ASHP for barn conversion.

[Craigjm]

Hi,

 

We are currently building a 4 bed barn conversion.

 

We are looking into heating options and was wondering if an air source heat pump is the way to go?

 

Current insulation is as follows.

 

250mm concrete raft slab with 150mm under slab insulation.

 

Double skin breeze block wall with 100mm cavity and 50 king span insulation panels.

 

150mm kingspan ks1000rm insulated roof panels.

 

Possible double or triple glazing.

 

If anyone has any info that would be greatly appreciated.

 

Thanks 

 

[IanR]

There's no reason why not.

 

Best coupled with UFH for the ground floor.

 

Are you saying it's a ground bearing, insulated slab and no screed?  If so, do you really need to go 250mm thick everywhere? Could it be engineered down to 100mm in areas not taking a load, so that you are heating up less volume of concrete to increase its reaction time. Less concrete and more insulation is better for the performance.

 

Have you had any heat loss calcs done on the conversion.  A correctly sized ASHP will be more efficient and potentially last longer.

 

 

[Craigjm]

 

23 minutes ago, IanR said:

There's no reason why not.

 

Best coupled with UFH for the ground floor.

 

Are you saying it's a ground bearing, insulated slab and no screed?  If so, do you really need to go 250mm thick everywhere? Could it be engineered down to 100mm in areas not taking a load, so that you are heating up less volume of concrete to increase its reaction time. Less concrete and more insulation is better for the performance.

 

Have you had any heat loss calcs done on the conversion.  A correctly sized ASHP will be more efficient and potentially last longer.

 

 

 

Yes we have been quoted for underfloor heating up stairs and down stairs.

 

There is no screed yet, the slab has been formed as specified by the engineer/architect to bear the load of a steel portal frame,we are currently building the block work at present.

I was thinking of adding another layer of 50-100mm of insulation before UFH installation and screed.

 

As for the SAPS we have only had the preliminary ones done.

 

Thanks.

[IanR]

That's a shame, the slab could almost definitely have been done with less concrete, with UFH integrated and no screed.

 

Not sure I understand about the steel frame. Have you knocked down and rebuilt, or "underpinned" the original foundations? I'd expect them to be on individual foundation pads (without insulation), but if you've found a way to get insulation underneath the steel columns then that's a plus. Be interested to know how it was achieved.

 

If the slab is in already, then I'd suggest as much insulation as possible under the screed to thermally break the screed from the slab, so that you are not heating it up.

 

Have you got the cavity of the outer walls, outside of the steel columns, so that steel frame is inside the thermal envelope of the house? If so you've managed to avoid another of the issues of converting a steel framed shed.

 

What's the SAP suggest your peak energy losses are?

Edited January 17, 2022 by IanR

[saveasteading]

33 minutes ago, Craigjm said:

the slab has been formed as specified by the engineer/architect to bear the load of a steel portal frame

As IanR....

I think there may be  a misunderstanding.

A portal frame would normally sit on a concrete pad arrangement, with one to each column about 1m deep, and perhaps about 1m2.

A 250mm slab is much thicker than the average warehouse requires, with loading 8m high, but still not suitable for a portal frame. However the insulation under such a floor would crush with the weight. So I am much confused.

 

What dimensions are the building (approximately) and how far between portals? 

[IanR]

I looked back at your earlier post

 

 

And it maybe making a bit more sense. Did you go with the Castleform raft and have to underpin the Steel columns to get the floor level lower?

 

I thought Castleform insulated rafts were similar to Advanced Foundation Technologies' and Kore, where they were generally 100mm thick, only going deeper where the loads are. And, provide the finished surface with no need for the screed.

If this is the route you went, have you got any photos of the slab going in. I have another barn to do and am looking at how I get an insulated raft under the existing oak/elm frame.

[Steve247]

I’d go for 250mm insulation under 150mm concrete raft slab.  Get it power floated too so no need for levelling compound and eliminate another trade, cost and time factor. 
150mm Conc slab will be a good thermal mass. 
I personally would go for rads upstairs incl bathrooms which have much quicker reaction times and minimal heat mass (hard to get rid of) which you don’t really want in bedrooms. 

[saveasteading]

OK I see now that the slab is a structural solution to retaining the frame. So I think, uneconomic as it seemed. it is probably a clever solution.

I had not heard of this method before so any photos or drawings would be appreciated, for my interest but may help towards a fuller answer to your query.

[ReedRichards]

10 hours ago, Steve247 said:

I personally would go for rads upstairs incl bathrooms which have much quicker reaction times and minimal heat mass (hard to get rid of) which you don’t really want in bedrooms. 

 

Rads requiring a higher water temperature than UFH?  So rads at the expense of economy of heat pump operation?  Or super large area rads that can work at the same temperature as the UFH?

[saveasteading]

3 hours ago, ReedRichards said:

super large area rads

 

[Cpd]

Are there not rads specifically designed to work with the lower temperatures that ASHP provided……. I hope so as this is where I am heading….. 

[TW9]

You can get fan assisted rads that work with lower temperature water. We have them. They work well but are expensive and having the fan come on in the bedroom in the night, if it gets cold, isn't ideal. I would probably go for big conventional rads.

[ReedRichards]

20 minutes ago, Cpd said:

Are there not rads specifically designed to work with the lower temperatures that ASHP provided……. I hope so as this is where I am heading….. 

 

Not as such, no.  Radiators aren't hi-tech; you can give then lots of internal fins to increase the effective surface area and you can increase their output by blowing air through them with a fan - that's really it.