Hi,

I'm just starting to look at using the stream at the end of my garden for a water source heat pump. I could use some advice on the practicality and whether I could do any of the installation work myself.

The stream is 50m from the house, downhill, about 15m below the house. It's small - running currently at about 10-15 litres/minute. The stream is fed by a spring up the hill, passes through a field and then goes underground for about 2-300m under the ground of an old folk's home. It exits the concrete underground pipe at the bottom of my garden. I've just measured the water temperature, and it's 14 degrees currently. I'm guessing that it might be around 12 degrees in winter, given the distance it travels underground? The stream runs very clear almost all of the time - I have been using the water for years for garden irrigation, toilet flushing and the washing machine. Occasionally, the farmer puts cows in the field and they paddle round in the stream turning it brown.

I've looked briefly at websites of people who fit water source heat pumps, and one site suggested that the height of the house from the water might be a problem as there is higher to pump the water. But I'd have thought the return water would balance the intake, and so there'd be little pumping energy needed?

A water temperature of 12 degrees or so might be fine in winter, but I wonder how practical it might be to heat the water further during summer, either in my greenhouse which is near the stream and gets too hot unless I ventilate it, or by having the intake pipe exposed to the air and so warm up somewhat as it travels up the garden.

There's the question of open or closed system.... I think given the height difference, there would likely be a problem with air getting into an open system. I could possibly lay a heat exchanger for a closed system inside the base of the concrete pipe - it is easily big enough to crawl up.

Would I be able to do some of the installation myself (I've rebuilt the house, and installed all the plumbing and a raspberry pi controlled irrigation system for the garden) or do I need to hand over all the work to some registered installer to qualify for the RHI payments?

Thanks for any suggestions.

John

The water source examples that I have seen used a slinky coil or two sunk into a large body of water .
I asked about it for our pond (it’s a decent sized pond) but was told that it probably wouldn’t be big enough - it has frozen over in very cold winters but can get quite warm in a hot summer.

I think you would have to dig a 1.2m x 1.2m “pond” by about 2m deep to accommodate the slinky.
You will need others more cleverer than wot I am to work out if there’s enough heat/ energy flowing through at 10-15l/m to extract any useful amount.
I don’t know about the height difference - ours is the other way around, goes uphill several metres to the end of the slinkies.

If you take the water itself from the stream you will need an abstraction license even though it’s all going back in.

On the plus side you won’t need planning permission for a water source heat pump if the garden is your domestic curtilage because it is now Permitted Development.

I was wondering whether time might be my friend. You'd think there'd be some kind of extension/enhancement of the RHI scheme in response to the latest IPCC report. But I don't want to count on that!

I've seen pics of those slinkys. I doubt 'd get permission to put one of them in the stream bed - the stream isn't actually in my garden, it's just beyond. I have a pipe going into it to extract water which I mainly use for irrigation. We're allowed 20,000 litres a day without needing an abstraction licence. I wonder if 20,000 litres of water would be enough?

Well, I've just written to Kensa anyway.

Thanks.

For the pipework I would dig a bucket say 500lts down by the stream that would be filled from the stream and put a submersible pump in it. Then run pipework to the house below the frost line both flow and return. The return I would put into the stream not into the 500ltr bucket. Done this way there would be no air lock problems with the pipe work and the pumping effort would be pipe resistance only.
The heat pump would be at the house with a heat exchanger. If you put the slinky down by the stream you will loose heat as the slinky won't get up to the same temp. as the stream so the heat pump will start off with an input colder than the stream temp.

20,000 litres a day is only enough for a few kW of heat. Would be much cheaper to generate that amount of heat using a small ASHP.

If the house needs more kW of heating than that, consider a big ASHP or GSHP ?

That’s the trouble with the RHI - the system has to be designed to heat the whole house to 20 or 21 degrees (can’t remember which)
I had the same question with our farmhouse - anything is better than the oil boiler which is 30kW but we hardly use - we have the house colder than most people would tolerate.
It has to all be worked out carefully to calculate the RHI payments. Gave up with it in the end to concentrate on the one in the barn conversion because it was more straightforward to work out (just waiting for the plumber to come now and connect it all up). Plus I quickly realised there wouldn’t be enough spare funds in the budget to do the house as well. It’s a shame really because we fully intend to switch the house over to a heat pump at some stage but we will miss the RHI deadline.

Posted By: John Pedersendetailed assessment of the house insulation levels

We had lengthy discussions about this, with photographs etc because the oldest parts are uninsulated then there are various extensions from different periods e.g. 70s and 80s

A smart meter comes in very handy here. We have one, and it logs daily gas use - the maximum daily gas use could be used to size a heatpump. If you heat the whole house to 21C or thereabouts, then the peak kwh/day divided by 24 is the heatpump power minimum needed. I expect this will be a lot more accurate than a paper assessment of insulation levels, etc, as it includes the ‘performance gap’ between intended and actual insulation automatically. I suppose you may have a mild versus harsh winter affecting things, but it must be possible to account for this with a small tweek.

I guess I was just thinking I should make more effort on account of climate change, but I live on a tiny income, and I guess I'm likely going to have to wait and see what further government initiatives are created. They'll have to do something to incentivise Joe Public to make the switch. I didn't want to wait for that, but I don't want to fork out a bundle based on the cost of heating every room to 21 degrees, and then have the government give me annual compensation payments. Perhaps lots of people will be holding back, waiting to see what the incentives might be. In that sense, lack of government action is holding up the switch to heat pumps.