28mm copper vs .....?

[Jenni]

Hello. 

My pipework from the ASHP to the UVC and 2 manifolds is spec'd to be 28mm copper.

I've spoken to several plastic pipe suppliers, who all say the plastic is smaller internal than copper. 

I checked with my heating designer, they say not to risk the restriction and to either use 28mm copper or up size the plastic. 

I'm keen to use plastic due to the reduced joins involved. My pipe runs are unavoidably long, hence the diameter. 

 

Am I stuck with copper or is there an alternative? 

Thanks. 

[dpmiller]

many bends? If you could replace an elbow on copper with a smooth sweep of plastic I'd say the slight difference in ID would be lost.

[ProDave]

I used 22mm copper and it proved too restrictive and I had to add a second pump to get enough flow rate. So don't cut corners.

[Conor]

You want 32mm barrier pipe, like this:

 

https://ingoodnic.uk/25-25-90mm-21.html

 

or

 

https://www.underfloorheatingtradesupplies.co.uk/32mm-rifeng-wras-approved-pert-al-pert-multilayer-composite-pipe-x-25m.html

 

with flexible pipes, you can reduce the number of bends as well.

 

[PeterW]

28mm Hep2O will be fine, just try not to use too many elbows. The flow paths in the H-Ex in the ASHP will be 3-5mm so the difference between 28mm Hep2O and 28mm Copper is negligible in the big scheme of things

[JFDIY]

When I looked into 28mm plastic it was quite a bit smaller internally and only came in 3m lengths so you have lots of joins anyway, I have used copper

[Conor]

As resistance squares with velocity, even a small difference in diameter can have a big impact on pressure loss.

 

If you know the intended flow rate, the length of pipe, and the diameter options, you can calculate pressure loss in Excel..

 

https://heatpumps.co.uk/2014/02/20/potential-perils-of-plastic-pipe/

 

 

 

 

 

 

[PeterW]

1 hour ago, JFDIY said:

When I looked into 28mm plastic it was quite a bit smaller internally and only came in 3m lengths so you have lots of joins anyway, I have used copper

 

https://www.bes.co.uk/hep2or-barrier-pipe-coil-white-28mm-x-50m-v2-20764/

 

It is about 1/2 the price of using copper for the same diameter.

[Nickfromwales]

2 hours ago, JFDIY said:

When I looked into 28mm plastic it was quite a bit smaller internally and only came in 3m lengths so you have lots of joins anyway, I have used copper

Hep is available in 6m lengths too. Quite handy for small projects where you don' want to buy a big coil but want to traverse a room / space without intermediate joints.

 

eg

Edited July 22, 2020 by Nickfromwales

[joe90]

Ah, I only used 22mm copper or hep and had no problem.

[Jenni]

5 hours ago, dpmiller said:

many bends? If you could replace an elbow on copper with a smooth sweep of plastic I'd say the slight difference in ID would be lost.

I need to put copper through the wall, I think those tails can be curved so that the plastic that comes down the internal wall joins it straight. The plastic is then straight with a few sweeps round to the uvc. 

 

5 hours ago, ProDave said:

I used 22mm copper and it proved too restrictive and I had to add a second pump to get enough flow rate. So don't cut corners.

This is my worry. I'd rather overspec now than find issues later on. 

 

4 hours ago, Conor said:

You want 32mm barrier pipe, like this:

 

https://www.underfloorheatingtradesupplies.co.uk/32mm-rifeng-wras-approved-pert-al-pert-multilayer-composite-pipe-x-25m.html

 

with flexible pipes, you can reduce the number of bends as well.

 

That second link looks like just the thing. Thank you. ?

 

4 hours ago, JFDIY said:

When I looked into 28mm plastic it was quite a bit smaller internally and only came in 3m lengths so you have lots of joins anyway, I have used copper

I've found some on a 50m roll, but the smaller inner diameter is a risk I don't want to take. 

 

Thank you all for replying. Hopefully the stuff in Conors link will be suitable. 

[PeterW]

Which ASHP is it and how far are you needing to go @Jenni..? Unusual to see 28mm as spec as it is a serious increase over 22mm which is standard so would like to know who specs that size 

[Jenni]

It's a NIBE F2040-8

About 18m

[dpmiller]

so only 8kW then?

[PeterW]

Can’t see why 28mm has been specified - the Nibe needs 0.29l/s minimum flow on defrost which is just over a cubic metre per hour. On 36m of pipe at that flow rate the head loss is 21.6KPa so a circulation pump would need to run at approx 3.2m head on 22mm pipe . That’s well within the capability of a 6m circulation pump. In standard heating mode it is 2.52KPa (0.11 l/s)
 

I checked the difference with 28mm copper vs Hep2O and it’s about 0.01kpa/m which is pretty negligible using Lamont’s 

[Nickfromwales]

32mm DuoPrimo underground every tme for me, and 28mm above ground, to a low loss header for unrestricted flow switch operation, is my benchmark. 
For the minimal uplift in costs it just isn’t worth counting bends and working out other such adversities afaic to warrant using 22mm. If the ASHP is more or less back-to-back with the plant location then it could be agreed that the uplift was unnecessary.

You'll save very little going to 22mm, so go for 28mm IMO. 

[Jenni]

It seems the 32mm pex-al-pex linked above is a comparible price to 28mm Hep2o, are there any reasons not to use the larger diameter pipe?

 

Are fittings available to connect 32mm pex-al-pex to copper pipe?

 

I worry that if I use the 28mm as you guys suggest, if there are any issues with the system, the supplier will site the 'incorrect' pipe and I'll be left high and dry. 

 

[PeterW]

47 minutes ago, Jenni said:

Are fittings available to connect 32mm pex-al-pex to copper pipe?

You’ll need to check as they may need Eurocone type fittings and they are not easy to find. Also may need inserts 

[Jenni]

Well blow me, I fired off an email to Underfloor Heating Trade Supplies to ask about fittings, not expecting a reply until Monday at the earliest, but I have a reply already.

https://www.underfloorheatingtradesupplies.co.uk/32mm-pex-al-pex-compression-to-28mm-copper-compression.html

 

Can anyone forsee any issues if I use this 32mm pipe and the compression fittings to attach to 28mm copper?

[Nickfromwales]

On 22/07/2020 at 15:22, Jenni said:

I checked with my heating designer

And you’ll need to do the same again. We can’t speak for them, bit technically it will be absolutely fine. 

[PeterW]

Unless there are a lot of bends, an 8Kw ASHP will be fine on 22 or 28mm. 18m is nothing in terms of distance and you may find that increasing the pipe size will cause low flow issues unless the pump is able to push some serious flow. 

[Nickfromwales]

The ‘head’ will be negligible though, no?

[Onoff]

59 minutes ago, Nickfromwales said:

The ‘head’ will be negligible though, no?

 

Tell me about it!

[PeterW]

2 hours ago, Nickfromwales said:

The ‘head’ will be negligible though, no?

Won’t matter. The issue will be that the flow orifice in the flow switch will be calibrated for a minimum flow. Even at 1m head (ie very little restriction) the pump will have to move 210% times the volume through a 32mm pipe to a 22mm pipe so your rate of heat transfer will be much lower. Circulation pumps are also incredibly poor at creating pressure so in going upward in size you don’t actually help yourself. If it was a diaphragm pump it would be different, and there is a point at which a larger pipe has a significantly adverse effect on performance.