Heating and Cooling
The diagram below shows a refrigeration plant with a reversing valve to reverse the direction of flow of refrigerant.
The reversing valve is set for the HEATING mode.
The indoor heat exchanger becomes a condenser giving out heat whereas the outdoor heat exchanger is the evaporator and takes in heat energy from a low grade source.
The diagram below shows the same plant with the reversing valve set for the COOLING mode.
The refrigerant travels around the system in the opposite direction and arrives at the Outdoor heat exchanger first after the compressor.
This is effectively the condenser where heat is rejected to atmosphere.
The refrigerant passes through a non-return valve and expansion valve where it then passes through the Indoor heat exchanger, which is the evaporator or cooling coil.
The reversing valve is an effective method of using one item of plant to heat and cool.
This is appropriate for rooms such as glazed foyers where the temperature is low in the morning and high when the sun shines.
Heat pumps are similar to room air conditioners in that the same components are used with the addition of a reversing valve.
This means that the designer could consider up-grading a room air conditioning scheme to a heat pump scheme.
A split system can be used for heat pumps as in air conditioning so that indoor and outdoor units are similar to those used in air conditioning. See Air Conditioning section of the notes.