Avoid the Heat Pump Villain: Why Low-Loss Headers and Buffers Can Sabotage Your Heat Pump's Efficiency
Coat tailing on this thread. I'm having a 5kW Vaillant put in and our house is only 3 bed (for idea of size). The installer has said two pumps on the heating system may be needed. It doesn't sound right to me but any help appreciated!
Posted by: @samiebon1Coat tailing on this thread. I'm having a 5kW Vaillant put in and our house is only 3 bed (for idea of size). The installer has said two pumps on the heating system may be needed. It doesn't sound right to me but any help appreciated!
It's unlikely you need 2 pumps, did he say why?
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @samiebon1@jamespa I think because they usually put buffers in and i've specified no buffers.
Well that's not really a reason.
If he had said "because the index circuit has a resistance that is too high for the water pump" that would be a reason.
Is there any reason to suspect the resistance in your system will be high like small diameter, circuitous or extra long pipework?
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @samiebon1I think i'll ak him about the index circuit. My own concern is the amount of 90deg elbows in my system!
Maybe best not to sound too clever, it might upset him. You might be better first to ask why he thinks you might need 2 pumps and then, if necessary, ask a follow up eg how he is going to ensure a second pump is fitted if and only if its actually needed.
Personally I doubt many plumbers calculate the index circuit not least because it's often not visible. I'm sure many if not most just assume the pump will be good enough which, in reality, it usually will.
Of course putting in loads of 90 degree elbows isn't best practice!
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
/a>
Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU
From Zero to Heat Pump Hero: https://amzn.to/4bWkPFb
Subscribe and follow our Homeowners’ Q&A heat pump podcast
I wonder how much efficiency it really costs - if there is unnecessary mixing it results in higher return temps so a "saving" on the next heating. Clearly there will be some heat & efficiency loss but perhaps not quite such a big problem?
I suspect in most cases it will not be worthwhile removing an existing buffer tank.
But on any future installation I would definitely question necessity if proposed as part of installation.
Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV
Posted by: @tim441I wonder how much efficiency it really costs - if there is unnecessary mixing it results in higher return temps so a "saving" on the next heating. Clearly there will be some heat & efficiency loss but perhaps not quite such a big problem?
I suspect in most cases it will not be worthwhile removing an existing buffer tank.
But on any future installation I would definitely question necessity if proposed as part of installation.
15% or more typically
The problem is not loss of energy (which as you say is small) its reduction in flow temperature to the emitters (due to the mixing) which means that the heat pump must be operated at a higher flow temperature than would otherwise be the case.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
@jamespa There again, I have my secondary pump set to match the average flow rate from the heat pump system; this is 15 lpm. When the pump speeds up (as it does periodically) to as much as 30 lpm for a short time, my secondary pump connected to the output of the LLH does not change. Efficiency loss? Regards, Toodles.
Toodles, he heats his home with cold draughts and cooks his food with magnets.
I doubt I could get my weather compensation curve any lower so must conclude my buffer is not hurting me tooooo much. Certainly accept the main point that buffer tanks are likely unnecessary.
My settings:
Leaving Water temp 30/45
Outside temp -4/15
Currently outside temp 6 deg. LWT 36 deg. Indoor temp 21 deg
Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV
@tim441 if you want to you can work out roughly how much it's costing by measuring the temperature drop across the buffer flow to flow. The cost is roughly 2-3 percent per C (more according to some, but I think the argument for more depends on deltaT flow to return being higher (than the typical 5C) on the emitter size.
It's entirely possible to set up buffer tanks not to mix, but unfortunately most installers appear not to do so, or fit a buffer tank that is to small to stratify. Of course some do, @toodles has for some while reported a buffer tank that doesn't mix to any great extent.
The real point is that they shouldn't be fitted in the first place because they are, in almost all cases, superfluous. Obviously once they are there it's a different calculation.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
-
Ideal Logic 10kW Heat Pump Pipes Noisy and Very Expensive to Run
3 months ago
-
Samsung 5kW R32 Monobloc Gen 6 ASHP
3 months ago
-
6 Red Flags to Avoid When Considering a Heat Pump Installation
4 months ago
-
L9 error with Mitsubishi ecodan heat pump
5 months ago
-
Ecodan DHW Settings missing
1 year ago
- 22 Forums
- 2,057 Topics
- 44.9 K Posts
- 36 Online
- 3,299 Members
Join Us!
Trusted Installers
Struggling to find a reliable heat pump installer? A poor installation can lead to inefficiencies and high running costs. We now connect homeowners with top-rated installers who deliver quality work and excellent service.
✅ Verified, trusted & experienced installers
✅ Nationwide coverage expanding
✅ Special offers available
Latest Posts
-
RE: Is Your 6kW Air Source Heat Pump Really a 6kW?
There are various ways to look at things related to CoP...
By Johnmo , 4 hours ago
-
RE: IVT Greenline high pressure switch and electrical cassette errors
@abbote thanks for that advice.There was a bit of air i...
By tdudgeon , 4 hours ago
-
RE: Heat Pump Manufacturers Recommending Buffer Tanks
One manufacturer Viessmann has to have their buffer, as...
By Johnmo , 7 hours ago
-
RE: How To Balance Radiators & the Role of the Lockshield Valve: A Homeowner's Guide
Good luck, I hope it all works out!
By JamesPa , 1 day ago
-
@johnd it's a difficult one, because we've seen instanc...
By Mars , 1 day ago
-
RE: Is your heat pump insured?
@johnmo sorry it comes across like that. The post is au...
By KevinPotts , 1 day ago
-
RE: Getting the best out of a heat pump - is Homely a possible answer?
@johnmo Perhaps a little detail might explain my reason...
By Toodles , 1 day ago
-
Win a 6-panel PV courtesy of egg and Renewable Heating Hub
Our epic giveaway just went live! Want to win a 6-pan...
By Mars , 2 days ago
-
RE: Yes, the "zoning with ASHP" topic again...
James, thanks again for your thoughtful and persistent ...
By HarryRea , 2 days ago
-
RE: Is this normal? Click of the DHW returning to space heating
So the Lone Ranger returned today! Even though we thoro...
By Grantmethestrength , 2 days ago
-
RE: Vaillant & OVO partner up to offer Heat Pump Plus
Hopefully iv done the right thing today by signing up t...
By Westkent , 2 days ago
-
RE: Battery sizing - How low can you go!
My own experience with connecting four batteries to thr...
By Transparent , 2 days ago
-
RE: Plate heat exchanger considerations
Work on 2-3 percent per degree. This is a reasonable e...
By JamesPa , 3 days ago
-
RE: Advice for ground source heat pump in new build with PV and batteries
The useful bit is the bit that specifies the heat loss ...
By JamesPa , 3 days ago
-
RE: Volumisers in Heat Pump Systems: Does Placement Matter?
You’re absolutely right that during defrost the refrige...
By Mars , 3 days ago
-
@editor thanks Mars that’s the same table I found in th...
By Gary , 3 days ago
-
RE: Tariff and charging strategy advice please
They haven't asked me to prove that I have an EV (I do)...
By JamesPa , 3 days ago
-
RE: Solar Power Output – Let’s Compare Generation Figures
Took a while to find on the OFGEN site: ”The FIT sche...
By AgentGeorge , 3 days ago
-
RE: why solar diverters for HW instead of the heat pump?
For me there are few factors why you may want to heat w...
By Johnmo , 3 days ago