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Author Topic: Ground Source Heatpump Power Consumption  (Read 11387 times)
brackwell
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« Reply #15 on: April 08, 2014, 09:08:43 AM »

The RHI is tied to MCS standards see http://www.microgenerationcertification.org/admin/documents/MIS%203005%20Issue%203%200%20Heat%20Pump%20Systems%202011.09.05.pdf

What people actually do and energy they use has nothing to do with it-we are now in the land of academic theory.  All rooms will be heated to 21C or 18C (see page 11) and all the emitters will HAVE to be sized to make this happen otherwise you do not achieve the minimum SPF rating of 2.5 to be eligible for RHI.  

I am sure that for most people this is a non starter, but as many have shown HPs do have a future in the right circumstances and therefore DIY maybe is the way forward particularly with A2A HP.

My current favorite is the one Alan found https://www.pmcoppack.com/shop/show_product_info.php?id=KIT-WF05CE5 because it can be run alongside whatever exists and can be programmed to use max pv

Ken

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brackwell
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« Reply #16 on: April 08, 2014, 09:54:37 AM »

And it just keeps coming - the emitter guide http://www.microgenerationcertification.org/images/MIS_3005_Supplementary_Information_2_-_Heat_Emitter_Guide_v2.0_Print_Version.pdf

I think people will fit HPs non RHI and then just later replace those rads as necessary.

Ken
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dhaslam
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« Reply #17 on: April 08, 2014, 10:58:49 AM »

It doesn't seem to be all that difficult to do the  calculations  for RHI.   Since there is already an underfloor system the calculations must have been done before.   It might mean adding a bathroom towel rail or two  at worst.     If the RHI  allows  the house to have  an efficient system that  works in all weather, with minimal electricity usage,  it is worth putting up with the  the paperwork.   The reason for the homeowner to have a reasonable calculation  of the heat requirement is to avoid the  contractors getting carried away with their estimates.   They should be prepared to review their calculations  if they give a result widely different than the actual usage.
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brackwell
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« Reply #18 on: April 08, 2014, 11:10:35 AM »

For many/most people it will be replace all the rads and fit a HP twice the size necessary.  Calculations is easy.

Ken
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BruceB
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« Reply #19 on: April 08, 2014, 09:58:01 PM »

I thought I might add a few points for accuracy's sake:

The link to the MCS 3005 standard above is out of date.  We are now on issue 4 which is more onerous.
http://www.microgenerationcertification.org/mcs-standards/installer-standards
It came into force on 16 Mar 14.

Getting a GDA done is good.  You need it for the RHI.  You can brief the assessor to make sure he makes no stupid assumptions about your property and make sure he only recommends additional wall or loft insulation if really appropriate.  You then have an EPC which gives you figures to let you calculate your RHI return, so you are no longer guessing.

An opinion: Whatever manufacturers say about the efficiency of ASHPs, I have reservations about their efficiency in domestic situations on cold, damp winter evenings.  If you have the capital gaining interest below inflation, then consider the GSHP option.

It states above that you must disconnect the wood burner.  Not true.  It is perfectly acceptable to design a bivalent system; the consequence is you trigger the metering requirement.

On the same point a heat pump does not have to be sized to provide 100% of the heating load if by design you are using another heat source to provide the additional heat requirements of the coldest days.  I suspect some installers might have to work to get their heads around MIS3005 Issue 4 on this point.

The outside temperature used in the heat loss calculation varies depending on where you are in the country.

As I think someone has said already, PV is largely irrelevant to the GSHP.  The times the GSHP is working the sun is unlikely to be shining.













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marshman
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« Reply #20 on: April 08, 2014, 10:16:18 PM »

Thanks for the continued "thoughts".

Well the Green Deal Assessor turned up at the appointed time. Very nice chap who was quite open and honest. As expected he said he needed to "go back and consult" on what he put in the report about my walls!  We had quite a good chat (OK old mans rant Grin) about government green policies. He has gone away to consult and submit his report to 1 Green Place - the firm that I contacted for the assessment. When I get my copy - complete with its recommendations I will then start contacting a few people about ground source heatpumps to get quotes - in the first instance only MCS ones with a view to getting the RHI.

With regard to the "numbers" and the SAP etc. I am sure that my "emitters" will be good enough (he says confidently!). I still have the original plans and design notes for the UFH produced by Wirsbo back in the 1980's. It was designed to cope then and the insulation level of the property has since been improved (an extra 250mm of loft insulation for a start).

Otherpower - lots is the answer to how much wood we get through! To be honest I would in the first instance see what the RHI/MCS/SAP numbers say about size of heatpump required then compare that with the specified heat output from my wood burner. If there is a big difference then I'll investigate further and see why.

Watch this space!



 
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marshman
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« Reply #21 on: April 08, 2014, 10:22:14 PM »

I thought I might add a few points for accuracy's sake:

The link to the MCS 3005 standard above is out of date.  We are now on issue 4 which is more onerous.
http://www.microgenerationcertification.org/mcs-standards/installer-standards
It came into force on 16 Mar 14.

Getting a GDA done is good.  You need it for the RHI.  You can brief the assessor to make sure he makes no stupid assumptions about your property and make sure he only recommends additional wall or loft insulation if really appropriate.  You then have an EPC which gives you figures to let you calculate your RHI return, so you are no longer guessing.

An opinion: Whatever manufacturers say about the efficiency of ASHPs, I have reservations about their efficiency in domestic situations on cold, damp winter evenings.  If you have the capital gaining interest below inflation, then consider the GSHP option.

It states above that you must disconnect the wood burner.  Not true.  It is perfectly acceptable to design a bivalent system; the consequence is you trigger the metering requirement.

On the same point a heat pump does not have to be sized to provide 100% of the heating load if by design you are using another heat source to provide the additional heat requirements of the coldest days.  I suspect some installers might have to work to get their heads around MIS3005 Issue 4 on this point.

The outside temperature used in the heat loss calculation varies depending on where you are in the country.

As I think someone has said already, PV is largely irrelevant to the GSHP.  The times the GSHP is working the sun is unlikely to be shining.


Thanks for the info Bruce - shame you are not in my neck of the woods.

Still not entirely convinced about the irrelevance of the PV - The house has a very large thermal mass so if the GSHP runs at a low level during the few hours of sun each day in the winter  it has to make a difference (well thats my "gut" feel anyway)   I do have 4 years worth of PV and weather/temperature daily data to look back on to work it out.

Roger
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gravelld
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« Reply #22 on: April 08, 2014, 11:12:33 PM »

Also, regarding PV, what about the heat pump heating a thermal store during the day, to be pumped around the CH at night?
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marshman
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« Reply #23 on: April 09, 2014, 07:37:13 AM »

Also, regarding PV, what about the heat pump heating a thermal store during the day, to be pumped around the CH at night?
Many years ago I did some calculations into the size of store required for "inter seasonal" storage. It was quite a big lump! To me that would be the better way to go - heat up in the summer when there is lots of spare "high grade i.e. hot heat" and use it throughout the winter.

As I have said the house has quite a high thermal mass so in principle that can be used as the store - I don't think the gains in winter when its needed would be enough to offset the cost and complication of short term i.e. daily heat storing - you could I suppose heat a buffer tank to at least make a contribution.

The final thing is at the moment I am going down the MCS/RHI route which means it will all have to be "by the book". If that gets too "silly" then I may well look at other solutions.

Roger
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Ted
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« Reply #24 on: April 09, 2014, 09:36:56 AM »

Many years ago I did some calculations into the size of store required for "inter seasonal" storage. It was quite a big lump! To me that would be the better way to go - heat up in the summer when there is lots of spare "high grade i.e. hot heat" and use it throughout the winter.

In theory, at least, this is how a GSHP works even if only partly. The summer sun heats the ground where your loop is and you extract that in the winter. The only thing missing is edge insulation and some type of 'forced' input in the summer.
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marshman
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« Reply #25 on: April 09, 2014, 02:40:20 PM »



In theory, at least, this is how a GSHP works even if only partly. The summer sun heats the ground where your loop is and you extract that in the winter. The only thing missing is edge insulation and some type of 'forced' input in the summer.
I hadn't quite thought of it like that!  but now you mention it all I need to do is insulate around the edges of the field where the ground loop will be installed (including top and bottom) and in the summer run the GSHP in reverse to heat the ground up (powered by the PV of course)  and the jobs a good 'un Grin
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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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« Reply #26 on: April 09, 2014, 02:53:13 PM »

Don't forget the mirrors! hysteria
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skyewright
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« Reply #27 on: April 09, 2014, 05:59:18 PM »

I hadn't quite thought of it like that!  but now you mention it all I need to do is insulate around the edges of the field where the ground loop will be installed (including top and bottom)  and in the summer run the GSHP in reverse to heat the ground up (powered by the PV of course)  and the jobs a good 'un  Grin
And I think you mentioned ground water, so job's probably not done till you've stopped that moving too...  Cry

'course it well may be that if you have moving ground water you'd be better off just letting it move through, grabbing a bit of heat from it as it passes?  Grin

But, hey, you were only joking anyway, I think?
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Regards
David
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« Reply #28 on: April 09, 2014, 09:40:10 PM »

Damn, that means I will need to build a dam!!

Heard from the "Green Deal" today, says he has put down solid walls as this was closest to what I have! I assume 450mm thick. In reality they are cavity walls - Approx 300mm external brick, 50mm cavity, 125mm thermalite block inner. Also no box for underfloor heating so had to put radiators!.

Looked at the original calcs for the UFH - done in 1984!  Says total heat loss is calculated to be 22kW - assumed room temps of 20 deg C (all rooms) and flow water temp of 46 deg C.  It will be interesting to see how that compares with the MCS/SAP calculations.

Roger
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« Reply #29 on: April 14, 2014, 09:58:15 AM »

Well got the EPC and the Green Deal Assessment Report.

EPC rates the property as D 59   a bit frustrating to say the least. No mention of insulated floors even though I showed the guy the insulation and he took pictures. Also walls down as solid. Top recomendations:

1. Internal or External wall insulation!!   (walls are at least 350mm brick, 50mm filled cavity and 125mm thermal block already)
2. Floor insulation - already has it
3. Heating controls - OK but I have a wood burner and there is a room stat!.

When I tacklled them on the floor insulation they said "underfloor heating is not regarded as insulation"!

EPC has space heating demand down as 30546kW per year.

QUESTION:  Should I worry about the numbers on the EPC and in the Green Deal Assessment - would they have any bearing on the Heat pump size and on the amount of RHI or is that all down to the MCS calculations and the installer??

Thanks
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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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