Air Source Heat Pumps – A Reality Check?

By Glen Greenbank F.Inst.R. Practical Refrigeration Training Centre Ltd

Air Source Heat Pumps have become increasingly widely used and adopted by governments as the solution to achieving all things ‘green’ but is all as it seems? To examine in more detail some of the issues which tend to be conveniently forgotten a rather different picture may emerge:

1. Are they to be used for heating/cooling or purely for heating? To achieve optimum performance the installation of the outdoor unit is different depending on the intended use.
2. As a small island surrounded by water and with the prevailing weather coming off the Atlantic, we suffer from a constant humidity. When operating between ambient temperatures of +10°C to -10°C the outdoor unit will build ice which will reduce its efficiency. There are very few days when we experience low humidity in this country.
3. The lower the ambient air temperature the less efficient the system as the refrigerant must boil off at a lower temperature to get the heat into it. This in turn increases the operating envelope of the system, using more power at the compressor and increasing the running costs – at a time when electricity is the most expensive power source.
4. There is also a potential issue with the ‘Noise Abatement’ law which means that at night the unit should not exceed 34 dBA when the unit will be working at maximum to maintain house temperatures. To reduce the noise level the unit will either have to be switched off altogether or run at a minimum to keep it below the 34 dBA and avoid possible problems.
5. Conversion costs for most homes will greatly exceed the government grant and on top of this, a separate hot water system will be required. This is also in view of the government’s accepted scenario that most of the existing housing is not suitable for heat pump conversion anyway.
6. Many systems are being installed by people who have not received sufficient training in how a heat pump works so the system is not fitted to achieve maximum efficiency leading to even higher running costs since the average run time will be about 18 hours a day.
7. A standard (ie no special coating and copper fins) air source heat pump fitted in a coastal area will have a much shortened life due to the corrosive effects of the salt.
8. The real issue that has been ignored and will prove an expensive cost to the homeowner within a relatively short time, is that all the systems fitted now but containing R32 refrigerant will need replacing in under ten years because the ‘F Gas’ refrigerants are being phased out by 2030 and this equipment is not suitable electrically to be retrofitted due to the flammability of the replacement natural refrigerant alternatives.
9. The other consideration which is yet to be tackled is that of the electrical supply system. The grid simply will not be able to cope with the increased load which would be placed on it with neither the infrastructure under the streets nor the substations designed to take the greatly increased load.

It has to be questioned as to how many MPs have actually looked at all the issues and spoken to industry before implementing this massive change, or is it to become another HS2 white elephant at the public expense?

It could also be speculated as to how many of the MPs themselves, or government buildings, have adopted heat pumps or whether this is just a programme to be forced on the long-suffering general public at a time when resources are already stretched to breaking point. No-one would deny that we have to find sustainable long-term solutions to the energy crisis, but it is crucial that the options are researched thoroughly before being actioned and all the options are explored not just the obvious favourite of the day.

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