Magic Thermodynamic box

[Chris B]

One of my drinking buddies has mentioned a couple of weeks ago that he had his heating and hot water system upgraded by the addition of a heat pump. He seemed to have difficulty explaining how it worked so today I went to have a look at it out of curiosity. On the side of one of the components was

so I was immediately a bit suspicious.

It is essentially a huge fridge evaporator panel on the outside of the house which serves a heat exchanger for the hot water, and what looks like a dumb box adjacent to the boiler, which has feed/return to the boiler and the radiators. They have also put thermostatic valves on all of the radiators.

I suspect that he has been right royally shafted but there are some good reviews on the net

(only joking there are twice as many saying stay well clear of this sort of stuff, the best one being)

I was too embarrassed to ask how much he had paid, but bear in mind we have no mains gas and his current fuel supply is oil, the existing boiler, which hasn't been touched, is many tears old.

Does anyone have any first hand experiences of these "magic boxes".

[Chris Hogg]

Tears of grief no doubt.

[Dave Plowman (News)]

A heat pump normally relies on a heat exchanger kept at a (reasonably) constant temperature. Normally pipes buried underground.

One on the side of a house would be hot on a hot day and cold on a cold one.

[dennis]

I don't think its a magic box like the one in the telegraph article.

It appears to be an air sourced heat pump with the panel made flat to catch a bit of solar heat.

You can get a whole house air sourced heat pump for a few thousand so it looks expensive if its the price the telegraph quoted.

A heat pump will use electricity but it will also transfer some heat from the outside to the house so for every kwhr of electricity you get about 3 kwhr of heat. It makes electric heating cost about the same as gas.

I have an air sourced heat pump to heat my conservatory. Really its an air conditioner that works both ways and it only cost £480 but it won't do hot water. It will chuck out about 5kW of heat which mkes it quick to heat in winter.

[Dave Liquorice]

Air source is an alternative, they don't like air temps between 0 and about 5C, condensation forms and freezes requiring regular, energy consuming, defrost cycles. Below freezing the air is dry and IIRC they'll still be effective down to about -10 C.

It'll be cold as the heat is being pumped out of it, it's not a passive heat exchange system a solar thermal setup.

[Brian Gaff]

Half the problem with these technologies is that they get used inappropriately in conditions where any gain would be outweighed by the lack of efficiency created by the additional pumps etc.

I know somebody in Chichester who was persuaded to have what basically was just what one might call a smart smoother outer of temperatures in the house by use of thermostatic valves and a simple additional boiler controller. Snake oil again? Brian

[Martin Brown]

In other more continental countries you do get air based heat pumps for air conditioning that can run to keep the house interior cool in summer and warm in winter - fine if the atmosphere is dry and not too cold.

The problem in the UK is humidity means that the external heat exchanger tends to ice up quickly and become useless. In a sunnier dry continental climate they work a bit better. We had one like that in Japan.

You can still steal some heat but in the UK ground sourced would be the way to go (although the only folk I know with one found it uneconomic). This is odd because they are retired and in the house most of the time. (basically I think they were sold a dud by a slimy salesman)

[dennis]

I think mine has defrosted twice in three years. It takes a couple of minutes and you get some vapour coming off the compressor and a load of water down the drain. Its nothing like the ones on youtube where they are defrosting inches of ice.

Its actually an advantage as you take the latent heat out of the air and the water drips off before it freezes. IME it seldom results in any ice forming.

There is a limit to how much heat you can extract before the ground freezes, You just can't keep taking a lot of heat out and if they are old and run the heating more than expected they may not have enough ground area to provide the required amount of heat. This causes the COP to fall and then it costs more to run. There is no such limit on air sourced heat pumps.

[Julian]

replying to Chris B, Julian wrote: Company has been dissolved following illegal claims of efficiency box has worked okay for 5 years BUT savings minimal and nor the unit not working and no one to fix it apparently so all in all an expensive con