frames from left are Heat pump unit (ヒートポンプユニット), Hot water storage unit (貯湯ユニット) and House part. Within Heat pump unit, closed loop in circulation manner, operates to transfer Outdoor air energy (2 or more) (大気熱2以上) into the refrigerant CO2 through Air Heat Exchanger (空気熱交換器) via fan, then follow in clockwise, the refrigerant compressed by compressor (圧縮機/コンプレッサー) operates under applied Electric energy (1) (電気エネルギー1). Next step, heat energy transition into cool water and warm up to hot water (水加熱) through Heat Exchanger (熱交換器), then flow proceed down to Expansion Valve (膨張弁), the refrigerant CO2 back to Air Heat Exchanger (空気熱交換器), as total refrigerant CO2 cycle (CO2冷媒サイクル). The device, at bottom right in Heat pump unit frame, is cool/hot water circulate pump (ポンプ) feed in to Hot water storage unit. At this stage, 1 + (2 or more) = (3 or more) energy transition realized. Cool/hot water tank store obtained energy of more than 3 (得られる給湯エネルギー3以上). Top right is the temperature adjustment valve (温調弁) to maintain suitable temperature of storage hot water and to supply for household use for kitchen (キッチン), washroom (洗面所), bath (お風呂), underfloor heating (床暖房). Cool water supplied into Hot water storage unit at bottom right. </ref> To produce 90 °C hot water, an EcoCute consumes 75% less electricity than an electric water heater, and costs 80% less than heating water by natural gas in Japan.<ref name=ITOMIC-1 /> Also, by reducing use of fossil fuels, the EcoCute results 50% reduction in CO2 emissions.<ref>Research and development of EcoCute Archived 2005-09-24 at the Wayback Machine CRIEPI (in Japanese) Archive indicates: Titled - Development of home appliance hot water supply by refrigerant CO2. In 2/2 page, last two sentences in area inside the bold line: EcoCute reduce primary energy 30% and CO2 emission 50% compared to water heating by town gas or city gas burning boiler type. There points well evaluated and awarded with prizes, on Energy Conservation Award (省エネルギー大賞) by Minister of Economy, Trade and Industry, and from other organizations in 2001–2002. </ref>

Not considering upstream losses of input source energy, as one example reference value, the EcoCute's COP is 3.8 in industrial use, while electric power water heating is 1.0, and gas boiler is 0.88 including pilot light loss.<ref name=ITOMIC-1 >Feature of industrial use Ecocute Archived 2008-06-10 at the Wayback Machine, www.itomic.co.jp (in Japanese) Archive indicates: Information from Nihon Itomic Co., Ltd. for their EcoCute: EcoCute effectively heat up water to 90 °C. First bar chart shows comparison of COP of, from top, Itomic industrial EcoCute COP:4.0, electric heather COP:1.0, gas boiler COP:0.88. Itomic industrial EcoCute having marginal tolerance from COP 4.0 to 3.8 as specification value on delivery from factory. Chart also implicates four COP:1 machines brings the same thermal energy of hot water in volume of one COP:4 machine does. Ratio is (COP:4 – COP:1) / COP:4=0.75 so that EcoCute consume 75% less than COP:1 electric kW. Second bar chart shows CO2 emission comparison: EcoCute:50% is half compared to town gas or city gas burning boiler type 100%.</ref>

See also

References

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Sources

IPCC reports

External links

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