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.

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 ;-)

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

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.

djh Thank you......Topher

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

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.

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

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.

Pual,

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

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

Regards

Barney

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

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?

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!

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.