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Author Topic: ASHP just as good as a GSHP - ?  (Read 6882 times)
mpooley
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« on: January 17, 2013, 01:31:28 PM »

I have just found out that I don't have enough land for the GSHP that I wanted to install so have been doing a bit more research.
I found this statement on 'You Gen' website which if true is very interesting.
It's dated 2010.
quote:
"System efficiencies for ground source heat pumps in the trial ranged from 1.3 to 3.3, with most in the mid range of 2.3 to 2.5. The system efficiency measures the amount of heat the pump produces for each unit of electricity needed to run the entire heating system (including hot water and supplementary heating such as an immersion). This is different from the COP (coefficient of performance) which just measures the amount of heat produced per unit of electricity used to run the heat pump.
Air source heat pump system efficiencies ranged from 1.2 to 3.2, with a mid range near 2.2."

so they are saying that
ground source heat pumps in the trial ranged from 1.3 to 3.3, with most in the mid range of 2.3 to 2.5
Air source heat pump system efficiencies ranged from 1.2 to 3.2, with a mid range near 2.2."
certainly not enough difference to pay the extra cost's of a GSHP

This sounds incredible to me but what do I know.

http://www.yougen.co.uk/blog-entry/1536/Heat+pumps%273A+field+trials+reveal+good+and+bad+installations/
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GavinA
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« Reply #1 on: January 17, 2013, 01:51:54 PM »

one major flaw in that trial is that it doesn't give geographic locations for the systems, or info about house insulation levels etc.

I strongly suspect that most of the GSHP were installed in the north, and in the countryside where winter outside air temps are lower so more of the heating is proportionally in deep winter at lower temperatures, and probably average house insulation levels would have been lower vs ASHP which I suspect would mostly have been in the south etc.

So my suspicion would be that it wasn't a true like for like comparison, and I suspect that it would make a significant difference where you lived - in the south an ASHP may well not be that different but in the north of scotland it could be fairly significant difference.

Unfortunately the dataset didn't give sufficient information to allow any clear conclusion to be drawn other than that the EST aren't very good at commissioning decent research.
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mpooley
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« Reply #2 on: January 17, 2013, 02:43:57 PM »

Do you know of any more thorough reports Gavin?
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Bodidly
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« Reply #3 on: January 17, 2013, 04:10:48 PM »

More testing here http://www.energysavingtrust.org.uk/Media/Generating-energy/PDFs/Full-heat-pump-field-trial-report
I was surprised how close they are in the tests myself. I think sam123 posted some tests on the continent that looked a bit better for GSHPs it might be worth having a search through some old posts to find it.
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dhaslam
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« Reply #4 on: January 17, 2013, 04:27:57 PM »

The biggest problem is system cost rather than efficiency.  The second report  suggests a ten year payback for air source and eighteen years  for ground source compared to direct electricity.   It is worth comparing  a  direct electric system and grid linked PV.  Taking the same  capital cost and  comparing the  net annual cost.       
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mpooley
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« Reply #5 on: January 17, 2013, 04:57:33 PM »


I'm not exactly sure what you mean?

Do you mean an either or situation?
where it might be better financially to have PV installed than heat pump?

I've already got the PV if that's what you meant

mike
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GavinA
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« Reply #6 on: January 18, 2013, 05:04:27 PM »

Do you know of any more thorough reports Gavin?
I think there's some feedback in the RHI consultation documents on their findings from the heat metering trials they've been doing, but don't think there's a full report - could be worth a look though as I wasn't really looking for heat pump stuff when I looked through that consultation.

It did give in use figures for the UK and for germany for both though, which IIRC were around 0.4-0.6 better COP for GSHP in both cases, though Germany had an average that was a whole 1 COP factor higher than in the UK as they know what they're doing, and by inference, most UK firms are just banging them in as straight boiler replacements / don't know what they're doing.

Bit more incentive in Germany though as their leccy is about double the price of ours, though ours is going to be rapidly heading that way in the next 2-3 years.
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todthedog
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« Reply #7 on: January 18, 2013, 05:44:04 PM »

When we looked a few years back nobody seemed to mention moving parts that wear out and need replacement.  This totally changes payback  periods.
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titan
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« Reply #8 on: January 18, 2013, 06:02:47 PM »


"System efficiencies for ground source heat pumps in the trial ranged from 1.3 to 3.3, with most in the mid range of 2.3 to 2.5. The system efficiency measures the amount of heat the pump produces for each unit of electricity needed to run the entire heating system (including hot water and supplementary heating such as an immersion). This is different from the COP (coefficient of performance) which just measures the amount of heat produced per unit of electricity used to run the heat pump.
Air source heat pump system efficiencies ranged from 1.2 to 3.2, with a mid range near 2.2."


That report is a great example of a good idea ie measure heat pumps in real installations ending up as mostly useless chaff for anyone looking for information to help them make a decision regarding whether to install a heat pump.The report does illustrate how important the design system specification  is, a lot of the examples in the report are clearly incorrectly specified for their application. There is some useful  information for  testing done by BRE on the Ecodan site http://domesticheating.mitsubishielectric.co.uk/case_studies
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davec
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« Reply #9 on: January 19, 2013, 08:37:01 AM »

I have just found out that I don't have enough land for the GSHP that I wanted to install ...

Did you consider drilling?
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mpooley
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« Reply #10 on: January 19, 2013, 09:29:57 AM »

I have just found out that I don't have enough land for the GSHP that I wanted to install ...

Did you consider drilling?
Yes I have two quotes for drilling but at £53.00 /mtr ! works out a lot more money.
I was told that the RHI might be better for boreholes though which could make it more attractive.
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It's not easy having a good time. Even smiling makes my face ache.

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davec
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« Reply #11 on: January 19, 2013, 11:36:43 AM »

I was told that the RHI might be better for boreholes though ...

That's a new one on me... I guess, until the scheme is finally announced, the significant word is 'might' Wink

Your original query was about efficiency and one big plus of a vertical collector over horizontal or air source would be no seasonal variation below 20m...
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mpooley
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« Reply #12 on: January 19, 2013, 12:09:08 PM »

they were talking about 4 boreholes of 30mtr though not 1 deep one - not sure why that is.
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It's not easy having a good time. Even smiling makes my face ache.

“Science is the belief in the ignorance of experts.” Richard Feynman
Bodidly
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« Reply #13 on: January 19, 2013, 12:17:11 PM »

Is there any chance you could fit in a compact collector like this?
 http://www.cernunnos-homes.co.uk/index.php?callback=image&pid=537&width=500&height=500&mode=
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mpooley
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« Reply #14 on: January 19, 2013, 12:20:47 PM »

Sorry couldn't work that picture out!

wouldn't a compact collector defeat the object ?


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It's not easy having a good time. Even smiling makes my face ache.

“Science is the belief in the ignorance of experts.” Richard Feynman
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