Mini split outdoor unit. Photo Courtesy LARES
LARES COMMITTEE NEWS RELEASE
Electric heat pumps will be in the headlines much more in coming years. They are expected to replace gas-fired furnaces, boilers and conventional air conditioners to heat and cool our homes. What are they? How do they work? And why would we want them?
Heat pumps are common. Refrigerators, freezers, and refrigerated air conditioners are heat pumps. They extract heat energy from cool or cold air, pump it “uphill,” and exhaust it into warmer air.
Heat pumps can be made bi-directional. Familiar examples include the popular “mini-split” air conditioners (which can also pump heat into a house) and the ubiquitous through-wall units that heat or cool many hotel and motel rooms.
Why replace familiar natural gas furnaces and boilers with heat pumps? The main reason is that when natural gas burns, it produces carbon dioxide, a major greenhouse gas that traps heat in the atmosphere and leads to the climate change we are experiencing. Any natural gas that leaks unburned into the atmosphere is even worse. Natural gas leaks in a house can be unhealthy or catastrophic.
Today’s heat pumps make typically 3-5 times more efficient use of electricity than traditional resistance-type electric heaters. Exactly how much depends on the temperature difference between the cold and warm air, i.e., how far “uphill” the energy must be pumped.
Air at any temperature contains extractable heat energy. Hence, heat pumps work even in climates much colder than Los Alamos County. The thinner air at high altitudes contains less heat. Pumps have to be sized accordingly, but they still work.
Heat pumps for home heating and cooling typically have two units. The main unit is located on a concrete pad outdoors. It includes a compressor, heat exchange coil, and fan. The compressor makes some noise, but it is outdoors. The coil and fan look (and function) somewhat like the radiator and fan in a motor vehicle. For a building with forced air heat, two small tubes carry a working fluid indoors to another coil that replaces the furnace burner. It heats or cools air for distribution around the house. Instant central air conditioning!
Hydronic heating (baseboard or in-floor radiant hot water) systems get more complicated in cooling mode. Circulating water can be heated by a heat pump but chilling it would cause condensation on the pipes. Separate cooling coils inside the house are required.
Heat pumps can also provide domestic hot water. Stand-alone heat pump water heaters are available, or water heating can be integrated into the space heating system. This system can already be found in some hydronic heat installations.
Although the cost is declining, heat pumps today are more expensive than gas furnaces or boilers. However, they cost less than separate heaters and air conditioners. The major uncertainty, especially for retrofits, is installation costs. Every home will be different. Heat pumps make the most sense for new construction, when furnaces and boilers need replacing, or when our longer and hotter summers make it time to add air conditioning. Several new housing developments in Los Alamos are being built with heat pumps.
Just as electric vehicles are expected to replace gasoline-powered cars over the next several decades, heat pumps are likely to replace gas-fired heating units and separate electric air conditioners.
For more information on the research of LARES Task Force check out the LARES Task Force tab on the Los Alamos County Environmental Services Webpage (www.losalamosnm.us/gogreen), or email LARES at LARES.TaskForce@lacnm.us for any questions or comments.