Posted By: WillInAberdeenLocal council here will not give PP for new houses off mains water network.

What has main water got to do with PP? Ruddy planners....

I like the idea of using flowing ground water to supply the energy for a heat pump it is a elegant solution. As you are in a hard water area, will that cause any problems?

How close are you now to being totally 'off grid', disregarding the PV export business, Bio-fuel 7.5 kW generator (or a gasoline one if you want it cheap and quiet) and some batteries next

Get a large hole dug and put some of those 1000 lt juice containers in it. Then when the time comes you can pop some batteries in 'the hole'. You could do it when the JCB is there but the workers are away

The house is effectively a passive house, and the 1.7 kW is the additional supplementary space heating only requirement in very cold weather, over and above the heat from occupants, cooking, appliances etc. When the outside air temperature is above about 3 or 4 deg C there is no significant space heating requirement.

There is, however, a modest DHW requirement in winter that cannot be wholly met by the solar thermal system, and this tends to dominate total energy usage through the winter months as a whole.

I know I need to be able to provide up to around 1.7 kW of heat for space heating for a period of around 2 to 3 months, plus I need a means to provide DHW for around the same period, or perhaps a little longer (I think the solar thermal will only really give me 100% for maybe 6 months of the year).

Heat pumps don't require annual servicing, as far as I can tell from the stuff read so far. They seem to be as reliable as refrigerators, with the only possible serviceable part in my case possibly being a filter on the water inlet.

It's not about money, primarily, it's largely about investing in a house that will use the very least amount of energy possible through it's life, within the constraints imposed by planning conditions and the site. The alternative to a borehole for a water supply is a mains water supply connection costing £16,000 as a minimum (the water company price is £23,378). It is significantly cheaper to drill a borehole, fit a pump etc, than it is to fork out for a mains water supply. Drilling a second borehole on site for a heat pump to use as an outlet only adds around 30% to the drilling cost and still comes in below the cost of mains water.

In terms of capital investment, I can pretty much pay for the boreholes, heat pump and UFH just from the saving in capital costs from not having to install mains water, so I get the heating system effectively for free. Add in the saving from no water charges, which will offset the energy cost of running the heating and pump, and it doesn't make sense not to take this option (unless there is a big unknown problem lurking out there somewhere!).

Electric UFH is out, as the electricity supply to the site is of limited capacity. It's near the end of a long run of 240V single phase cable. Upgrading the supply to allow the use of electric UFH would be costly, as around 1/2 mile of cable would need to be replaced, with a three phase run to a new sub-station near, or on, the plot, then a single phase run to the plot and the neighbouring house. The DNO have already said I can't run a big PV array for the same reason.

The investment cost comparison looks a bit like this (very rough numbers - I haven't had quotes yet!):

Mains water supply:
between <b>£16,000 and £23,000</b>

Water only borehole:
Drilling and lining cost (single borehole) ~ £5,000
Submersible pump and pressure vessel ~ £800

sub total about: £5,800

Second borehole for heat pump outlet:
Additional drilling cost ~ £1,500
Small heat pump ~ £3,500
UFH for 75 m² ~ £2,000

sub total about: £7,000

Total cost of water borehole and heat pump UFH and DHW (thermal store already part of solar thermal installation):
<b>£12,800</b>

So, not only do I get a "free" heating and DHW system by taking this option, I also save over £3,000 as a minimum.

Other than cleaning the outside air heat exchanger I can't honestly see what real servicing would be required even for an ASHP. Sounds like a way to extract money, to me. An ASHP is pretty much a sealed system, so I wonder what they actually "service"? My guess is that it's really just a check that the thing is still working within limits, but that should be something the owner can do I'd have thought. I always worry about over-servicing things, "if it ain't broke, don't fix it" seems to apply well in my experience!

The energy Saving Trust study on real-world heat pump efficiency did have quite a few examples where ASHPs has delivered a lower COP than the manufacturers implied. Overall they determined that ASHPs performed slightly less well than GSHPs in the sample they checked. ASHP COP varied from 1.2 - 3.3 over a sample of 28, with the "mid-range" point in the sample being a COP of 2.2. The data they collected for GSHPs was slightly better and gave a spread of COP of between 1.3 - 3.6 for a sample of 47, with a "mid-range" COP of about 2.5.

The continuous supply limit I have is 6 kW, with no more than 3.7 kWp PV input. I could run the 1.7 kW heating load, but I have to consider the other household loads that might be on at the same time, like DHW (which would be about 3 kW if I used an immersion heater) and other domestic appliance loads that might be needed at the same time as heating and hot water and which could use a kW or so.

A heat pump might consume 1 kW or so to run both UFH and DHW, leaving a healthy margin for other stuff.

Unfortunately DIY trenching is out, as the pipe run would be up a surfaced single track lane. Only a local authority approved contractor can do the work, as the lane would need to be closed for a few days and resurfaced properly.

I haven't considered RHI, so that will knock a bit off. If I don't go for the heat pump, then I'd still incur the cost of some other form of heating and hot water provision. This is quite limited, because I don't really want to burn fuel and I'd rather not have the heating system taking up wall space. This leaves me with direct electric underfloor and electric DHW, which together use up most of my allowable continuous electrical load.

I agree that, on the face of it, the economics of the heat pump don't stack up that well, but would guess that, after taking account of RHI and the need to provide electric UFH and DHW, the true differential cost would be closer to £4,000, rather than £7,000. The payback time would still be fairly long (assuming today's electricity prices and a £300/year saving around 13 years), but it would also get the house down to a near-zero carbon input, because the PV would pretty much cover the total annual usage I think. Also, I've assumed £3500 for a 4 kW output HP, but looking around that might be towards the upper end. There are GSHPs available at that sort of output for around £2000 to £2500, bringing the cost down a bit more and shortening the payback period to maybe 10 years at today's prices.

Thanks Chris, that makes a huge difference to the decision process and, perhaps, explains why less than 4 kW output GSHPs are so rare. It seems probable that there is a crossover point at around 4 kW output where an ASHP will be more efficient that a GSHP just because of the pump power needed, which is an interesting thing to know.

In my case the DHW requirement significantly exceeds the space heating requirement for most of the year, and is still a large part of the overall energy demand even in the coldest months.

Looks like a I need to go back around the decision loop yet again...........

but if the drill's already needed for a drinking water borehole, then it probably makes sense to get a GSHP borehole drilled at the same time, which changes the equation a lot I'd think.

<blockquote><cite>Posted By: Gavin_A</cite>but if the drill's already needed for a drinking water borehole, then it probably makes sense to get a GSHP borehole drilled at the same time, which changes the equation a lot I'd think.</blockquote>

Very true. I guess what I really need to do is look closely at the pump power requirements and factor that in to see what the overall COP might be, whilst ignoring the borehole because I'll have that anyway.

I do wish there were simpler ways to reach decisions about some of this stuff - I've spent tens of hours so far going around in circles trying to look at the various trade-offs.

CPB: the Volker system as put together by Newform Energy runs a heat-pump with the solar thermal panels, using them as its heat source, clearly with a large surface area all exposed whatever sunlight is available. At worst it should degenerate to being an ASHP.

Rgds

Damon

http://www.newformenergy.com/photovoltaic-thermal

«Photovoltaics (PV) as semiconductors have one drawback: degradation in performance due to temperature. In the UK on a sunny midsummer's day, when one would expect PV to be producing at peak capacity, panel temperatures can reach over 100oC. At this temperature the system will produce less than 10% of its maximum output, rendering it largely useless for much of the day.»

I think that if this were true I'd have heard somebody mention it before now.

If it is just a cheap installation for space heating (or water for that matter) then you can't get better than electrical resistance.
Then you have to look at the running costs and then the environmental costs.

On environmental costs, as we are legislated to 'greening yo the grid' over the next 20 years or so then it may not be so long till it is better environmentally that heat pumps are today (but in 20 years time heat pumps will be using greener power too). There will be a point where it is better than gas but never better than solar, as that is really the true source of our energy barring a small amount of gravity (tidal) and radioactive decay.

Would drawing break even charts show this better?

<blockquote><cite>Posted By: GreenPaddy</cite>Quote from Chris p Bacon - "It really makes me question the viability of using a GSHP for such low energy demands particularly so if a high percentage of the demand is for DHW."

This is exactly the point I'm trying to make on my somewhat maligned "£100 heating challenge" thread. JSH is yet another example of very low energy demanding homes being built, and we don't really have very obvious answers for low capital cost, simple systems to deliver heating & DHW. JSH has, as I understand it, an additional specific obstacle, in the form of restricted peak power, making his choice more difficult.

I suspect there is no "easy" technical solution to the gas boiler replacement (ie. cheap and simple for the masses), and no driver for industry to invent something they can not get either a high inital price for, or recoup the money in servicing charges.</blockquote>

Spot on! No clear choice indeed hence all this dithering around looking at combinations of systems to fit the bill.

eta - at Green Paddy

I think this is an area that helps the systems using PVT as the heat source make sense, as the pumps energy use should be more than offset by improved output from the PV panels being cooler.