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  1.  
    With all due acknowledgements to Shevek, whose original I shamelessly based mine on...

    First attempt so feel free to interrogate.

    Ours is all single storey, although the intention is to distribute the long cold feed to the ensuite water heater by running up to the eaves space (approx. 2.8m rise) before dropping down locally. (I'm a bit concerned by pressure drop here since the site is undeveloped so this will be a new connection and there's no way to predict what bar pressure we will get at the mains yet.)

    Microbore to basins to reduce standing losses (largest deadleg on the hot supply is 0.5 litres if I've got my sums right) and aim for AECB good practice guidelines. Primarily copper because of personal preference for drinking water etc. and to keep things as consistent as possible. We have plenty of low level cupboards for hiding manifolds.

    No standard boiler (!) as we have passivhaus u-values, no mains gas supply and planning drawings that show a 4kW PV array. Playing around in PVSol with Meteonorm data suggests we should get enough solar on our site to take the edge off the DHW demand for most of the year and we'll be space heating with towel rails in the bathrooms so the PV should all go into the water heating. I've read that a single SunAmp PV should be good for a couple of 10 minute showers and to avoid running a v. long dead leg to the en-suite it seemed more sensible to have a second unit locally to this room rather than one big stack.

    Image resolution is reduced from the original to fit the 800px rule. I can post a pdf if this isn't legible, but I'm aware a lot of older forum links are now defunct so hoped that an embedded image might last longer.
      PLUMBINGSCHEMATIC.jpg
  2.  
    OK, somehow the resolution has got even worse when posting, so here's a link to the pdf version...
  3.  
    My one regret on my own plumbing (which was all PEX, using manifolds) was running 15mm to the Kitchen sink. The run from the manifold is probably 5m or so but the delay before hot water runs is annoyingly long. If you're planning on restricting supply to 8L/min then I suspect 10mm will deliver that (someone else will confirm).

    Any reason for restricting bath taps to 8l/min? It will take a long while to run a bath at that and for your water use calcs it's the bath size that's relevant not the flow from the taps. If you've got a shower above, money permitting, it's much better to run a separate, thermostatic, shower. You really want to be able to get properly hot water out of the bath taps to top up a bath - even turned up, thermostatic outlets don't usually get hot enough IME.
    • CommentAuthorEd Davies
    • CommentTimeMar 31st 2017
     
    What's a circle with a T in it? Just a t-junction or something more complicated? Is the one to the right of the en-suite WC just for future expansion?

    Posted By: Doubting_ThomasOurs is all single storey, although the intention is to distribute the long cold feed to the ensuite water heater by running up to the eaves space (approx. 2.8m rise) before dropping down locally.
    How do you propose to get the air out of this and, more interestingly, avoid it accumulating in use?

    Posted By: Doubting_ThomasOK, somehow the resolution has got even worse when posting
    Yep, think the forum software reduced it to 600 pixels wide. Thanks for the PDF, much easier to read.
  4.  
    Simon,

    Thanks for the advice on the kitchen taps. I figured 0.5 litres of cold 'slug' would be acceptable, but in retrospect it's probably the tap we use most in the house so 10mm would certainly halve this if it can still provide the 8l/min.

    You're right on the bath too, the AECB limit is on volume so I might increase the flow rate here - again was just aiming at consistency rather than logic! We probably would have a fitting above the bath but I had anticipated a combi fitting rather than two feeds. These can be a bit 'clunky' though so I'll consider a separate shower pipe.

    Ed,

    Circle with T is just a t-junction. One by the en-suite was a leftover from when I tried to run this diagram horizontally and it all got very confusing. Will remove.

    Forgive my ignorance on the air in pipe issue (we never got taught any services classes at Uni or in practice so this is all new to me!). Are you saying that pushing the water up will increase the chances of air ingress somehow? Does this require an Air Release Valve (ARV), and if so how reliable are these?

    Our alternative would be a duct in the screed but we only have around 50mm depth here which might just be enough for a lagged 22mm pipe.

    Anyone got any lessons learned on screed ducts for DHW distribution?
    •  
      CommentAuthordjh
    • CommentTimeMar 31st 2017 edited
     
    Posted By: Simon StillYou really want to be able to get properly hot water out of the bath taps to top up a bath - even turned up, thermostatic outlets don't usually get hot enough IME.

    I completely agree but water regs forbid it. The maximum temperature permitted from a bath tap on a new bath is around 46°C.
    • CommentAuthorSimon Still
    • CommentTimeMar 31st 2017 edited
     
    <blockquote><cite>Posted By: djh</cite>I completely agree but water regs forbid it. The maximum temperature permitted from a bath tap on a new bath is around 46°C.</blockquote>

    Which means you should fit a Thermstatic mixing valve to the hot tap like http://www.screwfix.com/p/pegler-peg402-tmv-15mm/96288

    Nothing to stop you removing it once you've been signed off (or, safer, adjusting the temperature up by a few degrees which is what we did in the new build flat we lived in). Combine a low flow rate and a steel bath and the bath water is too cool before you get in it - and no hope for topping up with hot and sharing the water. The hot just wasn't hot enough to raise the temperature of a full bath.
    • CommentAuthorEd Davies
    • CommentTimeMar 31st 2017
     
    Posted By: Doubting_ThomasForgive my ignorance on the air in pipe issue (we never got taught any services classes at Uni or in practice so this is all new to me!). Are you saying that pushing the water up will increase the chances of air ingress somehow?
    IANAPE (I am not a plumber, either) but it seems to me that water will always have at least a bit of air dissolved in it and anywhere the pipe goes up then down again the pressure will be slightly lower so it's more likely to come out of solution and there will not be any route for it to escape (other than by dissolving again) so it'll accumulate tending to make flow noisy and increasing resistance. I don't know for sure but speculate that something like an air release valve is needed.
    • CommentAuthorringi
    • CommentTimeMar 31st 2017
     
    Airlocks are mostly a none issue with mains pressure systems, as the water pressure will push them out of the pipe to the taps. However they are a big issue if you have a cold water header tank.

    Before planning on putting in two SunAmps, check you are happy with the cost of them.
    • CommentAuthorCWatters
    • CommentTimeApr 1st 2017
     
    I note the incoming pressure is marked as unknown. You really need to check what the mains pressure and flow rate is like before deciding on a mains pressure system. Water softeners can reduce the pressure slightly.

    I note you have specified a 28mm water softener but with 22mm pipe before and after.

    Is it normal to put softened water into the washing machine? I'm asking as I don't know. Our washing machine is used a lot and if we had needed a water softener I suspect it might consume a lot of salt?

    One of the benefits of a mains pressure system (in my opinion) is being able to drink the water out of any tap so I would possibly run un-softened water to some or all of the cold taps on the wash basins. But then ours is a two storey house so it's further to go to the kitchen.

    The pipe to a garden tap is usually smaller than 22mm but nothing really wrong with having a larger tap.

    Is a single triangle symbol a one way valve or a reducer? If it's a one way valve then you seem to have lot. If it's a reducer do the thermal stores use pipe smaller than 22mm?

    Presumably the )( symbol is for an isolating valve. In which case I'm not sure why it shows a different type of isolating valve on the basins compared to say the WC fill? Is one a full bore type and the other not? Lever vs knob?
    • CommentAuthorCWatters
    • CommentTimeApr 1st 2017
     
    If it's a single storey house what are the distances like from the store to the WC hot outlets? Long enough for a secondary loop? We have a WC basin that is 3 meters of 15mm pex from the hot supply. There is a reducer to prevent splashing but the flow rate is pretty good. Yet you can still wash your hands before it gets hot. Almost not worth bothering with a hot tap. Any secondary loops must go all the way to the tap to make them worthwhile.
    • CommentAuthorCWatters
    • CommentTimeApr 1st 2017 edited
     
    Posted By: Ed DaviesIANAPE (I am not a plumber, either) but it seems to me that water will always have at least a bit of air dissolved in it and anywhere the pipe goes up then down again the pressure will be slightly lower so it's more likely to come out of solution and there will not be any route for it to escape (other than by dissolving again) so it'll accumulate tending to make flow noisy and increasing resistance. I don't know for sure but speculate that something like an air release valve is needed.


    We don't have any and it's never actually been an issue for us. I'm guessing that the problem occurs when the bubble of air can rise up the downward part faster than the flow of water can push it down. With mains pressure and small bore pipes the flow rate seems high enough to push any air that does accumulate out?
    •  
      CommentAuthordjh
    • CommentTimeApr 1st 2017
     
    I don't understand why some pipe is Cu whilst other pipe is PEX. We put softened water in the WCs as well as the washing machine. SWMBO doesn't like scale! She also only drinks boiled water so never wants to drink from a tap (that's the cats' job).
    • CommentAuthorEd Davies
    • CommentTimeApr 1st 2017
     
    Posted By: CWattersIs a single triangle symbol a one way valve or a reducer?
    Reducer. I typed that question then noticed the label on the diagram saying so.

    Posted By: CWattersPresumably the )( symbol is for an isolating valve.
    Flow regulator. Though isolating valves in those positions might be a good idea.
    •  
      CommentAuthordjh
    • CommentTimeApr 1st 2017
     
    Posted By: Ed DaviesThough isolating valves in those positions might be a good idea.

    The isolating valves are on the manifolds.
  5.  
    Posted By: ringiBefore planning on putting in two SunAmps, check you are happy with the cost of them.


    I'm not that happy with the cost, but I think in a passivhaus build we can't have that much heated pipework from a central store without overheating risk. For a while SunAmp had a 'buy one get one half price' offer which I'm secretly hoping might come up again in the next 12 months!

    Posted By: CWattersI note you have specified a 28mm water softener but with 22mm pipe before and after.


    This is a blatant example of where I copied Shevek's diagram...I suspect that was for a particular model and I need to do some more research.

    The AECB guidelines prohibit softeners unless your water hardness is over 200mg/l, according to Bristol Water ours will be 206mg/l so it's something I left in. Not keen on the extra power draw and maintenance though so if I can't find a passive solution it will probably get omitted.

    Posted By: CWattersIf it's a single storey house what are the distances like from the store to the WC hot outlets? Long enough for a secondary loop?


    The primary store is about 1.5m from the main bathroom basin and 2.4m from the understairs WC. But it's something like another 15m to the en-suite, hence the second water heater local to this room. I don't really know much about secondary loops, only that the AECB are dead against them! To be honest I had considered not running a hot feed to the understairs WC as this is really only for a quick handwash and could probably be an aerated spray tap. Only the thought of badly calibrated spray taps in a confined space is making me waver...

    Posted By: djhI don't understand why some pipe is Cu whilst other pipe is PEX. We put softened water in the WCs as well


    I would have done everything from Cu, but decided that if the WC's were effectively on a separate circuit they could be something different (i.e. cheaper). If I find a plumber that only wants to work in one then we may switch as I'm guessing there will be economies of scale etc. by sticking to one type.

    With the softened water I decided we could probably afford to clean them more regularly and accept some scale but I haven't checked that with my wife yet (!) so this could all change too..!

    Thanks for the responses guys. Must get to the bottom of this Air Release Valve issue. Any ideas on reference material?
    •  
      CommentAuthordjh
    • CommentTimeApr 3rd 2017
     
    Posted By: Doubting_ThomasI think in a passivhaus build we can't have that much heated pipework from a central store without overheating risk.

    I don't think that's a concern as long as the pipework is well insulated. Check with your designer. I've never heard of using two stores to reduce pipe length, but perhaps the low losses of the Sunamp have only just made it a possible, though extravagant, strategy.
    • CommentAuthorringi
    • CommentTimeApr 3rd 2017
     
    Don't discount point of use instant elastic water heaters, eg understair wc, and showers not used much along with kitchen.
  6.  
    My experiences of a hot water loop having had one for 18 months now.

    - the better insulated the pipes, the lower the losses (obviously). However, to get more than 15mm insulation on the pipes you need to get your plumber to install the loop on standoffs. The copper for the loop was the only plumbing I didn't do and there simply wasn't space to insulate it as well as I'd have liked
    - controlling when the loop runs is key. We have a storage combi so it only has a 60L tank but a recirc loop will cool that over the course of an evening if left running.... We have a home automation system so I've been able to do some fairly smart things with when it runs but it will never be perfect (unless you have a manual activation and then wait for the water to circulate).
    - the convenience of it is good. It means a 6 second wait for hot water from the shower or bathroom taps instead of a minute or more.

    Cold tap only for a toilet really is fine - the 'cold' water in the pipe will be at house temperature (ie c20C) most of the time anyway.

    Water softener. I'm glad we installed one - I wouldn't worry about power draw (it's tiny and only when regenerating) or maintenance (there isn't any other than topping up the salt as far as I can tell). Make sure you buy one that regenerates based on actual water used rather than a timer.
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2017 edited
     
    Posted By: Simon StillCold tap only for a toilet really is fine - the 'cold' water in the pipe will be at house temperature (ie c20C) most of the time anyway.

    Depends whether the cold pipes are insulated.

    edit: but I agree that cold only is fine. (I think it's the law in Frankfurt or somewhere)
    • CommentAuthorringi
    • CommentTimeApr 7th 2017
     
    For the hot water loop, consider having a push button that can be pressed before using the WC or cleaning your teeth, then the water can be hot by the time you need the shower etc.
    •  
      CommentAuthordjh
    • CommentTimeApr 7th 2017
     
    There's no point in a loop on a shower, or indeed for most uses of hot water. It's just as easy to run the shower until it runs hot, or even warm. That minimises the energy loss, which is most important; the small amount of wasted water can always be recycled if you're really keen. Why would anybody want hot water to clean their teeth? Or indeed for washing their hands?
  7.  
    <blockquote><cite>Posted By: djh</cite>There's no point in a loop on a shower, or indeed for most uses of hot water. It's just as easy to run the shower until it runs hot, or even warm.</blockquote>

    I seem to remember we've been round this discussion on here a few times. It depends how short supply water is in - Australia mandates recirc loops because of this IIRC.

    In the UK I think its very much a convenience factor. It's definitely nice to get in the shower and have hot water in a few seconds instead of 30 seconds or more. Good design with a central water tank and short runs eliminates the need but on a restricted site where the water source ends up being in a far from ideal position it can be useful.

    <blockquote><cite>Posted By: djh</cite>Why would anybody want hot water to clean their teeth? Or indeed for washing their hands?</blockquote>

    But to wash your face or at the kitchen sink. Working out how to drive the recirc pump is key.
    • CommentAuthorEd Davies
    • CommentTimeApr 11th 2017
     
    Posted By: djhWhy would anybody want hot water to clean their teeth?
    I think Ringi meant that the hot water could circulate while you used the WC or cleaned your teeth, ready for your shower or wash.
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