Heat pump data.

Things progress on my cost benefit analysis of putting a heatpump in: since I know I am not the only swine around here being thwacked by the high price of CH oil, I thought I'd share some of the salient points of a conversation with the 'heat pump' salesman.
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.
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Thanks for that TNP. I am thinking about it to supply my UFH if/when I ever get round to digging the floor up.
One of the reasons I am trying to buy a digger as well rather than just renting one for my most urgent project, 80 yards of replacement land drain.
One point though. I thought the heat supply was geothermal rather than solar. If solar then the efficiency in winter is going to be a bugbear.
Incidentally I am on mains gas and intend to keep that for everything other than downstairs UFH. UFH is out of the question upstairs with 4" (or less) floor joists.
--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
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Roger wrote:

Not really. AVERAGE soil temps *at the surface* in midwinter are about 0C..
The deeper you go the less summer to winter and diurnal variation you get..these pipes are only a meter down, so are more influenced by the sun than by the earths core..
IIRC is something like 3C for every 100ft, or is it 1C for every 300ft.. Ah its 30C per kilometer..so at one meter is about .03C hotter than at the surface..:-)
http://esrc.stfx.ca/borehole/node6.html
is an interesting read.
Geothermal is 0.06W/sq meter, whereas even in winter the UK gets about 50W/ sq m average in solar energy.

Mm. its not by any means impossible.. the issue there is the ratio between heat going up and heat going down..and is in direct proportion to the conductivity in either direction. MY problem is that with exposed beams there is no floor void at all!
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Yes.
It is not the problem of heat escaping but of fatally weakening the floor joists. The damage caused by wiring and central heating can't be reversed but I don't want to make the situation any worse.
--
Roger Chapman

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On Wed, 09 Jul 2008 21:08:55 +0100, The Natural Philosopher wrote:

For reference there is a very thin (c.15mm) wet UFH overlay system available. I think I put a link in the wiki.
Not a lot of thermal mass, natch.
--
John Stumbles

87.5% of statistics are made up
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HI TNP
We had a Hautec system installed last autumn - here's some comments on your message - based on our experience...
The Natural Philosopher wrote:

Wet land is good - the water has a high heat capacity - just what you want

Ours is 10kw - Hautec 42 is the model. As it was 'retro-fitted' it feeds conventional radiators - it's a particular model that's designed to deliver hotter water than the UFH model...

Ours pulls slightly over 3kw (measured) when it's running flat out - single phase.

Not wishing to rubbish your salesman - but I'd be surprised if you needed to run 24x7. Ours is controlled by a little computerised 'terminal' - and can work on a conventional day / night timeclock arrangement, with dhw linked to the on/off times or independant. It also looks at the outside temperature, and won't run the heating at all if the outside temperateure is above a preset point. It's a very comprehensive set of controls.....
The 3:1 or 4:1 correlates with what I've been told for our system (specs are in German so difficult to tell <g>)

We paid a total of 12,000 euro - offset by a grant of 4,200 euro

We have 600m in 6 x 100m loops with a couple of manifolds - but it's nowhere near the diameter you've mentioned - nearer one inch - looks like traditional 'alkathene' pipe. From memory, it's in 6 separate trenches - minimum of 3ft below ground...

We used a JCB... and a 3ft bucket... wet soil is good news....

Maybe. Our soil is fairly heavy 'oirish sod' <g>

Yes - make us of the kit while it's around <g> We had to level a section of garden to take a polytunnel - so we dug the trenches, laid the pipe, and then dumped loads of soil on top..... ...like the Battle of the Somme, it was !

Didn't take any particluar precautions in this install...

Don't 'sweat' it - the water/glycol that's circulating is going fast enough that there's little heat loss from it. The flow / return temps are pretty cool anyway - you'll not see much above 5C - and the return pipe is frequently covered with frost on our system...

Ours is two separate 600mm sq units - one is the heat pump and the other is the heat store (?200 litre, I think?

Our system produces a flow temp of 65c

..so no need for the immersion heater, unless the heat pump is 'down' for maintenance

Sorry - he's talking rubbish.... Don;t know why he's saying that - but the fact that he is, would worry me.....

Shouldn't need the immersion...

I wouldn't have thought you'd need to...

Ours is intalled in the stained glass studio (timber-built - outside 'shed'). You're aware it's running - but it's not noisy - at its most noisy when it starts up - and that's when it takes a fairly large current from the mains. Although it's rated 3kw when running we needed to use a D-rated 40A breaker to handle the start-up current.

Correct
<g>
It doesn't leak much heat - we have a small double rad in the studio just to keep the chill off in the winter

You'll need an uprated cct breaker - as I say - ours needed 40A to successfully start. However - it's cabled in 2.5mm T&E - which runs slightly warm to the touch.
As to the operating mode - there's three
1) Off <g> 2) Pumping heat (compresser / heat-exchanger running - pushing heat out into the rad or dhw circuit) (3kw) 3) Circulating (dumping heat from the heat store into the rad / dhw) - about 60W for the circulating pump

See above....

Not sure about that..... the mass of the earth surrounding the pipes is pretty large. Some of our pipes run under the polytunnel - which may help - but they are buried quite deep (3ft - 5ft) so at that depth the ground temperature is reasonably constant....
I have one of those energy monitors running on the system for the last few months - so if anybody's interested I can pull out the figures ??
HTH Adrian >
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Adrian wrote:

Excellent stuff. The salesman was very hazy about controls. But very knowledgeable about the ground work. I guess knowing both is too much to asks..
VERY mice to have the power requirements stated so clearly: thank you. Looks like I will need a second consumer unit anyway, so which MCB is no big deal..it will get its own.
As far as underground temps go, its an easy thing to assess. How cold is your incoming mains?. I'd say it was at 3-5C at winters end, and 10-12C at summers end..maybe more. Mains water is largely in pipes that deep.
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HI TNP
The Natural Philosopher wrote:

A bit worrying, nevertheless - it'd be ideal to find a salesman who knew about the _entire_ system.....

Ours went into the original CU - but we've taken out an electric hob in favour of a gas one - so we felt that was a fair exchange <g>

Not quite so easy out here. Our water comes from about 300ft down (private deep-bore well - which is very common out here in the wilds of West Cork). Haven't measured the temperature - but it's cold all the year round - probably in the 3 - 5C range....
FWIW - here's the energy consumption figures for our system so far
Month        Kwh / month        kwH/day (av) March        799            26 April        No data            No data May        637            21 June        475            16 July        139 to date        17
Three bed house in a fairly exposed location - heatpump is supplying all dhw and space heating through radiators...
HTH Adrian

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Adrian wrote:

Adrian,
what's the output temp of your heat pump?
Andy
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HI Andy
Andy Champ wrote:

I'm pretty sure it runs at about 65c - can't see at the moment as it's not running...
(as with almost everything on the system, it can be 'tweaked' through the little lcd display - but it's a bit late in the evening to start fiddling <g>)
A note of caution for the OP.... Our system was retro-fitted to take the place of a conventional oil-fired boiler. We found it necessary to replace the dhw tank - as the original (standard) one didn't have a sufficiently large heating coil - and so the return water from the heating coil was too hot for the heatpump to handle...
Seems that heatpumps like ours work best when they can dump heat fast - they really don't like a small differential between flow and return.
On ours, there's an overheat cut-out - which you can only access by taking the front off the unit and diving deep inside it... This cutout was tripping regularly until we fitted a new dhw tank - now it's not a problem (touch wood!)
HTH Adrian
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HI Folks
Adrian wrote:

Pump is running this morning - it claims that the boiler output temperature is 61c - we have the dhw set to 59c which was arrived at by trial and error ... works fine for us....
ISTR that the output temperature of the pump is settable via the engineers' screen on the controller - as are many other obscure but probably vital parameters... which I've not dared to fiddle with!
HTH Adrian
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Adrian wrote:

Bugger. Have to watch that.

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HI TNP
The Natural Philosopher wrote:

Might be a good question to ask 'a salesman' - see if they know what they're on about ...?
Easy enough to fit a new tank at the time you're fitting everything else - but might be a pain if you have to do it as another job...
Apparently our heat pump wanted a dhw tank with a heat-exchanger of 2 sq.m surface area - (= bigger coil - more turns) - whereas the bog standard one had a measly 0.6 sq metre - and the flow and return temps were much too close for the heat pump's liking...
Adrian
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Adrian wrote:

It occurs to me that simply toggling down the pump flow rate would sort that.
Mine has 0,94 sq m surface area of the heating coil...Mmm.
I cant find a UK distributor for Hautec..seems to be ireland only.
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HI TNP
The Natural Philosopher wrote:

Yes - we thought that too ! Trouble is - the pump is most efficient if it's running long periods without stopping/starting - and (unlike a gas / oil boiler) it's either 'on' or 'off' - no in-between.... You end up with fast cycling, or such a slow flow-rate that heating the water tank takes forever - trust me !

Well - on our experience - that wouldn't do...

I was sure I found somewhere on the web - maybe drop the German manufacturer a line... ?
As I said - there's enough 'incorrectness' in what your salesman said to make me concerned.....
Adrian
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Adrian wrote:

I could simply use immersion then. Its really not a major expense here.

I went to 'nearests distributor' and got ireland :-)
Ive also been collecting people who do heat pumps.
Not exhaustive but:-
Hautec Danfoss Veissman Dimplex. Nibe
Typical prices for a single phase unit in the 11Kw range seems to be 4k-5k..
Getting somewhat widely differing figures for the ground loop as well.
One guy says '25W/meter max 100 meters per loop' (i.e 400 meters total) whereas another says 'one 200 meter loop will be enough.
I suspect that on wet clay the salesman's 'Oh: clay? 35W/m' is nearer true, which means a 200m loop is marginal, and a 400meter is better.
Biggest bugbear is the better units with 2 stage compressors (higher output temps) all need 3 phase. BUGGER.

Thats why I am still here talking..trying to distil the real info from the BS.

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HI Again
The Natural Philosopher wrote:

Sounds about right

I guess you could talk to the people @ CAT in N Wales - they've got nothing to gain by their recommendations - so you might some real advice

Ours is single phase...

Wise man <g>
Adrian
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Adrian wrote:

Got some good info from a man at Nibe..
Essentially you CAN use the existing water tank, but you need an intermediate heat exchanger/heatbank..sort of 200 liter hot water tank that has GOOD conductivity from the heatpump primary: Once thats hot you then pump the cylinder primary from that ones secondary, and when it cools down a bit it fires up the heatpump again. Marginally cheaper than a whole new tank..
Looking hardest at the nibe and dimplex units..

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HI TNP
The Natural Philosopher wrote:

Don't know them...

Ah - that's a plan....
Not sure if I mentioned it - but with our system we have our own 'sort of heatbank'.... the c/h and dhw circuit returns end up in a 200litre, well-insulated 'oil drum-sized' store - before going back through the heatpump and round again....
When the heatpump decides it's done enough heatpumping then it turns off, and the warmed water in the circuit and the heatstore is pumped around unti it too has given up enough of its heat....
There's no heat-exchanger in our heatstore - it's just a big 'bucket'. Clown of a plumber who installed our system managed to do so without installing an air vent at the top end of the heatstore - which meant that air became trapped in the store and gave rise to an unfortunate 'header tank overflowing' situation....
One of the jobs for this summer is to install an air vent to prevent this...

Nibe seem to call these tanks 'accumulators'....
Regards Adrian
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Adrian coughed up some electrons that declared:

Sorry if I missed it Adrian: what energy monitor do you use?
I'm speccing up a heat bank and solar looks interesting...
Cheers
Tim
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