Tuesday, August 11, 2015

Air Source Heat Pumps

Air Source Heat Pumps
We have established that Passive Houses are air tight, super insulated and properly ventilated. Air source heat pumps are what we will be using to supplement the cooling and heating needs during the summer and winter months.

An Air Source Heat Pump is both an air conditioner and a heater.

In Cooling Mode

Starting at the compressor:

1) Refrigerant is compressed causing the pressure to increase and turn the cold vapor into hot vapor.
2) The hot vapor enters the outdoor coil and is cooled by the outdoor air. This causes the hot vapor to change phases into a hot liquid (still under a lot of pressure).
3) The hot pressurized refrigerant enters the expansion valve where the  pressure is relieved and the temperature of the refrigerant drops (A LOT)
4) The cold liquid refrigerant enters the indoor coil and is heated up by the indoor air (cooling the indoor air in the process). This causes the cold liquid refrigerant to change phases into a cold vapor.
5) The cold vapor refrigerant enters the compressor again.

In Heating Mode 

Starting at the compressor again - now everything is reversed:

1) Refrigerant is compressed causing the pressure to increase and turn the cold vapor into hot vapor.
2)  The hot vapor enters the indoor coil and is cooled by the indoor air (Heating the Indoor Air). This causes the hot vapor to change phases into a hot liquid (still under a lot of pressure).
3) The hot pressurized refrigerant enters the expansion valve where the  pressure is relieved and the temperature of the refrigerant drops (A LOT)
4) The cold liquid refrigerant enters the outdoor coil and is heated up by the outdoor air (cooling the indoor air in the process). This causes the cold liquid refrigerant to change phases into a cold vapor.
5) The cold vapor refrigerant enters the compressor again.

Some things to keep in mind.


  • Refrigerant pressures range from 0 - 250 psi
  • Refrigerant temperatures range from (-)14 - 150 F
So because of the temperature ranges of the refrigerant are greater than outdoor air temperatures the system should be able to provide heating in the harshest of conditions and cooling on the hottest of days.


The efficiency of these systems are upwards of 300% efficient. This is possible, since we are not creating heat (like in burning fuels with your furnace) we are simply moving the heat around to where we want it to be. The heat pumps are all electric, so for every 1 kWh of energy the machine uses, it moves 3 kWh of heat energy into or out of the house.

Any heating and cooling system needs to be properly sized to ensure maximum efficiency. The heat loss in a typical passive house is too small for any furnace or geothermal heat pump system. The cost to run even the smallest furnace would outweigh the cost of the air source heat pump and greatly decrease the comfort of the home due to short cycling creating a wide swing in air temperatures. An Air Source heat pump is the most economical and efficient way to keep the indoor air temperature pleasant and stable all year long.

Here is a video from Mitsubishi:


The ventilation system, in addition to controlling the humidity of the air, will be circulating the air throughout the house to help keep the air temperature even.

That pretty much does it for Passive House Components. Next week we will be breaking ground, so my posts from now on will be based on how the building process is going.





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