Hybrid heat pumps – the way forward for our aged housing stock

Some background

Many people will have heard of heat pumps and certainly AC – air conditioning units? Firstly a heat pump IS an air conditioning units and IS a refrigeration unit.

The function of a heat pump (the generic name for all 3) is to extract heat from one source and use it in another source. With a fridge, it’s job is to take heat from the warm air in the fridge and deposit it outside the fridge, leaving the fridge cooler. The heat pump does the same but takes heat from outside a building and sends it into a building to heat the living space.

We call this process a reversible refrigeration cycle because it uses no fuel such as oil or gas and all the energy it creates it reuses.

The process requires an electric pump (compressor) to circulate a fluid (gas and liquid) round the system from indoors to outdoors, it is this pump that requires energy in the form of electricity.

A heat pump is very efficient because it is using free heat from outside (as long as it’s above 7°c) and often has an efficiency of 500%. We call this efficiency a COP or coefficient of performance, which in essence means that for every KWh of energy consumed (in electricity) the heat pump produces 5KWhs of heat energy. Unfortunately the great drawback of heat pumps is two fold. 1) they run on electricity which is about 40p/KWh at current (June 2022) prices and 2) they are much less efficient on cold days so reducing the benefit.

So how can we use that efficiency in heating our homes? One approach is to us a gas boiler and a heat pump in tandem. The heat pump works during the cooler, spring / autumn months (6-8 months) and then the gas boiler takes over during deep winter (December and January). This is believed to reduce the gas consumption by over 80% which of course means a reducing in greenhouse gases.

This technology can be further advanced by installing a system where the electricity used is obtained for free*. If a property is capable of supporting solar panels (PV) then a good proportion of the heat pumps annual electricity usage can be supplied by a modest PV array.

The solar panels can also be linked to a battery pack that will store the electricity until it is needed, say in the early morning when the sun is still in bed! The battery pack would then charged up during the sun light hours when the heating system is switched off as the occupants would be out of the house at work, in many cases.

I am starting a project at home to link all of these technologies and will be updating my blog with progress. So far I have partly installed the buffer tank.

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