Final Qs about pipe diameters

[Adsibob]

I've learnt a hell of a lot from this forum over the last year or so and I'm so grateful to everyone for their help.

On pipe diameters, I THINK, the following is best practice for selecting HW pipe diameters to come off a secondary loop, but just wanted to double check before I go ahead with it:

 

• showers 15mm
• hand basins 10mm
• baths, can be 15mm unless bath tub is super big and you have a high flow bath filler in which case case 22mm till fill the super bath more quickly

 

My remaining questions are set out below (for context, we will have a UVC with about 3 bar of pressure and relatively good flow rate, although don't know what yet as Thames Water haven't done the upgrade yet; we currently have about 18L/min and they promised me something silly like 70 litres a minute, but I asked them to put it in writing and they refused, so I'm guessing it will be less than that):

1. Does the same rule about hand basins apply to kitchen sinks? Any reason why 10mm might not be enough in the kitchen. Looking at my kitchen tap, it has very narrow 9mm hoses, so I can't see why anything bigger than 10mm would be worthwhile. It would just increase the dead leg that needs to be cleared each time it's used, but thought I'd better double check.
2. what happens to an outlet further down the secondary loop when one opens the bath filler (which is rated at 33L/min) that is served by the 22mm secondary loop? Would the majority of the water in the secondary loop go to the bath meaning another outlet further along the secondary loop (i.e. further away from the UVC) that is trying to compete with the bath filler would really struggle, or would a fairly decent flow rate of say 25L/per minute, together with the 3 bar pressure from the UVC ensure that dynamic pressure is sufficient that the other outlet is still usable.
3. should cold water pipes feeding each of these outlets always match the diameter of the HW pipe feeding them?

[joe90]

That is the same as I did, no regrets. The kitchen sink I did do in 15mm but I don’t like those narrow flexi s, I prefer the soft copper tails with a bigger diameter.

[Adsibob]

47 minutes ago, joe90 said:

That is the same as I did, no regrets. The kitchen sink I did do in 15mm but I don’t like those narrow flexi s, I prefer the soft copper tails with a bigger diameter.

Thanks @joe90.  the Grohe taps I’ve bought come with the narrow flexi hosing attached to the pipe already. I assumed there was a reason Grohe were supplying them that; why don’t you like them?

[joe90]

1 minute ago, Adsibob said:

why don’t you like them?

Restricted flow unless you have high water pressure, I have found.

[Adsibob]

8 minutes ago, joe90 said:

Restricted flow unless you have high water pressure, I have found.

Hmmm. Can I remove them? My pressure oscillates between 2.8 and 3.2, depending on time of day.

[Bonner]

Standard flexies are suitable for the vast majority of mains pressure installations. You will be fine with 10mm unless it is a really long run (pressure loss is a function of pipe diameter and length).

[joe90]

9 hours ago, Adsibob said:

Hmmm. Can I remove them?

Not sure if the threads are the same diameter.

[Adsibob]

Cheers guys. Any responses to Q2 and Q3 of my OP please?

[PeterW]

Q2 - will be fine but flow will drop on both outlets

Q3 - always, and preferably from the same balanced supply 

[Adsibob]

1 hour ago, PeterW said:

Q2 - will be fine but flow will drop on both outlets

Q3 - always, and preferably from the same balanced supply 

Many thanks @PeterW.
Re Q2 : any way of mitigating the drop in flow?  Re Q3: When I’m inspecting the plumber’s work, how do I check he’s done this. What does that look like?

[PeterW]

Main cold supply goes to the control block at the UVC and the only thing they gets tee’d off before is the outside taps. Control block has a balanced cold outlet that feeds everything else. That way the hot and cold to all mixers etc is at the same pressure and flow. 
 

I prefer to tee off WCs too before the control block so a flush / fill affects both hot and cold but some others don’t like that approach. 

[fezster]

15 hours ago, Adsibob said:

although don't know what yet as Thames Water haven't done the upgrade yet; we currently have about 18L/min and they promised me something silly like 70 litres a minute, but I asked them to put it in writing and they refused, so I'm guessing it will be less than that):

 

Where in the country are you? 70 L/min sounds very optimistic!

 

I am in the SE and my 32mm MDPE has been measured at around 50 L/min off peak, but at any peak time it drops to around 20-25. 

[Adsibob]

1 hour ago, fezster said:

 

Where in the country are you? 70 L/min sounds very optimistic!

 

I am in the SE and my 32mm MDPE has been measured at around 50 L/min off peak, but at any peak time it drops to around 20-25. 

Yes, I knew it was bollox as soon as the telephone salesperson said she could not confirm it to me in writing. We are in N London. If the lowest we can get 30L a minute most of the time, I will be happy. I work irregular hours, so it’s actually quite rare that I shower during peak times. Didn’t really have space for an accumulator without building an outhouse for it in our front drive so this is the next best thing. 

[Dan F]

Did you rule out the manifold approach instead of a loop?

 

As for your questions on pressure drop, the best way to understand how what you have proposed will work in practice, IMO, is to model it using your specific scenario including pipe lengths, diameters and type.  How long your 22mm loop is will have an impact, as will if its copper or plastic. 

 

This tool is fairly easy to use, just ensure you use internal bore diameter, reduce pipe smoothness if using plastic and account for fittings and elevation.  Add your bath at 25l/min and a tap further along loop at 8l/min and see what pressure loss is.  Specification sheets for grohe taps will tell you how many bar you need at outlet for a given flow rate.

 

https://www.engineeringtoolbox.com/water-supply-system-design-d_2157.html

 

(The tool assumes that the flow rate specified can be achieved from supply)

 

Edited November 21, 2021 by Dan F

[Adsibob]

41 minutes ago, Dan F said:

Did you rule out the manifold approach instead of a loop?

How does a manifold system work? Now I'm really confused.

I now understand why plumbers make so much money. It's such a complex trade!

Also had no idea copper was smoother than plastic. I specified copper but plumber persuaded me to use buteline and he has already ordered it. He said the buteline works really well and that being plastic it doesn't conduct heat away like copper does (even though we'll obviously be lagging all pipes).

I should add that our three bathrooms are all next to eachother and next to the UVC in that we have the two main bathrooms next to eachother on the first floor, then above one bathroom is a shower room and above the other bathroom is the UVC, so most pipe runs shouldn't really be too long at all. Only long run is to kitchen sink (around 16m) and guest WC (around 12m).

Edited November 21, 2021 by Adsibob

[fezster]

I'm sure I've read that plastic pipe has less friction, although I don't have reference to where I saw that right now. However, plastic pipe does have a smaller internal diameter than the equivalent copper and the fittings are far more restrictive, so that negates any benefit of less friction. 

[Dan F]

19 minutes ago, fezster said:

I'm sure I've read that plastic pipe has less friction, although I don't have reference to where I saw that right now. 

 

The values I found and used when I used this calcutor were:

Copper: 0.001 - 0.002  10-3 m

Hep2o:  0.007                10-3 m

[TonyT]

For heating systems you get additives that make the water wetter to reduce friction and improve efficiency 

[Iceverge]

8 hours ago, Adsibob said:

How does a manifold system work? Now I'm really confused.

 

[Nickfromwales]

51 minutes ago, TonyT said:

For heating systems you get additives that make the water wetter to reduce friction and improve efficiency 

Usually only in district heating systems, and never in domestic ( not that I've seen in over 25 years of heating and hot water installation ).

[TonyT]

Will post a link tomorrow when I get the info from work as I can’t remember the name.

 

my mates the m&e clerical works manager at the local council,  and a few of the local universities have done trials/case studies..

 

 

 

[Nickfromwales]

14 hours ago, Adsibob said:

Any responses to Q2

The secondary loop is created by tee-ing off each hot water feed, just before it terminates at the outlet. Also, why on earth would you have a bath on the HRC? A few seconds of full flow from the highest flow rate outlet in the building will clear the dead leg in s few seconds max. As the bath is high volume / low frequency, I NEVER have the bath on HRC. Only will I ever put a shower on HRC, if it's literally the other side of the building and then I'll combine the basin and shower feeds to kill two birds with one stone. Rarely will someone be using a shower and a basin in the same room  simultaneously. 

[Adsibob]

1 minute ago, Nickfromwales said:

Also, why on earth would you have a bath on the HRC? A few seconds of full flow from the highest flow rate outlet in the building will clear the dead leg in s few seconds max.

You obviously are not a leisurely bather that stays in the bath so long you need to top it up. I am. After 30-40 minutes I add 5L or so of hot water. The rental I'm in at the moment makes this virtually impossible because the pipes aren't lagged so even just 20 min later in winter the hot water bathfiller has gone cold again. So there I am in my luke warm bath and I have to add quite a bit of cold before i get hot again. Will pipe lagging avoid this issue?

I agree no need to put the showers on the HRC.

 

[Adsibob]

21 minutes ago, Iceverge said:

 

Thanks. I remember watching a video about manifolds (which was also american) a couple of years ago when I first started on this journey and thinking at the time it was a bit of a gimmick, where the main selling feature was that you could isolate any outlet you wanted. But we are plumbing everything from new, I'm hoping it's done properly so that that won't be necessary.

I'm sure there are other benefits that I'm missing, but glad I went with secondary loop over a manifold. Not sure what @Dan F thinks is their benefit in this situation?

[Dan F]

23 minutes ago, Adsibob said:

Not sure what @Dan F thinks is their benefit in this situation?

 

The benefit in our case was that I was able to design out the need for a HRC loop (and the associate loseses) and still get hot water very quicily at outlets.  Also I think it probably also means less impact on one hot outlet when another outlet is used.