Posted By: Ed DaviesMaybe that's right for practical systems but I don't see why, in principle, you couldn't move heat around by just compressing and expanding a gas.

Oh you can, but the latent heat of condensation makes it much more effective as it magnifies the effective heat capacity of the gas. The limiting factor in many refrigeration systems is the volume of refrigerant you can move - this is why, actually, the output of A2A heatpumps falls with temperature - the volume of gas produced in the evaporator declines. I think the very low critical temperature of R744 (CO2) helps mitigate this.

Paul in Montreal.

Just in case anyone is still there . . . . . .

It is now 7 years since my GSHP was installed.

In 2015 I added a heat output measuring device. It measures the flow rate of the water by ultrasound and taking the supply and return temperatures calculates the heat output produced.

I measure the energy input with a standard kWh meter. I divide the output by the input to get the CoP (coefficient of performance.

Here are recent readings with their dates . . . .

7/5/18 - 3.74

20/4/19 - 3.74

10/4/18. - 4.23

23/2/18. - 4.27

I am constantly tweaking the parameters to get the compressor run time to be as long as possible. With the mild weather this is difficult.

Owlman,

I have been trying to find the spec for my heat pump, but can't. I remember a manufacturer's CoP of about 4.2 for 35 deg C output from 0 deg C primary. I sometimes get this.

I bought a meter that records heat output. It has an internal battery. It needs to be put in the heat output and have small pockets to take thermocouples for supply and return temperatures. It was fun to install and use.

Posted By: owlmanFor me sampling warm air supply and return may be a bit more onerous.

Easy enough to measure the temperature. I'd suggest measuring the flowrate with a hooded anemometer for particular fan speed settings and then relying on realtime collection of the speed settings to infer the flowrate.

It is the end of an era. I am selling the French house. A lucky Frenchman will have the benefit of the Nibe GSHP. A few final comments.
* It has been installed for 10 years and is still giving a COP of 4.35 with average run time of 16 minutes
* Only one problem with the Nibe equipment - the high power primary circulating pump failed during the warranty period and was replaced FOC
* All the other problems have been to do with plumbing, an enthusiastic young apprentice who overtightened union nuts that later cracked, expansion vessels that need a charge of nitrogen, air bleed fittings that need replacement. The latest repairs will cost me about 160 €.
* Some time ago I installed an output measuring device. Secondary water flow measured with ultrasound, supply and return water temperature measured with thermistors, a display unit measuring MWh. The incoming 3 phase power is measured with a kWh meter. Values from these meters produce the COP given above.

In all, I am really pleased with the results over the 10 years use.

Good bye. . . . .

I have been asked about the COP results over time. Here is my response. Anything missing please ask here, or 'whisper' to me.

Oct 2010 GSHP Installed, followed by a number of months of piping and sensor modifications. See above for details.
Nov 2015 put in system to give measure of heat output, details above in blog. I estimate the accuracy of the measurements to be not worse than 1%. I assume the accuracy of the kWh heat input meter to be 1% too.
COP measured from Nov 2015 to April 2021 when house was sold.
Worst COP 3.43
Best 4.55
Average 3.99

I recon that is pretty good. For every 1 kWh of heat I bought from EDF, I got 4 kWh of heat into the house.
Mitsubishi made the innards of the heat pump. Nibe (Swedish) made the control electronics, sensors, valves, and box. Atlantic (French) put their badge on it and a local plumber (French) installed it. And I paid for it.