Green Building Forum - Installing a ground source heat pump

Installing a ground source heat pump

Paul in Montreal — Tue, 06 Oct 2015 14:43:01 +0100

Posted By: ringiI expect that a water to air system would be more predictable (provided there a big ducts) as there are a lot less issues with sizing of radiators etc. (Or carpets on UFH)

Biggest issue with water-to-air (and air-to-air) for that matter are mis-sized ducts. If the ducts are too small, the velocities are too high and this leads to noise, or to poor heat/cool delivery. My ducts are large and so the system is quiet, especially in the bedrooms (which are furthest from the heatpump) where the supply vents are essentially inaudible.

Seasonal COP for me is about 3.0 - which I'm happy with as this includes the use of the auxiliary (straight electric) heat for the coldest days. The system was sized for 80% worst case, which, in effect, covers about 98% of the heating season. For the remaining 2%, buying extra electricity is cheaper than the extra drilling / equipment size would have been over a 25 year period (and which would have oversized us on the cooling side even more than the undersize on the heating side). Even with last winter's extreme cold temperatures (average -16C for the entire month of February) overall operating costs were still excellent. Of course, our hydroelectricity here is cheap, so the cost/benefit analysis here is different compared to the UK/Europe.

Paul in Montreal.

Installing a ground source heat pump

topher — Wed, 07 Oct 2015 22:21:01 +0100

SteamyTea, I have written kWh on a post-it and will get it right in future. Thanks. As you asked about rain, yes huge amounts, but with 2 x 100 meter deep boreholes, the temperature never changes. As the primary circulation pump starts, the supply temperature is about 13 degrees. The return temperature slowly drops and gets down to about 5 degrees minimum. If the compressor has been running for say 20 minutes, the supply drops to about 11 degrees. So 11 degrees supply and 5 degrees return is the lowest I get.

DyrlP, I have calculated using day and night tariff and standing charge and with today's Euro/Sterling rate 29.7kWh for two days cost Â£3.37 (GBP). I can give the details if you wish. It is French electricity and is about 75% neuclear.

Ringi, I don't agree. Hugely better than storage heaters. First the heating is exactly controlled to what is needed. Secondly the electricity cost is a third to a quarter of what a storage heater takes. However the installation cost of a ground source heat pump is many times more than a storage heater, and I probably won't get my money back in my lifetime.

Paul in Montreal, I agree with you. My problems have been with installation workmanship, hopefully now fixed. I am pleased with a COP of nearly 4.0. I also like the underfloor heating that gives a comfortable even temperature. Just closing one switch puts the heat on for the whole house.

Installing a ground source heat pump

mike7 — Thu, 08 Oct 2015 01:13:41 +0100

I've not read all of this thread but .... it does confirm for me that in more temperate climates than Montreal's a GSHP is not the way to go. In the UK and I guess western France much of the heating season is when air temps are well above zero when ASHPs will work very well at much lower capital cost, and it is not as if they don't work at all at colder temps. Now consider there's the possible introduction of smart metering when it will probably get much more expensive per kWh in midwinter, the high capital cost of sizing a system to meet 100% of demand, and the additional load on the supply grid during peak demand. Those considerations suggest a better way could be to use an ASHP sized to meet maybe 50-70% of the max demand, and leave the rest to gas or biofuel. There's advantage in not being entirely dependent on one fuel source, too. I've seen the terms 'bivalent' and 'hybrid' used in this area but I suggest 'mongrel' might be a better one, covering all likely combinations ;-)

Installing a ground source heat pump

Paul in Montreal — Thu, 08 Oct 2015 11:34:45 +0100

Posted By: mike7I've not read all of this thread but .... it does confirm for me that in more temperate climates than Montreal's a GSHP is not the way to go. In the UK and I guess western France much of the heating season is when air temps are well above zero when ASHPs will wor k[ ... ]Those considerations suggest a better way could be to use an ASHP sized to meet maybe 50-70% of the max demand, and leave the rest to gas or biofuel. There's advantage in not being entirely dependent on one fuel source, too. I've seen the terms 'bivalent' and 'hybrid' used in this area but I suggest 'mongrel' might be a better one, covering all likely combinations ;-)

That's what a lot of people do here in Montreal, too. ASHPs are quite common and work well, even when the temperature is below freezing. We have a special "bi-energie" electrical tarrif that gives half price electricity when the temperature is above -12C and then the rate switches to 4x normal when it's below -12. There's a special sensor which the bi-energy heating systems use to switch to the alternative fuel at the -12C cutover point - usually natural gas, but people also use oil or, less commonly, wood. Usually it works out cheaper over a year than the regular 1x rate, though last year, where we had 6 weeks with an average temperature of -15C or lower, it was less of a win. Due to the dry climate in winter when it's below freezing, frosting of the outdoor unit is not the problem that it is in a more humid climate.

One other factor, all ASHPs here are also used for cooling, so no-one has air-to-water systems as far as I know, though there are few water-to-water GSHPs (these can also do cooling if you have a fancoil unit).

Paul in Montreal.

Installing a ground source heat pump

SteamyTea — Thu, 08 Oct 2015 15:53:34 +0100

Are larger HPs more efficient? Quite often these things don't always scale in a linear way.

Installing a ground source heat pump

topher — Sat, 17 Oct 2015 13:04:50 +0100

SteamyTea,

I looked at Nibe (who make mine) and the 5 kW is rated A+++. The 17kW is rated A++. The specs are v complicated and I could not find a COP value. So in answer to your question it appears that smaller outputs are more efficient. It would be interesting to hear what Paul in Montreal thinks.

Topher.

Installing a ground source heat pump

topher — Sun, 23 Oct 2016 14:47:14 +0100

Report No 34. 23 October 2016.

This is probably the last report, as I don't think any one is reading it now. Some facts may be of interest. . . .

Installed and running for 6 years

Some leaking pipes caused by installer over-tightening joints

One failed primary circulating pump replaced under extended warranty

Compressor 9429 starts

Compressor hours 2946

18.7 minutes average run time -- to short in my view

Using input electrical power versus heat output COP = 3.86

That's it.

Installing a ground source heat pump

djh — Sun, 23 Oct 2016 17:49:31 +0100

Thanks for that. I'm still reading and I expect others are too. It will stand up as a useful reference for many years, I think.

Installing a ground source heat pump

topher — Sun, 23 Oct 2016 21:51:47 +0100

djh Thank you......Topher

Installing a ground source heat pump

Paul in Montreal — Mon, 24 Oct 2016 01:11:59 +0100

Posted By: djhThanks for that. I'm still reading and I expect others are too. It will stand up as a useful reference for many years, I think.

Me too! I look forward to these reports! Good to see a decent COP, too!

Paul in Montreal - where this will be the 12th winter my GSHP has been used

Installing a ground source heat pump

topher — Mon, 24 Oct 2016 11:54:42 +0100

Paul,

Thanks for kind words.

May I ask. . .How many hours on your compressor? How many starts? Who made the compressor? Do you know theCOP? Any major faults?

Regards,......Topher

Installing a ground source heat pump

Paul in Montreal — Mon, 24 Oct 2016 12:26:08 +0100

Posted By: topherMay I ask. . .How many hours on your compressor? How many starts? Who made the compressor? Do you know theCOP? Any major faults?

Sorry I don't have answers to most of your questions as the controller doesn't measure anything! The compressor is made by Copeland and the original one died after 2 weeks and was replaced. No problems since then, apart from the run capacitor for the air circulation fan dying about 5 years ago (at the hottest part of the summer). I replaced that myself. We did have an airlock, once, in the ground loop, but that was quite easily fixed and now I know what has to be done if it ever happens again. I'm not sure what the overall COP is - but, based on my energy consumption versus the measured heating (or cooling) degree-days, I know it's over 3, but not how much (as I don't know the operating time for the 10kW resistance heat that is staged to come on when needed in the coldest parts of winter).

By the way, my run-times in the coldest part of winter are of the order of several hours or more, but the controller forces an interrupt every 6 hours or so if it would otherwise run continuously (which it would when it's in the -20s outside :) ).

Paul in Montreal.

Installing a ground source heat pump

Sprocket — Wed, 26 Oct 2016 16:53:22 +0100

Topher, your install was about a year ahead of our first one so it was great to hear how you were doing - especially since you were on boreholes (like us) when most UK installations were slinkies.
Great to see you are running fairly smoothly and your COP is still really good.

Similar story here on data. Our GSHPs (Kensa) are pretty simple kit - they don't record that sort of data.

But from what I see runtime is typically a few hours per start in the coldest parts of winter (nothing like as cold here in Somerset as in Montreal though). Our COP must be pretty high but that is mainly because our ground loop temperature rarely falls much below 12 degrees. We have no buffer tanks, just big UFH zones.

The only problems we have had were
1) A compression joint on the bottom of our GSHP secondary blew apart. Fortunately the heat pump spotted the drop in pressure and shut down rather than dump all the fluid from the UFH.
2) Pressure dropped a little in the ground loop during the first year and again the heat pump shut down. It was a while before we noticed though and easy to top up.
No problems since 2012 though. It just works.
Unless we override for extra hot water we only run our heat pumps during the middle of the day, in order to make the most of PV.

I know Paul has commented that his boreholes were pretty cheap but ours were the priciest part of the install and there were quite a few problems with the drilling that did not help. I wish I had gotten a fixed price. Our ground loops are clearly a bit over-done too and we clearly could have got away with a lot less given the amount of groundwater here.

Installing a ground source heat pump

Paul in Montreal — Wed, 26 Oct 2016 19:39:44 +0100

Posted By: SprocketI know Paul has commented that his boreholes were pretty cheap but ours were the priciest part of the install

I paid $14 a foot (though nothing was factored-in for debris removal!) for a total of around $6000, which ended up being about 1/4 of the total price of the installation of the GSHP and all the ductwork and equipment (including the cost of the GSHP). That $14 a foot also included the loop itself, not just the drilling.

My ground loop temperature is closer to 4C here so that has an impact on ultimate COP - but note my system is water-to-air, not water-to-water.

Paul in Montreal

Installing a ground source heat pump

Silky — Wed, 26 Oct 2016 21:19:10 +0100

I just started reading the thread through.. so thanks!

Installing a ground source heat pump

SteamyTea — Wed, 26 Oct 2016 21:34:31 +0100

Paul
Does your W2AHP pump out hot water to a radiator that then had air passed though it (like a car cooling system).
Or is it the refrigerant gas that is cooled by the air?

Installing a ground source heat pump

Paul in Montreal — Thu, 27 Oct 2016 01:17:55 +0100

Posted By: SteamyTeaOr is it the refrigerant gas that is cooled by the air?

The refrigerant goes to a heat exchanger in the ductwork. There's two loops - the ground loop which circulates an antifreeze solution - this has one heat exchanger that's connected to the refrigerant/compressor loop. The refrigerant loop has what looks like a large car radiator in a plenum behind the air circulation fan. There's a reversing valve as well so the air heat exchanger can be used for cooling, with the coil in the water loop becoming a heater, warming the ground loop. There's a compressor and TXV in there too - but only one TXV (thermal expansion valve - this performs refrigerant metering) is needed due to the reversing valve (which switches between heating and cooling mode).

There's also an extra loop for the "desuperheater" that provides a pre-heat to our hot water tank. You'll have to google "refrigerant superheat" to fully understand how that works :) But essentially it proves a source of around 55C for pre-heating the hot water tank when the GSHP is running sort of for free.

Paul in Montreal.

Installing a ground source heat pump

SteamyTea — Thu, 27 Oct 2016 08:07:25 +0100

Possibly accounts for your good CoP when you get those low temperatures.

I still want to know how they are going to recharge then once HFCs are gone. We do have a few years on that though.

Installing a ground source heat pump

ringi — Thu, 27 Oct 2016 10:01:45 +0100

Pual,

Are you heating your outside air (I assume -20), or your already heated inside air with the radiator?

Installing a ground source heat pump

ringi — Thu, 27 Oct 2016 10:08:47 +0100

Does anyone know how hot the refrigerant gets in a UK GSHP when heating the water for UFH?

Installing a ground source heat pump

barney — Thu, 27 Oct 2016 11:17:00 +0100

Between about 70C and 100C depending on the refrigerant type and system working pressure and how much superheat can be tolerated

Regards

Barney

Installing a ground source heat pump

ringi — Thu, 27 Oct 2016 11:43:23 +0100

So we are heat the refrigerant to 70c, so we can heat the water to 40c, so we can heat the air to 22câ€¦

I now see way by heating the air from the refrigerant the CoP can be better as the refrigerant does not need to be heated as much. (However to move heat with air the air needs to be a lot hotter than 22c.)

If only we had a cheap, safe, and easy to install refrigerant that we could pump round pipes to each room we wished to heat the air in.

Installing a ground source heat pump

barney — Thu, 27 Oct 2016 12:17:39 +0100

Propane would be excellent for that - but we probably don't want to be piping that at high pressure around houses

Have you looked at so called Variable Refrigerant Flow systems - very common in small commercial applications - basically we pipe the gas and fridge lines via "shuttle boxes" or so called "branch controllers" that allows each room terminal unit (usually a fan coil) to provide heating or cooling as required - the shuttle boxes are 3 pipe back to the condenser to allow heat recovery

Various refrigerants are "cheap" and "safe" and "low flammability" - leaks are not that common. I was looking at a CO2 system recently as a potential refrigerant - although it's perhaps no better if you end up dumping it into a bedroom with sleeping occupants (although systems described above are routinely used in hotel bedrooms

refrigerant temperature is generally a function of pressure basically - it can be modulated to suit the application - 50C refrigerant temps are easily achievable if that's all you need - but remember the basic heat exchange equations - mass flow and temperature differences need to balance on both sides

Regards

Barney

Installing a ground source heat pump

Paul in Montreal — Thu, 27 Oct 2016 14:25:09 +0100

Posted By: ringiAre you heating your outside air (I assume -20), or your already heated inside air with the radiator?

Noooo! It's impossible to heat the outside air - the volumes are too large and the house would end up insanely dry! It's a closed "loop" of air with supply/return ducts to the heat exchanger.

Temperature at the heat exchanger is around 55C I believe. Output air temperature is in the low 30s C.

Paul in Montreal.

Installing a ground source heat pump

Ed Davies — Thu, 27 Oct 2016 14:45:13 +0100

I've been aware of COâ‚‚-based heat pumps for a long time - since bar discussions with one of my lecturers in college in the late 1970s who wanted to put in a river-sourced one to heat his home in south Wales. What I've not been clear about is if they need to operate at the pressures to liquefy the fluid or whether they can work with it just as a gas. Barney? Anybody?

Installing a ground source heat pump

Paul in Montreal — Thu, 27 Oct 2016 14:57:19 +0100

Posted By: Ed DaviesWhat I've not been clear about is if they need to operate at the pressures to liquefy the fluid or whether they can work with it just as a gas. Barney? Anybody?

All refrigeration systems require a liquid<->gas phase transition as the latent heat of evaporation is what gives the energy transportation ability :) That's why you have an evaporator and condenser in all refrigeration systems :)

Paul in Montreal.

Installing a ground source heat pump

ringi — Thu, 27 Oct 2016 15:16:08 +0100

Posted By: Paul in MontrealNoooo! It's impossible to heat the outside air - the volumes are too large and the house would end up insanely dry!

Not if your house is built to a passive home standard, but I question if that is cost effect in Montreal!

Installing a ground source heat pump

barney — Thu, 27 Oct 2016 15:23:53 +0100

Well commercially we'd be calling CO2 as refrigerant R744 - there is a lot of information available online

CO2 has an abnormally low critical temperature so my understanding is that the systems work totally in the gas phase - but we need really high pressures to make that work

Regards

Barney

Installing a ground source heat pump

Paul in Montreal — Thu, 27 Oct 2016 15:36:15 +0100

Posted By: ringiNot if your house is built to a passive home standard, but I question if that is cost effect in Montreal!

ipso factor if you have a PassivHaus you don't need a heating system, just ventilation (with a bit of heating for the really cold days). For regular forced-air heating, it's essentially a closed loop.

Posted By: barneyCO2 has an abnormally low critical temperature so my understanding is that the systems work totally in the gas phase - but we need really high pressures to make that work

I think you're right - they are using "transcritical" systems: https://emersonclimateconversations.com/2016/02/25/co2-as-a-refrigerant-introduction-to-retail-transcritical-systems/
See also https://emersonclimateconversations.com/2015/05/14/co2-as-a-refrigerant-properties-of-r744/

Paul in Montreal.

Installing a ground source heat pump

djh — Thu, 27 Oct 2016 16:08:00 +0100

With statements like: "Example: 1 oz. of dry ice will produce 845 oz. of CO2 vapor as it sublimes." it's difficult to trust https://emersonclimateconversations.com/2015/05/14/co2-as-a-refrigerant-properties-of-r744/ too far