Air or ground source heat pumps

[PeterL]

Does anyone have any views or experience, please? Good or bad.

[The Natural Philosopher]

Views and research yes, experience no.

Because the costings indicated it wasn't worth it yet. In my case.

Some things I learnt. (ground source only)

1/. For a decent output, you need a pretty big garden. Ok here. 2/. For a decent output, you need a pretty big pump. Enough to strain a single phase..three phase better. 3/. Its best delivering a lot of warm water: efficiency is poor at delivering hot water. 4/. Because of that, you need a lot of radiator or UFH. 5/. Because of that you need rather larger pipes in your CH circuits. 6/. Because of that you need rather more coil in the tank heat exchanger for hot water. 7/. Because of that you need a supplementary imersion heater to get teh water up to say 55 or 60C to make it sterile and safe in hot wate circuits,.

Bceause of 4,5 and 6, I was facing a complete replumb: hat pushed teh cost upp to about £20k.

IF I had been green fielding, I would actually have done it though. It should be fuel cost competitive with oil at 30p a liter.

However, with oil costs at £2500 a year these days, I might save £1000 a year BUT the installation looked like about 20 grand with all the mods.

I may live beyond 20 years, but probably not here..

[Adrian Brentnall]

HI Peter We have a ground-source heat-pump installation here (far south-west of Ireland) Total install costs were c. 12k euro - but there was a subsidy available (c. 4k euro) at the time.

Our heat-pump lives outside in the timber-built studio - and draws heat from 6 x 100m loops, set in three 50m trenches, partly under the polytunnel. The ground-work is a significant part of the install costs - in our cease we had to do some earth-moving anyway - so buried the loops at the same time.

Our pump is designed to replace a conventional boiler (original install was an oil-fired unit) - and circulates water at about 55 - 60c to radiators. If designing from scratch, you'd want larger rads or underfloor pipework.

Had to replace the hot-water cylinder with one that had a larger, longer coil, as otherwise the heat-pump got upset at the reduced heat-loss..

We like to have 2 baths one-after-the-other of an evening - and find that there's a tiny amount of mains immersion heater needed just to top off the tank and achieve this. If the DHW tank was a little larger then this wouldn't be a problem.

Can't comment on actual cost of operation - but I believe it to be cheaper than oil, more convenient and less smelly!

Servicing costs - so far (fingers crossed) - zero in 3 years. Electric supply needs to be sized carefully - unit takes 15A when running - but has a fairly high inrush on starting (32A slow-trip MCB required).

Hope this helps. Adrian

[Andrew Gabriel]

I installed mine (which is part of an aircon unit) about 5 years ago. I discovered that they don't work well when the outside coils drop to zero, as they ice up, or would do if the unit didn't keep defrosting them, which causes it's efficiency to plummet. This happens below about 5C.

Then when we had a really cold spell and it was more like -5C outside, I tried it and found it worked fine, without doing defrost cycles. So there's a window from something like -2C outside to +5C outside where it's inefficient due to defrost cycling (blowing large clouds of fog across the back garden), but above and below this window, it works fine. I don't know what the absolute lowest it works at is, as I've not tried experimenting.

Aircon units which can heat too are only subject to 5% VAT if the seller can be bothered to do the paperwork. However, I found that one which didn't bother with that and had a special offer was cheaper overall than one which did.

I use mine for probably 96% heating and 4% cooling. It's mainly used to heat my work room when I'm working at home, so I don't have to heat the whole house.

[Jules Richardson]

I think they're generally thought to stop working at around -20C (which renders them useless where I am; it was a nipply -34C this morning)

cheers

Jules

[PeterL]

Thank you, to everyone that replied. Some very good information there.

[Ian Stirling]

For the money you will spend on a ground source heatpump, you can often vastly improve the thermal efficiency of the building instead.

10K may go a long way to properly insulating a solid wall property, for example.

This means that in 10 years, you don't need to spend another

5-10K replacing the heatpump.

In some cases, combined with storage heaters, the running costs can be drastically cheaper than with a ground or air source heatpump.

Another fun thing to think about is a teeny groundsource heatpump that uses cheap-rate electricity to heat a thermal store for a well insulated property.

[The Natural Philosopher]

Very true. BUT we assume that's already been done.

Heatpump itself not expensive. Its the rest...

You would still be surprised..how much heat that takes.

It IS now cheaper to heat with a heatpump, running cost wise, no matter what the level: the problem is the installation and ancillary costs for houses simply not designed for it, are very large.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Jules Richardson saying something like:

Yes, that would stand out a bit.

[GB]

If the water from the heat pump is cooler than the water temperature in your cylinder, aren't you going to end up heating the house from the immersion heater?

[The Natural Philosopher]

Gosh. You would have thought that people had heard of motorised valves and separate circuits.

And timers.

[Ian Stirling]

I've quite often seen it unfortunately not done.

Can you point me at a source of inexpensive heatpumps? I have singularly failed to find them.

Teeny, compared to the uninsulated state, I mean.

For this house, at the moment, at 20C over ambient - 7.1Kw. (calculated - it's pretty close to this in reality).

Once I've got the insulation upgrades in, it's around 1.5Kw. (depending on stuff, I'm pondering on getting it to 1Kw, but that's probably in the diminishing returns range)

A 4.5Kw(th) heatpump, running into a thermal store off night-rate electricity could in principle do the heating for very little continual outlay.

Of course. If you've done the insulation to the best standard.

If you're not, then you can run into the scenario above - when the heatpump will take you back to the same power usage (more or less) as a properly insulated property.

Of course, comparing prices of heating with electricity, a heatpump looks a hell of a lot less of a bargain if you can heat with gas, or even a good night-rate storage based system.

If you have mains gas, your house is not properly insulated, then putting in a heatpump would be a very questionable decision indeed. (from a cost point of view, I can see it might be nice if you want to keep a 'historic' structure, and

[Ian Stirling]

I did that when my CH boiler died.

Needless to say, the element failed in fairly short order.