View Full Version : Advice badly needed re: replacement ground source heat pump

11-08-2016, 01:52 PM
Hello everybody,

I find myself in a rather difficult situation and would be extremely grateful for any advice.

My wife & I, now retired, live in a timber-framed house in France, near Geneva, where I used to work for the W.H.O. When we built the house, as we had plenty of land, the architect recommended that we install a ground-source heat pump with underfloor heating to the ground floor. This has served us pretty well for over 20 years, though it seemed to struggle a bit on the rare occasions when the temperature didn't rise above -10C for a number of days. We have, however, now provisionally sold the land on which part of the collection piping sits, so need to find an alternative.

This where the fun starts. The existing system is all R22, with no water at all, in 10mm copper pipes set in an anhydrite floor & 12mm (plastic-sheathed) in the ground. The estate agent, as they do, simplified the task by saying that all we had to do was change to air-source! Of course, I then discovered that underfloor heating these days is in larger, generally plastic, pipes that carry water, not refrigerant. I thought at first that I might get away with water through the copper pipes just by adding a fairly powerful pump. Then I did some calculations and these seem to indicate that I'd need a pump with about a 36 metre head. This is to get a flow of 300 litres/hour at a speed of ~1.5 metres/sec through about 120 metres of 10mm piping. (There are 5 such circuits in parallel in the floor.) A pump with such a head seems to need 3-phase electricity, which I don't have, but could get. I suspect, however, that there would be additional issues with such a setup. (Is this calculation really correct? I got a figure of ~3000N/m per metre for the pressure drop, which is mighty big when you multiply it by 120!)

An alternative has struck me, and I'd like your help to know whether this is viable or not. This would be to put in a replacement compressor for the existing Copeland and continuing to run refrigerant through the floor pipes. This compressor would then run refrigerant to a typical fan-based outdoor unit, thus completing the change to an air-sourced system. There are a number of refrigeration specialists in our area who may be able to do the work, but they're French-speaking. My French is OK, but I'd rather know in advance whether this should work or not.

I would be extremely grateful for any help, and would be happy to freely offer the benefit of 50 years of computer problem-solving experience in return.

Thanks for your time.

11-08-2016, 08:46 PM
this may be of some use http://www.daikin.co.uk/domestic/needs/heating/air-water-heatpumps-ht/index.jsp

11-08-2016, 11:03 PM
You've done your research, I would opt for the compressor replacement, maybe to 407c as this should keep component replacement to a minimum, only thing to really watch for is that any joint which has a gasket will need to be replaced.

Just rereading your post, to avoid reusing the ground collector you could opt for an air sourced evaporator with defrost heaters, not as efficient as the ground loop but removes the need to lay new pipe work etc.

14-08-2016, 09:26 AM
Many thanks, Al. Exactly what I needed to know.