Which kinds of heat pumps are available to consumers, and which ones are most effective in different situations? With air source, ground source, geothermal, geoexchange, seawater, and other versions touted as heat pump options, home and business owners are justifiably confused about what would be best for them.
Air Source
By far the most popular type, these systems transfer heat from the air outside your home to the air inside your home. Heat is gathered from an outdoor unit, such as this Daikin model below, which contains a heat exchanger and a compressor. Inside the home, heat can be distributed using interior units or forced air duct work. Air source heat pumps cost less than ground source heat pumps, but have lower seasonal efficiencies. Most homes will find that air source heat pumps offer lowest life-cycle cost.
- With ductless units, either wall mounted heads, floor mounted units or ceiling cassettes, refrigerant lines run directly from the exterior unit to the interior unit(s). A second heat exchanger in the interior unit allow heat to move from the refrigerant to the indoor air, which is then blown into the room.
- With ducted units, refrigerant lines run from the outdoor unit to a furnace-type heat exchanger. The warmed air is then distributed throughout the building using duct work.
- For buildings without pre-existing duct work, mini ducted systems can be installed on interior heads, which allow heat to be distributed to hard to reach parts of a building.
- Most houses with hot water baseboard are not compatible with air source heat pumps because the temperature of the water produced by heat pumps is much lower than that of boilers. Significant modification of the hydronic distribution system may be required to convert it to a water heat pump system.
Ground Source
These systems (also known as geothermal or geoexchange systems) transfer heat from the ground outside your home to the air in your home. Ground source systems come in multiple types, but each gather heat from the near-surface ground. Using refrigeration cycles, the ground heat is then transferred into your building and distributed using forced air ducting or a hot water radiant heating system. Ground source heat pumps can achieve higher efficiencies than air source heat pumps, but have considerably higher initial installation costs.
- Ground source heat pumps come in three main configurations: open source, closed source, and RX. Each vary based on how heat is brought to the refrigerant.
- Open source ground loops pipe ground water directly into a heat exchanger in your building. Heat is then transferred from the ground water to the refrigerant and is then distributed throughout the building.
- Closed source ground loops bury piping several feet underground. Water, mixed with a nontoxic antifreeze, is then pumped through the piping. Heat from the soil surrounding the piping is transferred to the water solution in the piping, and the water solution is then pumped back into the building and introduced to refrigerant lines in a heat exchanger.
- RX systems bury refrigerant lines directly in the soil, which makes pumped ground water or a pumped antifreeze solution unnecessary. While these systems are more efficient, the upfront costs are significantly higher.
- Heat captured by ground source heat pumps can be distributed throughout a home using either ducted forced air or hot water radiant heating systems.
- In a ducted forced air system, refrigerants release heat into a centralized furnace-type system, which is then distributed using attached duct work.
- In a hot water radiant system, refrigerants release heat into a hot water tank, which is then released by valve to different areas of a building. In each room, in floor radiant heat or hot water baseboards allow heat to be released into the air.
- For retrofits, most houses with hot water baseboard are not compatible with GSHPs because the temperature of the water produced by heat pumps is much lower than that of boilers. Significant modification of the hydronic distribution system may be required to convert it to a water heat pump system.
Seawater Source
These systems transfer heat from seawater to the air or water in a building. Because of high upfront costs, seawater systems are used primarily by large facilities which as the Ted Stevens Marine Research Institute in Juneau or the Alaska Sealife Center in Seward.