ian192744

What large bore Plastic Primary Pipe for ASHP?

Recommended Posts

Hi all

I have a long convoluted primary pipe run from boiler location to airing cupboard , where the distribution to radiators occurs. Logically the change to ASHP best works with the ASHP outside where the boiler is, buffer tank in the airing cupboard  where the radiator distribution is.

A lot of the existing primary is 22mm, and it has loads of elbows (7-10 in each direction) . I think its about 30m  its "evolved" over time due to various incremental changes in the heating setup of the house. I cannot get over 0.8m3/hr (13l/min) on it regardless of using pump speed III, number of rads open etc. Existing pump is a grundfos alpha2 15-50/60. 

 

various ASHP fitters who have visited are all sucking their teeth at the problem, suggesting pumping in both directions or very high heads or "it has to be 28mm". Even with 28mm I don't think it works. certainly not if using plastic. however, I can find an new primary route which will be about 12m each way with 3-5 elbows, and the potential to make some of them swept bends if in plastic. Call it 35m in total from HP->Buffer->HP. I am likely to need a 14-16kw heatpump. so I'm using 58l/min as my flow target for a samsung 16kw. If I get away with less, great.

 

using https://heatpumps.co.uk/pressure+flow/simulator.html to do the maths.

58 l / min over 35m of pipe, 20% glycol, 35mm copper => head of 2metres -> easy for pump

switch to 28mm plastic (22.4m ID) we only get  34l min with the max of 5M head.

switch 28mm copper needs head of 4.8m to attain 58l/min with same .. just about ok.

35mm copper is of course ridiculously expensive and hard to work with. particularly as I intend to lay this run myself to save cost (I have some spare time).

28mm copper still not great from a cost or working on it point of view.

 

bottom line question - why I am here : is there a plastic pipe size and type suitable for CH primaries that is greater than 28mm, available from UK merchants? Obviously also one that you can get elbow, coupling and reducing (to 28mm at the ends) fittings for? any specific references appreciated!

 

ta

Ian

 

 

Share this post


Link to post
Share on other sites

I understood, for efficency, the shorter distance between the outside ASHP and the inside buffer tank was the important thing.

 

 

Share this post


Link to post
Share on other sites

Watching with interest as I'm currently deciding between 28mm copper and 28mm plastic for my approx 20m run from the monoblock to the buffer position.

 

Mine's for 26kW with a min flow of 2.5m^3/hr or 42lt/min...

Share this post


Link to post
Share on other sites

Personally I'd say that the high flow rates an ASHP requires would mean 28mm above 10kW for sure.

Share this post


Link to post
Share on other sites
22 hours ago, ian192744 said:

. I cannot get over 0.8m3/hr (13l/min) on it regardless of using pump speed III, number of rads open etc. Existing pump is a grundfos alpha2 15-50/60. 


How are you measuring this ..? 
 

That Alpha pump will struggle to get you 3.3m3/hr anyway so if you think you need that then you need a bigger pump. 
 

What is slightly incorrect is the use of the open pipe scenario as a heating system is a sealed system and the return flow “helps” the overall flow rates. 
 

23 hours ago, ian192744 said:

I am likely to need a 14-16kw heatpump. so I'm using 58l/min as my flow target for a samsung 16kw


Min flow rate for Samsung 16kW is 12l/min - have you read the MIs to get to the minimum flow ..?

 


 


 


 


 


 


 

 

Share this post


Link to post
Share on other sites

28mm hep2o has a wall thickness of 2.75mm so that’s a fair reduction in diameter  compared to 28mm copper with 0.9mm

 

however the hep2o will come in coils, so less joins, has elasticity which will help with noise/vibration.

 

you could buy 2 coils for a flow and return, insulate individually and then pull in, in a ‘oner’

 

i understand a 90 deg bend adds the equivalent of an extra 1 m of pipe.

 

 

 

 

Share this post


Link to post
Share on other sites
On 19/10/2021 at 18:12, Marvin said:

I understood, for efficency, the shorter distance between the outside ASHP and the inside buffer tank was the important thing.

 

 

I have to have a long run somewhere. If I put the buffer next to the ASHP then I'd have 15 metres from the buffer to the rad distribution point. so I've still got to move the heat to the rad distribution point over that distance, at a lower temp, so need higher flow rate . albeit that the flow rate of the HP would now satisfied by the buffer.

I also know that the rad distribution is quite complex as well - so if I can split the circuit in half and make one half of it "clean" then I'll be gaining. 

lastly, in my case putting the buffer next to the ASHP is  not that easy in terms of the physicals of the rest of the property.

Share this post


Link to post
Share on other sites
21 hours ago, PeterW said:


How are you measuring this ..? 
 

That Alpha pump will struggle to get you 3.3m3/hr anyway so if you think you need that then you need a bigger pump. 
 

What is slightly incorrect is the use of the open pipe scenario as a heating system is a sealed system and the return flow “helps” the overall flow rates. 
 


Min flow rate for Samsung 16kW is 12l/min - have you read the MIs to get to the minimum flow ..?

 


 


 


 


 


 


 

 

I wsa reading the samsung 16kw data sheet. 12l/min minimum, 58/l min maximum. Given that we want to be able to run it at full chat in worst, surely designing the maximum is the sizing number?

agree with you , probably will need a bigger pump and am allowing for that. however what I don't want is to have to run a pump (or two) with very high head and high power due to noise and efficiency. would rather put in a bigger pipe!

 

do you know of a better online calculator? I do have an engineering degree but that was 25 years ago and I went into IT so all the fluid dynamics stuff is totally gone...

Share this post


Link to post
Share on other sites
21 hours ago, TonyT said:

28mm hep2o has a wall thickness of 2.75mm so that’s a fair reduction in diameter  compared to 28mm copper with 0.9mm

 

however the hep2o will come in coils, so less joins, has elasticity which will help with noise/vibration.

 

you could buy 2 coils for a flow and return, insulate individually and then pull in, in a ‘oner’

 

i understand a 90 deg bend adds the equivalent of an extra 1 m of pipe.

 

 

 

 

that is exactly my plan. except that I am not convinced that 28mm (hep2o or john guest type) is big enough.

Share this post


Link to post
Share on other sites
15 hours ago, Jenni said:

looking at exactly that kind of thing.

 

I've read previous posts on here mentioning the use of "32mm pipe"  for HP projects but without being specific about what they used.  really hoping someone will come along who said "we used <reference> and it works!"

 

 

Share this post


Link to post
Share on other sites

That's the pipe I'm using.

I bought 3x 25m rolls.

1 roll cut in half runs from the heat pump to near the cylinder and back. (28mm copper to connect to cylinder) 

The other 2 are flow and return to a distant ufh manifold. 

 

Edited by Jenni

Share this post


Link to post
Share on other sites

brilliant thanks jenni. that is way cheaper than any copper solution. Do you know what the inner bore size is for that pipe? What fittings do you use to reduce it to 28mm to connect to the rest of your system?

Share this post


Link to post
Share on other sites

I did check with the seller before buying, they said 32mm external - 26mm
internal. 

 

Joined to 28mm copper with these - 

https://www.thefloorheatingwarehouse.co.uk/product/pex-pert-to-copper-adaptors-compression-fit/

 

Also my plumber (who made all the connections where I'd already laid/prep'd the pipes) used 32mm crimp fittings to add some Ts for bleeding. 

 

Share this post


Link to post
Share on other sites

so at 26mm ID its the same bore as 28mm copper so flow rate calculators that assume 28mm copper should be valid. And the compression fittings make it do-able with a spanner.

that is really excellent thank you!

 

presume the crimp fittings need the right crimp tool (that your plumber had?), looks like they are about 100 quid, worth having if you are doing lots I guess.

  • Like 1

Share this post


Link to post
Share on other sites

Yes plumber had electric crimpers, lovely bit of kit. 

Plumber also had a kind of reamer that put a chamfer on the inside of end of the plastic pipe, which made a huge difference to how easy it was to push onto the compression fitting. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now