ASHP grant without radiators/heating upstairs

[BadgerBadger]

We have a good well-insulated airtight build with MVHR etc.  UFh throughout downstairs so have decided to skip the complexity of heating upstairs, as all the feedback we hear is that it won't really be used.

 

But we're having trouble accessing the BUS grant for our ASHP as the installers models are showing undersized emitters upstairs. Heat pump is plenty big enough to cover total heat loss. Have others who've done the same had similar trouble?

[nod]

Ours just said We will put it in for the grant and if you choose not to bother 

Simply amend later 

[JohnMo]

To have no emitters upstairs your downstairs UFH has to output enough heat to satisfy the whole heat house load.

 

The other thing is the assessor may have taken MCS default air changes and a bunch of other default numbers. So it's sh!te in, sh!te out heat loss wise.

1 hour ago, BadgerBadger said:

Heat pump is plenty big enough

That sounds worrying. It should be sized generally for the heat load. Which may indicate the issue in the second paragraph sh!te in...

 

Look for another installer. Or don't bother with the grant. Go and get a Panasonic, Hitachi etc heat pump from internet or local wholesalers.

[BadgerBadger]

7 hours ago, JohnMo said:

That sounds worrying. It should be sized generally for the heat load. Which may indicate the issue in the second paragraph sh!te in...

 

Look for another installer. Or don't bother with the grant. Go and get a Panasonic, Hitachi etc heat pump from internet or local wholesalers.

 

Let's go with "confident it's appropriately sized".  Design heat loss is about 5-6kW at -3C, I could squeeze into 6kW but could be marginal if house performance isn't quite as per theory, so we're going with 8.5kW Ecodan.

 

Annoyingly I've already paid/lost survey & design fees to another installer whilst chasing the grant, only to hit a dead end with design there too.

[JohnMo]

To give you feel, we are single storey very poor form factor, loads of glazing, MVHR etc. 192m² at -9 we have a heat loss of 3.2kW. That is using Jeremy's spreadsheet and tested with a heat meter to be correct. We have a 6kW heat pump, but due to it being a range rated larger heat modulation isn't the best, but does a good enough job.

 

If you are set on an Ecodan, don't do the 8.5kW, do the 8kW. The 8kW has two heat pump compressors in series. A fixed output 2kW and an inverter compressor at 6kW. So modulation galore and a more flexible offering.

[BadgerBadger]

Thank you - just looked it up and the 8kW looks to be R290, which we can't have unfortunately as there's floor void/air bricks next to it, so are stuck with R32!

[LiamJones]

I had to put in writing I only wanted heating downstairs, and then they only sized for heat loss downstairs, which I was confident after using Jeremy’s spreadsheet was more than enough for whole house heat loss. Otherwise they were going to way oversize. I’ve no emitters upstairs so it all sort of worked out. This was under BUS scheme

[zzPaulzz]

Although initially concerned my heat geek engineer is now confident my system will qualify for the BUS even though I have no emitters upstairs. The ASHP is sized for heating the whole two storey house using the ground floor in-slab UFH. He has said I need to minimise insulation between floors though to allow heat to rise. I have a full height entrance hall and MVHR which will help. 

[JohnMo]

2 hours ago, zzPaulzz said:

MVHR which will help

MVHR is unlikely to help that much, flow rates are just to low. But warm air is lighter so will rise via any open spaces.

 

Have you thought about bedroom cooling?

[zzPaulzz]

Agree with both those points. I have roof lights to help with passive cooling. Might also use the ASHP to cool the slab a little during heat extremes (being careful to avoid the dew point). 

[JohnMo]

32 minutes ago, zzPaulzz said:

Might also use the ASHP to cool the slab a little during heat extremes (being careful to avoid the dew point

We run ours 24/7, it's way more effective as the whole house temperature stabilises. Running for short periods isn't very effective and cost more. Bit like heating with ASHP.

 

 

This is the other day, basically managing UFH return temp. The heat pump reacts to demand. So this day was down to 5 degs at night, heat pump just circulating. You can see return drop (green line), as day gets hotter (we get solar gain and more PV generation) the heat pump starts managing floor temp. 

 

 

[JohnMo]

Another image on a hotter day and night. Looks like a lot of cycling but reality is just over one cycle per hour. Big spikes are DHW heating.

 

House still gets warm, but recovery is a lot quicker, and more importantly, it doesn't feel overwhelmingly hot, as it would pre cooling. It's not Aircon, but no air blowing either.