Ducting into a passive slab

[Nick1c]

The EPS is about to be laid for our slab and I would like to check what needs to be brought in through it & how. 

The house will be all electric with an ASHP situated directly outside the plant room.  It is being built from panels pre-filled with warmcell and will be timber clad. 

Water - 32mm MDPE into the plant room. Does the MDPE need protection in the concrete?

Electricity - ducting for armoured cable to the consumer unit. 110mm soil pipe with swept bends? Or does it need to be black? 

BT - ducting supplied by them. 

ASHP - either 2, 75mm, ducts for flow & return plus one for power & comms, or none & do everything through the wall?

Pv - no idea how that comes in. We will have a smallish loft space at one end of the house. Is it sensible to bring all the cabling to the inverters into it & site them there so it is easy to check individual items for failures?

 

WRT sealing the ducts is it just a sprayfoam job, or is it worth filling them with eps beads? How do you stop them filling with water before they are sealed, or do you just not worry about it?

 

Any information gratefully received.  

 

[jamieled]

Might be worth ducting the water pipe. Otherwise, with the exception of the ashp that's fairly similar to me. I taped plastic over the end of our ducting to prevent water and muck ingress.

[Jeremy Harris]

Tape or plastic bags taped over the ducts will temporarily seal them.  Once cables, pipes etc are in the ducts they can be sealed with a ball of chicken wire, fitted with a length of fencing wire as a pull, push down the duct and then filled with spray foam, leaving the pull wire accessible through the foam if you ever need to get the plug out.  The chicken wire embedded in the foam will act as a rodent barrier (rodents can very easily chew through spray foam).

[Onoff]

5 minutes ago, JSHarris said:

rodents can very easily chew through spray foam

 

As can birds and bees/wasps.

 

Lent my mate my foam gun to do gaps around his windows and he did some holes in the outer block wall too. Birds pecked it out to get in and bees/wasps too. Maybe previous/existing nests in the cavity they wanted to get to?

Edited September 16, 2019 by Onoff

[Jeremy Harris]

When we had a big wasp nest treated at the old house the chap doing the job told us that he'd heard of a case where someone had sealed up the entrance to a wasp nest in a loft and the wasps had chewed through a plasterboard ceiling, and filled the bedroom below.  If true, then I'd guess a bit of foam wouldn't be too much of a challenge for them at all.

[jamieled]

I can vouch for the fact that they can get through our chipboard walls in the caravan!

[Nick1c]

Would it work going through the wall for the ASHP, or are we better ducting it in?

Does the power duct need to be black & is 110mm soil pipe overkill?

What about the Pv?

[Jeremy Harris]

24 minutes ago, Nick1c said:

Would it work going through the wall for the ASHP, or are we better ducting it in?

Does the power duct need to be black & is 110mm soil pipe overkill?

What about the Pv?

 

 

For the flow and return pipes, plus cables, for the ASHP, then it's best, IMHO, to put them in underground if you can, as it makes for a neater installation.  Might be an idea to just run pre-insulated pipes in now, as pulling insulated pipes through ducts isn't that easy.

 

The PV connections depends very much on the layout and where your consumer unit and PV panels are in relation to each other.  If possible it's best to have the inverter outside the heated envelope, ideally somewhere cool, as you don't want the heat from the inverter inside the house when it's running at full power.  Also, the cooler the inverter the more reliable it will be.

 

If the power cable is your own, running from an external meter cabinet isolator to the internal consumer unit, then you can use whatever duct you like.  If it's the DNO's cable then they usually insist on the duct being black (but not always).  I ran our three core 25mm² SWA in through a length of 63mm flexible duct.  It needs gentle bends, as the cable is fairly stiff.  110mm soil pipe seems to be overkill for this size of cable to me, plus it will look like a foul drain, rather than an electrical duct.  Remember to put warning tape above the buried duct in the trench.

[jack]

Have you seen the threads below?

 

One thing that I'm less than happy about with going through the under-slab insulation is the transition from the ASHP feed and return into the ducts under the slab. We used Hep2O barrier pipe in a duct through the slab as described in a couple of the threads below, which meant a right angle HEP2O connection was needed just outside the vertical plane of the wall. Nothing wrong with that, but the elbow is very low relative to the surrounding ground, which made it a little awkward the insulate. Ideally you need to think about how you're going to insulate and protect this area longer term given its position.

 

Other than that, this arrangement works well. 

 

 

 

[joth]

6 hours ago, Nick1c said:

Water - 32mm MDPE into the plant room. Does the MDPE need protection in the concrete?

 

Do you want the kitchen cold water to be colder than room temperature without running the tap?  If so, you may want to run the pipe from plant room to kitchen under the EPS too. Trade off of more penetrations in the membranes vs longer time running the tap to get cold -- so more of an issue if you have a long distance from plant rm to kitchen

 

 

[Nick1c]

@jack I did have a look back, but not far enough so thanks for the links. I have decided to go through the wall for the ASHP, it allows more flexibility. 

I am using a hockey stick bend to bring the water pipe up so it sits easily. 

The electrician has asked for 100mm pipe to pull the armoured cable in. As the ffl is below the level of where the duct will start I assume I should drill some drain holes where it is sitting in the MOT to stop water getting in the house!

@JSHarris would the loft area be too hot? There will be 400mm of warmcell above it so the only real issue I can imagine is if the inverters generate a lot of heat. There will be MVHR ducting up there so I assume it could be ventilated to a degree if that would help. Where do these things normally go?

@joth thank you. The house is reverse level with the kitchen above the plant room so hopefully not a problem. 

Edited September 16, 2019 by Nick1c
For clarity

[MikeSharp01]

2 hours ago, JSHarris said:

 

For the flow and return pipes, plus cables, for the ASHP, then it's best, IMHO, to put them in underground if you can, as it makes for a neater installation.  Might be an idea to just run pre-insulated pipes in now, as pulling insulated pipes through ducts isn't that easy.

We didnt duct the ASHP pipes through the slab, felt like  phaff, but decided to run them through and along inside the walls, timber I joists, so the insulation in the walls insulates the pipes.

[Jeremy Harris]

16 minutes ago, Nick1c said:

@jack I did have a look back, but not far enough so thanks for the links. I have decided to go through the wall for the ASHP, it allows more flexibility. 

I am using a hockey stick bend to bring the water pipe up so it sits easily. 

The electrician has asked for 100mm pipe to pull the armoured cable in. As the ffl is below the level of where the duct will start I assume I should drill some drain holes where it is sitting in the MOT to stop water getting in the house!

@JSHarris would the loft area be too hot? There will be 400mm of warmcell above it so the only real issue I can imagine is if the inverters generate a lot of heat. There will be MVHR ducting up there so I assume it could be ventilated to a degree if that would help. Where do these things normally go?

@joth thank you. The house is reverse level with the kitchen above the plant room so hopefully not a problem. 

 

 

Ideally you want the inverter outside the heated envelope, I'd definitely not want one sat inside a well-insulated loft space.  They do give out a fair bit of heat, around 5%  of the power output, and that heat has to go somewhere.  If the inverter is inside the heated envelope then the heat won't have anywhere to go, so will just end up warming the space up and reducing the ability of the inverter to lose heat.  

[joe90]

40 minutes ago, JSHarris said:

Ideally you want the inverter outside the heated envelope, I'd definitely not want one sat inside a well-insulated loft space.  They do give out a fair bit of heat, around 5%  of the power output, and that heat has to go somewhere. 

 

Seems a shame to waste that heat when we go to all that trouble to use less energy, is there not some way to duct it into the MVHR (apart from when summer bypass is on)?

[Jeremy Harris]

29 minutes ago, joe90 said:

 

Seems a shame to waste that heat when we go to all that trouble to use less energy, is there not some way to duct it into the MVHR (apart from when summer bypass is on)?

 

The snag is that the heat is mainly available when you least need it, when it's sunny and the panels are generating a lot.  In winter, when you could usefully use the heat, the chances are that the panels won't be producing much power, so the inverter won't get very warm.

[Nick1c]

Thank you. 

[Jeremy Harris]

I mounted our inverter outside, on the North facing wall, so it stays nice and cool (most are available as an outdoor version for little or no extra cost).  The hottest I've ever seen it is about 45°C, which is pretty cool for an inverter (it's not uncommon for their heat sinks to run at well over 60°C).  Very roughly, every for 10°C cooler the inverter runs just about doubles the life of the commutation capacitors,  which are one of the most common failure modes.  The inverter is out of sight, around the back of the house, and it was easy to run the DC cables from the panels over the ridge and down the other side and out the eaves.  The DC cables are run inside flexible conduit,  that runs behind the slate battens and over the top of the membrane.  The only cable that then has to penetrate the house is the AC cable in to the services room to the generation meter and consumer unit.  This single cable comes through wall inside a bit of 25mm conduit, that's sealed up well at either end.