Cooling can be achieved with a ground source heat pump but there are a few things to remember.
There are two types of 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.
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.
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.