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Author Topic: GSHP versus ASHP  (Read 16325 times)
mpooley
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« Reply #15 on: February 08, 2011, 09:00:56 PM »

Thats what I have always thought but in another thread i found a link to a field trial of Both types by the energy trust and they conclude there is almost no difference!
these are a couple of quotes in the conclusions but it is quite an interesting read.

http://www.energysavingtrust.org.uk/Media/node_1422/Getting-warmer-a-field-trial-of-heat-pumps-PDF


quote
The sample of ground source heat pumps had
slightly higher measured system efficiencies than
the air source heat pumps. The ‘mid-range’ ground
source system efficiencies were between 2.3 and
2.5, with the highest figures reaching over 3.0.

The ‘mid-range’ of measured system efficiencies for
air source heat pumps was near 2.2 and the
highest figures were above 3.0. The sample of air
source heat pumps performed comparably with
other European studies
end quote

I am confused  surrender
« Last Edit: February 08, 2011, 09:06:22 PM by mpooley » Logged

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rhys
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« Reply #16 on: February 08, 2011, 09:17:22 PM »

The energy saving trust report is not that helpful in my view, very general, and is unwilling to identify which system was which!!!
Nothing wrong with ASHP for an off gas grid location, an option certainly if oil is the only alternative.
have a look at the ECOdan.
BUT you will need a big coil in the HW cylinder, and ideally bigger rads.  lots of insulation might mitigate small rads though. low flow temp is essential.
I have just replaced my oil rayburn with  a (no not a ECOdan ASHP) condensing oil boiler. ( and a WB stove)
Maybe a ASHP at next boiler replacement!!!
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mpooley
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« Reply #17 on: February 08, 2011, 10:38:03 PM »

Well I'm on Oil and its not getting any cheaper.
also got 6kwp PV system which might help a bit.

I take it you dont think much of having two compressors  to raise water to 75-80c ?

Mike
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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
rhys
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« Reply #18 on: February 08, 2011, 10:51:53 PM »

Not an expert but I guess that means most of the time the system runs at the lowest temp possible. that's what the ECOdan does controlling it's flow temperature. Presumably your kit then boosts that lower temp flow when necessary?
Why not post the details of the kit so we can look at the specs?
Martin hates heat pumps a few of us less so if other conditions are right?
Rule of thumb for now and the forseeable future in existing house Gas Condensing Boiler.
Off gas grid up for an interesting debate!
Oh and urban flats well there's fun
High Rise Urban hey now we're rocking!!! bring it on but I want a fee for advice. extrahappy ballspin
« Last Edit: February 08, 2011, 10:54:52 PM by rhys » Logged
mpooley
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« Reply #19 on: February 08, 2011, 10:56:11 PM »

The Guy only came today he is going to send someone else round to work out the plumbing whilst he works out the size etc

so no details yet.

I wont be rushing into this believe me and I will listen to all opinions especially if backed up by sound reasoning.

thanks

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

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rhys
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« Reply #20 on: February 08, 2011, 11:03:20 PM »

keep us up to date. Smiley
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titan
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« Reply #21 on: February 09, 2011, 08:41:54 AM »

i found a link to a field trial of Both types by the energy trust and they conclude there is almost no difference!


That says more about the installers and installations where they were poorly specified or not operated correctly. Look at the report  best GSHP and worst ASHP figures  to see the potential of GS over AS. Googling will turn up quite a few comparative test from around Europe. The UK being an island has generally higher humidity which in cold conditions can cause more frequent icing and the need for de-icing on ASHPs  which will lower the COP.  There is no denying ASHPs look attractive with simple and lower installation costs but if you are in it for the long haul GSHP I think  is a better option. However  in a poorly insulated house with standard rads needing higher flow temperatures neither may be the best heating  choice 
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Baz
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« Reply #22 on: February 09, 2011, 09:06:38 AM »

I think for a long heating season Air can look better because of the conditions and time of day. Say ground provides a constant 8C feed for 365 days, 24hours. But air will sometimes be working hard with 0C then a week later a warm front comes in at +12 or more during the day even in January. Then if the test period is taken from September to April inclusive the average will be quite high for air which really distorts the figures.
Would the test sample use people only using air and economy 7 who see night temps only or do they have a lot of daytime users at the high temperatures.

This distortion also applies big time to ASHP sales data.

It's the same with that wood stove that apparently manages to produce 10KW while only using 1 log a day and makes no ash. The log is 10ft long and the draught so intense the ash all goes up the chimney, but hey, they are technically not lying.
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mpooley
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« Reply #23 on: February 09, 2011, 09:51:38 AM »

Quote

Look at the report  best GSHP and worst ASHP figures  to see the potential of GS over AS

sorry Titan but that can be reversed ! what if if I look at the best of ASHP and the worst of GSHP ?
they are almost exactly the same.

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

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rhys
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« Reply #24 on: February 09, 2011, 09:56:46 AM »

Both wrong logically surely - look at the best of both to find best potential!!  whistlie
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mpooley
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« Reply #25 on: February 09, 2011, 10:01:03 AM »

I think for a long heating season Air can look better because of the conditions and time of day. Say ground provides a constant 8C feed for 365 days, 24hours. But air will sometimes be working hard with 0C then a week later a warm front comes in at +12 or more during the day even in January. Then if the test period is taken from September to April inclusive the average will be quite high for air which really distorts the figures.
Would the test sample use people only using air and economy 7 who see night temps only or do they have a lot of daytime users at the high temperatures.

This distortion also applies big time to ASHP sales data.

It's the same with that wood stove that apparently manages to produce 10KW while only using 1 log a day and makes no ash. The log is 10ft long and the draught so intense the ash all goes up the chimney, but hey, they are technically not lying.

Hi Baz
I am not sure how that example distorts the figures ? if the ASHP takes advantage of the higher air temp why is that a distortion?
each type works using its different source, sometimes that source will be higher or lower than the other source.
the average cop over the winter is surely what is important?
unless i am missing something?

If you use the heat pump in the summer for hot water the ASHP gains over the GSHP.

thanks
Mike
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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
Countrypaul
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« Reply #26 on: February 09, 2011, 10:13:45 AM »

In summer if you take the GSHP vs ASHP to its logical next step then that is using a back pipe (or panel) to take in the sunlight and heat the water - before using the HP. and if you miss the HP out your back to soalr thermal  genuflect


Taking the average over winter will help, but what about sustained very cold periods, in these cases the ASHP may work as such as low COP as to be less efficient than a storage heater. It would be useful to get some realword data on daily/nightly temperatures over the year (is this available easily?) and work out whether the ASHP would be able to cope with the longer cold periods. This is what I want to do for our renovation, but until we get planning permission through, it is not worth trying to work out the likely heat requirements etc. However if anyone can point me in the right direction for getting a years data on daytime&nighttime temperatures that would be very helpful.

Paul
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titan
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« Reply #27 on: February 09, 2011, 10:24:25 AM »

Quote

Look at the report  best GSHP and worst ASHP figures  to see the potential of GS over AS

sorry Titan but that can be reversed ! what if if I look at the best of ASHP and the worst of GSHP ?
they are almost exactly the same.

Mike

Quite right but the report also says that the ASHPs in the test generally matched European COPs but the GSHPs were lower which goes back to my point that look at the worst ASHP as this may be the best you get and compare that with the best GSHP or better still some European tests where the units have been installed and run correctly and the difference is much greater. Technically there is no argument but the installation costs ( and required ground) make the ASHP a very viable choice.
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dhaslam
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« Reply #28 on: February 09, 2011, 10:37:59 AM »

Comparing the average does make sense.   The  last month has been very mild so  air source heat pumps work well.    So far there has only been about two weeks that  were extremely cold and a few more weeks with temperatures down to -5C.   Once you have a way of covering those periods  then there is no difficulty.       I have been using the  heat pump for a few hours all summer to  supplement the solar panels in dull weather,  it uses an average of about 4 kWh per day for that purpose.       The main thing with heat  pumps is that they have enough capacity to  heat the house in normal conditions  using off peak electricity only and that they only need supplementary heat for short periods.    


* Winter10-11.jpg (66.47 KB, 627x385 - viewed 489 times.)
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A.L.
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« Reply #29 on: February 09, 2011, 11:01:24 AM »

hello Countrypaul,

Quote
However if anyone can point me in the right direction for getting a years data on daytime&nighttime temperatures that would be very helpful.

Not spreadsheet friendly but if you are in the U.K. try here - www.weatheronline.co.uk/weather/maps/forecastmaps?LANG=en&CONT=ukuk&UP=0&R=150&NOREGION=1&WMO=03772
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