ASHP - Investigations and calculations

Air source, ground source and associated systems for heating homes
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richbee
Posts: 412
Joined: Tue Apr 19, 2022 3:39 pm
Location: Northumberland

ASHP - Investigations and calculations

#1

Post by richbee »

I'm fairly well on my way down the ASHP rabbit hole - investigating, reading, watching, learning, calculating.....
This thread is intended to document my process - to get helpful advice from those who know more than me - and maybe eventually to help anyone else starting out on their heat pump journey.

We live in an 1830s stone farmhouse in rural Northumberland, currently heated by oil, which is maybe not the best starting point for a heat pump

I got a fairly comprehensive spreadsheet from my neighbour who is doing a whole house refurb from scratch himself, including ASHP.
Having worked through most of the external wall, roof, windows, doors etc to get U values - the excel sheet reckons a heat loss of ~12.5kW on the coldest day, based on internal temperatures of 21 in the living spaces and 18 elsewhere - which seems to be the standard, even though we only tend to have things at 18.
It also works out the annual kWh use of ~30,000kWh heating & hot water, but this is based on 'degree days' which seems to be a slightly old fashioned concept, with no reference to actual room temperatures, only days on which you are likely to need heating (if it is <15.5 degrees outside).

I have a quote from Octopus for £4.6k on top of the £7.5k grant - I'm holding off getting them to survey until I know a bit more and what questions to ask.

I've been reading / watching a fair bit from the Heatgeeks https://www.heatgeek.com/about/ - who have loads of detailed info.
Anyone else know much about them?
Their very rough website quote was much more expensive, at ~£10k on top of the grant!
Solar PV since July '22:
5.6kWp east/west facing
3.6kW Sunsynk hybrid inverter
2x 5.12kWh Sunsynk batteries
Ripple DW 2kW
Countrypaul
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Re: ASHP - Investigations and calculations

#2

Post by Countrypaul »

When I was looking at figures for our refurb the degree days base figure always seemed quite arbitrary and yet can have a significant effect on the overall expected energy consumption. For example, a leaky building that is then made airtight will use less energy to heat - seems obvuous but nearly all the calculations you see assume a baseline of 15.5C in the UK. I found this article helpful: https://www.energylens.com/articles/deg ... re-problem - it is from a UK company I believe.
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Joeboy
Posts: 6739
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Re: ASHP - Investigations and calculations

#3

Post by Joeboy »

Shall watch this one closely.
15.8kW PV SE, VI & DW
Ripple 7kW WT & Gen to date 11MWh
28kWh LFPO4 storage
95kWh Heater storage
12kWh 210ltr HWT.
73kWh HI5
Deep insulation, air leak ct'd home
Zoned GCH & Hive 2
WBSx2
Low energy bulbs
Veg patches & fruit trees
HML
Posts: 19
Joined: Sun Sep 03, 2023 1:56 pm

Re: ASHP - Investigations and calculations

#4

Post by HML »

Heat Geek seem to specialise in training plumbers in the design and installation of heat pump systems, they don't install systems themselves any more but have a list of people that they've trained who should be competent, but are likely to be expensive as they will try to make the system as efficient as possible which may mean more or less complete replacement of the system. There's lots of good info on the Heat Geek site though.

The Build Hub forum has lots of useful discussion about heat pump systems - https://forum.buildhub.org.uk/forum/119 ... umps-ashp/.

I found Glyn Hudsons' video of installing an ASHP himself interesting - His demonstration that an ASHP could operate very efficiently was one of the triggers for my conversion to ASHPs and doing my own install.

Graham Hendra has some interesting posts including a few where he's installed an ASHP in an old house without changing any of the radiators or pipework. https://www.linkedin.com/pulse/project- ... am-hendra/

Octopus may be cheap, but when I asked for a quote they wouldn't look at anything other than standard estate type houses, so 1830 would be out. That was a few months ago and they may have changed.
Ken
Posts: 400
Joined: Mon Jul 26, 2021 10:07 am

Re: ASHP - Investigations and calculations

#5

Post by Ken »

Countrypaul wrote: Thu Oct 26, 2023 11:31 am When I was looking at figures for our refurb the degree days base figure always seemed quite arbitrary and yet can have a significant effect on the overall expected energy consumption. For example, a leaky building that is then made airtight will use less energy to heat - seems obvuous but nearly all the calculations you see assume a baseline of 15.5C in the UK. I found this article helpful: https://www.energylens.com/articles/deg ... re-problem - it is from a UK company I believe.
You do realise that the 15.5C is the outside temp and the starting point for calculating degree days. Basically they assume that at this temp no heating is required due to passive heating from occupants and sun.
I think you need to look more closely at the SAP 2012 calculations which underpin the EPC ratings. Most installers start their quotes off by just using the EPC fig.

The SAP calculations take account of the locality and openings eg chimney, and vents but perhaps not so much leaky doors etc as it assumes these are airtight.
Countrypaul
Posts: 435
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Re: ASHP - Investigations and calculations

#6

Post by Countrypaul »

Ken wrote: Thu Oct 26, 2023 12:28 pm
Countrypaul wrote: Thu Oct 26, 2023 11:31 am When I was looking at figures for our refurb the degree days base figure always seemed quite arbitrary and yet can have a significant effect on the overall expected energy consumption. For example, a leaky building that is then made airtight will use less energy to heat - seems obvuous but nearly all the calculations you see assume a baseline of 15.5C in the UK. I found this article helpful: https://www.energylens.com/articles/deg ... re-problem - it is from a UK company I believe.
You do realise that the 15.5C is the outside temp and the starting point for calculating degree days. Basically they assume that at this temp no heating is required due to passive heating from occupants and sun.
I think you need to look more closely at the SAP 2012 calculations which underpin the EPC ratings. Most installers start their quotes off by just using the EPC fig.

The SAP calculations take account of the locality and openings eg chimney, and vents but perhaps not so much leaky doors etc as it assumes these are airtight.
Ken,

Have you read the article I posted a link to? It explains the base figure and why the UK uses 15.5C (basically because data was eaily available) as well as why getting a more accurate baseline will help get more accurate results.
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Joeboy
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Location: Inverurie

Re: ASHP - Investigations and calculations

#7

Post by Joeboy »

richbee wrote: Thu Oct 26, 2023 10:32 am I'm fairly well on my way down the ASHP rabbit hole - investigating, reading, watching, learning, calculating.....
This thread is intended to document my process - to get helpful advice from those who know more than me - and maybe eventually to help anyone else starting out on their heat pump journey.

We live in an 1830s stone farmhouse in rural Northumberland, currently heated by oil, which is maybe not the best starting point for a heat pump

I got a fairly comprehensive spreadsheet from my neighbour who is doing a whole house refurb from scratch himself, including ASHP.
Having worked through most of the external wall, roof, windows, doors etc to get U values - the excel sheet reckons a heat loss of ~12.5kW on the coldest day, based on internal temperatures of 21 in the living spaces and 18 elsewhere - which seems to be the standard, even though we only tend to have things at 18.
It also works out the annual kWh use of ~30,000kWh heating & hot water, but this is based on 'degree days' which seems to be a slightly old fashioned concept, with no reference to actual room temperatures, only days on which you are likely to need heating (if it is <15.5 degrees outside).

I have a quote from Octopus for £4.6k on top of the £7.5k grant - I'm holding off getting them to survey until I know a bit more and what questions to ask.

I've been reading / watching a fair bit from the Heatgeeks https://www.heatgeek.com/about/ - who have loads of detailed info.
Anyone else know much about them?
Their very rough website quote was much more expensive, at ~£10k on top of the grant!
I would love to dive right in and get a heatpump in Scotland but 30,000kWh hits me as a massive amount of power. So much so that I double checked on Octopus. 2022 we used a combined electric & gas of 14,800kWh (13,500E/1,300G) and that included a large percentage of our 12,000 miles in EV, say 90%+.

I can't get my head around that. We do have the WBS right enough. I assume a WBS and heat pump can both be in the same property? We are reasonably well.insulated but.not to today's standards and its only double glazing.

So far this year we have used 9,000kWh combined fuels and hope to close the year at around 13,000kWh combined incl a year's EV charging. I want someone to tell me what I'm missing, how can 30,000kWh with a machine who's cop is 4+ be possible?

I feel quite thick when it comes to HP's although I already have one for four years out here in Turkey.
15.8kW PV SE, VI & DW
Ripple 7kW WT & Gen to date 11MWh
28kWh LFPO4 storage
95kWh Heater storage
12kWh 210ltr HWT.
73kWh HI5
Deep insulation, air leak ct'd home
Zoned GCH & Hive 2
WBSx2
Low energy bulbs
Veg patches & fruit trees
richbee
Posts: 412
Joined: Tue Apr 19, 2022 3:39 pm
Location: Northumberland

Re: ASHP - Investigations and calculations

#8

Post by richbee »

Joeboy wrote: Thu Oct 26, 2023 12:47 pm
richbee wrote: Thu Oct 26, 2023 10:32 am I'm fairly well on my way down the ASHP rabbit hole - investigating, reading, watching, learning, calculating.....
This thread is intended to document my process - to get helpful advice from those who know more than me - and maybe eventually to help anyone else starting out on their heat pump journey.

We live in an 1830s stone farmhouse in rural Northumberland, currently heated by oil, which is maybe not the best starting point for a heat pump

I got a fairly comprehensive spreadsheet from my neighbour who is doing a whole house refurb from scratch himself, including ASHP.
Having worked through most of the external wall, roof, windows, doors etc to get U values - the excel sheet reckons a heat loss of ~12.5kW on the coldest day, based on internal temperatures of 21 in the living spaces and 18 elsewhere - which seems to be the standard, even though we only tend to have things at 18.
It also works out the annual kWh use of ~30,000kWh heating & hot water, but this is based on 'degree days' which seems to be a slightly old fashioned concept, with no reference to actual room temperatures, only days on which you are likely to need heating (if it is <15.5 degrees outside).

I have a quote from Octopus for £4.6k on top of the £7.5k grant - I'm holding off getting them to survey until I know a bit more and what questions to ask.

I've been reading / watching a fair bit from the Heatgeeks https://www.heatgeek.com/about/ - who have loads of detailed info.
Anyone else know much about them?
Their very rough website quote was much more expensive, at ~£10k on top of the grant!
I would love to dive right in and get a heatpump in Scotland but 30,000kWh hits me as a massive amount of power. So much so that I double checked on Octopus. 2022 we used a combined electric & gas of 14,800kWh (13,500E/1,300G) and that included a large percentage of our 12,000 miles in EV, say 90%+.

I can't get my head around that. We do have the WBS right enough. I assume a WBS and heat pump can both be in the same property? We are reasonably well.insulated but.not to today's standards and its only double glazing.

So far this year we have used 9,000kWh combined fuels and hope to close the year at around 13,000kWh combined incl a year's EV charging. I want someone to tell me what I'm missing, how can 30,000kWh with a machine who's cop is 4+ be possible?

I feel quite thick when it comes to HP's although I already have one for four years out here in Turkey.
Sorry, just to be clear, the 30,000kWh is heat energy - so if you had a SCOP of 4, it would take 7,500kWh of electricity to run the heating / hot water system.
We currently use around 1900l of oil per year - which works out as around 15,000kWh heat energy from the oil assuming 75% oil boiler efficiency. We do tend to use heating zones a lot, with only a couple of rooms heated during the day, and we are away with work a lot. We never have the heating above 18 degrees, and we do have a WBS as well.
I really want to work out for the heat pump how we would control it - as everyone says it needs to be on 24/7 'low and slow' to be efficient, which would be a big change for us.
Last edited by richbee on Thu Oct 26, 2023 1:07 pm, edited 1 time in total.
Solar PV since July '22:
5.6kWp east/west facing
3.6kW Sunsynk hybrid inverter
2x 5.12kWh Sunsynk batteries
Ripple DW 2kW
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Joeboy
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Location: Inverurie

Re: ASHP - Investigations and calculations

#9

Post by Joeboy »

richbee wrote: Thu Oct 26, 2023 12:59 pm
Joeboy wrote: Thu Oct 26, 2023 12:47 pm
richbee wrote: Thu Oct 26, 2023 10:32 am I'm fairly well on my way down the ASHP rabbit hole - investigating, reading, watching, learning, calculating.....
This thread is intended to document my process - to get helpful advice from those who know more than me - and maybe eventually to help anyone else starting out on their heat pump journey.

We live in an 1830s stone farmhouse in rural Northumberland, currently heated by oil, which is maybe not the best starting point for a heat pump

I got a fairly comprehensive spreadsheet from my neighbour who is doing a whole house refurb from scratch himself, including ASHP.
Having worked through most of the external wall, roof, windows, doors etc to get U values - the excel sheet reckons a heat loss of ~12.5kW on the coldest day, based on internal temperatures of 21 in the living spaces and 18 elsewhere - which seems to be the standard, even though we only tend to have things at 18.
It also works out the annual kWh use of ~30,000kWh heating & hot water, but this is based on 'degree days' which seems to be a slightly old fashioned concept, with no reference to actual room temperatures, only days on which you are likely to need heating (if it is <15.5 degrees outside).

I have a quote from Octopus for £4.6k on top of the £7.5k grant - I'm holding off getting them to survey until I know a bit more and what questions to ask.

I've been reading / watching a fair bit from the Heatgeeks https://www.heatgeek.com/about/ - who have loads of detailed info.
Anyone else know much about them?
Their very rough website quote was much more expensive, at ~£10k on top of the grant!
I would love to dive right in and get a heatpump in Scotland but 30,000kWh hits me as a massive amount of power. So much so that I double checked on Octopus. 2022 we used a combined electric & gas of 14,800kWh (13,500E/1,300G) and that included a large percentage of our 12,000 miles in EV, say 90%+.

I can't get my head around that. We do have the WBS right enough. I assume a WBS and heat pump can both be in the same property? We are reasonably well.insulated but.not to today's standards and its only double glazing.

So far this year we have used 9,000kWh combined fuels and hope to close the year at around 13,000kWh combined incl a year's EV charging. I want someone to tell me what I'm missing, how can 30,000kWh with a machine who's cop is 4+ be possible?

I feel quite thick when it comes to HP's although I already have one for four years out here in Turkey.
Sorry, just to be clear, the 30,000kWh is heat energy - so if you had a SCOP of 4, it would take 7,500kWh of electricity to run the heating / hot water system.
Aha, understood. PlusI have to add my 7.2MWh of PV self generation to my own total.
15.8kW PV SE, VI & DW
Ripple 7kW WT & Gen to date 11MWh
28kWh LFPO4 storage
95kWh Heater storage
12kWh 210ltr HWT.
73kWh HI5
Deep insulation, air leak ct'd home
Zoned GCH & Hive 2
WBSx2
Low energy bulbs
Veg patches & fruit trees
Bugtownboy
Posts: 908
Joined: Tue Jun 01, 2021 12:35 pm

Re: ASHP - Investigations and calculations

#10

Post by Bugtownboy »

Rich, I second Joe’s view that this will be a very informative thread - your ongoing musings and experience plus the input of others.

We are in the position of having a seldom used, 9 year old combi - tend to use WBS as main heat.

My biggest concern is provision of DHW - we don’t have a ‘hot water tank’ and due to using space afforded by not having one/having a combi boiler, would need some disruptive changes to provide one, that, from my
‘Survey’ would be relatively small and struggle to provide enough HW for multiuser showers and/or a bath.

Not having researched the grant T’s&C’s, presuming having a secondary form of heat (WBS) precludes qualifying for the grant ?
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