On 13/08/2020 12:38, David wrote:
I was thinking about air conditioning anyway - longer term fit because I
assume that installers will be very busy at the moment - and assumed that
the standard split unit air conditioning (compressor and heat exchanger
outside, fan unit inside) could also be run in reverse in the winter to
pump heat in the opposite direction.

This is the set up that I have seen abroad, anyway.

Searching UK web sites heat pumps seem to be targeted at grants for
renewable energy and positioned as an alternative heating system.

However one site does say that it can be run in reverse during the summer!

So what is the real difference?

Which heat exchanger has the compressed working fluid inside it and why.

Can only some systems be run in reverse?

Possibly if the low pressure side is incapable of standing the hot fluid
working pressure on the output side of the compressor or it is only
designed to pump the working fluid in one direction. All the ones I have
ever encountered could run either way like a true reversible heat pump.

The only catch I can see with using them for winter heating in the UK as
opposed to a continental climate is that our winters tend to be wet and
humid and the external heat exchange tends to ice up badly as a result.
No air flow through it rather limits how well it can work as a heater.

In Japan they spend most of summer in aircon mode making indoors less
humid and cooler and most of winter in heater mode - though many people
have scary hybrid paraffin heaters as well. They like it warm!

General idle musing, as air conditioning is what we need and the heat pump
sites (plus Which?) point out that a heat pump may be cheaper to run than
electric, bottled gas or oil heating it is not cheaper than mains gas.

Do the sums very very carefully. It has to beat electricity since you
get the gain of the heat pump. It might beat bottled gas. But with
prices are as they stand now it might not beat oil or mains gas.


--
Regards,
Martin Brown