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British Gas versus Octopus: Two possible heat pump routes - how to evaluate them?

 
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Air Source Heat Pumps (ASHPs)
Last Post by Judith 2 years ago
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Toodles
 Toodles
(@toodles)
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Joined: 4 years ago
Posts: 2727
12/07/2024 2:58 pm  

@johnmo Ours was insulated before we moved in in 1985 - we have ICI manufactured beads and they really did find their way everywhere. An extension had been built on and RSJ’s had been used that breached the original cavity of the original outside wall - the beads found ther way into those breach points in the brickwork and filled every gap! Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 4 years ago
Posts: 2727
12/07/2024 3:07 pm  

@lucia Rogue tradesmen have a lot to answer for! 😳😩 (Bring back Hanging I say!😉) Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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Jancold
 Jancold
(@jancold)
Estimable Member Member
Joined: 3 years ago
Posts: 171
12/07/2024 3:28 pm  

@johnmo Thanks, doesn't seem too difficult. how deep should I bury it?. He said a meter which seems OTT !


Daikin 6Kw ASHP.
MG4 EV, Solis 8KW inverter, 32KWh battery
1926 Semi with loft and wall cavity insulation, all radiator.


   
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DougMLancs
 DougMLancs
(@dougmlancs)
Trusted Member Member
Joined: 3 years ago
Posts: 48
12/07/2024 3:48 pm  

@lucia do you know when the CWI was carried out and did it have a CIGA certificate? if you do then it’s a 25-year guarantee against poor work and they will cover remedial works up to £20k. If you don’t have a certificate it’s still worth checking with them if your insulation work was covered by them and allow you to claim. https://ciga.co.uk/guarantee-holders/


Smart Tech Specialist with Octopus Energy Services (all views my own). 4.4kW PV with 9.5kWh Givenergy battery. 9kW Panasonic Aquarea L ASHP


   
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 Anonymous 5011
(@Anonymous 5011)
Joined: 3 years ago
Posts: 562
12/07/2024 4:13 pm  

Posted by: @jancold
↑

Thanks, doesn't seem too difficult. how deep should I bury it?. He said a meter which seems OTT

Mine is a couple spades deep, so about 600mm. 



   
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 Lucia
(@lucia)
Honorable Member Member
Joined: 2 years ago
Posts: 354
Topic starter 12/07/2024 4:27 pm  

@dougmlancs Thank you - that's definitely worth a try. I know the loft insulation was done in 2006 and the firm went bankrupt (my GBIS assessor found their business card in the loft and my EPC assessor told me the gory details). I can try and check if the same company did the walls. 

The house belonged to my parents in 2006 and they wouldn't have had a clue really, so I can't imagine they used 2 different companies. 🤞🏻



   
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 1009
12/07/2024 5:29 pm  

@lucia If you have larger emitters (radiators) then a lower flow temperature can be used to provide the same heat loss. As well as the COP varying with flow temperature, so does the output, here is an article https://www.firepowerheating.co.uk/heat-pump-outputs-explained-pumps-help-and-advice


House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 Lucia
(@lucia)
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Joined: 2 years ago
Posts: 354
Topic starter 12/07/2024 5:53 pm  

@bontwoody yes, I understand about larger rads and lower flow temperatures what I don't grasp (and that page doesn't explain because I don't see any mention of heat pump size) is how much a possibly undersized heat pump can make up the heat temps.

If my heat loss is 5.61 kw how much do I need to improve the emitters with a 4Kw heat pump to get it to supply sufficient heat to be warm? (I'm an absolute wuss about the cold 😁). 

Will exchanging my 11s for K2s make a 4kw heat pump meet or exceed that heat loss for example? Can a 4kw be coaxed to do that? I'm not considering water heating here either or defrost cycles. 

Or should I do both.... lobby for the 6kw and bigger emitters? 



   
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 GunboatDiplomat
(@gunboatdiplomat)
Trusted Member Member
Joined: 2 years ago
Posts: 40
12/07/2024 6:01 pm  

@lucia in your position, given a second survey that confirms what you suspected about the heat loss and agrees with your own calculation I wouldn't accept the Octopus proposal as-is. To me its a no-brainer to push for the 6kW Daikin if that meets the predicted heat loss. If you do get the cavity insulation fixed later that will mean you immediately reduce your individual room heat losses and can turn down the flow temperature and gain more efficiency

Also with the BG quote being higher than Octopus, how far off the estimate Heat Geek's site gives is it? Just curious as to the spread between the big energy suppliers and Heat Geek.



   
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 Lucia
(@lucia)
Honorable Member Member
Joined: 2 years ago
Posts: 354
Topic starter 12/07/2024 6:09 pm  

@gunboatdiplomat I haven't done a Heat Geek calc but have done a de Podesta calc on 1year's metered gas use (which HG reckon is ok). This gave me 5.61kw which interestingly, the BG MCS survey that was run as 'no wall insulation' almost matched.

This then computes as a 6kw heat pump and all the rads upgraded. and made the cost about £1,700 higher than Octopus (plus paying for gas capping and removal and much higher annual maintenance fees). 



   
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 Judith
(@judith)
Prominent Member Member
Joined: 2 years ago
Posts: 521
12/07/2024 6:11 pm  

@lucia don’t whatever you do go with a 4kW Daikin, our annual gas bill of 18000kWh means we need a 6.7kW ashp your 16000 means you need a 5.5kW (ish) The Daikin will be about 3.7KW you’ll be cold and it will try to go hotter and you’ll be skint too.


2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP >4) open system operating on WC


   
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 Judith
(@judith)
Prominent Member Member
Joined: 2 years ago
Posts: 521
12/07/2024 6:17 pm  

@lucia you can’t improve the emitters  to get more wattage out of a heat pump. All you can do is put an electric fire on!

or wear more clothes and live in a cooler house eg 15-18C. Not my idea of comfort.


2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP >4) open system operating on WC


   
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