General: Installing a ground source heat pump

91 to 120 of 342

- CommentAuthortopher
- CommentTimeNov 26th 2010
Can anyone help please?

I have a 200 litre buffer cylinder, or inertial cylinder. It is required because the heat pump needs a certain minimum heat load to work efficiently, and the water in my underfloor pipes is not enough.

Now I am tying to find out how this buffer cylinder should be connected.
1. In series with the underfloor, so that the water flows through both
2. In parallel so that the flow is shared by the cylinder and the underfloor.
3. If in series, which comes first? Does the warm output of the heat pump go to the cylinder first or the underfloor first?
4. If in parallel, how do you ensure adequate flow to the underfloor? The heat pump already has a circulating pump, does a second one have to be added to pump the underfloor adequately?

Any response gratefully received. Regards,..........Topher.
- CommentAuthortopher
- CommentTimeJan 11th 2011
11 January 2011. Report 16.

I had to return to the UK in October 2010 for a family emergency. I am still in the UK, but will return to the heat pump installation in France at the end of January. While I have been away, it has been holding the house at 16 degrees as I had set on the thermostat with outside temperatures as low as minus 5 degrees. I don't know if it has been short cycling - I hope not - I will find out.

On the question of how to connect the buffer cylinder, I have been struggling to get an answer from Nibe. At first I spoke to Nibe UK but could not get a clear response, so I was referred to Nibe Sweden. Finally today I made contact with someone in Sweden who really knows, and I am much clearer about what is needed.

Series connection is OK if the secondary load is fixed as mine is. The reason for parallel connection would be if there were individual circuits which had control valves that might shut them down and set the flow to near zero, or zero. Clearly this would be bad for the heat pump. In a parallel connection a second circulator would be needed. There is a circulator inside the heat pump which would pump into the buffer cylinder, the second circulator takes water from the buffer cylinder to the heat loads.

The most important point I have learned is that the temperature differential on the secondary should be 5 to 10 degrees, with max of 12. When I get back, I will see what differential I have, and take steps to get it to the ideal.

It is possible to connect an external sensor to measure water temperature. At present it is on the return to the heat pump. The technical expert said it could go on the supply side, and that I could experiment by first disconnecting it, and then trying it in different places. I will do this.
- CommentAuthorfclauson
- CommentTimeJan 11th 2011
For a table of COPs in real life check out

http://wp-verbrauch.in-tostedt.de/index.php?button=verbrauch&lang=en
- CommentAuthortopher
- CommentTimeFeb 13th 2011
13 February 2011. Report 17.

After an absence of 3 months we have returned to France. During our absence the heat pump has been holding the house at 16 degrees, and I don't think it has been short cycling. I had hoped the temperature would be more like 12, but as I had to leave in a hurry, I had no time to check it. During our absence, EDF have had lots of red and white days (expensive units) but I console myself with the lower house temperature using less electricity.

I have been studying the installation and discovered two problems. First the temperature difference (supply temperature minus return temperature) on the underfloor is too high. It runs at about 12 to 13 degrees. For a concrete floor it should be 5 degrees (7 degrees for wood). The way to solve this is to increase the flow. The secondary circulator in the heat pump is set to max, so an additional pump is needed.

This high temperature difference causes another problem - the warm water output from the heat pump can get too hot for underfloor if the outside temperature is cold the heat pump has to run for a long time. I have measured 47 degrees - the ideal is 30 to 35. I am concerned that my very old underfloor pipework, and floor concrete could be damaged.

The second problem is the connection of the buffer cylinder and the and the underfloor circuit. My underfloor circuit has no control valves that open and close, the flow is fixed. So the cylinder and floor are connected in series with the floor coming first then the cylinder, and finally returning to the heat pump.

Nibe (heat pump supplier) say the cylinder should come first. Nibe use the supply temperature as the control to the heat pump, most other manufacturers use the return.

So on St Valentine's day the pipework is to be modified and a pump added. Then on Wednesday an expert from Atlantic (heat pump distributor) will come and set up all the parameters. I will have some questions for him as you can imagine.

If anyone is interested, I think I now understand the reasons for parallel and series connection of the buffer cylinder. Also, I think I understand the degree-minute system that Nibe use to control the start/stop of the compressor.
- CommentAuthorDamonHD
- CommentTimeFeb 13th 2011
Thanks for the update.

So, can you expand on your last para?

Rgds

Damon
- CommentAuthortopher
- CommentTimeFeb 14th 2011
Damon,

OK. But a warning first - I am a retired electronics engineer, not a heating engineer, but I am fairly confident of my facts. It will be interesting to see if people disagree. I will do the buffer cylinder first, then the Nibe degree minutes separately.

The buffer cylinder (BC) is used to give a sufficient quantity of water as a heat load for the heat pump (HP). My heat pump needs a minimum of 300 litres of water. The BC has 200 litres and the underfloor about 160, giving a total of 360.

The BC can be connected in series or parallel with the HP. When in series, the warm water from the HP flows through the BC and underfloor or radiators sequentially. When connected in parallel the warm water from the HP flows through the BC and back to the HP. There is another circuit from the top of the BC through the underfloor/radiators and back to the bottom of the BC. This needs an additional circulating pump.

In series connection the flow from the HP can be through the BC first or the heat load first. There is a lot of debate about which is best. Nibe is clear in drawings that BC is first then the heat load. Nibe controls the start/stop of the HP based on the supply temperature, I believe that most other manufacturers use the return temperature. If the heat load is underfloor this stops the temperature getting too high. If you have radiators, then perhaps they should be first as a higher temperature is desirable.

If you have a heating load which varies, for example motorised valves which open and close then a parallel connection is needed. If it were to be connected in series and the heating load was suddenly shut down the heat pump could be damaged.

In a parallel connection the BC can have a '3 pipe' or a '4 pipe, connection. The warmer top connections are always separate - one to the HP and the other to the heating load. In the '4 pipe' system the return side on the bottom of the BC are separate, in the '3 pipe' the returns are joined with a T connection to a single point on the bottom of the BC.
- CommentAuthortopher
- CommentTimeFeb 14th 2011
Damon,

Nibe Degree Minutes. Same health warning â€“ I am not a heating engineer. It might be helpful to take a piece of paper and draw the â€˜heating curveâ€™ and the â€˜degree minutesâ€™ formula described below to help understanding. My apologies if this is too long, but I am trying to be clear.

Nibe â€“ the Swedish manufacturer of my heat pump uses a number of parameters to control the compressor. Supply and return water temperature is measured with sensors. External and internal temperatures are measured in the same way.

There is a graph of supply water temperature on the vertical axis and external temperature getting colder on the horizontal axis. This is the heating curve and represents the heat needed to keep the house at the correct temperature as the outside ambient varies. Looking at the curve, as the outside temperature falls, the supply temperature rises. The slope and offset of the heating curve can be varied; it can also have fixed upper and lower limits. With this flexibility, the heating curve can be adjusted to suit the heating needed by the house.

Degree minutes are calculated every minute by the control circuit. The formula is actual flow water temperature minus the calculated flow water temperature taken from the heating curve. As each minute passes, the new value is added to the previous. Suppose the actual flow temperature is 25 degrees and the calculated temperature is 30 degrees. At the start, the degree minute will be -5. Suppose one minute passes and things remain the same, a new -5 is added to the existing, and we get -10. Things continue in this way until the degree minute value arrives at a preset point. Letâ€™s say the preset is -60. As you will have guessed this preset can be changed too.

At -60 the compressor starts, and the flow water temperature starts to rise. When it gets to 29, a degree minute is -1. When it gets to 35, a degree minute is +5. These positive degree minutes eventually reduce the negative value to zero. At zero, the compressor stops.

While the flow temperature minus the calculated temperature remains positive, the degree minutes become a larger and larger positive value. On my machine when it reaches +100 it does not get any bigger. I donâ€™t know why, maybe it is a Nibe fixed value. However as the flow temperature falls, because the compressor is now off, it eventually gets below the calculated value and now the degree minutes become negative. The +100 reduces and eventually gets to -60 which is the preset compressor start value and the cycle repeats.

If you change the degree minute setting from -60 to say -100, then the hysteresis increases, that is the temperature has to fall further for the pump to start, and the temperature rises higher before it shuts off. It is not necessarily best to have low hysteresis because the pump will cycle on and off more frequently and compressor life will be reduced. Nibe say 20 minutes on, and 20 minutes off is ideal. As in life, the ideal is hard to obtain, as the on and off time depend on the external temperature and the sizing of the heat pump with respect to the heat load.
- CommentAuthorDamonHD
- CommentTimeFeb 14th 2011
I get the general drift: the scheme that you describe seems a sensible first-order model including the effects of limited thermal mass in the house.

Rgds

Damon
- CommentAuthortopher
- CommentTimeFeb 16th 2011
16 February 2011. Report 18.

This morning, the man from Atlantic arrived with my installer to carry out a commissioning process. I decided to pay for this (350 â‚¬ more), because it increased the guarantee on the heat pump from 1 year to 3 years, with the manpower guaranteed for 1 year, plus I would be confident that it was installed and adjusted correctly.

The Swedish Nibe heat pump (distributed by Atlantic in France) has a set up procedure which gets all the values set up according to the individual environment. For example there is a parameter which can be changed to reflect how good the house insulation is. I thought that my house, renovated 25 years ago, was well insulated â€“ apparently it is not that good compared to modern materials.

Everything was found to be satisfactory except for the temperature difference on the secondary heating circuit which supplies the underfloor pipes. The delta-T is 11 to 12 degrees, it should be 7 maximum. There are a number of solutions.

1. Change the circulating pump inside the heat pump to a more powerful version. I don't yet know if this is possible. In my view this would be the ideal solution.

2. There is already a second pump in the circuit which was added yesterday to boost the circulation, but it is less powerful that the pump inside the heat pump. It is best if they both have the same performance. However the result may still not be enough, but it would be relatively easy to do.

3. Change the connection to the buffer cylinder so that it is in parallel to the heat pump, with a more powerful circulator to pump from the cylinder to the underfloor. I think this would be certain to solve the delta-T problem, but it has probably has the most work to achieve. If you look back 3 posts you will see an explanation of series and parallel connection of the buffer cylinder.

This excessive delta-T is not harmful; it causes less than optimum performance, reducing the efficiency or COP of the heat pump.

The man from Atlantic is responsible for advising the best solution. I am keen to hear what he says.
- CommentAuthorDamonHD
- CommentTimeFeb 16th 2011
Thank you again! Goodness, I thought that it would all be fit-and-forget like my solar PV... %-P

Rgds

Damon
- CommentAuthortopher
- CommentTimeFeb 23rd 2011
Is anyone finding this useful? I know one person is. Are there more? What sort of stuff is interesting? Lessons learned? Technical stuff? Tell me please.

23 February 2011. Report 19.

Dangerous to put this in print, but I think it is complete. There are a few odds and ends to sort out, but it is practically done. Whew, it was started in August last year.

The buffer cylinder is now connected in parallel with a three pipe system, and a more powerful circulator added. Nibe Sweden advised 3 pipe in place of 4 pipe as it would give the best isolation from the fairly powerful underfloor pump from the less powerful circulating pump inside the heat pump unit.

I have an old gas boiler which I was using on EDF red days - red days are very expensive. I was advised to check the costs, and I found that the heat pump was cheaper (just a bit) than the gas using last years prices. I have to do an update on current prices, but I expect the same result. Amazing eh? I think so.

I am recording consumption data, and learning about the logging that the heat pump provides. If you put the logging data on a spreadsheet you can plot graphs of temperature and similar things.
- CommentAuthorSteamyTea
- CommentTimeFeb 23rd 2011
Does your system data log, I would find that kind of information very useful.
- CommentAuthortopher
- CommentTimeFeb 23rd 2011
Hi SteamyTea,

The data log is done by plugging in a USB key. The data that can be recorded is fixed - time, temperature and so on. There are quite a large number of parameters. The only option is choosing the time interval, this can be set from seconds to minutes. When you want to end the logging period, you just 'safely' remove the USB key.

I have learned to copy and paste the data on the USB key file into spreadsheet. Then graphs can be constructed from the data. Nibe have some analysis software, but it is only for their use.

I could send you a data log file if that would be useful.

Thinking about all this electronic stuff, I would expect the next generation machines would be connected by wifi to the internet. Then the manufacturer could interrogate each machine, upload logging data, analyse it and send signals to the machine to alter control parameters, or emails to the customer to get an manual intervention if needed. Cool eh? Perhaps I am dreaming too much. None of this stuff is new, just engineering existing technology to a machine.
- CommentAuthorSteamyTea
- CommentTimeFeb 23rd 2011
Topher
That would be brilliant as I have never had a good look at heat pump data.
I have a wireless electrical data logger, still working out the best way to connect it all up to the PC.
- CommentAuthorDamonHD
- CommentTimeFeb 23rd 2011
Topher: if you want I could host a csv file or spreadsheet full of the data so far for ST and all who come after him! B^>

Rgds

Damon
- CommentAuthorSteamyTea
- CommentTimeFeb 23rd 2011
csv is good, makes it easy to play with
- CommentAuthortopher
- CommentTimeFeb 23rd 2011
OK. No problem. I am in the middle of a logging session at the moment which is scheduled to end on Saturday. My installer has asked that it should be run that long - he wants to look at it too. The time interval is 5 minutes so there will be lots of numbers, but I suppose it will be easy to delete excess stuff. So I can send the file to DamonHD, and you too SteamyTea, if you want. I will also need to tell you what each parameter means, for example the one I am very familiar with is BT25, it is the Nibe reference for an external sensor connected to my buffer cylinder. It is used in the degree-minute calculation to tell the compressor when to switch off. Just tell me what to do.

The outside temperature is quite high here at the moment (about 8 degrees) , so the compressor runs will be on the short side at fairly widely spaced intervals.

Regards,.............Topher.
.
- CommentAuthorSteamyTea
- CommentTimeFeb 23rd 2011
That's great, look forward to getting it. Thanks.
- CommentAuthorDamonHD
- CommentTimeFeb 23rd 2011
Yep, sounds good. Thanks.

Damon
- CommentAuthordavidfreeborough
- CommentTimeFeb 24th 2011 edited
Posted By: topherIs anyone finding this useful? I know one person is. Are there more? What sort of stuff is interesting? Lessons learned? Technical stuff?
Thanks for the regular updates. This is all useful background for planning my build, particularly how to optimise the set-up & control of the system.

Am I right in thinking that the heat pump's circulation pump runs continuously whenever the heating zones call for heat & the compressor only runs as & when necessary to put the right amount of "degree minutes" into the house?

David
- CommentAuthorFlubba
- CommentTimeFeb 24th 2011 edited
Topher in response to your question this diary of sorts is indeed very interesting Iâ€™ve even read the thing from start to finish and itâ€™s full of useful information for anyone interested in ground source heat pumps.
- CommentAuthortopher
- CommentTimeFeb 24th 2011
David,

The answer is 'it depends'. Not helpful I know.

In my system there are two secondary circulating pumps. One in inside the heat pump and the other is external. If the circulator inside the the heat pump has enough output for your system then this is the only one needed. In the Nibe heat pump this circulator can be set to run continuously or intermittently, its output can also be varied. When it is on intermittent it only runs with the compressor. I believe that if you have a heat pump and radiators - no buffer cylinder then an intermittent mode will be OK, because once the heat pump has shut off there is no more heat to be had, so it might as well stop. In my system, with a 200 litre buffer cylinder there is a lot of heat to be taken from the buffer cylinder and released to the underfloor.

An important point - a heat pump is a binary device, it either runs or it does not. When it is running it is going flat out, no modulation (like a gas boiler) is possible; the circulating water temperature just rises and rises until it reaches the max possible, or until the compressor is stopped by the degree minutes formula.

You said. . . "Am I right in thinking that the heat pump's circulation pump runs continuously whenever the heating zones call for heat & the compressor only runs as & when necessary to put the right amount of "degree minutes" into the house?". . . . I can only say with confidence how my system works. The heat pump runs when the degree minutes calculation and the heating curve tells it to. About 20 seconds before the compressor starts the brine pump starts - that circulates the water at about 10 degrees from the bore holes, also the secondary circulator in the heat pump starts and heats the buffer cylinder. The underfloor circulator is running 24/7. So as the heat pump warms up the water in the buffer cylinder the underfloor circulator takes the heat away. The heat pump gradually raises the water temperature until the degree minutes go sufficiently negative and the compressor shuts off. At the same time the brine pump stops and the secondary circulator stops. The underfloor pump, running 24/7 takes the heat out of the buffer cylinder, and so the cycle goes on. If you have radiators the system will be different and I don't know how it works.

Underfloor heating is the best possible system for a heat pump. It runs at its most efficient. If you have radiators they will have to be generously sized and the heat-pump will have to run hotter and therefore less efficiently.

Hope this is of some use.
- CommentAuthorevan
- CommentTimeFeb 24th 2011
Is your house maintained at the same temp 24/7, topher?
- CommentAuthortopher
- CommentTimeFeb 24th 2011
Evan,

Yes. When I leave the house to go back to UK, I set the temperature at about 12 or 13 degrees. When I return and put it to 19 degrees, it takes 3 days to get there! The huge lump of concrete on the ground floor and the smaller piece that forms the floor for the upstairs bedrooms takes ages to heat as you can imagine.

There is a little trick that I am going to try at some future date. The heat pump has a sophisticated time clock that would normally be used with a radiator system. I plan to have the over night temperature set just a little down from the day temperature. Then at say 7.30 am when the temperature goes up a bit the heat pump will run a bit longer and the floor will be warm for bare feet on the tiles.

With underfloor systems, the spacing of the pipes can be made closer together in certain places - say in front of the wash basin in the bathroom - so that your feet are gently warmed. Cunning idea eh? Nothing to do with me. The previous owner designed it so.
- CommentAuthortopher
- CommentTimeFeb 24th 2011
Flubba,

Wow, I am flattered. You have read all of it! Well done.

Thanks to all for telling me that you find it interesting.

Regards,............Topher.
- CommentAuthordjh
- CommentTimeFeb 25th 2011
Posted By: topherAn important point - a heat pump is a binary device, it either runs or it does not.

Is that correct? I thought that so-called "inverter" heat pumps are able to modulate their output, as described at http://homepages.ihug.co.nz/~eeh/heat_pump.htm for example. And I believe that there are also scroll compressors that are inherently capable of modulation by varying their geometry?

But don't let my niggle mislead you. I think this is an excellent series of postings; very useful
- CommentAuthorPaul in Montreal
- CommentTimeFeb 25th 2011
<blockquote><cite>Posted By: djh</cite>I thought that so-called "inverter" heat pumps are able to modulate their output, as described at http://homepages.ihug.co.nz/~eeh/heat_pump.htm for example. And I believe that there are also scroll compressors that are inherently capable of modulation by varying their geometry?</blockquote>

Correct on both points. See this video from Copeland: http://www.youtube.com/watch?v=h2h2iG5strY

Paul in Montreal.
- CommentAuthortopher
- CommentTimeFeb 25th 2011
My mistake, sorry. I should have said that my heat pump was a binary device. I assumed too much.

Groveling,.............Topher.
- CommentAuthortopher
- CommentTimeFeb 26th 2011
Hi,

Off to Blighty tomorrow. Will be off the air till Monday. Back with the heat pump in 2 weeks time. I have sent the logging files to DamonHD, I understand that he will put them up on his website = http://www.earth.org.uk/ground-source-heat-pump.html#real1

Regards,............Topher.
- CommentAuthortopher
- CommentTimeFeb 26th 2011
If you want a copy of the logging files, send me your email by 'whisper'.

91 to 120 of 342



	Site Map \| Home \| View Cart \| Pressroom \| Business \| Links	Contact Us
Logout
© Green Building Press

Green Building Forum

Categories

Feeds

General: Installing a ground source heat pump