Another ASHP flow and return question

[Mr Blobby]

So I'm trying to finalise services through the KORE slab and would like some help on heat pump and manifold connections please.

 

So, for context, the house is masonry (250) cavity on kore slab to passive standard.

ASHP will sit outside the plant room at the rear of the property.  UVC and buffer tank in plant room.

UFH manifold in centre of house under stairs.

 

Two questions:

 

1.  ASHP flow and return, is it:

(a) 32mm pre-insulated FR pipe through floor to ASHP.  Its rocky at about 400mm and so with the bend radius requiring a deep hole is it worth it?

or

(b) seperate plastic insulated pipes through a hole in the wall.  This seems simpler, but what about airtightness etc?  Do I build in a pipe or core drill after?  Does that matter?

 

2. Flow and return to UFH manifold from buffer tank.

What pipe specification?

Where to run it.  Within the floor insulation or under the insulation?  Or not in the floor?

 

 

Please help me decide before I meet the plumber and builder to decide this stuff next week. (who will probably ask me why I'm not installing an oil-fired boiler like everyone else 🙄)

 

 

Edited March 29, 2023 by Mr Blobby

[Nick Laslett]

I think with the ASHP being on the same wall as the plant room, a pipe connection through this route would be the more simple option. I have the 32mm insulated pipe under the foundation, and its bend radius makes locating it in the ideal location a real challenge. Air tightness is easily covered.  You might even struggle to get the insulated pipe to fit looking at your floor plan. 

[JohnMo]

I would copper pipe through wall airtight expanding foam and the a bead of sealant between pipe and wall.

 

[JohnMo]

Not sure of your flow rates, but a flexible hose to 28mm then through wall.

[markocosic]

Through wall in 28 mm copper for <10 kW.

 

You'd core through larger (say 70-80 mm), lag the pipes through the hole with the watertight/airtight lagging, then foam between the lagging and the masonry.

 

 

 

 

[Mr Blobby]

The plumber wants the flow and return to go through the slab, which I'm ok with (the ASHP has moved a little further away from the entry point), but plumber has told builder to put in a 160mm pipe and then run 2 * 28 mm plastic pipes through it.  160 mm sounds like overkill.  Is it? 

 

The 160mm pipe is big, and the long radius bend is long. Think pi r2

 

The question is then, will the two 28mm pipes, with insualation like armaflex or whatever, fit through a long radius 110 bend ok?  Or should I do what the plumber wants and put a 160mm bend in the floor?

 

Edited April 13, 2023 by Mr Blobby

[TonyT]

2 pipes with insulation passing through the hole plus a couple of cables too.

 

[Mr Blobby]

1 hour ago, TonyT said:

2 pipes with insulation passing through the hole plus a couple of cables too.

 

So 110 is big enough?

Edited April 13, 2023 by Mr Blobby

[IanR]

2 hours ago, Mr Blobby said:

The question is then, will the two 28mm pipes, with insualation like armaflex or whatever, fit through a long radius 110 bend ok?  Or should I do what the plumber wants and put a 160mm bend in the floor?

I used 32/150 Rauvitherm pre-insulated twin duct from Rehau. I don't think you'll get the same performance if you make it up yourself.

 

 

Ref. https://www.rehau.com/downloads/1042866/district-heating-technical-information.pdf

 

They don't do a Ø28 version though, but the Ø32 connectors/adapters were easy to come by.

[TonyT]

I’m all for making life easy, so oversizing penetrations to give a bit of wiggle room, best to confirm with your plumber, your concerns as he’s doing the job not us!

[PeterW]

28x25 Armflex on 28mm PEX is going to give you a 78mm wide pipe that won’t fit side by side with another down a 110mm duct, and will be tight in a 160mm too. Going down to 28x19 is still 66mm, anything less and the heat loss is substantially greater.

 

I’d be going with the pre-insulated stuff and getting it in now as it’s a pain in the arse to get 28mm PEX through ducts at the best of  times.

[Nickfromwales]

10 hours ago, PeterW said:

28x25 Armflex on 28mm PEX is going to give you a 78mm wide pipe that won’t fit side by side with another down a 110mm duct, and will be tight in a 160mm too. Going down to 28x19 is still 66mm, anything less and the heat loss is substantially greater.

 

I’d be going with the pre-insulated stuff and getting it in now as it’s a pain in the arse to get 28mm PEX through ducts at the best of  times.

I've just done the same pipe / insulation detail on my current job, and I just drill 2x 78mm core holes and put 1x through each hole. @Mr Blobby wont even have to core drill, just install the ducts as he's going. But core drilling afterwards, which is what I'd do ( so they can be pin-point accurate ) will be 1 hour or less, if you drill slowly!

For me, it would be pipes and cables punched out retrospectively, and the pipes surface mounted in the plant room. IMHO, this is too short a run to be faffing about with the big Duo pipe.

[JohnMo]

I just did underground duct, used 28mm Hep2O pipe, 25mm thick black insulation, which I wrapped in aluminium tape, and inserted each length in 110mm flexible twin wall duct.  Made 2 x 4m lengths.  Terminated the duct at both as they went in to our out of ground.  Used stainless steel mesh spray foamed in place at each end of the duct to stop rodents making their way into to duct. The pipe was taken the through wall about 300mm above ground at both ends, into house and into shed the other end. Exposed pipe will be wrapped UV stable insulation.

 

[Mr Blobby]

And the winner is...  Though the wall.

 

We were originally going to follow the plumber's recommendation of both pipes through a single 160 long range bend but in practive the bend radius was massive and would mean the pipes emerge too far from the exernal wall outside.

 

Questions:

1. Should the conduit (we will be blowing balls into the cavity) be built in or core drill the wall later.  Building in seems better, is it? 

 

2. How high up? (I assume about 40cm)

 

3. Two holes or one? 

I see @Conor and others did a single 100mm conduit for both pipes then foamed it.  I guess two 50mm conduit would be ok too, and easier to build in. 

 

 

Edited May 18, 2023 by Mr Blobby
crap spelling and grammar

[Conor]

@Mr Blobby reason for a single hole was because ours is through the basement tanked wall, fewer potential points of failure. And drinking through 200mm of RC isn't easy 

[Mr Blobby]

10 minutes ago, Conor said:

@Mr Blobby reason for a single hole was because ours is through the basement tanked wall, fewer potential points of failure. And drinking through 200mm of RC isn't easy 

 

And did you weather seal it on the outside?  (Sorry if this is a stupid question)

[Conor]

1 hour ago, Mr Blobby said:

 

And did you weather seal it on the outside?  (Sorry if this is a stupid question)

Yes, foamed, airtight paint on the inside and tanking tape on the outside. Nothing getting through.

 

[Mr Blobby]

Reading other threads on this and it looks like 28mm in armaflex through 80 mm conduit build into wall.  How does that sound?

 

What about the power, another conduit through wall to the isolator switch outside? What diameter?

 

So three holes then.

 

Is there any value in positioning the ASHP on the East wall instead of North to get some sunlight in the morning?  I have options here.

 

[JohnMo]

Just make sure anything sticking out of the wall exposed to UV, is UV protected. Normal armaflex isn't UV stable.

 

It may make a small difference on the east wall, but it's air temperature that's important and that doesn't really change.  Also make sure the temperature probe on the ASHP isn't exposed to the sun as it screws up your weather compensation curve.