Manifold plumbing pipe routing problem

[divorcingjack]

Hi all, 

 

MBC are coming back next week to seal up the house and pump the insulation, so we are trying to get all the piping we need into the ceilings before they arrive. We thought this would just be the MVHR pipes (which are now done), but it looks like this may affect the plumbing as well. 

 

I had intended a UVC, buffer tank (for UFH), small system boiler, manifold system with supplies to each shower/sink/WC as required, but the location of the boiler and the manifold are proving problematic. If we have the manifold next to the boiler (as I have seen in the majority of pics), then I don't think the number of pipes we have to run to the 2 bathrooms (7 cold/5 hot) are going to fit into the service cavity as there are pinch points around a door and a full height sliding window. Even if they would fit, it's a reasonable distance from the boiler to the 2 bathroom locations. 

 

So, my questions: 

- Is it a problem to have multiple manifolds in a radial system?

- Will a second manifold lead to the problem of a cold shower when a tap is run in the second bathroom? 

- If we go for a single manifold next to the boiler, will the length of supply to the bathrooms mean that we have to wait ages for the hot to come through? 

 

I'll attach a marked up plan when I get home to try and make more sense of this question. 

 

 

[bassanclan]

I had similar issues with pinch points, so decided to run one hot and one cold to each bathroom and teed off for basin/shower. After all you aren't likely to be washing your hands at the same time as having a shower. 

[Oz07]

If you have a bath could tee off for basin and shower underneath this. Keeps joint somewhat accessible and as said, not often washing hands whilst showering. 

[Nickfromwales]

@divorcingjack

With the time constraints and lack of space to a) get services through, and b) keep a distance between the hot and cold feeds so the hots don't warm the colds, I think you'd be better off either dropping the manifold idea all together or doing the two remote manifolds, ( if you have sensible and accessible space to locate them adjacent to the rooms ).

If you go 2x remote manifolds then don't forget to size them accordingly so you can take the kitchen and utility off the one closest. Either that, or as I'm not familiar with the layout of your house vs plant location etc, mount one larger manifold centrally to the two bathrooms / kitchen / utility. 

What I'd do, is then run a hot return circuit ( HRC ) between the UVC and the manifolds, with the HRC pumping through each manifold therefore keeping the entire manifold and the beginning of the connected pipework hot. This is achieved by connecting the HRC to the opposite end of the manifold to which the hot water arrives from the UVC, so basically your removing almost the entire dead leg of cold water, ( bar whatever is left in the now shorter final pipe runs from manifold to outlet ). 

The advantage here for you with that solution is only having to run one 22mm hot pipe from UVC to each manifold, and one 15mm or even 10mm HRC pipe back alongside it. The HRC can be 10mm without any problem whatsoever and it'll help too with being smaller as it really needs to be well insulated, as will the 22mm hot supply pipework, as when the HRC pump is running they'll be constantly hot and you want to reduce the losses as much as possible. 

If you insulate the HRC pipework well then the losses from running it will be negligible, but there are other measures to reduce that like putting occupancy switches in the bathrooms which only trigger the pump when the bathroom is occupied. I'm personally of the opinion that you'd be better off just running the pump when the house is occupied, as I don't see the appeal of having the slugs of static cold water in the dead legs of both bathrooms pumped back to the UVC to be reheated every time someone just has a pee and washes their hands being a good thing. You could argue that the cost of reheating that water would be similar to the losses from running the HRC constantly through the day. Maybe one of the resident uber mathematicians here could crunch the numbers on that, but if there is solar Pv in the picture then it's a no-brainer, just let it run from 06:00 to 23:00 or if your creatures of habit, with occupancy.

Tbh, if I had my own to do, it would deffo be a cylinder, a HRC, and ( even without MCS ) I'd put at least 2-4 Pv panels on the roof to contribute towards any household daily background consumption, such as white goods / electronics and HRC etc.

 

Just for clarity, what exactly are the distances between the UVC and the furthest hot outlet ?

 

16 hours ago, divorcingjack said:

I'll attach a marked up plan when I get home to try and make more sense of this question. 

Maybe helpful to see this  

[Nickfromwales]

Also, if easier, with the HRC you could just run a 15mm hot to the kitchen and utility direct from the UVC and run a 10mm HRC back to the UVC for absolutely instant hot water there. No need to manifold those tbh, as a ballofix isolation valve in the kitchen unit will suffice. 

 

Note : You'll need a ballofix isolation valve on both the hot and the HRC at each point they converge for service and maintenance. Water will travel back down the HRC so just shutting the one isolation on, for eg the kitchen sink, would still see water coming out of the tap. 

Edited December 10, 2017 by Nickfromwales
Additional info.

[TerryE]

My immediate thought is to use 10mm runs for all of the low flow runs -- the hand basins and toilets, and only use 15 for the baths and showers, and keep the manifolds central.  Route the 15s first, then the 10s and it doesn't really matter that much if you have to take a slightly roundabout route for the 10s because they have a third of the cross section of the 15s, so even if the run is twice  long, there is still less dead water in the pipe runs.

 

The alternative is as @Nickfromwales says and to use an HRC, but in this case you will get heat losses because of the standing water at 43 °C or whatever in the main 22mm even if insulated as it will be radiating 24hrs a day.  One to do the sums on, I think.

 

I defer totally to Nick on matters plumbing, but it's the potential heat losses that I would check.

[TerryE]

How about http://excelcalculations.blogspot.co.uk/2012/12/heat-loss-from-insulated-pipe.html.

[MikeSharp01]

8 minutes ago, TerryE said:

How about http://excelcalculations.blogspot.co.uk/2012/12/heat-loss-from-insulated-pipe.html.

That's a good one Terry !

[Nickfromwales]

32 minutes ago, TerryE said:

My immediate thought is to use 10mm runs for all of the low flow runs -- the hand basins and toilets, and only use 15 for the baths and showers, and keep the manifolds central.  Route the 15s first, then the 10s and it doesn't really matter that much if you have to take a slightly roundabout route for the 10s because they have a third of the cross section of the 15s, so even if the run is twice  long, the is still less dead water in the pipe.

 

The alternative is as @Nickfromwales says and to use an HRC, but in this case you will get heat losses because of the standing water at 43 °C or whatever in the main 22mm even if insulated as it will be radiating 24hrs a day.  One to do the sums on, I think.

 

I defer totally to Nick on matters plumbing, but it's the potential heat losses that I would check.

I've argued about this ( in my head ) as I'm often suprised that someone would starve themselves of such a worthy luxury for the sake of a few pennies a day in lost latent heat and the 20-25w pump power. I fail to comprehend how, after building a low-energy, cheap to run home, there would be such concern. ?  

@TerryE, would you be a darling and run some numbers for us? Based on 9mm Armorflex insulation maybe with 30m of 22mm pipe and 30m of 10mm pipe, and as much as all the juicy bits in that link appeal to the boffin in me ( ?? ) could we get a real world ( aka thick plumber ) POV in pence per day estimated running / losses costs ? 

One for @SteamyTea too, me thinks. He loves this kind of thing, nudge nudge wink wink. 

[TerryE]

Nick, normally I would do, but we are aiming to move into the new house in 5 days time +/- and we have 3 "kids", 2 spouses and 1 grandson staying for Christmas!  So every room has to be commissioned and things are a tad hectic here. ?

 

Since we are only working in the new house and only run the hot occasionally, I have noticed that heating up the hot manifold does add a good 30sec lag to the flow coming hot at the tap, but the manifold box is pretty lagged so it then only loses a few degrees an hour.  But I put 2 hours of heat, E7, into one SunAmp every couple of days and that keeps the hot available.

[jack]

44 minutes ago, Nickfromwales said:

I've argued about this ( in my head ) as I'm often suprised that someone would starve themselves of such a worthy luxury for the sake of a few pennies a day in lost latent heat and the 20-25w pump power. I fail to comprehend how, after building a low-energy, cheap to run home, there would be such concern. ?  

 

I made this mistake. I don't really know what we were thinking at the time, but my best recollection is that we were paranoid about overheating. I doubt it has anything to do with cost.

 

Upon reflection, we could have just turned the system off in hot weather. In cold weather it would just have contributed to the background heating of the house. You can also run such systems off PIRs, so they only operate when someone actually comes into the room.

 

Live and learn - I'd definitely have pumped hot water circuits if I were doing it all again.

[Nickfromwales]

19 minutes ago, jack said:

 

I made this mistake. I don't really know what we were thinking at the time, but my best recollection is that we were paranoid about overheating. I doubt it has anything to do with cost.

 

Upon reflection, we could have just turned the system off in hot weather. In cold weather it would just have contributed to the background heating of the house. You can also run such systems off PIRs, so they only operate when someone actually comes into the room.

 

Live and learn - I'd definitely have pumped hot water circuits if I were doing it all again.

PIR's aka occupancy switches . 

@jack, I think back in the day I was SLIGHTLY more conservative with my 'suggestive nature' plus iirc you said you had a designer / installer who was reasonablely fluent with the type of system / installation that was being discussed at the time so I didn't get overly involved ? but thanks for adding this as it could reinforce the decision @divorcingjack makes now in favour of doing the 'right thing'. 

Fwiw, with decent insulation, id be extremely surprised if the HRC added any 'heating' to the house, even in summer.

 

[billt]

1 hour ago, TerryE said:

The alternative is as @Nickfromwales says and to use an HRC, but in this case you will get heat losses because of the standing water at 43 °C or whatever in the main 22mm even if insulated as it will be radiating 24hrs a day.  One to do the sums on, I think.

 

I haven't done the sums, but I installed hot water pumps when I revamped our heating system. (About 15M pipe to the kitchen.)

 

You don't need to run the pump continuously, unless it's in a hotel. We insulated the hot water pipes and have found that running the pump for 2.5 minutes every 70 minutes during waking hours is enough to keep the water at the taps warm enough. I doubt tat the losses are much greater than just running lots of cold water off.

[Nickfromwales]

@TerryE, you had better concentrate on the house . Thanks for replying. ?

[divorcingjack]

Very helpful responses all round, gents, thank you. Husband did his ankle ligaments in last night at the site so didn’t get a chance to upload the plan. Will do today after we get home - site working at a balmy -6 deg  

[SteamyTea]

What needs working out?

[Nickfromwales]

Just now, SteamyTea said:

What needs working out?

The cost, ideally, for running a hot return loop over say 24 hours. 

As above and for a basis, 65oC water temp, 18oC ambient service void, 30m of 22mm pipe and 30m of 10mm pipe insulated with this stuff.

Maybe the spec is here ?

[SteamyTea]

What thickness as it ranges from 6mm to 19mm for 10mm pipe and 9mm to 32mm for 22mm pipe.

The thermal conductivity is 0.033 W.m^-1.K^-1

 

[TerryE]

The data sheet quotes 0.034 W/(m ∙ K) for the 25mm insulation so for a hot return circulate at ambient + 30 °C and a 15m pipe run this would work out at roughly ⅓ kWh per day.

[Jeremy Harris]

As a hot return loop only needs a really low flow rate on the return side, has anyone ever tried plumbing one in 10mm?  It should reduce the losses a fair bit, without compromising the performance I'd have thought.

Edited December 10, 2017 by JSHarris

[TerryE]

Just thinking off the top of my head if we are talking about 1W/m ish and are happy to have, say, a 3°C drop along run.  Again picking numbers out the air say 10m, then this would be radiating roughly 30W and 10m of pipe has 10*pi*9.8^2l or just over 3kg of water in it, so the flow rate needed to achieve this would be tiny.

[Nickfromwales]

17 hours ago, JSHarris said:

As a hot return loop only needs a really low flow rate on the return side, has anyone ever tried plumbing one in 10mm?  It should reduce the losses a fair bit, without compromising the performance I'd have thought.

I normally do them in 10mm. As they have a double check nrv back at the pump return, the HRC pipework cannot contribute to flow rates at the outlet. Water can only pull through the hot delivery pipe so going bigger on the HRC pipework is a complete waste of time. The flow rate should be defined by the pump, as in it only needs to be on speed 1 / lowest setting which is ample. 

@TerryE @SteamyTea my argument is running the HRC from say 06:30 ( everyone waking up ) to 23:00 ( everyone tucked up in bed ) vs a system that utilises pir sensors aka occupancy switches which trigger the pump when a person walks into the room. If there are a couple / few bathrooms then all the cool / cold ( ambient ) water that has gone 'dead' will be circulated back to the uvc / Other and will drop the temp according to volume / frequency. It will ALSO draw unwanted hot water into the rest of the entire DHW network, serviced by the HRC.

So.......my multi-faceted argument is which is the lesser of the two 'evils' ? I for one would say do away with the complexity of the room PIR's etc and just whack the HRC pump on a simple timer. 

For the occupancy switched setup to be completely comprehensive it would also need to be extended to cover the cloakroom / kitchen / utility, so, afaic, that could soon see a lot of cycles of hot water being drawn into already dead legs, which will be hugely wasteful as it'll be unwanted in all areas other than the target outlet that triggered the pump, and all those dead legs will have fired all the static water back to the cylinder. 

Id rather it was up to temp, left on, insulated as well as practicable, and controlled by a simple timer. 

The additinal volume of circulating DHW is also useful as an addition to the volume of hot, stored water, thus slightly increasing the DHW capacity. 

Bingo. 

[PeterW]

32mm Nitrile Rubber insulation (Armaflex, InsulTube etc) will comfortably fit both the 22mm flow and 10mm return for a HWC. Means that losses are lessened too. 

[Nickfromwales]

1 minute ago, PeterW said:

32mm Nitrile Rubber insulation (Armaflex, InsulTube etc) will comfortably fit both the 22mm flow and 10mm return for a HWC. Means that losses are lessened too. 

Good tip. I often have those sharing the same space, but I always run the HRC's for customers on a timer to suit occupancy. 

Ooh, just had a thought. You could connect the HRC from the burglar alarm panel....HRC on when alarm disarmed. 

Dragons den here I come ??

[TerryE]

14 hours ago, Nickfromwales said:

pir sensors aka occupancy switches

 

@Nickfromwales, Nick, I think that your approach / design template will fit many architectural layouts where there are clusters of HW services physically remote from the boiler / DHW tank. it will provide responsive HW without significant delay, and without any material running cost. So long as it is implemented as you describe.

 

My concern is that few plumbers are at your level of sophistication.

• Proper insulation is essential.
• The asymmetric 22 / 10 loop plus trickle flow HRC pump will help.
• Activity based priming will help, but you could consider on of the new Doppler radar sensors in lieu of PIR.

That being said, our setup where there is about 1m of pipe between the SunAmp and a heavily lagged HW manifold is a lot simpler.  The first person in the morning has an extra 30 sec of so delay as the manifold warms and that's it.