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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorwookey
    • CommentTimeJun 9th 2015
     
    Is there such a thing as a warm-water input instant electric (or gas) shower?

    We have solar thermal, so most of the year it's fine and the main thing the show has to cope is mixing enough cold from the 70 or 80C input water to get the 43C you wanted. However in the winter and shoulder periods the water is not always quite hot enough for a shower and sometimes you'd like one without having to wait a week then take it at an optimum 2:30pm.

    So what I really want is something that will heat up the usually warmish water to a bit more than 40C. But all electric shows seem to only have a cold input, which is deeply inefficient when 80% of the time it needs to do no heating at all, and even in winter it only needs to add ~20C.

    Does such a thing exist? Perhaps it needs to be a normal thermostatic shower with a separate pre-heat unit if there is no such combined device.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 9th 2015 edited
     
    You can get in-line power modulating water heaters. Our old mate JSH has one.
    http://www.zipheaters.co.uk/SiteMedia/W3SVC1317/Uploads/Documents/InLine%20DEX%20%20&%20DBX%20cropped-1.pdf
    • CommentAuthorDarylP
    • CommentTimeJun 9th 2015
     
    A modulating gas/LPG 'in line' water heater such as the Rinnais or WBs will do. They both can accommodate input up to 50+ IIRC, so you only pay for the energy used to bring up the water used to the temp required.

    However just for showers, it may work out as an expensive option?
    Good luck...
    • CommentAuthorringi
    • CommentTimeJun 9th 2015
     
    Why can't you put hot water into the cold input of an electric shower? You will need one with a good thermostat.

    In Turkey I saw an electric shower connected to the output of a shower mixer. You only turned on the electric shower if you needed more heat.


    However think about legionella as you seem to be storing water in a way that will become a breading ground.
    •  
      CommentAuthordjh
    • CommentTimeJun 9th 2015
     
    Our ex-mucker Jeremy describes his system over on ebuild; it's based on a Stiebel-Eltron inline heater I think and appears well thought through as usual. I think one or more people on here have looked at Andrews inline heaters; I don't remember the outcome.

    IIRC, you have a thermal store, so legionella is not a concern?
    •  
      CommentAuthorjoe90
    • CommentTimeJun 9th 2015
     
    I definitely will be using the same as Jeremy to top up warm water in shoulder months and winter, his blog on the ebuild forum is an absolute mine of information.
    • CommentAuthorwookey
    • CommentTimeJun 12th 2015 edited
     
    Posted By: ringiWhy can't you put hot water into the cold input of an electric shower? You will need one with a good thermostat.


    Hmm. I thought that they only had one input, so if I put hot in it would be way too hot all summer. And as they are designed for cold-input only they'd complain and just lock-out, or hopelessly overheat the water, if given a >25C input, but maybe not if you get the right one.

    In Turkey I saw an electric shower connected to the output of a shower mixer. You only turned on the electric shower if you needed more heat.


    Perfect. Simple and cheap if it works.


    However think about legionella as you seem to be storing water in a way that will become a breading ground.


    I did. And yes we're not taking any notice of the 'heat it all once/week' stuff. It's been OK for the last 5 years and I consider it a very small risk. It will eventually become a thermal store and then I really don't care.
    • CommentAuthorwookey
    • CommentTimeAug 30th 2020
     
    So I haven't done anything about this problem in the last 5 years, but winter is coming again and I really should. I come here to discuss it and find my old post :-)

    At this point I see no future in gas and am working to get rid of mine, so the gas inline heaters are not a useful solution. An electric inline heater seems reasonable, but I worry about the modulation and control algorithms on the inline heater and shower not mixing well. The nice thing about one unit is that it controls its own flow and temperature. Two units both trying to control flow and temp, or one controlling flow and the other temp could do unhelpful things. But I see the Steibel Eltron range is quite swish and you can choose open loop, closed loop or closed loop with flow control. And you can use it to supply all hot water if you want to.

    My latest idea was just to fit an electric unit next to the existing mixer shower and the human can decide if the input is more or less than 43C today and thus which shower to turn on. The tricky bit is that it would be nice just to have the one shower head and there is no such thing as a 'dual-input' shower hose SFAIK. But they are just 1/2" paralell BSP so it's easy enough to plumb the two outputs together and connect a hose to that. Probably a good idea to put check valves on both sides so the water goes out the shower head and not backwards through the other shower.

    A bit unconventional but can anyone see some important reason why it wouldn't work?

    The turkish 'series' option suggested above is another option. Easier to plumb, but requires the 'off' shower to allow water through and it seems to me that most will not do that - when they are off they must close a water valve. Perhaps that can be nobbled?

    The advantage of 2 showers is that it's a lot cheaper than the Steibel-eltron inline heater. I can have a top-of-the range mira advance flex (refurb) (which I know is a really nice shower - they have them at work) for £99. The SE inline heaters are £200-£380 and not much available s/h. But one of those could do the whole house.

    So anyone know a reason why plumbing two showers in parallel is a really dumb idea?
    • CommentAuthorphiledge
    • CommentTimeAug 30th 2020
     
    If theres going to be human intervention, you could put the immersion on 15 mins before showering to heat the top of the tank, assuming your solar is heating a DHW tank? Weve got a push button operated timer that puts power to the immersion for 15 mins with a push of the button and that works fine for when the ST hasnt quite heated the tank enough.
    •  
      CommentAuthordjh
    • CommentTimeAug 30th 2020
     
    I was just googling around and coming to the conclusion that you probably need to ask the manufacturer of any particular inline heater exactly how it can be connected and what temperature limits it has. Some disallow thermostatic mixers on the output for example.

    Then I came across a buildhub discussion where Jeremy was explaining to somebody about the problems of the current draw of an inline heater where the available supply was already committed to other things. So that's another thing to think about.

    It all puts me off the idea of inline heaters. I'll stick with my immersion for now, using mains to top up the PV as necessary, and maybe consider getting an ASHP one day.

    Redring or Stiebel-Eltron seem to have reasonable products.
    • CommentAuthorbhommels
    • CommentTimeAug 30th 2020 edited
     
    My shower mixer (MIra electronic mixer station) has the mains pressure hot feed from the heat bank looped through a Zip CEX inline heater. The Zip can be set to a user defined temperature, and modulates its power consumption to achieve just that temperature. It can be set to 7.5 or 10kW rating, depending on the spur. If it has trouble meeting the output temperature, it starts to pinch off the flow rate until it does.
    It has more clever features, and it works very well without intervening or thinking about.

    There are situations where the Zip and the mixer are fighting each other, mostly in the middle of winter when the cold feed is really cold and at the same time the heat bank is depleted. A heat bank temperature top-up, by either immersion of boiler normally solves this.
    •  
      CommentAuthordjh
    • CommentTimeAug 30th 2020 edited
     
    The Zip product looks good to me - it mentions solar-heated water input and specifies a maximum input temperature of 70°C (though I don't think it would cool that to say 45°C!). Same order of price as the S-E or Redring products it seems.

    Our (Bristan, mechanical thermostat) shower and Gledhill (somehow electrically-controlled pumped heat exchanger) thermal store sometimes seem to argue about the water temperature, with the result of brief periods of cold water during a shower - very bracing! If I ever/ When I replace the shower, I'll buy a fast-acting electronic controlled one. I would have said an Aqualisa Quartz because of prior experience, but I see they've discontinued them.

    But given Wookey has a cylinder of some kind to store the solar thermal heat, I'd be inclined just to use an immersion in [the top of] that cylinder when the solar isn't enough. On E7 or a more advanced TOU tariff it's reasonably sensible it seems to me and doesn't get into flowrate/power issues.
    • CommentAuthorbhommels
    • CommentTimeAug 31st 2020 edited
     
    Posted By: djh

    Our (Bristan, mechanical thermostat) shower and Gledhill (somehow electrically-controlled pumped heat exchanger) thermal store sometimes seem to argue about the water temperature, with the result of brief periods of cold water during a shower - very bracing! If I ever/ When I replace the shower, I'll buy a fast-acting electronic controlled one. I would have said an Aqualisa Quartz because of prior experience, but I see they've discontinued them.

    Our Mira keeps the temperature very constant, sometimes when dealing with pipe lag the flow can be a bit variable. The main thing you want to look for in an electronic unit is that the valve can accurately adjust the flow in very small in/decrements. This information is not easy to get out of manufacturers BTW.

    But given Wookey has a cylinder of some kind to store the solar thermal heat, I'd be inclined just to use an immersion in [the top of] that cylinder when the solar isn't enough. On E7 or a more advanced TOU tariff it's reasonably sensible it seems to me and doesn't get into flowrate/power issues.

    I see your point. In my case, the immersion sits at the bottom of the tank, and most of all I wanted something that does not require the showeree to think about anything beforehand.
  1.  
    Wookey, whatever your chosen solution (and I'd go along with an immersion, maybe trying to make it a bit smarter - simple push button count back timer), you should really have a tempering valve fitted at the outlet of the solar tank (or thermal store if that's what it is/will become) eg...

    https://www.advancedwater.co.uk/prod-520-373-0842.html

    water at over 70oC could cause bad burns very quickly, and some mixers will struggle to blend down 70+oC water to say 42oC in a stable way, and may cause give issues with the wax temp controller.
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