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Author Topic: Never use a slinky in Scotland?  (Read 14061 times)
baker
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« Reply #45 on: December 10, 2015, 02:05:57 PM »

looks like we got a few  more experts here hysteria
baker
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titan
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« Reply #46 on: December 10, 2015, 02:44:15 PM »

Exactly and after you have spent all your money buying the thing you discover it uses 3 or 4 kilowatts of electricity, in other words 12 pounds per DAY to run.

I am not sure where you get the figures for your running costs but  current ones from here  http://www.nottenergy.com/energy_cost_comparison/energy_comparison_data/october_2015/  seem to show a GSHP is similar to gas So if a dwelling needs 12 a day it will be the same with gas ie a poorly insulated draughty place. I have a GSHP I installed myself heating a 300 m2 house and looking at the last three year since installation it works out around 75 pence a day or 1800 kW/h a year.
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JonG
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« Reply #47 on: December 11, 2015, 07:34:58 AM »

The Scandinavians have developed heat pumps that can operate at -10 and below, but rarely do they design in that way, it is better practice to cover around 80% of the load on a heat pump which is then more efficient at more average operating temperatures when you use it most, and back it up with another source for peak load.

Sizing a heat pump for an unusual set of climactic conditions will result in higher installation costs, higher running costs and potentially performance issues when the power in the summer due to oversized loops and therefore high brine temps could cause high pressure errors on the fridge circuit if the cylinder coil cant cope.

The government mania for 100% coverage is wrong and compounded by heat loss calcs that are generally 30% higher than reality.
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baker
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« Reply #48 on: December 11, 2015, 10:34:49 AM »

jong
 
I don't understand ,  high brine tempature is a problem/  error
the brine is on the low side
baker
 
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dhaslam
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« Reply #49 on: December 11, 2015, 11:36:20 AM »

Excess heat pump capacity can help by allowing  usage when electricity is cheapest.   However there is a limit to the size of  heap pump that can run on single phase electricity so in large installations  it would be better to have two smaller ones.   A larger ground loop is always going to be more efficient and if deep enough it should stay  at moderate temperature in summer.  However     it  probably is best not to use  the heat pump for mid summer water heating.  Solar panels  in the long term should  save  their cost in   heat pump  repairs and replacement cost.  At night in winter  electricity from  renewable energy companies is  something like  80%  wind sourced  so a combination of solar panels in summer and GSHP in winter is close to the ideal.             
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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
JonG
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« Reply #50 on: December 11, 2015, 06:30:28 PM »

Ground source outputs are usually quoted at brine 0 water 35, as soon as you move away from these the output changes up or down depending on the change.

In the summer a loop which is oversized will have much higher brine temperatures which then also increases the power output available.

If this output exceeds the power rating of the cylinder coil the heat pump either cycles or goes out on a high pressure (refrigerant too hot) fault. Neither are desirable or good for longevity.

Bigger loops are not always better, we have seen this quite a bit this year with high brine temps due to a mild winter last year, loads of rain etc.

MCS standards are not helping either, the calculators tend to overstate the power heating requirements by about 30% by not factoring in latent heat, solar gain etc, 100% sizing is preferred (otherwise heat meters are required that increase costs) and incoming brine temps have to be above 0 for 20 years.

Everything just compounds and the result is an over engineered, over expensive solution, which is arguably less efficient than what the Northern Europeans have been doing for years without issue.

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baker
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« Reply #51 on: December 12, 2015, 10:09:06 AM »

jong
whats the max temperatures you have seen in the ground loops
machine f-gas
baker
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JonG
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« Reply #52 on: December 12, 2015, 10:36:02 AM »

Around 12 but a colleague had around 13-14 recently.
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titan
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« Reply #53 on: December 12, 2015, 02:31:37 PM »

Ground source outputs are usually quoted at brine 0 water 35, as soon as you move away from these the output changes up or down depending on the change.

In the summer a loop which is oversized will have much higher brine temperatures


How can any array be warmer than the ground temperature ie the size of the array should not be a factor in the max brine temperature . I see also up thread you have said  array temperatures of  13- 14 deg C that has to be very unusual at 80-100cm in the UK. I thought the ground temperature is similar to the yearly average air temperature which is 8 - 11 deg C
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skyewright
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« Reply #54 on: December 12, 2015, 02:44:47 PM »

Everything just compounds and the result is an over engineered, over expensive solution, which is arguably less efficient than what the Northern Europeans have been doing for years without issue.
Or, as in our case, it results in dropping the whole idea because the systems being designed to meet RHI/MCS requirements were just so OTT they wrecked the economics of the whole idea. Instead I'm DIY fitting even more insulation (my Christmas project this year is to IWI the external walls of our North corner room. If that goes well, others may follow in due course) & may eventually fit (probably also DIY) a small air-to-air unit (or possibly two, one at either end of the house [bungalow]).
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Regards
David
3.91kWp PV  (17 x Moser Baer 230 and Aurora PVI-3.6-OUTD-S-UK), slope 40, WSW, Lat 57 9' (Isle of Skye)
titan
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« Reply #55 on: December 12, 2015, 03:29:48 PM »


Or, as in our case, it results in dropping the whole idea because the systems being designed to meet RHI/MCS requirements were just so OTT they wrecked the economics of the whole idea.

Have you looked at the cost of doing the whole install yourself and forgetting about the RHI.  When I did my install it was in between schemes, Blue skies or whatever the name was and the latest one. I was going ahead regardless of the RHI.

I have posted the cost on here before but off the top of my head it was around 6,300 which was a Kensa 8kW GSHP  4000 500 for the 500M of 40mm pipe 200 for the manifold fittings 200 for the antifreeze 600 for sand as my ground was quite rocky and 800 for digger hire.
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JonG
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« Reply #56 on: December 12, 2015, 03:45:23 PM »

I can't tell you what the actual grond temp was in the cases stated, I am confirming the brine sensor temps but depending on ground conditions location etc. temps will vary around the country and this year especially we have seen them higher than usual.  We have had to leave one install  on immersion for the cylinder cos it is cycling too much,  it is a bad match 16KW to a 180 litre cylinder.
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knighty
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« Reply #57 on: December 12, 2015, 09:04:58 PM »

you shouldn't have any problems at all with high ground loop temps around 10'C

sounds to me like the condenser is too small (the hot heat exchanger), or the expansion valve is incorrectly sized, or the accumulator is too small or incorrect charge (too much gas in system)

or the system is badly designed and has a bunch of problems


also... why not just fit a multi speed pump to the ground loop and turn it down when the flow temp is higher ? - inverter pump would do it automatically and be more efficient

or fit a flow thermostat
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JonG
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« Reply #58 on: December 13, 2015, 08:06:23 AM »

Usually high brine temps aren't an issue, but I am just making the point that as the temps rise al of the points you have mentioned are important in terms of design, but with the UK stepping away from normative design used elsewhere there are risks associated.

The unit in question is a Danfoss and the 16kw to internal 180 litre cylinder is no longer manufactured, but highlights the need for a large enough cylinder to absorb the heat output in the summer when the heat pump power spikes.

This wasn't an isolated case though and HP manufacturers will state the requirements for the cylinder based on output, but this needs to be compared with max potential loop temps to ensure compatibility and that the manufacturer is not working with lower potentials in their design literature.



 
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skyewright
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« Reply #59 on: December 13, 2015, 03:19:09 PM »

Have you looked at the cost of doing the whole install yourself and forgetting about the RHI.
I might have at one time (though the very soft ground would mean that a professional on the digger would probably be wise), but the whole exercise caused us to look closely at the bigger picture (the house, our pattern of use, etc.). Our total heating bill (DHW plus space) is already down to around 700 per annum. Having done a study with OpenBEM (getting a 'current' use that was very close to our actual[1]), I think there is scope for reducing demand by up to a third with additional DIY insulation. Once that's done, we'll review the situation. Every reduction in the demand (& thus the bill), makes a high capital cost solution like GSHP even less attractive, hence the idea (hope?) that a small Air-to-Air heat pump (or two, or a multi-head) will suffice.


[1] Unlike the EPC, which thought we would be using ~3x the heating energy we do (another reason for the GSHP quotes being OTT).
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Regards
David
3.91kWp PV  (17 x Moser Baer 230 and Aurora PVI-3.6-OUTD-S-UK), slope 40, WSW, Lat 57 9' (Isle of Skye)
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