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Author Topic: GSHP Install - opinions please  (Read 18953 times)
dhaslam
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« Reply #45 on: December 16, 2015, 11:52:12 AM »

It is important to know the flow rate because all of the loops may not be working fully.    Is the feed pipe and the pump large enough to  handle  flow to the separate  circuits?  

Underfloor heating flow temperature should be  fairly low  to avoid overheating  on sunny days.  Mixer valves tend to have the lowest  setting of 35C  but in a well insulated house  circulation temperature  can be ten degrees lower for much of the year.    The outside temperature isn't always a good guide  because  houses with lots of windows can  be warmer  inside  in  frosty weather than on wet  days with  milder temperature.    
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Fionn
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« Reply #46 on: December 16, 2015, 12:41:06 PM »

With regard to efficiency drop, the only reason that this can happen is if you extract heat each winter at a higher rate than it is replenished in the summer.
Normally this indicates that the ground loops are undersized.
Back feeding solar thermal energy into the ground has a bad reputation on this site.
Notwithstanding this it is undeniable that if you added back the same amount of energy that you extract in winter during the summer you would slow or reverse this trend.
If you had good ground conditions with rapid groundwater movement then you wouldn't get progressive cooling one season after the other in the first place, and dumping heat into the ground in summer would be a fruitless exercise.
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PV - 2.75kW East, 1.5kW South, 2.5kW West. 3 x Flat Plate Solar Thermal with side arm FPHE on 268L cylinder
marshman
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« Reply #47 on: December 16, 2015, 02:17:47 PM »


I'm tempted to dive in with a calibrated thermometer and measure the flow and return temps direct to see if the displayed temperatures are correct, or even monitor the volts on the pump to see if it is running flat out.


I use one of these    http://www.ebay.co.uk/bhp/infrared-thermometer

Yes got one of those. Great for checking the flue temp on the wood burner amongst other things but in this case where where I am looking at just 1 degree or so I'm not sure it will be good enough. Also they are "calibrated" on the emissivity of a certain surface. On the shiny copper pipes I suspect the accuracy will be worse. I would prefer to clamp my own sensor onto the pipes as they enter and exit the heat exchanger but to be honest I don't think that both sensors in the unit will be wrong.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
Fionn
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« Reply #48 on: December 16, 2015, 02:24:28 PM »

I find one of these very useful and both accurate and precise.
http://www.ebay.co.uk/itm/171488826237
It's a handheld digital K type thermocouple thermometer with 4 input channels.
You can plug in pipe clamp or probe type sensors into the unit.
« Last Edit: December 16, 2015, 02:54:17 PM by Fionn » Logged

PV - 2.75kW East, 1.5kW South, 2.5kW West. 3 x Flat Plate Solar Thermal with side arm FPHE on 268L cylinder
JonG
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« Reply #49 on: December 16, 2015, 04:21:50 PM »

Hi Roger, a very rough rule of thumb on flow rate across the ground loops is 3 litres per min per kw of heat pump, so in your case 30 lpm. It will settle as the fuzzy logic in the software learns the resistance but with propylene glycol that gets more viscous as it gets colder you will need to keep an eye on things.

In terms of resolution if there does transpire to be an issue, it may be possible to fit an inverter driven pump from a larger Thermia heat pump, or an external pump in parallel to increase flow rate (assuming that the head is sufficient on the existing pump). Pumps in series increases head but not flow rate, pumps in parallel increase flow rate but not head.

There is no inverter on your compressor it is direct on line on/off, any extra capacity is stored in the buffer (but will be marginal given buffer size). Buffers are not mandatory in MCS installations and we quite regularly go straight to screed for simplicity.
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marshman
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« Reply #50 on: December 16, 2015, 06:22:33 PM »

It is important to know the flow rate because all of the loops may not be working fully.    Is the feed pipe and the pump large enough to  handle  flow to the separate  circuits?  

Underfloor heating flow temperature should be  fairly low  to avoid overheating  on sunny days.  Mixer valves tend to have the lowest  setting of 35C  but in a well insulated house  circulation temperature  can be ten degrees lower for much of the year.    The outside temperature isn't always a good guide  because  houses with lots of windows can  be warmer  inside  in  frosty weather than on wet  days with  milder temperature.    

Flow rate is the same, according to the individual flow meters. Based on JonG's "rule of thumb" my total flow rate of around 32 ltrs/min is about right. So I guess the pump is capable of doing the job - unless it can't hack it as the loop temp drops and the fluid gets more viscous.

Don't have many big windows, and certainly not many that catch the sun so solar gain is not much of a factor.

I agree regarding UFH temps. Mine is  happy to run a very low temps. As I said its's running 24/7 and the average temp is well below 35 deg C at the moment, but then its not exactly cold outside, wet and windy but not cold.


Hi Roger, a very rough rule of thumb on flow rate across the ground loops is 3 litres per min per kw of heat pump, so in your case 30 lpm. It will settle as the fuzzy logic in the software learns the resistance but with propylene glycol that gets more viscous as it gets colder you will need to keep an eye on things.

In terms of resolution if there does transpire to be an issue, it may be possible to fit an inverter driven pump from a larger Thermia heat pump, or an external pump in parallel to increase flow rate (assuming that the head is sufficient on the existing pump). Pumps in series increases head but not flow rate, pumps in parallel increase flow rate but not head.

There is no inverter on your compressor it is direct on line on/off, any extra capacity is stored in the buffer (but will be marginal given buffer size). Buffers are not mandatory in MCS installations and we quite regularly go straight to screed for simplicity.

Thanks Jon, as I said above mine is flowing at over 30 ltrs / min so that would appear to be correct. I know the compressor is on/off with no inverter - Danfoss/Thermia have just announced an inverter driven one. I was referring to the brine pump being variable speed. I will keep an eye on things as you suggest as the temperatures drop.

Interesting about buffer tanks not being compulsory as I have been told by more than one installer that they are, it does allow the option of easily connecting another heat source in the future should it be needed (can't think why though). I would have been happy to do away with my buffer as well as there is enough liquid in the UFH loops for it to all work OK without excessive cycling.

Thanks again for you inputs.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
marshman
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« Reply #51 on: December 18, 2015, 12:54:25 PM »

OK I think the "mystery" is solved. The Brine in and out temperature sensors were not reading the correct temperatures - as suspected. There is a sub menu in the installer section for sensor calibration. Believe it or not they were a long way out, just under 3 degrees on the difference. Once set the display now shows the expected difference of 3 deg C, as set in the install menu, confirmed by independent thermometer on pipes in and out of the heat exchanger and the brine pump is no longer running flat out. Flow meters in the chamber now showing just under 8 ltrs / min each (there are 4 loops), which tallies with JonG "rule of thumb" statement of 30 lts/min.  So now all looks a lot more sensible.  I did also use my IR thermometer (as sugested by Titan) on the black manifold pipes in the manifold chamber outside and it confirmed a temp difference of 2.8 deg C.

There is no mention of checking the calibration of the sensors in the installation manual but to me it seems fundamental to the correct operation of the system.

Thanks to all for your input and suggestions.

As a foot note it seems the incoming temperature is really closer to 11 degrees C than the 13 that I originally quoted!

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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