This is a schematic drawing of a heat pump system that seems to be doing the rounds at present. Now I’m not saying that a system won’t work like this but its just that it could be so much better. If you are investing in a heat pump system then surely you want the greatest possible benefit from it and this design does not allow that by a long shot. I’d be interested to see what other people think of it and how they think it could be better. From our point of view it looks to be sacrificing efficiency for the sake of simplicity. Keeping the UFH & DHW supply from the same tank means that only one tank is required but on the other hand it also means that there is no way of utilizing the weather compensation function built into most modern heat pumps. I can see the logic behind using only one tank but by combining the UFH and DHW this way means that this type of tank (thermal store) will have to be over-sized considerably to avoid there being a shortfall of energy for DHW. With a small tank the energy is likely to be diminished fairly quickly when there is a heating and hot water demand at the same time. So any benefit of using a single tank is likely to be eroded by the fact that it will have to be over-sized to make it work properly. There is also the fact that during the summer, when there is no heating demand and the DHW is the only requirement, the tank will be a lot larger than is necessary and standing heat losses from this are simply wasteful. Surely its far better to use a heat pump optimized DHW tank and either open zone UFH or a small dedicated heating buffer which won’t be heated when its not needed. The SPF (Specific Performance Factor) for a GSHP running at 60°C is typically around 2.8 according to the DECC/EST Heat Emitter Guide. With a well designed UFH system in a modern building you can normally achieve the required heat output at a flow temperature of 35°C which corresponds to an SPF of 4.3. Now just to put that into context – this difference in SPF for the heating system running at 60°C is equivalent to an increase in energy use of over 53%. That is a lot of energy wasted by a system intended for saving energy.