Heat Pumps

Heat pumps are among the newest energy-efficient solutions for home heating and cooling on the market today. The technology behind them is not new—refrigerators run on the same basic premise of condensing and vaporizing a liquid to transfer heat from one place to another. They provide both heat and air conditioning by reversing direction based on the season.

Heat pumps do not generate heat by burning. Because of this, they can provide nearly 4 times the amount of energy as they consume. A key concern with heat pump technology is their drop in performance as the heat source temperature decreases. They are good for moderate temperatures, but generally require supplementation in extreme cold. In order to qualify for a heat pump, your home must remain in the 40º–90ºF (4.4º–32.2ºC) range year-round. The pump should be situated in an area such as a furnace room with excess ambient heat that provides at least 1,000 cubic feet (28.3 cubic meters) of air space around the water heater.

Product Types

• Air-Source

  

• Ductless Mini-Split

  

• Reverse-Cycle

  

• Geothermal

  

• Dual System

  

How It Works

The technology of a heat pump is rather complicated. First and foremost, there are different sources for the heat that is exchanged: geothermal or air. The most popular type of heat pump is the air-source option. This technology enables the production of higher volumes of slightly lower temperature air, meaning that the periodic “blast” produced by forced air furnaces is avoided. At the same time, there is a “balance point” of outdoor temperature below which the pump will not be able to produce the desired amount of heat and will require supplementation by another heating unit during a portion of the year.

Air-source pumps are the most common, though geothermal technology is improving. The explanation below is tailored to air-source pumps. Secondly, the power source can either be electricity (compression pumps) or, using new technology, heat from combustible fuels or electricity (absorption pumps).

The key components of a heat pump include a compressor, expansion valve, and two coils. There are two types of systems—split and packaged—with split being the most common. In these systems, the compressor and one coil are located outside of the home, and the second coil is housed indoors. Supply and return ducts connect the outdoor components to the indoor central fan and coil. Packaged systems feature the entire unit on the exterior of the home.

In heating mode, a liquid refrigerant (very similar to the refrigerant found in your refrigerator) is evaporated in the outdoor coil, then compressed and transported as a high-pressure, high temperature gas into the indoor coil. There, it releases its energy and is returned to a liquid. It returns to the outdoors and passes through an expansion valve, which reduces the pressure and allows the liquid to evaporate with the relatively low amount of heat available in the surrounding outdoor air. The cycle then begins again.

The system works exactly the same in cooling mode, except that the system of air flow is reversed, allowing the heat to be released outside of the home instead of inside. Packaged systems employ the same technology, but use a system of ducts to transport air to and from the home’s interior.

When deciding on a heat pump, examine the EnergyGuide Label for both the heating efficiency (the heating season performance factor, HSPF) and the cooling efficiency (seasonal energy efficiency ratio, SEER). The HSPF should be between 8 and 10 for the most efficient models, the SEER between 14 and 18. Another rating is the Coefficient of Performance (COP), which compares output to electricity input. COPs usually fall between 2.0-3.0.