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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthormarsaday
    • CommentTimeJan 9th 2022
     
    After some discussion on choices for electric showers here, I have started to look at HW cylinders as a way to provide my HW needs.

    I need to supply an electric shower and two sinks with HW. The flat is all electric. The size of cylinder is probably going to be the 90L size. It should stand in a cupboard in the bathroom no problem.

    Does anyone have any recommendations for the most energy efficient heater ?

    Using this to heat the HW means I should be able to use a normal shower valve, rather than an electric one.
    • CommentAuthormarktime
    • CommentTimeJan 9th 2022
     
    We use a 50l Junkers cylinder for two people but we also use a dishwasher so we rarely use hot water in the basin or kitchen sink. It it operates at 60º C and is time switched for one hour twice a day during low cost electricity periods.

    The size you need probably depends upon your shower routine, we don't use a continous flow but that's a personal issue.

    https://www.junkers.es/ocsmedia/optimized/full/o493858v272_AF_JUBO_monohoja_termo_elacell_4000_2021.pdf
    • CommentAuthorowlman
    • CommentTimeJan 9th 2022
     
    I'd go down a bespoke route,- not as expensive as you may initially think.
    Buy an appropriate sized simple SS cylinder with one or two suitable, immersion bosses, plus cold and hot inputs and outputs etc.. Having the immersion boss/es bespoke may open up the possibility of installing higher quality immersions. You can also insulate to a higher standard than is usually available.

    I use this company for immersions, I've always had great service from them:-

    http://www.midlandelements.co.uk/
    • CommentAuthormarsaday
    • CommentTimeJan 9th 2022
     
    I have a lot on so wont have time to bespoke this.

    The junkers one is going to be to small as i need this to satisfy paying guests as well. It is going to be a holiday let flat. I think 150L is the minimum size i need.
  1.  
    How big is the flat - or rather what is the occupancy and how will the DHW tank be heated (night rate or normal day rate)
    Over here the standard mains DHW tank is 120 ltrs. on night rate which is 8 hours over night and a couple of hours around midday. This is typically enough even for holiday lets up to 4 people although the DHW is usually heated to about 80 deg and then mixed down.
    If the DHW is on normal day rate then a smaller tank can be used because the thermostat will run on demand so less storage is needed.
    We are a (very) hard water area and running at a higher temp. increases the speed of furring up but even so we get about 5 years between problems and then it is a case of removing the base plate with heating element and anode and bolting in a new set. About 1 hours work plus 30 quid in parts.
    • CommentAuthorrevor
    • CommentTimeJan 10th 2022
     
    Have you considered point of use water heating and stick with an electric shower, I see no point in the expense of cylinder and associated pipework when electric is the only energy source at the property. Storing hot water is expensive and wasteful.
    • CommentAuthormarsaday
    • CommentTimeJan 10th 2022
     
    I thought about going for individual point of use heaters, but I am coming round to the idea of a storage tank is going to be better. I just think the electric shower will not be that good.

    The flat is 55sqm and 2 bed. So generally it will be used by 2 - 4 adults or kids visiting only 4 months of the year. The rest of the time it will be empty or we will use it occasionally.

    When not being used, I will turn off the HW cylinder.

    The flat is on a single meter rate currently, but it might be worth going over to the economy 7 rate and look to heat the cylinder up at night time. Then it can be heated again in the day to top up.

    The expense of the heater is about £380 for 150L. I will need to get an installer put it in, but the pipe work I can do myself. Currently the flat is a shell, so everything has been ripped out and I am slowly putting it all back.

    The two sink HWH's will cost £200 for both, so I will have only a bit more expense if I go for a storage tank.

    so the upfront costs are a bit more for a storage heater, but will it really be that much more expensive if i use a storage heater over individual heaters ?
  2.  
    Posted By: marsadayThe flat is on a single meter rate currently, but it might be worth going over to the economy 7 rate and look to heat the cylinder up at night time. Then it can be heated again in the day to top up.

    The expense of the heater is about £380 for 150L. I will need to get an installer put it in

    If you are going to stay on a single meter (no E7) then a smaller tank should suffice because it will reheat immediately on usage.

    Over here a mains pressure DHW tank is a DIY job. The tanks we get over here have a combined pressure relief and non-return valve which vents pressure (= water) as the water heats up so provision has to be made for piping away this outflow. (I believe the pressure relief valves are set at about 5-6 bar and the tanks are rated at 6 bar working pressure. FYI a 120lt. pre-insulated tank is about 150 quid, but then there is volume production/sales i.e. more than UK)
    • CommentAuthormarsaday
    • CommentTime6 days ago
     
    Thanks for the info Peter. They are cheaper than over here.

    Hoping to get onto dual rate, so will heat up at night, but it can also top up if needed in the daytime as well.
  3.  
    Marsaday, you need to use something like 30% of your energy in the 7 hour night time window before you break even with Eco7 (that will vary of course with the rates, but it tends to be around that number). I was surprised how difficult it was to get our usage to 30% night time.

    Heating 150 litres from say 45oC to 70oC each night would use around 5kWh of energy. That would point to you always using less than 10kWh of energy during the day 16hours? Renters may regularly boost the DHW during the day?

    The standing charge may be a more dominant factor, if as I think you mentioned it may be empty for long periods of time. Heating is likely the larger component, so play that into your 24hr/seasonal energy consumption estimate.

    You can't know the answers to many of these usages, but try to bear all aspects in mind, and not just DHW, before selecting the elect tariff type.
    • CommentAuthorMike1
    • CommentTime3 days ago edited
     
    Posted By: GreenPaddyMarsaday, you need to use something like 30% of your energy in the 7 hour night time window before you break even with Eco7 (that will vary of course with the rates, but it tends to be around that number). I was surprised how difficult it was to get our usage to 30% night time.

    I agree that the economics may be questionable, unless (being all-electric) the place will be let in during the heating season. Ideally you'd want any washing machine & dishwasher to work off-peak too, which may perhaps be less compatible with holiday accommodation.
    • CommentAuthormarsaday
    • CommentTime2 days ago
     
    Thanks greenpaddy.

    Let during the summer months predominantly. Washing machine will be in, but prob no dish washer.
  4.  
    You can't expect tourists to use any appliance according to the timing of your chosen tariff. They will want to use kit at their convenience not yours. Same with showers - they will probably have longer showers than they would at home. At least that was what it was like when we had tourist lets.
    • CommentAuthorrevor
    • CommentTime2 days ago
     
    Posted By: Peter_in_HungaryYou can't expect tourists to use any appliance according to the timing of your chosen tariff. They will want to use kit at their convenience not yours. Same with showers - they will probably have longer showers than they would at home. At least that was what it was like when we had tourist lets.


    That is the experience of my neighbours who have holiday lets. It infuriates them when guests have the heating on all day when not there and then open windows because it gets too hot. Unless you meter and charge them separately for energy use they will want their money's worth.
    • CommentAuthorJonti
    • CommentTime2 days ago
     
    Posted By: revor
    Posted By: Peter_in_HungaryYou can't expect tourists to use any appliance according to the timing of your chosen tariff. They will want to use kit at their convenience not yours. Same with showers - they will probably have longer showers than they would at home. At least that was what it was like when we had tourist lets.


    That is the experience of my neighbours who have holiday lets. It infuriates them when guests have the heating on all day when not there and then open windows because it gets too hot. Unless you meter and charge them separately for energy use they will want their money's worth.


    Best to have the energy metered separately and charge a usage deposit which will more then cover the usage and return the remainder at the end of their stay.
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