Can it be done? How?
Cooling can be achieved with a ground source heat pump but there are a few things to remember.
There are two types of cooling:
- Active cooling
The compressor circuit is essentially run backwards, so that chilled water is fed to the heating system in order to provide cooling. Heat gleaned from the property is dumped back into the ground. In order to run the compressor in this way, modifications must be made to it, so we need to know that you want to do this at the point of order.
- Passive cooling
The heat pump is essentially taken out of the loop here - the cold heat transfer fluid from the ground arrays is circulated around an additional cooling heat exchanger, which is interfaced with the existing heating system. Basically you are cooling the heating system.
Points to bear in mind:
Cooling is generally done best by blown air systems. Cooling is all in the name of comfort, and if you consider it, a cool draught over your skin is far easier to detect than a cold floor.
Even using a simple desktop fan can make you feel more comfortable, and there is no chilling of the air occurring here - so with passive cooling, certainly it will be more effective with heat emitters such as fan convectors or air handling units.
Passive cooling with underfloor might only knock 1 or 2 degrees off the ambient room temperature. - and you need an extra heat exchanger.
Cooling, when used with an underfloor system, can cause condensation to form.
What about MCS and RHI?
Things can get a little sticky with MCS and the RHI regarding cooling.
Firstly, if you change a heat pump so that it is capable of active cooling, you are altering the heat pump to the point that it is considered a whole new model. So any unit that was previously MCS approved without cooling would not be approved any longer.
Secondly, if you want to run a unit for cooling (whether it's active or passive), any hours of cooling the heat pump does are ineligible for the domestic RHI. This means that to count the hours when the heat pump is heating, you have to add metering. If that cooling isn't hugely effective (perhaps you are using a radiator based system), then you're paying for metering, and not getting any real benefit from the cooling either.
What does MCS say?
MIS 3005 (the MCS installer standard) does actually lay out guidelines for systems used for cooling.
As long as the system is predominantly used for heating, then MCS would still apply.
In the Non-Domestic RHI, there is a clause that says that heat from the ground arrays must be "naturally generated" - for example you cannot directly use warm water that is a by-product of an industrial process or from space cooling as a heat source, then expect to get better RHI payments because your inlet temperature is so good.
This does not cover heat that's stored in the ground.
It is proposed (as at end May 2016) that ground source and water source systems will be eligible for non-domestic RHI when using "waste heat" or "recovered heat", provided they use some heat from the ground as well.
At present, if this waste/recovered heat is stored in the ground or in ground/surface water, the system is eligible for non-domestic RHI.
The proposal suggests that the heat will no longer have to be circulated into the ground first. This makes sense - any extra circulation means loss of heat and therefore efficiency, so it's sensible to remove this step.