REVERSE CYCLE CHILLERS
One of the more notable innovations in air-source heat pumps is called a Reverse Cycle Chiller (RCC). It offers the advantages of allowing the homeowner to choose from a wide variety of heating and cooling distribution systems, from radiant floor systems to forced air systems with multiple zones. It also offers the potential for lower winter electric bills and hotter air out of the supply vents for greater comfort.
An RCC is especially economical for all-electric homes or in areas where natural gas is not available. Depending on other fuel rates, it may even be the least expensive heating option over all of the remaining heating fuel choices.
The system consists of a standard 12 SEER, single speed, air-source heat pump, sized to the heating load rather than the usual smaller summer cooling load. The heat pump is connected to a large, heavily insulated tank of water that the heat pump heats or cools, depending on the season of the year. Most systems will use a fan coil with ducts, employing the stored water to heat or cool the air and distribute it to the house. During the heating season, the hot water can be distributed through a radiant floor system.
The RCC eliminates one of the biggest complaints about air source heat pumps, which is the periodic blowing of cool air during their defrost cycle and during the initial start of the heating cycle as the distribution ducts warm up. The RCC system solves these problems by using the stored heat in the water tank to defrost the cooling coils, rather than the room air.
The RCC system also allows the heat pump to operate at peak efficiency even at low temperatures. This provides greater comfort and economy without the need for electric resistance auxiliary heating coils. For example, in one Michigan installation, the RCC system supplied 115°F water to the air handler and a radiant floor system even though the outdoor temperature was negative 15°F.
Another significant energy saving benefit is that the RCC can be equipped with a refrigeration heat reclaimer (RHR). This is similar to the common desuperheater coil found on the high-end heat pumps and air conditioners (discussed below). The main difference is that the RHR not only makes hot water during the cooling season, but also does it during the heating season by using the excess capacity of the outdoor unit during the milder winter weather to make essentially free domestic hot water. In the summer it makes free hot water by reclaiming the waste heat from the house as long as the system is also cooling the building.
The combined RCC and RHR system costs about 25% more than a standard heat pump of similar size. The simple payback on the additional cost in areas where natural gas is not available is in about 2-3 years.
COLD CLIMATE HEAT PUMP
One company has developed the Cold Climate Heat Pump, which features a two-speed, two-cylinder compressor for efficient operation; a back-up Booster compressor that allows the system to operate efficiently down to 15°F; and a plate heat exchanger called an "economizer" that further extends the performance of the heat pump to well below 0°F, according to the company.
The system has been tested favorably by several utilities in the Northwest, which announced that the heat pump showed a 60% efficiency improvement over standard air-source heat pumps in preliminary testing.
The product has never been made available to consumers on a large scale, but it appears that manufacturing may resume and the heat pumps will soon be available to consumers.
ALL-CLIMATE HEAT PUMP
Another technology showing promise is an All Climate Heat Pump, which the manufacturer says can operate in the coldest days of winter without supplemental heat, maintaining comfortable indoor temperatures even when the temperature outdoors falls below zero. The heat pump could reduce heating and cooling costs 25%-60%. Wenatchee Valley College in Washington has installed the heat pump and campus and has been testing it since October 2006.
While the design of most heat pumps puts the focus on cooling, the All Climate Heat Pump was designed with heating as the primary focus. Initial costs for the All Climate Heat Pump are high, but if it continues to work as well as predicted, the energy savings over the life of the system would more than make up the up-front cost. The All Climate Heat Pump is currently available for consumer purchase.