Fabric and ventilation heat loss calculator

[JohnMo]

I would size heat pump based on a few criteria 

 

Over size ashp approx 1.2 to 1.4 for region of +5 to 0 to allow for defrosting. 

 

Make sure heat pump puts out a genuine minimum of 7kW at you design temp. Take note also of oversize to cover defrosting.

 

Get a heat pump with good modulation.

 

Size system volume based on

20L per kW output at minimum modulation of heat pump. Exclude in volume calculation any radiators with trvs and their pipe work. Exclude any UFH loops with actuators. Any volume needed, add by volumiser not buffer.

[Sparrowhawk]

3 hours ago, timhowes said:

However, as someone with no prior experience, I will have to be quite brave to source my own ASHP, design the system and ask them to fit it.

 

Consider going to a HeatGeek accredited installer, because they know their stuff and will install outside MCS or may be able to get a reasonable system design through MCS. And a HeatGeek installer will appreciate that you've already done a basic heat loss calculation to size up the previous system design!

[timhowes]

Thanks @Sparrowhawk - I contacted a HeatGeek recommended installer back in July who sent me a quote for a mere £25k!!! This included 7kW ASHP (a premium Stiebel Eltron model), all of the UFH I will need, and before the BUS grant. But still...

 

So this sort of put me off. I have gone back to them to ask to discuss, as they are the only company who have entertained the idea of an appropriately-sized ASHP. I have said no buffer, single zone... Let's see what comes back!

[timhowes]

4 hours ago, JohnMo said:

 

Over size ashp approx 1.2 to 1.4 for region of +5 to 0 to allow for defrosting. 

 

Thanks @JohnMo

 

By this, do you mean I should look at the heat loss in the deltaT columns 15 and 20 (assuming I want 20C in room)?

 

 

 

So multiple 5689 by 1.4, allow for DHW and go from there?

 

(Values slightly greater as I had underestimated roof area)

[Sparrowhawk]

1 hour ago, timhowes said:

I contacted a HeatGeek recommended installer back in July who sent me a quote for a mere £25k!!!

Do you have more than one HeatGeek installer in your area? They come with a premium, but there was a 50% difference between the two quotes I got. Some are just taking the mick with their prices (and if people will pay, who can blame them).

[timhowes]

Yes there are a couple of other options - I have today submitted the plans via the Heat Geek portal (seemed to need to be channelled into their "black label" system which sounds even more expensive!) - waiting to see what happens.

[JohnMo]

15 minutes ago, timhowes said:

submitted the plans via the Heat Geek portal (seemed to need to be channelled into their "black label" system which sounds even more expensive!) -

I got some stupid quote, a massive heat pump offered, even with an 'A' EPC. And an actual heat loss for house, close to 3.5kW even at -9 outside.

[JohnMo]

52 minutes ago, timhowes said:

So multiple 5689 by 1.4, allow for DHW and go from there

 

54 minutes ago, timhowes said:

By this, do you mean I should look at the heat loss in the deltaT columns 15 and 20 (assuming I want 20C in room)?

Yes, but you don't need to add anything for DHW. The way they test heat pumps is more for central Europe, which has a dryer atmosphere, so less defrosting goes on.

 

So I would look at nearer 8-9kW (at -3) not a 6-7kW. But as mentioned turn down and modulation is important.