Designing a new hw/ch system

Discussion in 'Plumbing and Central Heating' started by indus, 8 Jun 2013.

  1. indus

    indus

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    Hi

    I did ask a similar question over a year ago when my house refurb/extension was meant to happen. This was delayed for loads of reasons and actually only started last week! :oops:

    So here we go again but this time I've tried to gather as much solid information as possible. At present I have

    1) A 22mm inlet pipe

    2) A thermal store in the loft.

    3) A WB system boiler.

    To be honest the system has never really performed, the biggest issue being trying to run a shower and any other outlet at the same time ie the flow becomes poor.
    Over the years I think the TS has become sludged on the inside coil as now in winter I'll only get hot water in the shower for about 5 minutes and then it starts to cool.

    I'm having some major works done on the house including quite a large extension. When all the work is done the property will have

    1) About 3200 sq/ft over three floors.

    2) An electric shower(back up) on the ground floor, three shower rooms on the first floor and two shower rooms on the third floor.

    3) About 30 rads.

    My measurements are

    1) I have a prv on my system set to 3 bar. If I turn this up I can get about 5.5bar.

    2) Dynamic pressure and flow; I added a pressure gauge (as adviced) onto the prv and got the following numbers

    a) PRV set to 3 bar, gauge reads 2.6 bar and dynamic pressure (garden tap on full) dips to 1.8bar. Flow rate is 19l/min.

    b) PRV set to 4 bar, gauge reads 3.6 bar and dynamic pressure is 2.8 bar and flow is 24l/min

    c) PRV set to 5bar, gauge reads 4.6 bar and dynamic pressure is 3.6 bar with flow rate of 26l/min.

    At 6 bar the flow rate is 28l/min.

    My requirements

    1) To be able to regularly use two showers at the same time, both providing an adequate volume of hot water. There should be an additional bit of slack in the system ie if somebody fills a sink or wants to fill the kettle then the showers should still perform.

    2) Two more concurrent showers should be able to function about 15-20
    minutes later.


    My first question is should I upgrade the inlet pipe from 22mm to 35mm? A new drive was laid a few years ago so I would have to call in a mole company at some cost.

    Secondly, how would you design the new system to meet my demands? I know there is more than one way to skin a cat but ideas would be welcome.

    My own feeling is this;

    1) A second boiler added.

    2) A 300l unvented cylinder.

    3) Two 500 litre accumulators.

    Thanks in advance
     
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  3. Agile

    Agile

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    Do you really believe ( or understand? ) that you have a dynamic flow rate of 28 li/min at a pressure of 6 bar? That would be very unusual!

    I don't remember even seeing a static pressure that high in London during the day!

    There is a lot of undefined information!

    Flow rate of each shower?

    How long each shower?

    How many pairs of showers every 20 minute?

    Tony
     
  4. Homesafe

    Homesafe

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    How do you cook the perfect lasagne ?? Thas what I'd like to know.
     
  5. indus

    indus

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    Tony, I never measured the dynamic pressure at 6 bar (I did from 3-5bar). But I can tell you that the flow at 6 bar is 28l/minute and at 3,4 and 5 bar the pressure dips by about 1 bar when the garden tap is opened.

    As for the static pressure I can confirm it is in excess of 5bar, I've confirmed this from two separate guages ie one on the garden tap and one on the prv.

    [​IMG]

    The other information should be fairly 'average' ie showers flow rate at 15/lmin each, duration of average shower is 10 minutes etc.

    For your last question what I mean is; two showers and some slack and then within twenty minutes be able to repeat. There are four of us so that should see us sorted in the morning, after that demand is low.

    Thanks
     
  6. indus

    indus

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    Anybody?

    Is there something wrong with my line of questioning?

    :)
     
  7. dcawkwell

    dcawkwell

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    I would go for two glow worm ultrapower boiler/unvented cylinders
    a cross between a combi and unvented cylinder never run out of
    hot water. Boiler and cylinder all in a nice box.
    Spread the boilers through the house near the demands for hot water.

    You will need to set the pressure to about 2.5 bar.
    I would add an accumulator tank of maybe 150 litres to keep a store
    of cold water at pressure.

    Sorted.
     
  8. indus

    indus

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    Thanks dc.

    I'll look into the specs of those but I must say my previous experience of Glow Worm has not been good.
     
  9. dcawkwell

    dcawkwell

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    Comes with 5 years warranty. Plus you still have immersion heater backup for hot water.
     
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  11. indus

    indus

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    Does nobody else have any other suggestions?

    I'm not after the exact design brief of the pipework just in general what kind of system you would suggest.

    Also whether given my numbers would it be wise to increase the inlet pipe size from 22mm?

    Come on guys, I'm beginning to feel ignored ;)
     
  12. indus

    indus

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    So if I post endless silly questions about how little I can pay a plumber or even defraud him out of money owed that will get four pages of answers.

    I ask, what I hope, is a sensible question and I get one response :(

    Maybe I'm not deluded enough :LOL:
     
  13. indus

    indus

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    Thanks for all the ideas guys :LOL:

    Anyway, I have Thames Water coming around to do a site survey/quote next week. I maybe on a shared supply and so I may benefit from having this converted to a dedicated supply
     
  14. ALEC1

    ALEC1

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    skill knowledge and experience is what it takes to install a decent system, and its now many of us make a living..

    If I want professional services I pay for them, as you do except apparently when it comes to plumbing and heating..

    Plumbing design may be a hobby for you but its our livelihoods, there is no real reason why we should share it freely on an open forum
     
  15. silverback

    silverback

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    Why on earth would you install two boilers, there is no need
     
  16. indus

    indus

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    That is a very unfair comment Alec and does not reflect how I behave. I will be paying to have this done as I can't change a plug.

    All I was after was some general advice, ideas etc not schematic drawings of the design. When I asked a similar question before I was told I needed my pressure, flow etc readings. I have those now but nobody wants to play.

    It is not a 'hobby' for me but how on earth would I know whether whoever I employ has designed a good system unless I understand a little myself? That is not me trying to do anybody out of work, far from it.
     
  17. indus

    indus

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    Though nobody really seems to want to help me with this I won't take it personally :LOL:

    I will continue to update the thread in case it is of help to others in the future. I'll also try and post a photo diary.

    I've had Thames Water out to give a quote to upgrade their supply pipe to a 32mm, I'm awaiting the figures.

    I've also had a 'moling company' out to quote for upgrading the supply pipe within my boundary from a 22mm to 32mm. This is about £750. I was quite worried about this as I laid a new drive at considerable cost a few years back. However the moling company has told me that the pits dug out on the drive will be put back to exactly as new.

    If the quote from TW is reasonable then my plan is to upgrade both sections of the pipework to 32mm. I will then see what the flow rate is like and plan the next step from there.

    Thanks for reading
     
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