Cooling and district cooling in heat pump systems

The cooling needs of a building can have a significant impact on the profitability of a heat pump purchase. There are several cooling methods depending on, among other things, the amount of cooling required, the heat pump model, the heat collection circuit and/or the ventilation system of the building. Some cooling methods have the advantage of a low purchase price or running costs, while others have the advantage of a high cooling capacity. In large systems, such as those often found in hospitals, shopping centres, offices and ice rinks, the cooling load can be used for heating or charging energy wells.

Cooling and cooling with air-source heat pump

The use of air-source heat pumps for space cooling is the most common and efficient way. The excess heat that is extracted is usually transferred to the outside air. In general, a cooling effect of just a degree or two is enough to make the indoor air comfortable, as it also removes humidity from the room air.

When managing cooling needs, the following must be taken into account:

• If the heat energy collected by cooling is not recovered, cooling should be used moderately and as needed.
• If the room is only used occasionally, the air-source heat pump should only be used for cooling when really needed.
• When the building/room is not occupied, the pump should be switched off.
• You should not let the sun shine directly through the windows into the room when you need cooling. Awnings, curtains, blinds, etc. can be used for sun protection.
• It takes longer to cool a room if the ceiling and floor structures in the room are heated.
• To keep the coolness from escaping from the room, windows, doors and other shutters should be kept closed.
• Take advantage of night-time coolness with ventilation and mechanical ventilation (maximum fan power at night).

Cooling with district cooling

In some cities in Finland, district heating companies offer district cooling alongside district heating. District cooling is available in Helsinki, Lahti, Pori, Tampere, Turku and Heinola, for example, at least in some parts of the city. District cooling pipes circulate cold water, which receives heat energy from the building, i.e. the reverse of district heating.

In apartment buildings where district cooling is used, the rooms are usually cooled by fan coil units, which are similar in function to the indoor unit of an air-source heat pump. District cooling is efficiently utilised in district heating plants, so there is no need to limit the use of district cooling from an environmental point of view. However, district cooling is at a cost to the user, which should be borne in mind when using it.

Cooling with a heat well in a geothermal heat pump

Depending on the connection, the thermal energy of the warm exhaust air is either transferred to the heat well via a heat recovery pipe or heated on the return side of the same pipe, which improves the thermal coefficient and output of the geothermal heat pump. Cooling can be distributed through separate fan coils, chilled beams, floor ducting, roof radiators or mechanical ventilation ducts. Ground source cooling is a very environmentally friendly and cost-effective way to cool indoor spaces.

Cooling with water piping in connection with a geothermal heat pump

The low temperature level at the bottom of the water body can be used for cooling, but in this case the exhaust air cooling radiator connection should be made on the same side of the pipework returning from the water body, as this improves the heat coefficient and output of the geothermal heat pump. The heat transferred to the open water system is not stored but dissipated into the environment.

Active cooling with geothermal heat pump

A ground source heat pump compressor can also be used for active cooling when passive cooling of the premises is not sufficient and mechanical cooling is required. When cooling, it makes sense to use the heat extracted from the premises for heating domestic hot water, for example. Where heat cannot be stored, it is usually transferred to the outside air by means of separate fans.

When using a geothermal heat pump for cooling, the heating circuit and the collection circuit of the unit are reversed by means of reversing valves. This requires special skills in the automatic control of the unit. In active cooling, the cooling is distributed indoors in the same way as when using the cooling from thermal wells.

Active cooling with air/water heat pump

The air/water heat pump can also be used for active cooling with a compressor by reversing the direction of the refrigerant circuit. The heat cannot be stored but is transferred to the air in the heat pump’s outdoor unit. In active cooling, the cooling is distributed indoors in the same way as when using the cooling from heat wells.