19 March 2011. Report 20.

I got back to France yesterday. House temperature was 14 degrees. I had set the thermostat to 12; I need to find out what parameter to change to get it right. With the low temperature setting and the warmish days, the heat pump has not been running much. If my calculations are right, the average run time was 14 minutes, and the average starts, 39 per week. I don’t know if this is good, bad, or unimportant. What do you think?

After having watched a compressor cycle at the unchanged thermostat setting of 12 degrees, (it ran for 11 minutes), I increased the thermostat to 19 degrees. Due to the sudden large demand, the degree minutes became a very large negative number (measured return temperature minus calculated return temperature from the heating curve). I had set -100 for pump start. It started, and as the difference was so large, the number got more and more negative while the heat pump output warmed up. When it got to -400 the auxiliary resistance heating cut in and the temperature rise got faster. Eventually the underfloor temperature got too high in my view, and I switched off by lowering the thermostat. I subsequently found that the resistance heating was set to come on at -400; I have left it there for the moment.

There is a setting for max flow temperature and it was at 48 degrees, much too high in my view. I have lowered it to 32, but I still get high temperatures. It does not control the pump directly as you might expect. I need to study the operation to get it right.

As the house is now close to 19 degrees inside, the temperatures are lower at pump switch off. I now see the reason for resistance heating. If you have a sudden demand for a big temperature difference, adding on peak electric heat will get there faster, but will cost more of course.

Hi DamonHD,

I agree about the resistance heat. I can switch it off or I could set the degree minutes for switch on to an impossibly high value. If I leave it as it is it will only come on if I set a very large temperature change on the thermostat - a rare event.

I realise you are joking, but a training course on the operation of the pump is available. It is run by Atlantic, the French distributor of the Nibe product. The problem is that it is for installers only and it is in French. I have met the trainer. He is the only Frenchman I know who really understands in detail how it works. It won’t take me long to get these final questions sorted. Telephone and email support from Nibe in Sweden is excellent, but not readily available, I will have to wait a bit.

Considering Europe as a whole, I wonder how many heat pumps are not correctly set up and therefore not saving as much electricity as they could. If I was not interested in the controls and tweaking for best performance, my machine might be continually short cycling, it might not have the correct delta-T on the primary and secondary heat exchangers, and the buffer cylinder might not be correctly connected. In a country like Sweden where heat pumps are a well established technology, the set up is probably totally correct; but in France and the UK, I suspect that a significant number of installations are not correctly tweaked.

The Energy Saving Trust's survey showed that probably most UK heat-pumps are badly specified and/or installed I think.

Rgds

Damon

Here's the report:

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Heat-pump-field-trial/


"The findings illustrate that heat pump performance is highly dependent upon appropriate installation and integration with the building’s existing heating system, as well as appropriate control by the customer. "


Rgds

Damon

So, a new business opportunity perhaps. Train a group of people on the main manufacturer's equipment and offer a free service to adjust and inspect heat pump installations.

If the installation is OK but the adjustments are wrong then the customer gets the benefit - no payment or a small fee. If the installation is wrong, it is an opportunity for someone to come and correct it. This second situation will be the one that makes the money to fund the scheme. In the case of the Nibe products and the data logging, the customer could email the data log to be remotely analysed. Nibe could be doing this today. I wonder why they don't. Perhaps they have not thought about it yet. I would willing to pay a small fee for this service.

Maybe a university that runs a heating engineering course could get the students to do the work with the Uni Department offering the technical assurance of correct work.

In my experience, if uni staff spent less time bitching about how hard life is and alienating the bright people who actually want to learn, they'd find life a lot better... But that's only 8 years' experience of someone actually paying the fees (sans grant).

Rgds

Damon

ST: you're clearly on the side of the angels! B^>

Rgds

Damon

OK, so a bad business idea then.

I have found out how to control the upper temperature. First there is setting to flatten out the top of the heating curve to a preset value if needed. Then there is an offset to allow the temperature to rise to a preset figure above the heating curve. I think this makes sense. If the outside temperature is very mild, the curve will ask for a relatively low temperature. If the heat pump is shut off at this low value it will tend to short cycle - a positive offset will reduce this problem.

With a Kw/h meter able to show instantaneous power, I notice that when the compressor starts, the consumption is lowest. As time passes and the output temperature rises, the consumption increases. I guess the motor has to work harder as the compressed gas gets hotter. The important result is that the COP gets worse. I suppose the compromise is between lower temperature to get a good COP (sorry for pun) and the need to minimise short cycling.

snyggapa is also interested in this and has read the lot, albeit with the benefit of a bottle of red

definitely going to look into GSHP for my renovation - although interested in what is needed to dig the trenches as we have a weak bridge between the road and the property... but that hampers bringing in any fuel apart from electricity.

likely a ground trench for me rather than a borehole, although I guess I need someone who knows what they're doing to advise, I guess it boils down to a cost/efficiency measure on trench digging against hole boreing. We're on a fenland though, which I guess makes the likelihood of finding water at low depths quite high.

-Steve

9 April 2011. Report 21.

Now that it is much warmer, the heat pump runs very occasionally, and I have discovered a new problem. Due to the high ambient, say 13 degrees, the heating curve will calculate a low temperature for the heating flow. This may be just a little above the actual temperature in the buffer cylinder. The result is a short run time for the compressor. Not good.

I have found these ways of increasing the run time.

1. Increase the degree minute setting at which the compressor starts. During the winter it was minus 60, I have now set it to minus 120. This means that the temperature in the buffer cylinder will have to get colder before the compressor starts, so it will have to run longer before switch off.

2. Increase the offset allowed on the max flow temperature. Previously I had 31 degrees max on the heating curve and an off set of +10. This gives a max temperature of 41 degrees at which point the compressor stops regardless of degree minutes. I changed the heating curve to a max of 29 and the offset to +12. This still gives a max of 41 degrees, but allows the temperature to get higher by 2 degrees than the heating curve calculation or the max of 29 degrees.

This seems to work. I now get a run time of about 20 minutes, I got 10 or less beforehand. I will have to wait until next heating season, to see the effect of this when it gets seriously cold outside. Always a compromise as we all know.

I am still recording the consumption, but I am not sure how best to use the numbers. Next week I will switch off the system at the main circuit breaker.

Damon,

An interesting point. The makers (Nibe) say that once the system has been set up correctly, the user can forget about it and just use it. My case is different as I am an 'tweak-freak', I want the best results. I know what changes I have just made, and when the heating season comes round again I will be able to see the effect of what I have done. If I decide to make any more changes, I will be hopefully moving towards the best compromise. I am aware that my learning curve has slowed things down too.

Think of all the systems out there that are not set up correctly. What a waste of energy and shortening of compressor life. What an opportunity?

Your system sounds interesting, will you have to learn how to tweak it too, or does the computer do it all for you?

I have just checked my average compressor run time and it is just over 20 minutes, so my tweaks were correct for today's ambient.

Regards,.............Topher.

Yesterday I was pleased to show off my system to a neighbour. He is considering a geothermal system. It would be very useful to have comparative cost ratios between the three systems.
1. Water – Water. Vertical borehole or boreholes.
2. Water – Water. Horizontal trenches.
3. Air – Water. A system with a fan coil unit.
4. Difference in running cost between underfloor and radiator heat.
4. Perhaps cost per kilowatt too.
We can always convert between GB Pounds, US or Canadian Dollars to Euros. It would be a guide and very helpful to him. Anyone got any figures or links to references?

Regards,...........Topher.

Topher: should be data from Energy Saving Trust (and Carbon Trust) in the UK, DoE in the US, etc?

Rgds

Damon

Topher,
1 loop per bore and the depth is 100 mtrs. I am drilling slightly deeper though, about 110mtrs. Just for peace of mind that I have some extra heat extraction possible if I ever need it. After watching the team drill my holes will never be dry. I will upload some pics later!!!
Gusty.

Gusty,

In France they don't put grout in. I believe at some future date it will be made compulsory. I do have some sort of sealing material just at the top to prevent any potential fountains. No chance for me I think.

I believe the idea of the pipe is that it is very cheap and easy to do and in the unlikely event of the bore drying out, water can be added.

What country are you in? Are you having grout?

Regards,..........Topher.