Ducting for ashp

[Pete]

Further to ducting post, what size ducting have people used for the flow/return pipes for the ashp as we are not planning on fitting the pump straight away. We will see how the house performs so would like to put the ducting in place for future proofing.

TIA

[jack]

I think I used 50mm polypropylene drainage pipe for mine.  Worked okay.

How are you planning to insulate?

[Pete]

Not looked at that yet but from previous post's would look at insulated pipe. Distance is about 7/8 metres each way. What type did you use and what diameter?

[IanR]

I used Rehau Rauvitherm twin 32 dia pre-insulated.

[jack]

On 17/05/2017 at 12:57, Pete said:

Not looked at that yet but from previous post's would look at insulated pipe. Distance is about 7/8 metres each way. What type did you use and what diameter?

 

As above, I used 50mm polypropylene drain pipe.  I then ran 28mm Hep2O pipe for the actual ASHP connections.  If you use plastic, you must be sure to use the type with an oxygen-proof barrier.

 

This approach was relatively easy for us, because our runs were completely straight (except where they come out of the slab in the plant room), and ran within the EPS under our slab, so didn't need separate insulating.

 

Where is yours running?  Underground?

[Pete]

Ours is a raft design. So the pipes can be laid between the xps insulation that is within the house and then there will be a short run from where the pipes leave the house wall to the ashp, approx 1 to 2 metres.

[IanR]

The pre-insulated pipe has a relatively large Min Bend Radii. The Rehau stuff we used needed a 1m deep trench to come up vertically through the slab.

[PeterW]

28mm pipe fits into 28/25mm Armaflex that feeds into 80mm duct ...

 

or 22mm pipe fits 22/25mm and 68mm rainwater

 

Both are DIY

[Pete]

Thanks guys

[dnoble]

Can I bump this topic please?

 

I have an MBC timberframe up and am frantically arranging first fix and window installation before insulation is blown in. 

I'm planning to use a sunamp product for hot water. 

 

I may or may not charge this with an ASHP, and may or may not connect an output from it to UFH (pipes installed)

 

Want to see how house performs first. Have 6kw Solar PV to install (though obv these won't provide much energy in winter)

 

I may not end up buying an ASHP but it's make sense to install a duct before the insulation goes in, cladding goes on etc just in case. 

 

As I haven't bought one, I dont know what size hole to make.

 

Are they fairly standard?

 

Is there just one duct or an inlet and outlet.

 

Would Jack's suggestion above of 50mm pipe suit most models? (could presumably temporarily fill it with some insulation if I don't use it)

 

Many thanks in advance

 

Dan

[Jeremy Harris]

I fitted out ASHP flow and return pipes after the house insulation was blown in.  Not a significant problem or hard to do.  I made a special very long (around 400mm) 6mm drill to drill a pilot hole right through the wall and insulation from the inside, sloping slightly down towards the outside.  I then used a 25mm hole saw to cut holes either side, through the panels.  To make a hole through the insulation I made a gadget from a bit of 25mm conduit with a conical end fitted to it that I turned up from a bit of ABS rod, but a bit of suitable dowel with a point carved on the end would do.

 

I then wiggled this tool through from the inside and it pushed aside the insulation.  The tricky bit was trying to get it to line up with the hole on the other side, but with perseverance I got through OK.  I them just ran 22mm copper pipes through the holes, sealing either side with sealant.  On the outside the pipe insulation is tight against the wall and glued in place with some sealant, after I'd made all the connections.

 

You could put conduits through the wall ready for the pipes, but you would have to be confident that you knew where to put them - I hadn't a clue, as at that stage I'd not bought the ASHP and didn't know where it was going exactly anyway.  If putting conduit in the walls then I don't think you need to make them as large as 50mm, a bit of 32mm waste pipe would probably be fine.  To temporarily fill and insulate it, put a plastic bag inside the duct, spray some water into it, then squirt in some expanding foam (the water will ensure it cures inside the sealed bag).  That should give you a tight fitting insulated plug that can be pulled out when you want to fit the pipes, as there will be the plastic bag between the foam and the duct, to stop it sticking.  After fitting the ASHP pipes you can use expanding foam to insulate around them in the ducts.

[dnoble]

Thanks for this Jeremy. 

That sounds ingenious, though I wouldn't describe making a special drill as simple compared to pre-installing them!  Good to know it's do-able though.

The positioning of the pipes is an important point, though. Presumably using some flexible pipe between the unit and the duct-through-the-wall would provide some flexibility around this?

I like the wet bag in the pipe idea too..

[Jeremy Harris]

You need to have long flexible pipes between the ASHP and the house wall, if it's going to be located fairly close to the house, but those flexible pipes need to bend around in a loop so they don't transmit vibration into the house structure (I found this out the hard way and had to replace mine).  This means you have some leeway when it comes to positioning pipes, and you could always run short length of insulated rigid pipe along the outside of the wall to get the terminations for the long flexible pipes in the right place.

 

There's a bit in our blog about the need for long flexible pipes for the ASHP, part way down this entry: http://www.mayfly.eu/2014/07/part-thirty-one-its-slow-going-on-your-own/