ASHP & UFH/rads

[Jonesy]

Hi. Just finished a new build, approx 310m2. heating and hot water is serviced by a 17kw grant aerona 3 ASHP behemoth. UFH downstairs with 150mm pipe spacings and rads 1st floor (9 in total, x2 towel rads and 7 oversized rads for thr bedrooms and landing). Grant did the heat loss calcs and specified the 17kw unit - i have no doubt that it’s perfectly fine on the heating capacity vs demand. The house has been insulated above building regs standard and not a massive amount of glass. Grant sized the ASHP on the basis that the rads upstairs may need a 50degC flow temperature; and that the UFH manifolds should then allow mixing down to 40ish degrees. We have two uponor UFH manifold with pumps, and both are fitted with thermostatic sensing heads. We can set these as high as 60 or as low as 30degC. Currently, I’m experimenting with the flow temp, and have the ASHP pumping out 43degC, with the sensing heads on manifolds both set to 38degC ish. The house is perfectly warm and the rads upstairs come on occassionally. My head says I should be able to get the ASHP flow down to 35degC, but not sure how best to do this. If I set the manifold sensing heads to say 40degC and then set the ASHP flow temp to 35degC, i’m effectively making the sending heads redundant, allowing the lower temp to pump round for longer, the ashp would have less short cycling and we wouldn’t be wasting energy mixing/controlling down at the manifold? Because we have a big open hallway and stair well, the upstairs is mainly serviced heatwise from the ufh in the hallway in the ground floor, with the stat upstairs occassionally firing up - we have a wireless stat that we move around depending on which room is the coldest. I wish we’d had ufh on the 1st floor also, but hindsight and all that! Any advice greatly appreciated.

[Bonner]

Bit late this reply ... just wondering how you got on with tweaking flow temperatures?

I am having a Grant 13kW installed under the BUS. Installer will set flow temperature to 45C for the upstairs radiators, to comply with MCS. Since radiators are unlikely to be needed much if at all, I intend to reduce flow temperature to optimise COP.

[shuff27]

1 hour ago, Bonner said:

Bit late this reply ... just wondering how you got on with tweaking flow temperatures?

I am having a Grant 13kW installed under the BUS. Installer will set flow temperature to 45C for the upstairs radiators, to comply with MCS. Since radiators are unlikely to be needed much if at all, I intend to reduce flow temperature to optimise COP.

 

Just wondering, do you think you'll need rads upstairs?  I decided not to have them, just heated towel rails & elec UFH in the upstairs bathrooms.  Downstairs is 8.5kW heat pump with wet UFH in the screed.  MCS signed off this arrangement after some discussion (I provided my own heat loss calcs based on Jeremy's spreadsheet).

[Bonner]

1 hour ago, shuff27 said:

 

Just wondering, do you think you'll need rads upstairs?  I decided not to have them, just heated towel rails & elec UFH in the upstairs bathrooms.  Downstairs is 8.5kW heat pump with wet UFH in the screed.  MCS signed off this arrangement after some discussion (I provided my own heat loss calcs based on Jeremy's spreadsheet).

 

Not sure if radiators will be really needed but don’t want to risk it. Also thinking of future resale. Installer has specified oversized double radiators but I won’t be going that far, normal singles and large towel radiators for bathrooms.