I've been reading a book ("Sustainable Energy - without the hot air"), which is always dangerous. The book advocates the use of heat pumps for domestic heating, and does a convincing job of it. Apparently it's common in Japan.
Does anyone out there have any practical experience they could share, e.g. on costs, efficiency, effectiveness, aesthetics?
Thanks, J.
PS
I'd recommend the book to anyone with an interest in renewable energy
may disagree with McKay's analysis or figures in some areas but that's exactly the point: because he lays out his reasoning and his figures you
*can* disagree with them.
As for the heat pumps, at a seminar at EcoBuild earlier this year some folks connected with an Energy Saving Trust project monitoring some early HP installations found them running at anything from COPs of over 4 down to about 1 (which was basically heating the place on peak-rate electricity, due to incompetent set-up of system!). Apparently in Switzerland (IIRC) they routinely get COPs of 4-5+
Costs are still quite steep - several £K for smallish HP units, plus vast amounts for installation.
Effectiveness I guess will depend on the installation being correctly sized and installed for the property.
Aesthetics: ground-source are innocuous (if large) boxes which can be hidden away. Air source involve units much like office aircons with external boxes containing large fans.
Someone also pointed out that these external boxes contain large amounts of copper ...
It is common in Japan (and has been for more than two decades). We had one when we lived there. BUT there is a very important point here - Japanese winters are for the most part continental cold and *very* dry (uncomfortably so). The grass goes brown in Japanese winters. An air source heat pump behaves very well under these dry cold conditions. And at latitude 36N the sun gets a lot higher in the sky than in the UK.
A major advantage is in summer you can run the thing in reverse to pump heat out of the house into an ambient of 38C and close to 100% humidity.
I would expect air source heat pumps in the UK to die a horrible icy death in typical wet foggy British winters (or at the very least lose all semblance of efficiency). And even in mid-summer there are perhaps at most a dozen days when domestic aircon cooling might be needed.
Waste of money...
Ground source heat pumps might be OK if you can find a good competent installer. I was overhearing some poor pensioner complaining bitterly about one they had been sold which seemed to chew up electricity at a huge rate without really giving any useful heat in return. Likely they or their installers had done something badly wrong but it did not seem to have anything like the gain it should have had on paper. Another larger one at a school seems to have insane annual maintenance charges. I suggest you research it very carefully and get something in writing about the guaranteed performance of the system supplied.
At present the technology to beat for space heating is a gas fired condensing boiler based central heating coupled with decent home insulation. Not much use if you don't have mains gas though :(
Insulation is still the best of the low hanging fruit to pick first.
Ground source is the way to go, air source can suffer the collector icing up when it's roughly between 0C and 5-10C outside. A properly designed and installed system should be able to cope and defrost itself automagically without any noticeable impact on the heating system.
Without going to a two stage system they only produce "low grade" heat. This is suitable for underfloor heating but not a conventional CH system or DHW. Bear in mind that to get 20kW of heat you'll be having a 6kW compressor or there abouts, this may give problems via your electricty supply, make sure it has good "soft start" otherwise the lights will dim when it cuts in. The droop might be enough to upset "sensitive" electronics.
government sites about:
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Gone very quiet about it lately, dunno if it's still on or not.
Not heard that it's been scrapped. Last information came out on 26th Oct, changing the large biomass tarrif to make europe happy and opening for applications by end of Nov, but that is probably only the commercial/public side rather than domestic. I wouldn't be surprised to see the tarrifs as published in March being changed by the time it gets introduced for domestic customers. The big worry is the money is coming from the government rather than a levy on other energy sources like the FIT monies.
In the meantime the Renewable Hat Premium Payment (RHPP) is about, up to 25,000 applications budgeted for:
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exclusion is availabilty of mains gas. If you have no mains gas you can get a payment for air/ground source heat pumps, biomass boiler and/or solar thermal. Not great amount compared to the capital cost but better than nothing.
If you need 20kW then spending the cash on insulation will save you a fortune. I don't need anywhere near 20 kW to heat my house, even if I put the conservatory on 22C. If the 20 kW is to give hot water then fit a tank.
Finger in the air figure, and getting power and energy confused again... B-)
Sort of based on the house/barn needing the best part of 38kW and the cottage having around 10kW of electric storeage heating. But yes, insulation, insulation, insulation ...
If one was putting in a heat pump it would have an associated heat store. Big heat pumps don't like being short cycled, for best effciency you run 'em flat out then let 'em rest for as long as possible, gives the ground a chance to recover as well.
You'd also have to do the maths on the costs of a *big* store, say
1500l that will hold enough heat to provide space heating through the day and charge it at night on E7. I think you can still get E10 that would allow charging mid afternoon and evening as well as at night.
A big single store wouldn't work if one was thinking of solar thermal alongside the heat pump. You could have a smalle store sized for and heated by solar thermal to preheat cold mains before going through the main store to final temperature.
Surely you would re-cycle stored water in a closed system. None of the above is going to produce water hot enough for washing.
Umm... If your ground source heat pump is oversized, couldn't you use solar thermal to put some energy into the store and then run your GSHP on E7? Use thermostat to advance *on* time if cloudy day.
A screed installed UFH system IS a bloody great heat store :-)
Note that much about 15KW you need a three phase supply, ideally.
The other issues I ran into - well tow acctually - wehn looking at GSHP was that
1/. It wouldn't get the DHW hot enough..need 60C ideally to keep bacteria down, UFH needs immersion top-up top reach that.
2/. The whole system APART from UFH needed redesign as the conventional rads were sized and the pipes were sized and the immersion heater was sized for water at 60C+ Not 45C.
The latter point ruled the project out. It was not just a question of a new replacement GSHP boiler: It was new pipework rads and tanks everywhere.
Waste of time. The days when you really need heating are the days of no sun...
Which bit? Big heat pumps have to cool down the "cold bit" that has warmed up before they start to really pump the heat. OK the heat in the warm cold bit come out of the out put but effciency isn't that high...
When you pump the heat out of the ground it's possible to freeze the ground this is not good as ice is a pretty good insulator. If you are pumping heat out of the ground faster than it can conduct in then it will freeze, eventually. But of you cycle things a bit you can pump out faster and the ground recovers when you aren't pumping. The overall heat moved remains the same of course.
The primary water would be recycled and yes a single stage heat pump produces 45C or so output. Not hot enough for conventional heating or DHW You can get two stage devices that lift that 45C to more usual heat levels... you could use one of those to heat a big store to 80C or there abouts.
It's the big store (1500l...) that is the problem. A 3m^2 Solar thermal panel will (should!) raise a 300l store to 80C mid summer. That is enough stored energy to provide DHW for a day but if you have a store 5 times the size you aren't going to get much of a temp rise in that store. Yes you will have added a bit of energy but you'll still need to run the (two stage) heatpump to bring the store up to useable temperatures. All that energy that your don't actually need.
Probably best to have a smaller solar thermal store for DHW for use in the summer directly then switch over to using it to preheat the water before feeding it through the big store in autumn/winter/spring.
That really only applies to stored hot water that comes out of the taps. The system going in here heats the hot water on demand from the store. The store water is closed, like the primary in an open vented system.
Things are moving on two stage heat pumps are about the produce more conventional temperature outputs. I might look at that sort of system for the cottage to replace the E7 storeage heaters.
Space heating yes. The whole lot is linked here but I don't expect much contribution from the solar thermal in the winter but in summer it should provide most if not all our hot water requirements.
Presumably the system designer would match collector pipe length, ground conditions and heat pump size at the design feasibility stage. Or is that too hopeful for a relatively young application?
My interest is limited to underfloor heating. I have outbuildings which could be converted to commercial use and a *green energy* source would be a huge help with planning consents. I can find enough South facing steel roof for 24m2 of solar thermal and about 2000m2 of river margin land for a GSHP. DHW use would be limited to hygiene/crockery washing so immersion fine.
I haven't asked. They wanted to charge for extracting river water with a second charge for returning it:-(
The stretch I have in mind is pretty shallow and gin clear so no hope of hiding anything substantial. A finned heat exchanger would quickly clog with weed etc. so the series of single panel domestic radiators suggested earlier might do.
As is always the problem finding a tradesman/company who knows that there is a little more to it than digging a big trench and bunging some pipe in it.
24m2 of solar thermal would get you a lot of heat but in the summer when you don't need it... I think (but I'm no expert) that a GSHP in that river margin would be the best bet, wet ground conducts heat better than dry. Even better if you have the water table flowing through it. I can envisage all manner of red tape from the EA and/or Natural England if you wanted to extract directly from the river or from the river bed.
Solar thermal can get damn hot, the kit has warnings about high temperatures and stuff in contact with the pipe work has to be specified to cope with temps over 150C... The solar circulation loop is sealed and pressurised and on bright sunny days can easily exceed
100C.
I don't think it would work. Ground temperatures, before you start pumping out the heat, are only around 10C so that is the maximum input temp to the heat pump. The fluid circulating in the (primary?) ground loop flows in at or below freezing, is warmed by the ground and then that heat extracted by the pump to produce the 40 odd C heat pump output (secondary?) side.
The figures and layouts are all well documented..its no more than a length/spacing/depth/soil type relationship.
It's possible to actually use the river itself..if you own it..laying pipes in deep lakes and rivers is a well known way to pump.
But you should be able to pull 20-30KW out of that land area easily.
Whether solar thermal is worth it is moot: I personally would not.
The ground itself is your solar collector: You are using that as your heat bank. Using the direct sunlight in summer when you don't actually need it seems a bit dim.
Most heat pumps will allow you to tank, if not hot water, pretty WARM water (45-50C) and immersion can take that up to scalding at relatively low cost.
Given that the property is agricultural-ish, and you probably have 3ph, this seems like an excellent project.
I would begin by assuming conversion to habitable property standard with a modern level of insulation, and assume also an in floor screeded UFH system: straightforward heating calculations should reveal what peak heating demands are likely to be (and use heat recovery ventilation if you can afford it).
That will tell you what you need in terms of electricity and the pump itself, and what land area you need, given the soil type. Soft wet clay water meadow is the best. Tree covered dry sand is the worst.
In addition you will be able to spec. out UFH pipe density as well with these calculations.
Armed with that you should be able to estimate costs: If it all looks reasonable, then a planning application can result.
I would say that for habitable use about 50W/sq meter is the peak demand with modern insulation..that should be a reasonable enough figure to cope with short term 'heat from very cold' type applications and more than enough to maintain 20C internal down to very low outside temps.
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