Heat Pumps

A heat pump is essentially an air conditioner with a few additions. A heat pump has a reversing valve, two metering devices and two bypass valves. This allows the unit to provide both A/C and Heat. The diagram above shows a HP (heat pump) in cool mode. The cycle goes like this; Energy Management starts at the top.

Heat Pump Cooling Mode

The compressor (1) pumps the refrigerant to the reversing valve (2).

The reversing valve directs the flow to the outside coil (condenser) where the fan (3) cools and condenses the refrigerant to liquid.

The air flowing across the coil removes heat (4) from the refrigerant.

The liquid refrigerant bypasses the first metering device and flows to the second metering device (6) at the inside coil (evaporator) where it is metered.

Here it picks up heat energy from the air blowing (3) across the inside coil (evaporator) and the air comes out cooler (7). This is the air that blows into the home.

The refrigerant vapor (8) then travels back to the reversing valve (9) to be directed to the compressor to start the cycle all over again (1).



Heat Pump Heating Mode

The difference in the two diagrams is the reversing valve (2) directs the compressed refrigerant to the inside coil first.

This makes the inside coil the condenser and releases the heat energy (3-4). This heated air is ducted to the Unit.

The outside coil is used to collect the heat energy (3-7). This now becomes the evaporator.



Ideally, we would like to design heat pump systems with “free” energy sources rather than supplemental sources (ex. boilers for heating the loop temperature). These “free” energy sources are found in outside air, river and lake water, ground water and soil. However, the vast majority of these systems are designed without these types of heat sources and heat sinks.