The requirement:

To heat a house with a worst-case total space heating requirement (at -5 deg C) of 1.7 kW (assuming nil solar gain, and 85% heat recovery from MVHR).

To provide DHW when solar water heating is zero. Estimated daily DHW usage is approximately 80 litres, giving a daily energy input to DHW of about 4.6 kWh. A water re-heat time of 2 to 3 hours would be acceptable, so a heat input to DHW from non-solar could be around 1.5 to 2.3 kW.

The house:

The house will have a high solar gain in both bedrooms, and low solar gain on the ground floor. This isn't great, but is something I have to live with because of planning constraints. Because the bedrooms are partially in the roof space I can't turn it into an "upside down" house. I will need to shift heat from the bedrooms to downstairs to balance the heating requirement. The plan is to fit UFH downstairs only (approximately 75 m²). Supplementary bedroom heating may be needed occasionally, but either small low temperature radiators or even electric panel heaters, should be enough to do the job on the few occasions when this might be needed. The bathroom is small and a large towel rail will provide more than enough heat, even when run at UFH temperatures.

The plot is small, but I could just about accommodate a 200m long heat collector loop over an area of around 200 m², including the drive and parking area. The ground is likely to be wet a metre down, as there is a stream running very close (that I cannot access) by and small seasonal springs seeping from the bank that will be dug away to build the platform for the house.

The plot will have a 31 m long, 1.8 m average height, retaining wall at the north boundary (the wall will face south). This retaining wall is 50% shaded by the house, but offers some potential for heat collection, perhaps.


Thoughts on heating so far:

I've been looking at using the Ecocent and MVHR combination that would allow external air to be used for heat pump input in extreme conditions, but doing the calculations it looks as if under these worst case conditions I would not be able to extract sufficient energy to make it work. The Ecocent/MVHR combination looks good for milder weather, but falls short of providing enough heat for a prolonged spell of cold weather.

I've been searching for something that could provide a little more heating performance than the Ecocent and perhaps use a modest ground source collector. Ideally a unit that worked as a combined MVHR, exhaust air heat pump and also allowed ground source collection when needed would seem to fit the bill, but such units don't seem to exist. The Paul combined ASHP and MVHR unit looks like a possibility, but is a bit more powerful in terms of water heat output than I need. Hard data from other GSHP manufactures seems scarce - their websites seemed full of fluff and little in the way of real performance data. I've spent hours searching the web for information and so far haven't found anything that fits my needs well.

Given my modest heating and DHW requirements, and the need to shift heat from upstairs to downstairs when the sun shines, has anyone any suggestions please?

Thanks, the drive will be gravel, probably contained by one of the mesh systems (I have potential problems with run-off drainage, so am sticking with a permeable surface). The MVHR system has to potential to move a small amount of heat around in the way you suggest, but it may not be enough, as air has a pretty low specific heat. The nice thing about the Ecocent is that it has the potential to shift heat from the warm air in the bedrooms to the UFH on the ground floor pretty efficiently. In many ways the Ecocent is ideal, except for the need to provide an additional 1.7 kW of space heating (plus a bit for DHW) when the weather turns really cold (by south west England standards!).

If I could get a small GSHP that would deliver just a couple of kW to the UFH then that would be fine I think, but no one seems to make such small models, AFAICS. I could get a 4 kW one I suppose, but it seems wasteful to spend out on something that's twice the size I'll ever need, especially as it won't be used as the primary heating system for much of the time.

It seems that heating system manufacturers aren't up to speed with the need for low output heating for houses that are close to passivehaus standards and are still focussed on big, multi kW units.

<blockquote><cite>Posted By: Ed Davies</cite>Yes, a small heat pump which could take, say, 800 W of electricity and 1600 W of cool water and product 2000 W of warm water (and leak a few W to the surroundings) would be very handy. Sort of falls in the gap between a fridge and heating heat pump. I wonder if any commercial refrigeration devices would be suitable. When I get a little closer to needing such a thing I plan to get this chap's book:<a rel="nofollow" href="http://www.heatpumps.co.uk/">http://www.heatpumps.co.uk/</a>then, likely, ask him for advice.</blockquote>

One thing I've found that is the right sort of energy level are the units available mainly in the US that are used like the Ecocent, to extract waste heat from warm air in building and heat water. In fact I strongly suspect that the Ecocent is one of these US type units (like this one: http://www.geappliances.com/heat-pump-hot-water-heater/electric-water-heater-features.htm) re-engineered to work in the UK. They are typically around 600 to 800 W input, 1.5 to 2 kW output. If there was something like this that would run on a small ground loop, instead of using air, then it would be ideal, but search as I might I've yet to find one.

Posted By: JSHarrisIf there was something like this that would run on a small ground loop, instead of using air, then it would be ideal, ...

Exactly. Not just ground source, though. My plan is a large (10 m³ or so), partitioned, low-temperature thermal store with the temperatures in the warm part of the thermal store boosted by a heat pump from the cooler (and hence cooled) part which is, in turn, recharged from a large ET array. All or most of the thermal store will be inside the insulation envelope of the house.

My house design is predicated around this thermal store. It sounds like you're far enough down the road not to consider radical changes of that sort. Still, with your large ET array you could consider an external heat store as the source for your heat pump. For example, a few IBCs boxed in and wrapped in whatever insulation comes to hand (straw bale, Warmcel, rockwool, ...). When the ETs aren't producing a high enough temperature to be useful for DHW, etc, they could feed the thermal store.

An external thermal store of this type could double as a rainwater store in summer.

ST,
Thanks, I'll ping Kensa and see if they have anything smaller than 4 kW.

Ed,
I'd have liked to put a big thermal store in, but ground conditions and space limitations make that difficult. I will already have a big piled retaining wall and am reasonably sure that I will have running water under the plot at a depth of a metre or two down. This makes a buried thermal store difficult to implement. I don't have space inside the house for one wholly inside the envelope, either, as I am floor area and height limited under a planning condition. A friend implemented a big (around 50 m²) thermal store using granite rocks in a 12ft square room in the centre of his chapel conversion years ago, which I believe worked well. He'd charge it to high temperatures during the summer and autumn, using a wind generator running electric heating elements, and just pass air through the rocks and out through vents into each room through the winter.

CPB,

Thanks for that link, that little 2 kW unit looks ideal. If I can get that to charge the Ecocent cylinder when the outside temperature drops to the point where supplementary heating is needed then it would make for a really good system, I think. The Ecocent has the capability to run up to 80 m² of UFH and also has a powerful heat extraction capability from warm rooms. Coupled with a decent MVHR unit I think this would make for a versatile solution, needing only around 50 m² of collector pipe area in the garden. I've emailed them for more information (their contact form doesn't seem to accept non-Austrian address details), and will let you know what I hear.

Crispy, good link, bookmarked, thanks. Looking forward to hearing what JSH finds out.

The Neura HP comes with a tank AFAIK I'm sure they probably have a distributor in the UK if you look around.

I would install it in preference to the ecocent to be honest, what worries me about the ecocent is getting bits for it if it breaks in 8 or 9 years time.

And being ground source it will give you much better cop than the ecocent, your site sounds like ideal conditions for a ground source collector.

Then use joe90's solution to pipe the hot air from upstairs with a simple pipe and a fan powered by a small pv panel.

Found the funny short story by AC Clarke, one of my favourites.

<blockquote><cite>Posted By: skyewright</cite>I think that billi on the Navitron forum has mentioned a 500W heatpump, but I can't find the reference at the moment? IIRC is was something like Ecocent minus the tank but with a model that could use ground source. Probably German?</blockquote>

Thanks for that, I'll pop over to the Navitron forum and see what I can find out.

The problem is the amount of heat that needs to be shifted. The air to water heat pump (something like an Ecocent) can suck a great deal of air from a room (around ten times more than you could move via redistribution fans) as it doesn't have to shift air via ducts to the place where it's needed. it does need distributed air feeds back into the house, but these can be distributed around the house so as to minimise draughts in the living space. In effect a system like this can pump heat relatively quickly from one area to another, using UFH to get the heat where it's needed, as water has a much higher specific heat than air.

“Ochsner” rings a bell. It's probably the one Billi mentioned in Naviland. However, I previously thought they were air source only (like the Ecocent) so that's interesting.

Definitely looks like sourcing from German speaking peeps - Anglophones just don't get it, yet. “The low heat output required in a low-energy house and the controlled home ventilation system mean that special heat pump systems are necessary.”

Wouldn't be on here apart from having sit in front of the computer while rebooting a logging system after a short power cut (windy, but not amazingly so, up here on the north coast this evening). Still, happy Christmas all.

The HPs with copper collectors are direct expansion (DX) heat pumps.

I've found an old export price list from 2010 for it and it is listed at €1,707 +VAT for the heat pump (without tank) and €2.769 +VAT with a 300 litre tank or €2,950+VAT with a 500 litre tank and the ground collector is listed at €533+VAT Not sure is they are wholesale or retail prices, carriage to be added of course but not as bad as I was expecting, unfortunately they don't have a distributor here in Sweden but I might contact them myself in any case.

http://www.accubel.be/pdf/ESPACE-PROFESSIONNELS/Liste_de_prix/Ochsner_liste-prix_2010_EN.pdf

Interesting find! The EsaveP people are certainly helpful and do seem to have done a lot of work with the Ecocent, but this might easily have been getting to grips with an imported product. I'll admit to having been surprised to find just how many of these things there are around, as the Ecocent seems to be the pretty much the only one sold here AFAICS.

Having just looked at Alibaba I found this one: http://www.alibaba.com/product-gs/472568197/Sluckz_domestic_heat_pump_air_to.html that looks absolutely identical to the Ecocent (apart from the flowers etc) thats here: http://www.esavep.com/products/domestic-hot-water

If you have links for any other 3-5kW ground source heat pumps I'd very much appreciate if you can post them as neither the Neura or the Ochsner units I have posted are sold here in Sweden and I'd much prefer to buy something with local back up available rather than getting into the realms of importing myself.

Thanks.

<blockquote><cite>Posted By: CWatters</cite><blockquote><cite>Posted By: JSHarris</cite>am reasonably sure that I will have running water under the plot at a depth of a metre or two down</blockquote>

Hope your foundations aren't too expensive then!</blockquote>

Unfortunately they are a bit, but the water is at the other end of the plot from the house. The plot is a fairly steep bank, so the house will be set down nearly 2 metres below the soil level on the north side. There is some water seepage at the west end of the plot, but the east end (where the house will be) seems to be fairly dry and is land that has previously been built on (I believe there was an old forge there until it was knocked down about 30 years ago). The main problem I have is that virtually all the soil on the plot is made up ground, from the time of the demolition of the old forge I think.

There will be a 31 metre long retaining wall screw piled into the bank, with more piles under the slab. Luckily the bed rock is only a couple of metres below the dig out ground level, so the slab piles will be just be concrete pillars that rest on that.