First of all, the basic situation here is a rural location with plenty of land available of sodden clay.
My total requirements are around 10-15KW output, and the house is largely, though not completely UFH.
I only have a single phase, but its a new installation with good upstream capacity - me own substation in the garden corner. :-)
TOTAL installation costs look to be around £10,000 but with a conservative 3:1 gain over electrical input, that places my average cost per KWh heat delivered at 1/3rd of the cost of electricity - say around 13p a unit averaged between day and night. It is expected that the unit would run 24x7 anyway, so lets say around 4.3p/unit cost. That compares with pul currently at 50-60p/liter, or around 5-6p/unit (Kwh)
My consumption s around 6000 liters a year, so thats a saving of 0.7-1.7 x 6000, or between £420 and £1000 a year MINIMUM. f course the salesman reckoned on more..but a ten year payback at current rates was felt to be a decision point, and as I cant see anything getting better in oil versus electricity prices (base cost to grid of coal/gas/nuclear electricity is around 2-4p/unit: gas going up quite sharply), its probably a decision that will look better rather than worse over time.
So I am planning on a next summer install, tentatively.
The heat pump itself is about £4000, with another £1000 for actual installation and commissioning by the company, plus around £1000 budget for ancillary bits and pieces - electrical, maybe pressure regulators vessels, etc etc.
That is the bits inside the house. Outside I need to lay around 300 meters in the biggest loop possible of 40mm pipe, at 1m depth or more. Apparently soggy wet clay is tops for this, and efficiency improves the better the garden heat exchanger is. In clay he recommended use of a trencher rather than digger, as getting the subsoil tamped back around the pipe is the best way to get heat transfer, and merely backfilling clods is not good..the trencher tends to produce more 'crumby' type grade of spoil, and this is better. 300m is the longest run of single pipe that is practicable: larger installations use a manifold and two loops of pipe.
In other soils its is apparently recommended to backfill with a load of sand as this when wet gives good heat conduction to the pipe.
thse bits and pieces are probably getting on for £1000 of pipe and insulation a,d an estimated £1000 to hire a trencher, and generally bugger around with the garden: we would actually lay some armour cable and mains water pipe for hoses at the same time, so there is a bit of a plus there as well.
Other issues outside are the need to insulate the pipes where they are close together as they approach the pump to avoid heat transfer between them. The pipes are filled with a glycol type antifreeze ('brine' is apparently an incorrect term used for historical reasons) and on account of the nature of this fluid, no mechanical joints are permitted in the pipes underground. Insulation on the pipes is via a impermeable high density expensive butyl foam sleeve, which he said 'is manna to rats and mice: never use it above ground' ..so where the pipes enter the house I am thinking of a small 'construction' filled with expanding foam to avoid heat loss on the return loop.
The actual unit is massive. Although its on a 600mm square foot print, its 2 meters high with potentially another 200mm above to carry pipework in: there are also potentially extra expansion vessels needed. Fitting this in will be my biggest problem I suspect.
The basic workings are that the ground circuit heats a refrigerant - standard gas type AFAICT on one heat exchanger, and then that gets 'pumped' to supply the hot water heat exchanger: that takes the primary circuit to 45-50C, and a direct immersion heater is inbuilt if you need to go above that for e,.g. health and safety hot water tank reasons. Or possibly to run my upstairs fan convectors that won't run off less than 65C (thermostats in them), but could be removed I suppose...
The Man was very hazy about controls: he didn't seem to think that timing as possible, and the units generally run 24x7 (which betrays their Scandinavian origins) based on return water temps. I hope to get more information on this later.
I'd be looking to tweak the installation to essentially use it ff peak as much as possible, and also to only use the hot water immersion heater to 'top up' the temperature to our nice sizzling 60-70C we like late in the night at the end of 'off pek' times, with probably a boost override on a timer for when SWMBO has left the hot tap running in the sink and I want a bath..
Likewise the internal immersion would probably want to run to boost the upstairs radiator/convector systems - generally on a timer for toasty morning baths, and to put some heat into te bedrooms before going to bed.
Soundwise he reckons the units is no noisier than a domestic refrigerator - certainly better than the normal balanced flue roar from the oil boiler, and the stink of burnt kerosene would be nice to eradicate as well.
The only other control is apparently an air temp sensor that goes up under the eaves on a north west facing wall. Thats the easy side of the house as far as I am concerned.
The other £2000 is really to cater for e fact that to fit the monster in, I will have to totally rip the utility room apart, and lay circuits and pipes to connect it all up and make good afterwards.
SWMBO is delighted as she doesn't use what is in there anyway, and wants other stuff fitted,...
Apparently heat spillage from the unit is lower than a conventional boiler due to overall lower operating temps..this is not an issue in our case as that room is stifling in winter, as all the UFH circuits run under its floor to connect back to the manifold.
Electrical requirements he was hazy on, saying that an additional 'soft start' unit would be required on single phase: it looks like the normal operating current with - say a 3KW heater and a 12Kw pump operating at 4:1 thermal gain would be around 6-8Kw total. So some kind of 30A type breaker and 30A cable should suffice. I am not clear as to whether the thing modulates, and if so what efficiency gains or not are available.
I am more or less committed mentally to starting planning this for a next summer install: that's the time I don't use CH at all, beyond the oil fired Aga (we will keep that: its peanuts compared with the boiler consumption, and is very efficient as a space heater: I wont discuss its cooking qualities here in tis thread.), and when ground conditions will be optimal.
If anyone wants to abstract any of this for the basis of a wiki, feel free. My gut feeling is that heatpumps if you have the room for a decent ground or pond source, are very cost competitive right now against oil, or tanked butane, are actually probably no worse than gas, on a new install: however the lower operating temperatures at which the efficiencies are obtained do mean some kind of pretty large radiative surface is needed. UFH is good, and has thermal mass in screed to take you through the day allowing most of the energy to be off peak..but a more typical small house installation is likely to be less cost effective as up to three times larger radiators would be needed..or a backup heat source to take the temps up to around 65-70C.
One thing he did say, was that with ground source, trying to use pipe spirals to minimise the ground loop size was almost a complete waste of time. The key here is I think that there is an incident solar energy per unit ground, that is what feeds the base of the pump heat cycle, and there is no substitute for ground AREA. Even vertical bores are not as good, as eventually the localized ground are becomes cool, and efficiency drops when you need it most..at winters end.
I didn't discuss air source pumps. or indeed the possibility of refrigerating my floors or running cold air convectors upstairs in summer, but I think this is possible.
That's all so far. I hope it helps others who are considering this route to get some feel for the cost/benefit and installation issues.
For the greens, I will simply say that if I end up abstracting 50% or more of the heat I need FROM the atmosphere/ground, and with nuclear electricity providing the motive power, it makes far far more sense to me to cool my garden to heat the house..than any amount of silly solar panels and windmills ever would.