Solar thermal does produce warm water even in winter but nothing like enough to make any reasonable contribution to heating in winter. In all events you should consider adding insulation and for sure deal with all draughts and air leaks.

One deeper borehole should be used if you have more than one they need to be quite far apart.

It is important to size the borehole correctly and generally gshp systems are sized to meat the heating loads on all but the coldest days when additional heat added from a different source.

Yes but not enough to make it worthwhile, better to spend on insulation.

How would you stop it cooling the loop at night say?

Wouldn't you just not put the fluid through the solar collector when the collector is cooler than the fluid coming out of the ground? One or two motorized valves and simple differential temperature controller would do it.

I think you would be better of going a few feet deeper or having a few feet extra on a horizontal slinky.

Should be easy enough to work out what contribution could be expected.

If this is to sell systems then maybe use PV to heat a store (as Ed suggests on another thread) and show how this can perform better in the winter than ST.

Like all these systems they have to be matched to the demand. It is no good just going 'big' in the hope that you scavenge enough energy as you lose overall efficiency.

Hi Nick
I have been trying find good info on GSHP etc. I am convinced it is a good idea and there is a decent market for this stuff together with the RHi for commercial properties. The trouble is the people selling the stuff dont seem to now much about it and the people installing it have all got their own views not all based on fact. So what i want to do is install a system that can demonstrate the benefits of different approaches. I think its the only way I'm going to find out I wouldn't want to experiment on a customer. Our unit is similar to thousands, reception and workshop downstairs and offices upstairs. As the ground floor might have heavy stuff dropped on it, pallet trucks etc I want to have oversized, fan assisted radiators etc. Also for existing buildings it would less disruptive. The UFH upstairs is going on existing concrete floor - and so I think insulation wont be a problem as it is over the heated area downstairs. The first thing to do in will be the UFH pipework i' think I'm going to use the polystyrene preformed slabs with the spreader plates attached and cover it with laminate flooring. I dont want tall people scraping their head on the ceiling and this way I'll see if it works without screeding over the top

Posted By: mikeambroseThe trouble is the people selling the stuff dont seem to now much about it and the people installing it have all got their own views not all based on fact.

Too true. I had to size an ASHP after our salesman had promised the Earth. Was not that difficult but took time and care.

Posted By: mikeambroseI dont know how to calculate how long it would take to heat up the water going back into the ground

Fairly simple calculation, just the mass of water, the specific heat capacity of water and the temperature difference between the water and the ground. So you will need to know the ground temperature and the water temperature.
Then comes the tricky bit. How much solar energy can you reasonably expect to collect and when can you collect it. The stochastic nature of cloud cover causes problems here, as does seasonal temperature variation.

You may be better off designing a system that uses 2 or 3 GSHP or maybe one GSHP and an ASHP or 2 that can be used to 'boost' when needed.
If the larger system is sized so that it is below the peak demand (say 70% of peak demand), then a smaller system can be used to 'fill in the gaps'.
It is what happens already except that supplementary heating is used (usually electrical resistance).

I do think that there a false worry about using resistance heating when needed. The thing about resistance heating is that is is very cheap to install and if used in conjunction with off peak electricity no more expensive than gas.

Thank you Chris that's really useful stuff. I left a message with NIBE UK after reading a great series of reports from guy on this forum who installed one of their heat pumps in France - I do hope they come back to me most of these people just ignore me - maybe its me. Anyway I need to install a solar thermal panel to get MCS accreditation for it, the thing is there is not much use for hot water in an insdustrial unit but I heard you can get a surprising amount of heat from evacuated tube arrays even in winter and one of the problems you might need to overcome is the overheating of the collectors in the summer. If we use the extra heat generated to warm up the area around the boreholes we can get some of the energy back in the winter and if we can say temperatures above say 10 in the winter we might still be able to help with the heat pump. If all else fails I guess I'll have to have a hot tub in one of the offices !!

We are at Long Crendon near Oxford, HP18 9RW is our old place HP18 9EJ is the new one but the postcode doesn't seem to work.

At that flow temperature, radiators would need to be very large to make any difference to heat output unless fan assisted. The usual approach is to reduce spacing between pipes where you need more heat output.

David

Have you got the performance charts for the different heat pumps. Then the size of your thermal store (assuming your using one).
The Weather side of it is pretty easy if you can get decent data, trouble is that generally the monthly data is calculated from min and max range, which tells you very little. If you can get daily data that becomes a lot more accurate. Hourly is better still.

For the MCS you have to do a room by room as well as an overall building heat loss.

Had a quick look at the temp data for Oxford, anything below 0°C accounts for 0.6% of the data, below 1°C accounts for 1.5% of the data.

I need to recheck my figures but assuming they are correct I can get a 3 phase 15KW heatpump from NIBE which can / may have internet reporting and remote control functions and give me a decent COP at 40K flow and 30K return. The guy had not heard of the solar thermal heating of the ground loop water but it appears that the COP calculations are worked out on a theoretical zero K ground loop supply temperature with a 35K average flow & return temp for the heating circuit - no mention of hot water at all no wonder people get it all wrong. I don't understand where all the figures tie up because depending on the efficiency of the ground loop and the running time of the heatpump ( which will change with the weather) you will get all different temperatures going through the ground loop and therefore all different COPS. With the RHI giving 4.8p per KWh with a stated aim of providing purchasers a 10 percent return on investment it doesn't seem to work. Say the install comes to 35K including the boreholes you would need £3500 per year I don't know how many 4.8 pences that is but i'm going to work it out - more later when my head gets better

mikeambrose

Those are seriously low temperatures. I doubt your ground loop will get to zero Kelvin (or -273 degrees Celsius) in our lifetime.

Even more pedantically: K = Kelvin; k = kilo.

David

Hi Mike,

We are installers of NIBE amongst other units, if you get in touch with your local NIBE rep as opposed to tech, they will produce what is called a VPDIM which is a software model that they have for predicting various parameters based on the design requirements you give them.

Don't confuse COP with SPF (Seasonal Performance Factor), COP is a one off measure at a single point in time, SPF is measured over a heating season and includes additional peripherals like pumps and immersions, but there are different standards and criteria of what is included all over Europe!

Heat pump design is relatively simple when you know how, but the there is a great deal to learn to get it right.

In terms of what I have picked up from a quick prasee of your post, the following high level stuff might help;

Boreholes have to be dimensioned based on the heat load of the property, run times annually, the brine you intend to use, whether you want hot water too and the geological substrata.

They have to be at least 5m apart and flows have to be balanced across them, so interconnecting pipe runs to the manifold need to be considered carefully along with header size.

The heat distribution circuit has to be designed to run at the lowest potential temperature which generally means UFH at very close centres and reduced loop lengths, screed and tile or stone, laminate over spreader plates will require too high a flow temp to be sensible given that you are at start up. Oversized rads are an option but need careful dimensioning.

In a commercial it is not unusual to use larger diam UFH pipework than domestic say 18mm at wider centres, you could use a supplier but even those who say they are familiar with renewable design often get it wrong in our experience which is why we tend to do our own.

The property needs to be air tight and preferably well insulated, but definitely air tight.

Solar thermal does help but the costs do not always stack up in terms of payback. It is feasible to use it to heat the ground loops, which helps the ground recover over the summer, but if you do have DHW, it will be a difficult set up to control and install, because you would have to disconnect 1 while the other was in operation.

To feed ST to the ground you will need to spec PB pipework to take the heat as opposed to the probes you will get from most places. Go Geothermal can supply these for you, if you want them.

You could use ST to heat the HW over the summer and rest the ground but we have never been able to make the costs stack up to make it worthwhile.

In our experience the best heat pump systems are the simplest, especially if its your first. There is also good evidence that the commercial tariff will be upgraded soon, I haven't got the figure to hand at the moment though.

If you struggle to get in contact with your local NIBE rep, let me know and I'll ask ours who it is.

Cheers,

Jon

Hi Mike, the VPDIM software can be set up to various parameters, including the differential in brine temps and also the average brine temp. However as you allude the best way to achieve greater efficiencies is to modulate the ancillaries around the compressor.

We import a heat pump that does just this, the compressor, expansion valve brine pump and heating circ pump all modulate in concert with each other, they also twin pass the refrigerant to pre-heat the return via another heat exchanger before it returns to the condenser.

It is not uncommon for manufacturers to use modulating pumps now, but very few GS in the UK modulate the compressor, even though it is common on ASHP's. NIBE have a version in Sweden but not here yet.

The units we import have achieved COP's of 7-9 but not on brine, but they do outperform fixed speed compressor heat pumps.

The best performing heat pumps are DX where refrigerant is circulated through pipework in the ground or water to water, where 1 well pumps through the heat pump and then out to another well, the water temp is consistently higher than the ground. These are uncommon in the UK and DX does not qualify for the RHI, we are researching branching out into water to water at the moment.

I have just returned from training in Austria with the modulating units and can size and spec one for you but we would have to install it if you were interested, but they are typically £5-6k above what the regular units cost in the UK. If you wanted to sell them though you would need to be accepted by the manufacturer as a partner.

We start our first one next month just south of Manchester if you wanted to visit and see it in more depth, failing that ask away and I will fill in the blanks for you as much as I can.

With any unit though the golden rule is that the source and sink have to be as close to each other as possible, but the economics have to stack up in terms of the return and outlay.

I saw a case study in Austria where a 1.5km bore hole is being used as the source, and the SPF's are 9, but at what drilling cost! The Swiss have also mastered a system using just water in a closed loop, but again it is tricky to do without ending up with a frozen circuit. CO2 probes are also incredibly efficient but we don't have the expertise or knowledge in the UK to deploy these, we are still just scratching the surface in comparison with Europe (if you pardon the pun).

PM me for my number if you want to talk.

Jon