• Air Source Heat Pumps

    Air source heat pumps are the most common type of heat pump in residential use. In heating mode they use a vapor-compression refrigeration system to extract heat from the outside air. The heat is transferred to an indoor coil and is then released into the heat distribution system. A reversing valve allows the system to operate as an air conditioner during the cooling season. The illustration shows a split-system air source heat pump operating in the heating cycle.

    Heating performance (heating capacity and efficiency) is directly affected by weather conditions and temperature. When operating within their acceptable outdoor temperature range, air source heat pumps deliver more energy than they consume, generally by a factor of 2-to-5 times. In heating mode when the outdoor temperature drops below 40 degrees, the efficiency of the heat pump is compromised and it operates at the lower end of the efficiency range. Heat pumps are equipped with a 2-stage thermostat – when it’s too cold outside for the heat pump to keep up with the interior heat loss, electric resistance coils (the second stage of heat) come on to assist. Connecticut has the second highest residential electric cost per Kwh in the United States, so operating at the lower efficiency levels can be very expensive.

    There are two types of air source heat pumps — air-to-air and air-to-water. Air-to-air heat pumps are used for ducted air space heating. Air-to-water units are used to heat water for domestic use and for space heating through radiant panels or air-handling units.

    In Connecticut, air source heat pumps can be used efficiently in combination with other heating sources as a back-up system and/or to optimize the overall performance of the equipment mix. A small split system can be an ideal solution for a small annex room or outbuilding. An air-to-water heat-pump water heater (shown in left photo) is significantly more efficient than a traditional electric water heater and is a logical substitute – it also has the added benefit of dehumidifying the surrounding area.