Navitron Renewable Energy and Sustainability Forum

HEAT PUMPS & Geothermal Energy => Heat Pumps => Topic started by: mpooley on February 02, 2011, 06:22:09 PM



Title: GSHP versus ASHP
Post by: mpooley on February 02, 2011, 06:22:09 PM
I have a salesman coming round tomorrow who has told me there is little difference between the efficiency of an ASHP and a GSHP.

now i dont realy believe that, but am going to listen to what he says.

what do you guys think?


mike



Title: Re: GSHP versus ASHP
Post by: BruceB on February 02, 2011, 06:45:42 PM
The ASHPs at their best can have COPs as good as GSHPs.  But in a domestic setting you have to think when it is you want the HP to be working really well and it is those prolonged low temperature periods in winter when  an ASHP will struggle in my opinion.  I do not have one though; I am sure others here will.

Regards
Bruce


Title: Re: GSHP versus ASHP
Post by: qeipl on February 02, 2011, 07:48:43 PM
The thing that I didn't fully absorb when first considering heat pumps is that they are solar collectors.
All they are doing is moving solar energy from outside your house to inside.
Air source gathers solar energy directly from the air.
Ground source gathers solar energy from the ground via pipes filled with water.

The efficiency of a heat pump depends on the density of the solar energy in the medium and the cost of pumping the medium through the heat exchanger.

In winter the energy density of air will be low, so you'll have to pump lots of it to get a kWh of heat.
Ground source in winter will have a comparatively high energy density, so you'll have to pump a smaller volume of water to get your kWh.
In winter ground source will be more efficient.

In summer the energy density of air will be much higher than in winter, while that of ground will only be a little bit higher.
Air is much easier to pump than water - uses less energy.
So in summer, air source could be a lot more efficient.

Taken over 12 months the efficiencies might be comparable but, as Bruce points out, winter is when you want to heat your house, so ground source will be more appropriate.

Personally, I think ground source is an expensive way to stay warm and is only useful where a building cannot take advantage of insulation, draught-proofing and solar gain.
These three have almost no ongoing costs after installation. If done well enough they will minimise your heating requirement to such an extent that you won't need a big expensive heating unit.
Air source for DHW and background heating backed up by gas or biomass will be much cheaper to install and operate.




Title: Re: GSHP versus ASHP
Post by: titan on February 03, 2011, 08:47:51 AM

Personally, I think ground source is an expensive way to stay warm

Air source for DHW and background heating backed up by gas or biomass will be much cheaper to install and operate.


You must be doing your calcs different to me. If you have mains gas then why bother with ASHP and biomass , if you don't then oil is actually cheaper than LPG but a GSHP will outperform them both. Have you looked at the price of biomass boilers installed certainly not cheap or that practical for most people with the need for pellet or chippings storage/handling.


Title: Re: GSHP versus ASHP
Post by: martin on February 03, 2011, 09:05:51 AM
"I have a salesman coming round tomorrow who has told me there is little difference between the efficiency of an ASHP and a GSHP.

now i dont realy believe that, but am going to listen to what he says.

what do you guys think?"

- the guy's an eejit - cancel the appointment, or show him the door pdq! ::)


Title: Re: GSHP versus ASHP
Post by: skyewright on February 03, 2011, 09:50:43 AM
Maybe your first question should be "Are you or have you ever been a double glazing salesman?".


Title: Re: GSHP versus ASHP
Post by: dhaslam on February 03, 2011, 10:02:14 AM
BruceB's answer  is bang on.   You have  to have an alternative heat source  for very cold weather.  If the house is very well insulated  then off peak electricity is OK as a backup.   


Title: Re: GSHP versus ASHP
Post by: qeipl on February 03, 2011, 10:29:42 AM

You must be doing your calcs different to me. If you have mains gas then why bother with ASHP and biomass , if you don't then oil is actually cheaper than LPG but a GSHP will outperform them both. Have you looked at the price of biomass boilers installed certainly not cheap or that practical for most people with the need for pellet or chippings storage/handling.


My point (inadequately explained) is that if you reduce your space heating requirement enough (insulate/draught-proof/solar gain) then you don't need to invest in big expensive heating equipment.

Solar gain is the key.

I have an ASHP cylinder that does DHW and UFH, rated at 810W.

For 50% of the year the sun does all my space heating directly (UFH doesn't run at all).
For the other 50% of the year the sun provides at least half of the space heating (so 25% of the annual total) via the ASHP and UFH.
The other 25% (in the dark days of winter when the sun isn't working) the ASHP is supplemented by a solid fuel boiler rated at 10kW.

I ran out of wood at NY (too busy building last year to get wood supply organised) and have been burning coal since then at a rate of 100kg/month = £32. Wood, when I'm organised will cost much less.
My total electricity use in January equates to £75, of which, lets say, £50 was space heating.
That's a total heating cost of £82/month for 25% of the year = £246 for the winter quarter.

Let's be generous and assume a GSHP would, in the winter quarter, have half the running costs of my ASHP/solid fuel combination and the same running costs for the other 25% that my UFH runs.
So the annual saving I'd make, in running costs, by opting for GS is around £123.

The ASHP cylinder cost £1,700, but you need a cylinder for GS which will cost c.£1k, so the net capital cost of my heat pump is £700.
The multi-fuel boiler cost £500 plus another £500 to install.
So my total capital cost is £1,700.

A quick google tells me that a 7kW GSHP (probably suitable as a replacement for my 10kW boiler) costs £4k to buy and probably another £3k? by the time I've bought the pipe, fittings, etc. and hired a man with a digger to bury it.
So that's a total capital cost of £7k - £5,300 more than my setup.

In terms of economics, the ground source system would have to run for 43 years before it caught up with my air source/solid fuel combination.

GS is a good option in some circumstances but the capital cost is high.
Using your capital to reduce the heating requirement to the point where you can use smaller, cheaper equipment seems to me to be a much more sensible approach.



Title: Re: GSHP versus ASHP
Post by: mpooley on February 03, 2011, 04:45:37 PM
Thanks all for your replies.

I am only in the early stages of assessing the merits of heat pumps.
I have a modern oil boiler and to be honest if i wasn't terrified that Oil supplies are running out and prices would not shoot up above inflation I would probably stick with Oil.(no gas out in the sticks)

I know the capital cost is high but heat security is important to me.
I am getting on a bit now and I just dont fancy being one of those pensioners found dead huddled round a candle trying to keep warm.
The price hikes of this winter were truly horrifying and we had to turn the heat right down for a few weeks while we waited for the prices to fall again.  :winter (still 27% higher than my last delivery though!)

Another consideration will be the renewable heat initiative (subsidy!) which understand will be available in June.
No idea what that will be yet.
so I am trying to get my head around COPs etc and wether i will have to get larger rads etc at the moment.
So I will get a few salesmen round, listen to their BS and test their claims on this forum.

BTW said salesman didn't even turn up lol he has deferred to next week.

Thanks
Mike



Title: Re: GSHP versus ASHP
Post by: sam123 on February 03, 2011, 04:52:51 PM
I have a salesman coming round tomorrow who has told me there is little difference between the efficiency of an ASHP and a GSHP.

now i dont realy believe that, but am going to listen to what he says.

what do you guys think?


mike



In Finnish forum there is no reports ASHP with YEAR COP 2, but 1.5-1.8 can be reached. GSHP has in same conditions regularly (floor heating) YEAR COP 3-3.5.

It is said that ASHP needs about 5 degree warmer air comparing to GSHP ground fluid.

If you get 5 degree ground fluid to GSHP, then you need 10 degree outside temperature to ASHP.

In practice situation is not so black/white, because ASHP suffers moisture near zero temperatures.



Title: Re: GSHP versus ASHP
Post by: baker on February 08, 2011, 01:24:45 AM
hi
if you have football Field, and wages, UFH , damp loamy soil or a lake; which is not common.  if not you will have to spend a fortune on bore holes or dig up the whole place,
at the end of the heating season the energy bank will have run out with low cop.s
what you see today is  old technology tarted up
ASHP
have made life easier for us and have done well in the last 2 years through the  coldest season
new high/pressure temperature units are being tested at the moment
and maybe will see today's heat pumps obsolete in a year  or so
john


Title: Re: GSHP versus ASHP
Post by: mpooley on February 08, 2011, 03:35:39 PM
Hi
Yes I  must admit the guy has just been and can see the potential of ASHP's .
as you say a lot easier to install.
and a lot cheaper probably.

He was talking about a 2 stage high temperature system which would mean not changing rads at least.

I will cogitate  bike:


Title: Re: GSHP versus ASHP
Post by: A.L. on February 08, 2011, 04:36:42 PM
hello,

Quote
Yes I  must admit the guy has just been and can see the potential of ASHP's

I must warn you that IMHO if you try and run radiators at 60-65C or higher off an ASHP your are likely to achieve an average COP no higher than 1.5 and probably considerably less.

You might as well use immersion heaters and a good electricity tariff.


Title: Re: GSHP versus ASHP
Post by: martin on February 08, 2011, 05:19:05 PM
As AL says, ASHP and conventional rads is a recipe for penury! I repeat, the rep is an eejit, who gives atrociously poor advice! whistle


Title: Re: GSHP versus ASHP
Post by: sam123 on February 08, 2011, 06:26:24 PM
Here you go: http://www.elisanet.fi/sanyoco2log/

ASHP probably works much better in UK than in Finland, but ASHP don´t work with good COP anywhere as long as you try to rise temperature over +35. It is almost as bad situation with GSHP, so my advice is to change big radiators or use few convectors to lower temperature. Or add some blowers to your existing radiators  stir:

Sami


Title: Re: GSHP versus ASHP
Post by: mpooley 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:


Title: Re: GSHP versus ASHP
Post by: rhys 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!!!


Title: Re: GSHP versus ASHP
Post by: mpooley 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


Title: Re: GSHP versus ASHP
Post by: rhys 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. exhappy: :ballspin


Title: Re: GSHP versus ASHP
Post by: mpooley 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


Title: Re: GSHP versus ASHP
Post by: rhys on February 08, 2011, 11:03:20 PM
keep us up to date. :)


Title: Re: GSHP versus ASHP
Post by: titan 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 


Title: Re: GSHP versus ASHP
Post by: Baz 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.


Title: Re: GSHP versus ASHP
Post by: mpooley 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


Title: Re: GSHP versus ASHP
Post by: rhys on February 09, 2011, 09:56:46 AM
Both wrong logically surely - look at the best of both to find best potential!!  whistle


Title: Re: GSHP versus ASHP
Post by: mpooley 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


Title: Re: GSHP versus ASHP
Post by: Countrypaul 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


Title: Re: GSHP versus ASHP
Post by: titan 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.


Title: Re: GSHP versus ASHP
Post by: dhaslam 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.    


Title: Re: GSHP versus ASHP
Post by: A.L. 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 (http://www.weatheronline.co.uk/weather/maps/forecastmaps?LANG=en&CONT=ukuk&UP=0&R=150&NOREGION=1&WMO=03772)


Title: Re: GSHP versus ASHP
Post by: titan on February 09, 2011, 11:34:53 AM

   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.    

    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.
   

What do you mean by covering those periods of extended cold. If by a woodburner are those costs taken into account for the overall heat load.Wood is not cheap.  Whenever I have calculated off peak tariffs  they have not been viable unless you use a lot of off peak electricity because of the price differential between day and off peak units


Title: Re: GSHP versus ASHP
Post by: mpooley on February 09, 2011, 11:39:58 AM
Dhaslem
Do you have ASHP then?

and to use off peak I assume you need a heat bank of some sort.

The guy that came to me said he didnt see any need for one?

mike


Title: Re: GSHP versus ASHP
Post by: cornishben on February 09, 2011, 12:20:05 PM
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.  
This is the part I'm trying to understand/convince my wife about.  Our current plan is for ~8kW ASHP for UFH/rads and we have a 10kW woodburner in the living room. The intention is that the ASHP will work well for heating over the majority of the year and the WBS can supplement it on those coldest periods.  Trouble is the WBS doesn't have a back boiler so in those coldest times we're only going to have a warm living room... which is what my wife has a problem with - spending a load of money on a heating system that doesn't keep the whole house warm at the coldest times.  However, what are the alternatives for off gas/no room for gshp/can't afford pellet £ or space..  

we're on Eco7 so my intention is to run the ASHP on that early morning to heat the UFH slab and fit the biggest buffer tank we can so that we can have a store of heat built up over the eco7 hours.


Title: Re: GSHP versus ASHP
Post by: rhys on February 09, 2011, 12:32:17 PM
My understanding is that if you size the ASHP correctly ot should then be able to heat the house throughout the year. Obviously in deepest winter the COP will be much worse, than the annual average.
But it'll still work for those relatively few days. Anything the WBS can do will just impove things. UFH if the insulation is good will act as a really good heat store too. The lower the flow temperature the better. If you haven't put the UHF down yet make sure you space the pex pipes as close together as possible, much closer than for a Gas or Oil fired system, then the flow temperature can be lower.


Title: Re: GSHP versus ASHP
Post by: mpooley on February 09, 2011, 04:34:54 PM
Just an extra thought.
how do you calculte the actual COP of a sytem?

You know what goes in but how do you measure the heat output?

mike


Title: Re: GSHP versus ASHP
Post by: titan on February 09, 2011, 05:41:30 PM
An independent report that may be of interest  www.fuelcells.bham.ac.uk/.../review_of_domestic_heat_pump_cop.pdf


Title: Re: GSHP versus ASHP
Post by: mpooley on February 09, 2011, 06:02:27 PM
Hi Titan
I am getting a "File not found"  error 404 with that link



Title: Re: GSHP versus ASHP
Post by: titan on February 09, 2011, 06:13:51 PM
Hi Titan
I am getting a "File not found"  error 404 with that link



The mods don't allow editing so if you highlight  the address then right click and choose the option "search Google" it is the first hit,  I don't know why the link doesn't work it looks OK . That is with Firefox with another browser just search with Google for the address.


Title: Re: GSHP versus ASHP
Post by: mpooley on February 09, 2011, 06:39:19 PM
Thanks Mate
Had a quick look at it.

I can see that the GSHP cops are significantly better - i wish i understood it all though lol ???

I will sit down tonight and try to get my head round it,

at one point it talks of SPF . whats that?

mike



Title: Re: GSHP versus ASHP
Post by: sam123 on February 09, 2011, 07:15:39 PM
http://www.fuelcells.bham.ac.uk/documents/review_of_domestic_heat_pump_cop.pdf

Should work


Title: Re: GSHP versus ASHP
Post by: martin W on February 10, 2011, 09:54:16 AM
thanks for the link sam (second one works).

very interesting reading.

I think in summary it seems to show that ASHP with oulet temp at around 50-55°C and air temp at -5 to 0°C have COPS at around 2-2.5. GSHP seem to have COPS of 3-4(ish) when outlet temp of 50-55°C. At least that is my view.

I wounder what the cost comparision would be over a 10 year running period (including installation) of ASHP and GSHP.

Some rough thoughts, calc.... I could be way off here
For most of us using gas for heating and hot water we can get a average yearly usage of gas consummed. Say 15,000 - 20,000 kWh of gas used to heat a average UK house. Say boiler is 75% real world efficent = 12,000 - 16,000 kWh of energy required in home p.a.

So
ASHP will use 6,000 - 8,000kWh of electricity at COP 2
GSHP will use 4,000 - 5,333kWh of electricity at COP 3

Yearly cost at £0.13 GBP per kWh (not economy 7 rate)
ASHP = £780 - £1040 p.a.
GSHP = £520 - £694 p.a.

so using my assumptions ASHP cost about £250 - £300 more per annum to run that GSHP, or you could say a GSHP about 66% the cost of an ASHP to run.


Anyone think this simplified view is somewhere near real world? We always seem to be focusing on COP's, but I've never before though about actual yealy runing costs.


Title: Re: GSHP versus ASHP
Post by: mpooley on February 10, 2011, 10:05:42 AM
thanks for the link sam (second one works).

very interesting reading.

I think in summary it seems to show that ASHP with oulet temp at around 50-55°C and air temp at -5 to 0°C have COPS at around 2-2.5. GSHP seem to have COPS of 3-4(ish) when outlet temp of 50-55°C. At least that is my view.

I wounder what the cost comparision would be over a 10 year running period (including installation) of ASHP and GSHP.

Some rough thoughts, calc.... I could be way off here
For most of us using gas for heating and hot water we can get a average yearly usage of gas consummed. Say 15,000 - 20,000 kWh of gas used to heat a average UK house. Say boiler is 75% real world efficent = 12,000 - 16,000 kWh of energy required in home p.a.

So
ASHP will use 6,000 - 8,000kWh of electricity at COP 2
GSHP will use 4,000 - 5,333kWh of electricity at COP 3

Yearly cost at £0.13 GBP per kWh (not economy 7 rate)
ASHP = £780 - £1040 p.a.
GSHP = £520 - £694 p.a.

so using my assumptions ASHP cost about £250 - £300 more per annum to run that GSHP, or you could say a GSHP about 66% the cost of an ASHP to run.


Anyone think this simplified view is somewhere near real world? We always seem to be focusing on COP's, but I've never before though about actual yealy runing costs.

just two thoughts (can only manage two at my age  ;) )would a gas boiler be that inefficient ? my oil boiler is supposed to be 90% +  ?

also I have noticed here and in other forums that when people calculate electricity cost the usually seem to be in the 12 to 14p per kwh

am I incredibly lucky that I get the bulk of my leccy at 8.2p per kwh (Not economy 7)  ?

thirdly (ooh i managed another thought 8) )
I did the sums yesterday and realised that at a cop of 2 my costs would be greater than using oil  so i would need to get a lot better than that to make it worthwhile.

Mike


Title: Re: GSHP versus ASHP
Post by: martin W on February 10, 2011, 10:21:34 AM
mpooley,

My gas boiler is 84% efficent (well on the label). I actually monitored the heat gained into my thermal store against the gas used the other day.... it worked out just over 45% efficent ??? outside air temperture was -5 or so. Whilst I might have some errors in my calculaitons / heat lost in pipes etc, it would be a  big stretch to think the boiler was even 60% efficent. (Oh and the boiler is working correctly).

Someone on here (ecentric?) hinted it might be a fair bit to do with how they calculate a boilers efficency  - using perfect world conditions (air temp at 20°C not minus 5).

13p per kwh is the average cost of the electric... ie 2500kwh per year at say 20p (so much a quater to cover a standing charge) and the rest at 9p or so.


Title: Re: GSHP versus ASHP
Post by: mpooley on February 10, 2011, 10:46:57 AM
martin hi

I am surprised about the gas boiler  :o  thats quite shocking!

Ah I see what you mean about the leccy.

personally i dont think that is a fair/reasonable way to do it, as most people are already using well over the amount charged at the higher rate just for normal leccy use so any additional used is always at the cheaper price.

mike


Title: Re: GSHP versus ASHP
Post by: qeipl on February 10, 2011, 12:26:03 PM

I did the sums yesterday and realised that at a cop of 2 my costs would be greater than using oil  so i would need to get a lot better than that to make it worthwhile.


Mike,

You're trying to work out whether ASHP or GSHP will be more cost effective given your current heat demand.
Don't forget that reducing your heat demand is the first thing to tackle.

For example, I seem to recall that you were asking elsewhere about draught seals on your windows.
New windows will have zero heat loss from draughts and a U-value of 1.9 or better.

Another example would be solar gain.
My parents live in a 1980s bungalow that has electric heating and an open fire.
They built a small conservatory off the main sitting/dining room to catch the afternoon/evening sun.
The reduction in electricity and logs, over the year, was a pleasant surprise - an additional benefit that they hadn't expected.

Older houses are notorilously 'leaky' (heat and air) where the roof meets the walls. More insulation and better draught-proofing?

Apologies for banging on about this again.
You may have already done as much as you can on these fronts but I feel we get too easily absorbed in the technicalities of the equipment and miss some less exciting stuff that is more cost effective.

Malcolm


Title: Re: GSHP versus ASHP
Post by: dhaslam on February 10, 2011, 12:28:30 PM
Heat pumps should  only use  off peak electricity, otherwise there isn't  much advantage other than  saving  fossil fuels by using renewable sourced electricity.  


Title: Re: GSHP versus ASHP
Post by: titan on February 10, 2011, 05:39:06 PM
Heat pumps should  only use  off peak electricity, otherwise there isn't  much advantage other than  saving  fossil fuels by using renewable sourced electricity.  

It depends on the situation. My calculated heat load is around 15,000kWh  and estimated normal usage around 3000kWh. With a heat pump the actual heat demand with a COP of 3 is 5000kWh put these figures into a power comparison site and because of the high day tariffs with off peak ,  25.14p and 4.97p the difference is small. You can fiddle with the figures, standing charge, no standing charge etc but the principal remains unless you have a high off peak demand off peak is quite often not the best option. There is also how best to use the off peak power, my floor may hold enough heat to last all day or maybe I could use a large thermal store but with high levels of insulation and low flow temperatures the heat demand may not be high enough make off peak worthwhile.


Title: Re: GSHP versus ASHP
Post by: baker on February 10, 2011, 08:25:21 PM
 
Hi a thought
geothermal ground horizontal heat pumps are at rated output at brine 0c
when the demand is on and the loop temperature drops,  the cop also drops. the output drops,and power con sumsion may increase if inverter technology
the soil conditions and
the climate also has a influence
so calculations most of the time guess work if working with the factory test conditions
the energy bills will increase as the season progresses
john


Title: Re: GSHP versus ASHP
Post by: titan on February 10, 2011, 10:44:41 PM

 calculations most of the time guess work if working with the factory test conditions
the energy bills will increase as the season progresses
john

There are plenty of independent reports showing GSHPs when installed and operated correctly give COP figures similar to the EN 14511 manufacturer test figures.


Title: Re: GSHP versus ASHP
Post by: billi on February 10, 2011, 11:50:36 PM
for the time beeing  my opinion is to  raise  electricity costs per unit  for heating


Title: Re: GSHP versus ASHP
Post by: titan on February 11, 2011, 08:33:31 AM
for the time beeing  my opinion is to  raise  electricity costs per unit  for heating

And the logic behind this opinion is ?


Title: Re: GSHP versus ASHP
Post by: baker on February 11, 2011, 09:53:01 AM
 Hi
I have called to many heat pumps with horizontal ground loops
and have never see 0c in the latter season  maybe its because they were not installed correct
and i see all the problem installs,which makes sense
 can i ask anyone out their if you can recall
what was  the average temperature in their horizontal ground  loop in the latter season
 the temperature on the ground loop return/ inlet when pump running for 4 hours or more
thankyou



Title: Re: GSHP versus ASHP
Post by: billi on February 11, 2011, 10:21:39 AM
Quote
And the logic behind this opinion is ?

..... that i have my reservations , that too much support like RHI for heatpumps and it is too early   that we can focus to shift our energy consumption towards electricity  and (H)eat a big proportion  of the Renewable electricity units supported by FIT 

A COP under 3  as far as i have read  can not  be called climate friendly

Billi


Title: Re: GSHP versus ASHP
Post by: qeipl on February 11, 2011, 02:04:56 PM
Quote
And the logic behind this opinion is ?

..... that i have my reservations , that too much support like RHI for heatpumps and it is too early   that we can focus to shift our energy consumption towards electricity  and (H)eat a big proportion  of the Renewable electricity units supported by FIT 

A COP under 3  as far as i have read  can not  be called climate friendly

Billi

Billi,

If not now, when?

We need to be doing everything, now - installing heat pumps, developing renewable electricity generation, and insulating/draught-proofing on a massive scale.

Even if we get a bit ahead on the heat pumps, burning gas to make electricity to run heat pumps in properly insulated buildings is more carbon efficient than burning gas in domestic boilers in averagely insulated buildings.

We get confused by people who tell us that electricity is 'high-grade' energy and shouldn't be used for heating.

When oil and gas become scarce and expensive electricity will be the only viable source of heating energy (additional to the sun) for the mass market - we will all be using electricity.

Heat pumps are far and away the most efficient use of electricity for heating because they are adding local solar energy to the electrical energy that they consume.

We must promote the development and use of heat pumps now so that when the crunch comes we already have a good base load of installations and new, improved models coming to market.

Rant over.

Malcolm


Title: Re: GSHP versus ASHP
Post by: billi on February 11, 2011, 02:44:00 PM
Sure i understand that heatpumps are playing a big role and are generally fine in my opinion

But  there should be a setpoint    of COP  agreed  for heatpumps  that will receive  financial help,  as well if the house  and the existing system is fine to run a heatpump

It does not make sense to me to  support heatpump ideas with a lousy COP the same way like units with COP of 4-5

And  consequently  one could ask why one that installs a gas boiler is not getting payed , cause he heats his house more environmental sound than with a inefficient heatpump

Billi









Title: Re: GSHP versus ASHP
Post by: qeipl on February 11, 2011, 09:02:02 PM
Billi,

The graph on this page suggests that a heat pump with a COP as low as 2, run on electricity from a gas power station, will be more efficient than a domestic gas boiler running at 90% efficiency.
http://www.inference.phy.cam.ac.uk/withouthotair/c21/page_150.shtml (http://www.inference.phy.cam.ac.uk/withouthotair/c21/page_150.shtml)

I'm guessing that my ASHP runs at a COP of between 2 and 3 for the times in the year that it's running the UFH without any input from the wood boiler. (It'll be doing 3 or 4 in the summer for DHW).
It may be 'lousy' but it's still producing less CO2 than if I had mains gas and a condensing boiler, and lots less CO2 than the oil/LPG/coal/raw electricity alternatives that are available here.

As for incentives, I confess that I don't understand the logic behind the RHI.
Surely we should be incentivising insulation, triple glazing, and the like - reducing the demand for heat - before we encourage people to install heat pumps and pellet boilers.

Maybe the first 500 units of electricity per month should cost 3p/unit and everything thereafter should cost 50p/unit.
At the same time we should grant aid insulation etc. - the installer (tradesman or DIY) gets the grant when the house passes a heat loss test (like Ivan's thermal image thing, maybe?).
Then put zero VAT on heat pumps, pellet boilers, etc. and let the rising gas prices gradually drive people away from gas boilers.

Malcolm