Heat pump calculation load

[JohnMo]

Just now, SBMS said:

conscious that that it's not part of Jeremy's spreadsheet.

Spreadsheet is targeted at well insulated pretty airtight. 

 

2 minutes ago, SBMS said:

0.58ACH50 this is 574 watts of additional heat required from the ASHP

But it's about being in the right ballpark, you will not get to exactly the heat losses to match the heat pump output. In 24 hrs you have moved from is 16kW plus ok, to now knowing that about 5 to 6kW is a better estimate. The 2 hrs off time for DHW gives you wiggle room, you can always flick the immersion on for DHW

 

11 minutes ago, SBMS said:

assume that MCS when doing their sizing calculations should take into account the AP50 (or ACH50) targets to generate an accurate figure?

They will need as built test data to even consider it, some will not from what I have seen.  So will not be interested in target figures.  So everything just happens in the wrong order for the grant and getting a well sized heat pump. Just buy a Panasonic heat pump.

[SBMS]

56 minutes ago, JohnMo said:

But it's about being in the right ballpark, you will not get to exactly the heat losses to match the heat pump output. In 24 hrs you have moved from is 16kW plus ok

Yes @JohnMo you're 100% right.  So easy to get lost in the detail though.

 

56 minutes ago, JohnMo said:

They will need as built test data to even consider it, some will not from what I have seen

It's a fair point and perhaps I'm being a bit critical on them. I suppose last thing they want is to install something undersized or risk their MCS.

Can they design the underfloor heating (e.g. the number of loops and energy output of the UFH) without knowing the 'as built' heat requirements though? I'd be happy for them to quote at the stage of wind and watertight if they needed to know the actual as built insulation and airtightness figures...

[JohnMo]

1 hour ago, SBMS said:

Can they design the underfloor heating

Can't see why they couldn't, floor output is just a matter of average flow temperature. So if they put 100mm centres in the heat pump doesn't really care, you just flow at close to 25 degs, even though they had a design flow. They would insist of heating in all room and all heated by the heat pump. Think you would get blank looks from a lot of installers if you mention fan coils.

[SBMS]

40 minutes ago, JohnMo said:

Can't see why they couldn't, floor output is just a matter of average flow temperature. So if they put 100mm centres in the heat pump doesn't really care, you just flow at close to 25 degs, even though they had a design flow. They would insist of heating in all room and all heated by the heat pump. Think you would get blank looks from a lot of installers if you mention fan coils.

Yes that’s my worry. I guess if they spec an emitter size for rads I can just guide them to installing a fan coil. 
 

What if the UFH needed a higher output overall (say 4kW instead of 3kW when they had the as built, because air tightness went to s**t) than the loops were designed for? Are you saying they would just increase flow temp? Is that suboptimal as opposed to reducing centers and putting more pipe in?

[JohnMo]

1 minute ago, SBMS said:

What if the UFH needed a higher output overall (say 4kW instead of 3kW

Really it makes very little difference with UFH. Once your at that level of output your talking 1 or 2 degs difference in flow temp. We have 300mm centres across 190m², just 7 loops, -6 last night our flow temp was 32. UFH spacing is more about reaction time to heat input. Chart to allow you to compare different spacing flow temps and outputs 

 

 

 

[SBMS]

3 minutes ago, JohnMo said:

Really it makes very little difference with UFH. Once your at that level of output your talking 1 or 2 degs difference in flow temp. We have 300mm centres across 190m², just 7 loops, -6 last night our flow temp was 32. UFH spacing is more about reaction time to heat input. Chart to allow you to compare different spacing flow temps and outputs 

 

 

 

That’s really interesting @JohnMo - it looks like I’d need roughly 40 watts per sqm to do no upstairs heating. That’d be pretty wide spacing and still maintaining a low flow temperature for the 29 degree differential. I wonder what spacing they would ordinarily use. It’ll Probably be over specified.