Our team review 100’s of heat pump system designs. One thing has become clear. Many designs are predicated on the expectation that a heat pump cannot fulfil the whole heat demand of a building and will require fossil boiler support in the winter months. Some of the effects of this are;
Integrating two heat sources with differing flow and return temperatures results in confused hydronic designs which are often overly complex and therefore expensive to install.
Controlling the change over point for max efficiency is difficult to achieve in reality so the boiler becomes the lead and the heat pump rarely functions missing the whole point.
Why is there this expectation of heat pumps?
Refrigerant choice – e.g. an r32 heat pump won’t perform at low ambient temperature due to the thermodynamic properties of the gas.
Heat pumps sized at 0 or 5C ambient and so is too small when it gets cold
Low flow temperatures from heat pumps mean DHW can’t be generated
Some customers are a little unsure of the heat pump technology and so retaining boilers as back up is a valid approach. This is simpler to design, install and commission and is different to the above case.
Use CO2 or r290 refrigerants that can generate 80C+ and 63C respectively at high COPs
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