Green Building Forum - Installing a ground source heat pump

Installing a ground source heat pump

Ed Davies — Thu, 27 Oct 2016 16:08:23 +0100

Posted By: Paul in MontrealAll refrigeration systems require a liquid<->gas phase transition as the latent heat of evaporation is what gives the energy transportation ability

Maybe 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.

Installing a ground source heat pump

Paul in Montreal — Thu, 27 Oct 2016 16:57:12 +0100

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.

Installing a ground source heat pump

djh — Thu, 27 Oct 2016 18:28:56 +0100

Posted By: Paul in Montreal
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.

See also - heat pipes, as used in PCs or solar thermal tubes. See also - phase-change materials for heat storage. Just for two more examples.

Installing a ground source heat pump

topher — Thu, 22 Nov 2018 14:33:08 +0000

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.

Installing a ground source heat pump

owlman — Thu, 22 Nov 2018 15:09:13 +0000

That's interesting topher, and to me those figures seem good for a 7 year old install. How do those figures relate to the mfs. published COPs
I'm well on with my own ASHP install ( A2A ) and I may look at somehow recording output in a similar manner.

Installing a ground source heat pump

topher — Thu, 22 Nov 2018 17:03:11 +0000

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.

Installing a ground source heat pump

owlman — Thu, 22 Nov 2018 18:16:00 +0000

I've gone for a Toshiba SDI R32 outdoor unit and coupled it with a standard duct indoor unit. The mfs. say it'll produce a CoP of 5.52 for heating, with an A+++ efficiency rating. For me sampling warm air supply and return may be a bit more onerous. Maybe sampling the refrigerant loop may be easier and perhaps more accurate.

Installing a ground source heat pump

djh — Thu, 22 Nov 2018 20:51:01 +0000

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.

Installing a ground source heat pump

topher — Wed, 06 Mar 2019 14:57:22 +0000

Owlman, That spec looks very impressive. When it has a CoP of 5.52 what is the air temperature, and what is the output temperature?

Installing a ground source heat pump

topher — Mon, 19 Apr 2021 10:37:34 +0100

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 â‚¬.
* 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. . . . .

Installing a ground source heat pump

DamonHD — Sat, 24 Apr 2021 13:08:40 +0100

Topher has very kindly supplied me with extra photos, etc, which I have 'curated' here (and I am still working on):

http://www.earth.org.uk/GSHP-case-study-France.html

Rgds

Damon

Installing a ground source heat pump

topher — Thu, 16 Sep 2021 11:46:19 +0100

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.