Air source heat pump
[5] 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.
[12] An air source heat pump issues no carbon dioxide, nitrogen oxide or any other kind of gas.
[22] 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.
To clear this condensation, the unit operates a defrost cycle, switching to cooling mode for a few minutes and heating the coils until the ice melts.
As discussed above, typical air-source heat pumps (ASHPs) struggle to perform efficiently at low temperatures.
A GSAHP has three components: a GHE (vertical or horizontal), a heat pump, and a fan coil unit (FCU).
Installation costs for GSAHPs are intermediate between ASHP and GSHP systems; while they eliminate the need for indoor pipework, they still require drilling or digging for the GHE.
GSAHPs demonstrate a coefficient of performance (COP) approximately 35% higher than ASHPs under certain conditions,[32] due to the stable ground temperatures they leverage.
Additionally, the operation phase accounts for 84% of its climate impacts over a heat pump's life cycle,[34] highlighting the importance of efficiency (i.e., higher COPs) in reducing emissions.
The global warming potential (GWP) of GSAHPs is nearly 40% lower than ASHPs,[31] further demonstrating their environmental advantages in cold climates.
An air source heat pump requires an outdoor unit containing moving mechanical components including fans which produce noise.
[41][42] By contrast a ground source heat pump has no need for an outdoor unit with moving mechanical components.
[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).
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,[50] as most countries have now ratified the Kigali Amendment to ban HFCs.
[55] 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.
[56] Replacements, including R-134a and R-410A, are hydrofluorocarbons (HFC) with similar thermodynamic properties with insignificant ozone depletion potential (ODP) but had problematic GWP.
[71] 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.
[73] 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.
"[74] As of 2023[update] 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.
[77] 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.
[82][83][84] Since a heat pump running in cooling mode operates essentially the same as a conventional air conditioning system, these measures primarily concern the performance of ASHPs during the winter, especially in colder climates.
[85][86] In colder climates, where the compressor works harder to extract heat from the outside air, it is critical to prevent the buildup of ice and frost on the outdoor coil to maintain ASHP performance.
This buildup acts as an insulation layer and decreases the rate of heat exchange by blocking the continuous flow of air over the outdoor coil.
[88] In addition, it is necessary to keep the fins surrounding the condenser coil and air intake grill of the outdoor unit free of any debris, such as leaves, that could further block airflow and impede heat exchange.
[97] 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".
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 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.
Together they produced 30 prototype 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.
During the early 21st century CO2 heat pumps, under the EcoCute patent, became popular for new-build housing in Japan but were slower to take off elsewhere.
