ASHP - Investigations and calculations

[richbee]

OK, so I've had the new heat loss survey and received the quotation from Greenhome.

They use the Heatgeek methods, and most different from Octopus, they assume much lower air exchange rates for the rooms - to the point where their total heat loss comes in at 9.4kW, against my self calc at 12.5kW and Octopus at 14.5kW (although they would not consider the insulated solid walls as it was 'the wrong sort of insulation'.)
I rechecked my calcs with lower air exchange rates and it does cut a big chunk off the total.
He reckoned that a 10kW ASHP would just about do it, but gave me the option to be conservative, so I opted for a 12kW. I'm now not 100% sure this is the right way to go - I would normally tend on the cautious side, but as this is intended to be worst case scenario, at 21 degrees downstairs, which we never use, and we do have a log burner to top things up - I do wonder if it might be better to go with the 10kW?

Based on that, they have quoted for Vaillant Arotherm Plus 12kW, with Vaillant 200l water tank and all the associated controls, including only 2 radiator changes.
They have calculated flow temp for worst case days at 50 degrees, and expected SCOP of 3.6.

Price is, not surprisingly, up from the £5k of Octopus to £9.5k (on top of the BUS grant).
The only thing not included is electrical work - I asked them to look into fitting a mini consumer unit and running an EV charger supply at the same time as the heat pump, to save on getting someone out again later on, and they are still putting together a cost for that.

Would be interested to hear peoples thoughts

[Andy]

Another thing to consider is inverter vs on/off type hp. An inverter will run lower power to fit under solar generation. On/off may be drawing a lot of power in its cycles.

Inverter more expensive parts. On off generally simpler to fix from what I can see.

Have you tried running your heating system with the temp turned down. You can record the burner on/off time and then work out heat input into the house. I did that and it was pretty accurate. What you have to consider is that when it super cold it isn’t windy. Tends to be g high pressure say over the UK. Then the air changes are negligible. Our house can use similar power at -5 as at zero on a windy day.

[Stinsy]

OK, so I've had the new heat loss survey and received the quotation from Greenhome.

They use the Heatgeek methods, and most different from Octopus, they assume much lower air exchange rates for the rooms - to the point where their total heat loss comes in at 9.4kW, against my self calc at 12.5kW and Octopus at 14.5kW (although they would not consider the insulated solid walls as it was 'the wrong sort of insulation'.)
I rechecked my calcs with lower air exchange rates and it does cut a big chunk off the total.
He reckoned that a 10kW ASHP would just about do it, but gave me the option to be conservative, so I opted for a 12kW. I'm now not 100% sure this is the right way to go - I would normally tend on the cautious side, but as this is intended to be worst case scenario, at 21 degrees downstairs, which we never use, and we do have a log burner to top things up - I do wonder if it might be better to go with the 10kW?

Based on that, they have quoted for Vaillant Arotherm Plus 12kW, with Vaillant 200l water tank and all the associated controls, including only 2 radiator changes.
They have calculated flow temp for worst case days at 50 degrees, and expected SCOP of 3.6.

Price is, not surprisingly, up from the £5k of Octopus to £9.5k (on top of the BUS grant).
The only thing not included is electrical work - I asked them to look into fitting a mini consumer unit and running an EV charger supply at the same time as the heat pump, to save on getting someone out again later on, and they are still putting together a cost for that.

Would be interested to hear peoples thoughts

I would er on the side of smaller where HPs are concerned. Even the most thorough heat-loss surveys tend to be conservative and the vast majority of the heating season is comfortably above the design conditions. Better to go with the smallest HP the installer will allow and rely on aux heating (eg WBS, a SH, or even ordinary resistive) to get the house up to 21℃ In the very coldest weather.

By upsizing you lose more through excessive cycling in mild weather you gain in exceptionally cold conditions.

[Andy]

The smaller heat pumps tend to be more efficient. It won’t cycle as much which will be better for the life span I should think. If you have a log burner then they tend to be 4-5kw minimum which almost gives 50% more than the 10kW unit.

[richbee]

For the size issue, apparently the 10kW and 12kW models are at least on the same chassis, not sure how much varies internally. I've asked the guy to see if he can confirm what level of modulation each one goes down to - He suspected they could be the same but wasn't sure.

I tend to assume that all the modern HPs are inverter controlled to help with modulation & efficiency, but I haven't asked TBH

The other thing I've just noticed is that both are pretty big units - 1.6m tall, and will fall foul of the permitted development limits of <0.6m3 (they are more like 0.8). I'm hoping that doesn't mean I have to pay for planning permission

[Fintray]

The 10kW unit shows "Heat output, minimum/maximum, A7/W35 5.40 to 12.50 kW"
whilst the 12kW shows "Heat output, minimum/maximum, A7/W35 5.40 to 14.00 kW"

[Fintray]

Based on that, they have quoted for Vaillant Arotherm Plus 12kW, with Vaillant 200l water tank and all the associated controls, including only 2 radiator changes.
They have calculated flow temp for worst case days at 50 degrees, and expected SCOP of 3.6.

Price is, not surprisingly, up from the £5k of Octopus to £9.5k (on top of the BUS grant).
The only thing not included is electrical work - I asked them to look into fitting a mini consumer unit and running an EV charger supply at the same time as the heat pump, to save on getting someone out again later on, and they are still putting together a cost for that.

Would be interested to hear peoples thoughts

The heat loss calculation I did using Heat Engineer software gave a 9.33kW heat loss so I've opted for the 10kW Arotherm Plus.
The quote I accepted came in at £13449 less £9000 grant, this includes 4 new K3 radiators and a large output towel rail but I am installing the primary pipework and the radiators along with HP base (pipes and fittings supplied by company).

[richbee]

The 10kW unit shows "Heat output, minimum/maximum, A7/W35 5.40 to 12.50 kW"
whilst the 12kW shows "Heat output, minimum/maximum, A7/W35 5.40 to 14.00 kW"

That sounds promising - if the minimum output is the same for both units - doesn't it?

[Fintray]

The 10kW unit shows "Heat output, minimum/maximum, A7/W35 5.40 to 12.50 kW"
whilst the 12kW shows "Heat output, minimum/maximum, A7/W35 5.40 to 14.00 kW"

That sounds promising - if the minimum output is the same for both units - doesn't it?

It gives a 57% reduction and a 61% reduction from max resp.
I'm hoping to use mine purely on weather compensation to control the indoor temperature.

[sharpener]

The 10kW unit shows "Heat output, minimum/maximum, A7/W35 5.40 to 12.50 kW"
whilst the 12kW shows "Heat output, minimum/maximum, A7/W35 5.40 to 14.00 kW"

That sounds promising - if the minimum output is the same for both units - doesn't it?

There is a detailed Vaillant output chart available AFAIK only on their Czech web site(!) and also this FB group which confirms that the 10kW has identical performance to the 12 except the top two columns of compressor speed or so are missing from the chart. So not a lot to be saved by specifying the 10, I don't even know why they make the two different models, maybe there is some Euro regulation it just squeezes into.

Yes the twin fan Aerotherm plus models require specific planning permission as they are too big for deemed PP.