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  • Solar water - gravity system, pressure for downstream devices

    I've just had a gander at some of the messages in this section, there's some good stuff here, members evidently know their stuff.
    I hope that I'll be pointed in the right direction.

    Presently I have a 1st floor gravity fed tank (25 gal cold header in the loft), hot feed by garage boiler. When it's sunny, fed by a 18 tube rack via a heat exch (in the immersion heater access hole), tubes are positioned south facing but is shaded from 10am to 7pm.
    Realistically, this tank only supplies taps, and the shower is mains cold, electric 7kW, costs a fortune to run.

    I have now fitted 2 evacuated tube racks to the roof (no tubes in yet), piped it through the slate, and hope to have a tank in the loft.

    Because of building regs (hi pressure stored water), I opted for a vented system, so the tank will have to be higher than the cylinder (in the loft).

    The shower is on first floor.
    The cold tank will be head hight in the loft, so the available head of water for the shower will be about 2metres.

    The problem i cant fathom is the pressure that is available for the safety control devices.

    Because of the potential higher temp that the cylinder may rise to, I'm assuming a tempering valve is needed (instead of a blend valve), these can cope with 95degC possibilities.
    Running down to the shower, will be a thermostatically controlled mixer, (cold inlet side will be fed from the cold tank (balanced pressures).

    The sink/bath taps will be fed from the cylinder / tempering valve.

    Regarding the shower, will there be enough pressure in the 2m head to ensure the effective operation of both mixers?

    I inderstand that devices can work with 0.1 bar pressure, but there may not be enough pressure left for a good flow of shower water, despite being run in 22mm copper.

    Is it likely that I need a booster pump on hot/cold shower feeds.

    If so, between what points in the piping should the pump be fitted, I've never used one, but understand it senses the water trickle when the shower valve is opened and activates the pump (until the valve is closed).

    Also, I heard a while back, that fitting a number of thermostatic mixers in the same run can cause them to fight against each other. Not sure if there's any truth in it, perhaps it was a mashup about not using a tmv with a non-modulating boiler perhaps.

    Anyway, I considered a thermal store/heat bank, but because of price and having to ensure piping hot water for an efficient heat exchange, I'm going for vented. I may use a high pressure unvented cylinder, but gravity fed/ vented to atmpsphere, (so that in the future, if I want to change over, it's in place and just needs commissioning by one of the many friendly G3 wolvo plumbers).

    If there is a better way to do this, then I'm open to suggestions. If models / makes could also be specified with any guidance please, that would help me to understand the parameters a bit better.

    With mixer valves being used, is it an idea to get a strainer in line or would all the detritus just fall to the bottom of the cold tank.

    I'm hopefull of including (eventually) a heat recovery option from the shower grey water, to pre warm the shower mixer cold inlet. No big ask there then!

    Thanks in advance for any suggestions.

    (This was submitted yesterday, but doesn't seem to be in the thread, so resubmitted. Pls ignore if diplicated).

  • #2
    Wow, you are covering a lot.

    So, first, I think that the hot and cold tanks can be at the same elevation, and will each provide the same pressure, if you use larger bore pipe, it will have less resistance and better flow rate, even with low pressure.

    I think having just 1 mixing valve, is all you need. A strainer would be good to have, but it will also introduce resistance to flow.

    Do you have a sketch you can post, as I am having a hard time following all the words.

    HotWaterSchematic_h.jpg
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      Diagram

      Thanks, the diag that you attached is for a pressureised system unless I'm mistaken, I'd need a G3 plumber for that, and with xmas coming, I aint got the savings.

      My diag attached. Its a bit sketchy.

      I'm trying to keep it as simple as possible to minimise fail points.

      Basically - Tank feeds shower.

      Available head 2m.

      Tank will mainly be in the 50-60degC range, but being solar intended, it may peak to 90+ degC.

      Taps - I can fit a tempering valve for those if needed (probably), head will be 3m+ above the taps.

      Shower, if I cant get a gravity suitable / high temp ThermoMix tap, then I'll need to feed the TM from the tempering valve.
      Will the resistance to flow mean that I need a pump?

      Thanks for the reply by the way.
      Attached Files
      Last edited by stewby; 10-07-2015, 09:42 AM. Reason: grammar

      Comment


      • #4
        Nothing in my sketch requires pressurized system. It would work fine as open, just lower pressure.

        You have to work out pipe sizes and flow rates to get it to work on first pass.
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Thanks

          I saw the T+P reliefs and mains cold supply and thought it was pressurised only.

          Looking analytically at it, if the header tank would be at the highest point, then it could be vented, but that would mean being on top of the chimney. (because the solar thermal circuit is direct into the store, then to the DHW).

          If the solar is made indirect to the store through a tank coil, then it would prob work, but with the store outlet going by an anti scald valve, and then to a shower TMV (not shown on the diag), it would be down to the available head(2m), the 2 flow-opposing devices and whether there would be enough pressure for a good stream.

          If I can get a decent quote for unvented, I'll go with it, but at the mo, vented is most likely, and in all likelihood, a boost pump.

          I'm a bit cautious about blumber quotes, because a gas safe friend of a friend came to quote for a boiler swapout in our garage.
          Pipework already there, he specified a WB 24Ri, plus flush for £2k4. Prob a grand+ for the labour, just for a days work.
          Didn't think that was reasonable, when most PAYE days rate is £100 to £150. OK, we dont have to shell out for accreditation for PAYE, but still high.
          Not that I'm moaning. If folks are happy to pay that, then fine, for me, it would be too painful, when I can do quite a bit myself.

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