On days when solar gain is low and additional heating is required, its unlikely that there'll be excess heat available upstairs to move downstairs & on some days both upstairs & downstairs will need heating. So I would be inclined to separate the "heat moving system" from the heating system itself.

As you've pointed out, air is not the best medium for moving heat around. So how about installing underfloor heating pipes upstairs & downstairs with recirculation when heat transfer is required? The same pipes could be connected to a 4-5kW GSHP or ASHP outside when there isn't internal heat available to transfer.

This allows you to use off-the-shelf GSHP/ASHP/MVHRs, avoids paying for the Ecocent's compressor to move heat around your house, allows the MVHR to operate continuously through the heating season reducing ventilation heat loss and avoids the risk of cold draughts from the untempered air drawn in to replace that exhuasted by the Ecocent.

Alternatively, if you want to keep the Ecocent for heating/hot water in times of high solar gain, then how about using one of the Genvex MVHR units with integrated ASHP to provide additional heat input in cold conditions?

David

Why not just get a mini-split ASHP? These support several internal fan-coil units for each outdoor unit and you can both heat and cool with them. The Japanese ones have a very high COP and will work well below 0C. No futzing around with ductwork. Way cheaper than a GSHP which sounds like it would be complete overkill for this application. Of course, a mini-split won't do hot water ....

Paul in Montreal.

I would really like to use one of those Sanyo ECO-CUTEs, with a decent CoP too, but when I last looked they weren't MCS certified for example.

Rgds

Damon

I think I'd go with the smaller heat pump, as you have a couple of boost options too.

Could you use the saved money on capital cost of the smaller HP to reduce thermal losses anywhere? Insulated shutters or something novel like that?

BTW, you'll lose some heat through the stove when it's off... Can you use a room-sealed one, and then put an insulated door in front of it for when it's not in use?

Posted By: JSHarrisI'm absolutely NOT putting a hole in the building for a stove (even a room-sealed one) I'm afraid, nor am I going to contemplate burning wood that costs more that electricity around here.

Yay! If somebody said “here's a kg or so of steel, use it to cool the house as best as you can” you'd come up with something like a stove pipe; the “mother of all cold bridges” I've called them elsewhere.

Brilliant description "The Mother of All Cold Bridges"- somehow conjures up an image of a middle eastern dictator...............

I've just done a quick sum based on the price the lady over the road from me paid for a "load" of logs the week before Christmas. I reckon they were around 15p per kWh, with electricity here currently being around 13p per kWh.

Posted By: JSHarrissomehow conjures up an image of a middle eastern dictator

Or a Russian Energy Oligarch

Lets say that you need 10 kWh a day to heat your house. A thermal store would need to be at least double the temperature difference between the radiator and the air to get a decent heat transfer. So if your air is at 20C, radiator at 50C, you need to keep that store at at least 65C. That seems a tall order to me.
Now 9 tonnes of water that can drop by 15C could supply about 5.6 MWh of energy. If that is needed for 90 days, then you can have 6.3 kWh a day. So close.

Now lets look at the heat loss. Say the ground is at 8C during the winter, and you have to keep the tank of water at above 50C, that is a 42C difference.
If there was no insulation and the temperature gradually decreased over the 90 days, then that is a heat loss of 6.2 kWh a day, or about equal to what you need.
To keep the heat loss to 1 kWh a day you would need an R-Value of 24 or about 2 foot of aerogel all round your tank. PU would be over a yard.

Now I may well have gone astray somewhere, but insulating a buried thermal store is not easy and you still only get half the energy needed (assuming no meaningful input for 3 months)

What about investing the cash you'd otherwise spend on GSHP (or whatever) in off-site wind or PV and then using electric panel heaters to fill the gap? Cheap to install, maintenance free, maybe more sensible than trying to capture solar energy on site?

<blockquote><cite>Posted By: qeipl</cite>What about investing the cash you'd otherwise spend on GSHP (or whatever) in off-site wind or PV and then using electric panel heaters to fill the gap? Cheap to install, maintenance free, maybe more sensible than trying to capture solar energy on site?</blockquote>

I do keep coming back to the idea of just using a few small panel heaters. They would be cheap and easy to install and probably very reliable. I suppose I just have this ingrained feeling that using direct resistive electrical heating just seems wrong! Financially I think you're spot on, I could probably invest the money that a GSHP would cost and use the interest to cover the difference in running cost for direct electrical heating. It looks like I'll have about 2.8 kWp of PV on the south facing (unshaded) roof, so this would offset the electricity used to some extent. I just like the idea of only using a third of the electrical energy input that I'd have by using a heat pump, which boils down to a moral decision, rather than a financial one.

Posted By: JSHarris
I'm absolutely NOT putting a hole in the building for a stove

Sorry, I should have quoted him, but I was responding to the post immediately above mine by Chris Bacon, where he said:

Posted By: Chris P Bacon
will probably have a water jacket wood stove in the living room particularly as SWMBO has said she wants a real fire

I've pretty much concluded not to put a wood stove in my new house now, partly because of the difficulty in reducing lost heat when it's not in use, and partly because it'll end up with something like a 20+ year pay back on such a highly insulated building. Instead it'll just be gas-fired UFH (using the existing 2 year old Vaillant Ecotech Plus 24kW condensing boiler which was in the place when I bought it).

Out of interest, I still get all my wood here in Brighton for free (construction/joinery waste etc.) and it does most of the heating in my flat...

Tim.

Posted By: JSHarrisI've been looking at the costs of GSHP collector systems and came across the principle of using a wet borehole system (essentially two boreholes linked to a common underground aquifer).

... I could solve my water supply and supplementary heating provision ....

Can anyone see the obvious snag that I must have missed, please?

I have no experience of boreholes for GSHP but there has been a trend here of boreholes for water supplies (lots of sites where mains water is distant) and there have been some reports of wells running dry, so there is a risk involved.

A friend of mine had problems with her borehole pump draining back because of a bit of grit in the non-return valve down at the pump. I did a temporary fix by putting a non-return valve on the pipe at ground level, which the installer left in place after lifting the pump to clear the grit. So there are maintenance issues with borehole water which have to be considered.

<blockquote><cite>Posted By: qeipl</cite><blockquote><cite>Posted By: JSHarris</cite>I've been looking at the costs of GSHP collector systems and came across the principle of using a wet borehole system (essentially two boreholes linked to a common underground aquifer).

... I could solve my water supply and supplementary heating provision ....

Can anyone see the obvious snag that I must have missed, please?</blockquote>

I have no experience of boreholes for GSHP but there has been a trend here of boreholes for water supplies (lots of sites where mains water is distant) and there have been some reports of wells running dry, so there is a risk involved.

A friend of mine had problems with her borehole pump draining back because of a bit of grit in the non-return valve down at the pump. I did a temporary fix by putting a non-return valve on the pipe at ground level, which the installer left in place after lifting the pump to clear the grit. So there are maintenance issues with borehole water which have to be considered.</blockquote>

Thanks, that's worth knowing. I've managed to download a few borehole records for holes around my plot and it seems the water table varies from 3 metres ABOVE my plot (!) to about 5 metres below it, with none of the holes being deeper than 15 metres and all flowing large volumes of water. The nearest borehole is a disused one about 100 metres away, that was drilled by the army around 100 years ago. It apparently flowed 20,000 gallons an hour with no measurable drop in water level with the pump running. It looks like this was the regional mains water supply for years, until new water mains were laid when a lot of houses were built in the 1960's. The last analysts report for the water I can find looks good, no treatment needed, so that bodes well for a borehole being a reasonable option.

From what I can gather, the process they use now is to pump the hole clean after it's dug with a temporary pump, then once everything's been flushed through the permanent pump is dropped down. As it seems likely the the pump may only be ten or fifteen metres down getting it in and out may well be a relatively simple DIY job, should it need attention. We're lucky here in that we have masses of groundwater under the chalk. I had a chat with a local farmer at lunchtime and he reckons his borehole water levels don't ever change.

I've had confirmation that it's fine to extract drinking water and heat pump inlet water from the same bore hole and it's also fine to just discharge the heat pump outlet water down another borehole nearby. The underground aquifer is apparently at around 8 to 10 deg C all year round, so the heat pump COP should be constantly good, even in the coldest weather. All told this it looking to be a good option, there would be a less initial capital outlay than laying pipes, less disruption to the locals (as I don't then need to dig up 100 metres of single track lane), a virtually "free" ground source heat pump collector and freedom from water and sewerage bills. The latter would pay for the boreholes in less than ten years alone, even allowing for the odd spare pump.

Looking at a few water borehole company web sites it seems that since the 2003 water act, that removed all the need for licensing etc for private boreholes of limited capacity, it is now getting increasingly popular for people to go for this option for private houses. The payback period when compared to water charges is reasonably short, especially if you only need a single borehole and the water isn't too far down. I currently pay about 0.36 p per litre for water and sewerage, which equates to around £550 to £600 per year including standing charges. I'd have to factor in the servicing cost of the sewerage treatment plant (maybe £200 to £300 every three years), the cost of running the water pump (maybe £30 to £40 a year, but offset by PV on the roof) and the need for replacement pumps (maybe £300 to £400 every ten years?), but even so it looks like a good option.

Can you get some samples from the neighbouring boreholes and get that water checked before you invest in a drinking water borehole.
Am I right in thinking that you will put the waste from the sewage plant into the groundwater. Makes me feel a bit queasy, even though I know the percentage is tiny, just that I often look at the waste pipe that runs along the pier at PL, true it does not smell like the one at St. Ives, but that is a larger town. Does smell a bit though.
I lived in places where the local water killed people, so always a bit cautious.

Dragging the discussion back to the heating solution, our house, floor area equivalent 150sq metres has an actual heat requirement of 3.4kw at 0C to maintain our 18.5 C inside - a bit more than you but reasonably low. When considering how to provide heat, I too was fixed on the CoP of a heat pump and eventually went for an exhaust air heat pump, thinking like you, that I would always benefit from the 3 to 1 ratio. Turns oyut my unit is way undersized and has to rely on immersion back up to meet the shortfall. Working on a solution at the moment, but it has made me very wary and is the only real regret I have about my house. Without drivelling on about my woes, all I would say is do not get too fixated with heat pumps. As suggested, panel heaters / kickspace fan heaters could be a simple and cheap solution. Small gas bolier off LPG (twin 47kg cylinder arrangement like static caravans use rather than big tank) plumbed to a small radiator circuit, would be a bigger outlay to panel heaters, but fuel price is lower (at the moment) and perhaps worth considering given the flexibility it would provide for DHW.