Any underslab requirements for ASHP???

[connick159]

Hi guys,

Have a quick question about whether I need to provision any pipes etc under the slab in prep for air source heat pump?

 

We are due to pour the slab later this week and we've changed our minds from using oil to going ASHP for underfloor heating and DHW.

 

What I'm trying to find out is if I have to allow for pipes for the ASHP now before I pour the slab or can all that be done later?

 

Make up of flooring is as follows:

1. Hardcore

2. Sand Blinding

3. Membrane

4. Concrete slab

5. Insulation

6. UFH

7. Screed.

 

Any help would be greatly appreciated. Thanks in advance.
 

Edited July 15, 2019 by connick159

[Jeremy Harris]

It very much depends where you are going to site the ASHP.  Ours sits around the back of the house, a foot or so away from the wall, and I just ran the pipes through the wall, so no need to put them in the slab. 

 

Out of interest, had you thought about reversing the order and putting the UFH pipes in the slab?  We did this and it works well.  From the bottom up we have compacted type 3, grit blinding, 200mm of EPS insulation, DPM, 100mm of EPS insulation, 100mm concrete slab, with steel fabric set in the centre and the UFH pipes cable tied to the steel before the pour.  we also have 200mm of peripheral insulation around the slab to reduce the edge heat loss.

[connick159]

Hi, thanks for response,

I did think about ufh pipes in the slab but there was no one around here used to doing it that way so I ended up going slab the insulation then screed. I was interested in same as you but decided to stick with what they know around here.

We definitely don't have as much insulation either as I struggled on several fronts for design. We are restricted in height (small quarry mans cottage in a conservation zone so not allowed to exceed existing ridge height) and also can't dig down too much as both water table and unstable clay if we went to far. Upshot is we have opted to stick with just enough insulation as we can manage while keeping under height restrictions. In hindsight I should have pushed more for the ufh in slab as we could have got 50mm extra I place of slab but found it hard enough getting trades here as it is.

Thanks again.

 

[joe90]

I originally wanted UFH pipes in slab but because of illness and other problems we ended up with slab, insulation then screed with UFH pipes (flow screed). It also depends where your manifold is compared to ASHP, I ran the pipes from the ASHP to the manifold between the two layers of insulation under the screed.

[connick159]

Thanks Joe, sounds like a good way to insulate the pipes.

Where does the manifold have to sit? Is it by the tanks on the inside of house? Not to sure how far the run from the ASHP to the tank will be yet as still unsure of location for both pump and tanks.

 

Cheers

 

[joe90]

8 hours ago, connick159 said:

Thanks Joe, sounds like a good way to insulate the pipes.

Where does the manifold have to sit? Is it by the tanks on the inside of house? Not to sure how far the run from the ASHP to the tank will be yet as still unsure of location for both pump and tanks.

 

Cheers

 

 

Centrally in the house is quite usual for the manifold simply to make pipe runs easier, ours is under the stairs, 8 mtrs from the buffer tank and ASHP gubbins.

[connick159]

Thanks Joe.

 

[Pete]

Not wishing to hijack this thread but my ever evolving DHW system plus UFH means I have not yet decided on which way to go with the source of heat. When we did our slab I put numerous 50mm ducts under the slab (Passive) for a means of getting pipes/cables in/out of the house but if I am now thinking of an ASHP then will I get pipes from the ASHP to the inside through this 50mm duct? I wish now I had put some of the pre-insulated pipe in just in case. 

(IF Mods think should be on a new thread please advise.)

[Jenni]

Hi, also tagging onto this thread as it seems like a relevant place. 

 

In attached pic of UFH pipes just installed, my ASHP is going to the left of the glass door. Current plan is to run flow and return in a void in the corridor ceiling (approx red route, but higher.) the 'bay' this end of the photo is lofted (warm), other 2 'bays' are vaulted. 

 

But this thread has made me wonder about running the flow and return within the 150mm concrete slab, in ducts directly above the UFH pipes, which will then be under reinforcing mesh. Following the red line approx. 

 

I can see several advantages -

- warmth from UFH pipes beneficial to ASHP? 

- ducts above congested UFH pipes mean less warm spots on floor. 

- ASHP pipes get to where they need to be without getting in way of anything else.

 

Disadvantages -

- slab depth reduced on route of duct. 

- tricky to penetrate wall with ducts and maintain DPM? 

 

Any thoughts would be very welcome. 

 

 

[john0wingnut]

When I renovated the current bungalow I am in, we had a beam and block floor put in, DPM, then 100mm insulation and UFH pipes fixed to the top of that in a 70mm screed.

 

The flow and return to the ASHP was channelled into the insulation layer, so I think they had 50mm underneath, then the pipe