Is my Heat pump system OK?

[rogermunns]

Hello, my first post. I was recommended to come onto this forum because of all the specialised advice available here.

I bought a Chinese 9kW GSHP (407) six years ago in UK and brought it over to France where I was about to build a house. House took a long time to build but eventually on 30 December I was able to switch on the Heatpump.

My system takes it's 'groundwater' from a well and the water temperature in this well was 12.5deg. C. when I started on Dec. 30.

The output hot water feeds seven underfloor loops. I have no mixer valves or thermostats. Being retired I have time to experiment and adjust.

The problem I think I might have concerns icing leading to a cool-down of the UFH water temperature, at which point I switch off.

I am a retired engineer with no particular experience in air-conditioning or heatpumps. And in France it is near impossible to get things quickly or cheaply.

The photos show the situation inside the heatpump cabinet after 3 hours' running. The pipes and smaller black canister ice up (although the smaller black canister seems to warm up sometimes and partly defrost). But the larger canister has also iced up and this is when I have noticed the the UFH water has cooled down.

My well water temperatures started on 30Dec at 12.5deg. with the return temperature at 6.2deg. C.

I have run for a total of about 9 hours in three or four sessions and the well temperatures are now at 9deg.C and 4deg. C (i.e. heatpump inlet at nine, output at four. The outlet water returns to the well; I have no choice at present. UFH water supply reaches about 38deg. C but, as I said, reduces back at some stage (I only go down to the basement to check every half-hour or so).

Ambient temperature in the basement is about 9deg. C

Might the system be going through a 'defrost' period and I should just leave it to run on? I am concerned at seeing the frosting up on the large canister.

I hope that my use of Centigrade is OK.

[rogermunns]

sorry! didn't submit the photos properly!

[monkey spanners]

I don't like the look of the frost on the compressor (bigger black pot) but would need to know evaporating pressure/temperature and compressor inlet temp to be sure.
If you run the system with a frozen evaporator you risk splitting it, this will likely write off the system.
I wouldn't expect to see frost anywhere on a chiller system, i wonder if your well water flow rates are correct?
The temperature drop in the supply water after only 9 hours is cause for concern too.....

[Bigfreeze]

The water return temp to the well should really only be about 3C below the supply temp. So either your water supply is too slow (pump or piping too small) or you have a blockage, either at a filter or from debris from the bore getting to and clogging up the heat exchanger.
You also need to check the gas charge in the unit. An overcharged unit can frost up at the compressor similar to what you have there due to liquid feedback. However this may be contributed to by the poor water flow through the evaporator so fix that first.
Once the water drops to 4C you're in icing territory and run the risk of bursting the HX.

[Bigfreeze]

BTW water to water systems don't defrost, they have no need to

[Gary]

The water return temp to the well should really only be about 3C below the supply temp. So either your water supply is too slow (pump or piping too small) or you have a blockage, either at a filter or from debris from the bore getting to and clogging up the heat exchanger.
You also need to check the gas charge in the unit. An overcharged unit can frost up at the compressor similar to what you have there due to liquid feedback. However this may be contributed to by the poor water flow through the evaporator so fix that first.
Once the water drops to 4C you're in icing territory and run the risk of bursting the HX.

I agree. There is insufficient water flow... but no reason to believe the system is overcharged. We really can't tell if there are other problems until the water flow is right.

[Bigfreeze]

Actually, reading your post again, you have 2 problems.

The flow is too slow,

Secondly your dump well is either dumping too close to the supply well or is upstream from the supply well and the water is short cycling i.e the same water you just extracted energy from is cooling the water that is being extracted from the supply well and dragging down your supply temp and efficiency of the unit.

The first is an easy fix, the second may require you to drill a new dump well or switch the pump from bore 1 to bore 2

[rogermunns]

Thank you all for speedy and informative replies.

I have to work within serious constraints. One is that, for this winter, the single well is my only possible source. By next winter I will have got my ground loop installed as well. There is no way that I can afford to have another well dug - space and expense and difficulty (rock from 1 foot down).

(For the ground loop I am going to lay the pipe on the rock and then build a raised bed 1.5 metres deep on top).

I don't really have enough ground available to supply all the heat I need.

Also, if the two methods of collection (well and ground) are not enough I intend to use swimming pool heat (through a heat exchanger) as well. My pool will have solar assistance, so hopefully the 55 cubic metres volume will help the complete overall requirement.

Hope that makes sense. The well supply was the easiest to get ready and the hope was that the groundwater surrounding the well would top up the water temperature within a few hours. I do have a second pump which I could use in addition
and also I could dump some return water to waste, thus encouraging the groundwater supply to replenish the well with warmer water.

[Bigfreeze]

You're going to be spending money for no end result if you follow the mismash plan you have in mind. Heatpumps need to be installed exactly and correctly, cobbling together a collector from here with supplementation from there (I'm not even sure how you intend to couple a closed loop with an open loop) it will never work.
You should really get some professional advice about the best set up for your site, bite the bullet and pay for a properly set up system. Either that or you will pay in the long run with huge bills and loss of compressors and heat exchangers.

[Gary]

Add the second pump and see what that does.

[nevgee]

My well water temperatures started on 30Dec at 12.5deg. with the return temperature at 6.2deg. C.

I have run for a total of about 9 hours in three or four sessions and the well temperatures are now at 9deg.C and 4deg. C (i.e. heatpump inlet at nine, output at four. The outlet water returns to the well; I have no choice at present. UFH water supply reaches about 38deg. C but, as I said, reduces back at some stage (I only go down to the basement to check every half-hour or so).





The symptoms suggest there is iether insufficient well water being pumped or, most likely, he may not have a large enough "sink" or thermal store in the well.
It would appear the system is pulling down the temperature of the primary circuit (well) too quickly. If the starting temp of the well water was 12.5C then after a short time it drops to 9.5C This suggests he is cooling his well down faster than the surrounding earth can replace the heat!

A safety measure needs to be put in place to prevent the sytem freezing up. say a stat on the return temp set at say 7 -8 C to stop the compressor but to leave the sump pump running. This will hold off the compressor until the well recovers sufficiently. I would assume, but it needs to be checked that a delay timer exists to hold the compressor back from short cycling.

[nevgee]

. . and the hope was that the groundwater surrounding the well would top up the water temperature within a few hours. I do have a second pump which I could use in addition
and also I could dump some return water to waste, thus encouraging the groundwater supply to replenish the well with warmer water.

Sorry I just realised I didn't read the whole post .....

As you have stated, It might be worth a test and to dump return water to see if the replenishment rate in the Well improves. That way you will be able to verify there is adequate Well water for the duty you need.

[nevgee]

Actually, reading your post again, you have 2 problems.

The flow is too slow,

Secondly your dump well is either dumping too close to the supply well or is upstream from the supply well and the water is short cycling i.e the same water you just extracted energy from is cooling the water that is being extracted from the supply well and dragging down your supply temp and efficiency of the unit.

The first is an easy fix, the second may require you to drill a new dump well or switch the pump from bore 1 to bore 2


Missed this also . . it would have saved me some typing, can only blame Xmas for dulling the senses.;)