Usage
Air source heat pumps are used to provide interior space heating and cooling even in colder climates, and can be used efficiently for water heating in milder climates. A major advantage of ASHP's is that the same system may be used for air conditioning in summer and heating in winter. Though the cost of installation is generally high, it is less than the cost of a ground source heat pump, because a ground source heat pump requires excavation to install its ground loop. The advantage of a ground source heat pump is that it has access to the thermal storage capacity of the ground which allows it to produce more heat for less electricity in cold conditions.
ASHP's are often paired with auxiliary or emergency heat systems to provide backup heat when outside temperatures are too low for the pump to work efficiently, or in the event the pump malfunctions. Propane, natural gas, or oil furnaces can provide this supplementary heat. All-electric heat pump systems have an electric furnace or electric resistance heat, or strip heat, which typically consists of rows of electric coils that heat up. A fan blows over the heated coils and circulates warm air throughout the home. This serves as an adequate heating source, but as temperatures go down, electricity costs rise, and power outages pose an even greater threat.
The outdoor section on some units may 'frost up' when outdoor temperatures are between 0°C and 5°C (between 32°F and 41°F) and there is sufficient moisture in the air which restricts air flow across the outdoor coil. These units employ a defrost cycle where the system switches to "A/C" mode to move heat from the home to the condenser to melt the ice. This requires the supplementary heater (resistance electric or gas) in the indoor section to activate, to temper the cold air being distributed. The defrost cycle reduces the efficiency of the heat pump significantly, although the newer (demand) systems are more intelligent and need to defrost less. As temperatures drop below freezing the tendency for frosting of the outdoor section decreases due to reduced humidity in the air.
It is difficult to retrofit conventional heating systems that use radiators/radiant panels, hot water baseboard heaters, or even smaller diameter ducting, with ASHP-sourced heat. The lower heat pump output temperatures would mean radiators would have to be increased in size or a low temperature underfloor heating system be installed instead.
Read more about this topic: Air Source Heat Pumps
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