Best spec for high pressure hot water to multiple outlets?

[Dan F]

55 minutes ago, hendriQ said:

Is that the same recommendation regardless of whether one is using plastic or copper pipes?

Need to consider that plastic pipes have a smaller internal bore. We used 16mm for showers (13.6mm internal i think).

 

Ideally you'd calculate pipe size based on required flow rates and lengths, attempting to use minimum possible diameters for hot to avoid wait times and heat loss. 15mm over 2m is very different to 15mm over 20m.

 

I found this useful:

https://www.engineeringtoolbox.com/amp/hot-water-heating-system-design-application-d_2155.html

[Dan F]

Sorry, this is the correct link:   https://www.engineeringtoolbox.com/water-supply-system-design-d_2157.html

[Nickfromwales]

I regularly run 15mm hep2o across new builds, many runs often in excess of 15-20m, and showers work perfectly well, very well in fact. That's running to large rainfall heads etc so I wouldn't panic about running 15mm Hepworth to baths and showers. I've many many live installs under my belt and all customers super happy with the flow rates. I always run all the hot and cold supply in a radial arrangement from large bore primary feeds, 22mm or even 28mm at the hot and cold manifolds depending on system spec etc, so the results from series plumbing would be worse if you were considering that?

[Adsibob]

13 hours ago, Nickfromwales said:

I always run all the hot and cold supply in a radial arrangement from large bore primary feeds, 22mm or even 28mm at the hot and cold manifolds depending on system spec etc, so the results from series plumbing would be worse if you were considering that?

I’m a bit confused now. Was going to do a secondary loop for all the hot water outlets so that we can have near instantaneous hot water supply, but that would be in series, not a radial arrangement. Is a radial really better, and if so, how does one combine it with a secondary loop.

[Nickfromwales]

30 minutes ago, Adsibob said:

I’m a bit confused now. Was going to do a secondary loop for all the hot water outlets so that we can have near instantaneous hot water supply, but that would be in series, not a radial arrangement. Is a radial really better, and if so, how does one combine it with a secondary loop.

Simple. You just add another small manifold, run individual hot returns ( HRC ) pipes back for each outlet, and connect the hot return pump to the manifold. I do this on nearly every job.

Series plumbing will see a lot of waste of potential and much larger bore primary pipework, plus you would then have to have the HRC on all the time ( in lie with occupancy / demand ) or serving all of the house. With radial hot and HRC you can pick and choose as to where to implement HRC.

I run a 15mm hot and a 10mm HRC together in one piece of 25mm wall pipe insulation to minimise losses. Virtually nothing escapes from those runs in terms of heat loss. You just split those immediately as they arrive at the plant room and then insulate them separately to the manifold. Box clever and take the HRC outlets from the end of the hot manifold and then the entire manifold gets 'pre-heated' thus reducing wait times on the non HRC outlets. 

Edited July 18, 2021 by Nickfromwales

[Adsibob]

On 18/07/2021 at 10:02, Nickfromwales said:

Simple. You just add another small manifold, run individual hot returns ( HRC ) pipes back for each outlet, and connect the hot return pump to the manifold. I do this on nearly every job.

Series plumbing will see a lot of waste of potential and much larger bore primary pipework, plus you would then have to have the HRC on all the time ( in lie with occupancy / demand ) or serving all of the house. With radial hot and HRC you can pick and choose as to where to implement HRC.

I run a 15mm hot and a 10mm HRC together in one piece of 25mm wall pipe insulation to minimise losses. Virtually nothing escapes from those runs in terms of heat loss. You just split those immediately as they arrive at the plant room and then insulate them separately to the manifold. Box clever and take the HRC outlets from the end of the hot manifold and then the entire manifold gets 'pre-heated' thus reducing wait times on the non HRC outlets. 

I'm trying to visualise how this radial system would work and apply it to my house where I have hot water needs on three floors (shower room on top floor; two bathrooms on middle floor and kitchen, utility and WC on bottom floor. Is the attached diagram what you would suggest to get the manifold and secondary loop benefits you mention, i.e. manifolds are in series, but outlets serviced by each manifold is supplied radially from the manifold?

[Nickfromwales]

Run 15mm radial pipes back to a single manifold at the cylinder. Manage one lot of manifold related losses not 3    
Your option would also have a huge detrimental effect on the delivery time to basins / sinks etc if the HRC was off / outside a timed event due to the huge amount of 22mm pipe aka dead legs.

You only need the HRC to service high frequency low volume / flow rate outlets such as modern basin and sink taps. IMO just waiting 20 seconds or so for a bath or shower to get to temp is of little concern vs having to keep those runs warm too just in case someone wishes to bathe.