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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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  1.  
    Posted By: bhommels
    Posted By: SimonD
    I think a lot of people make the mistake to think that a thermal store functions in the same way as a dhw water cylinder and assume that reducing the storage temp is going improve energy efficiency. Thermal stores are designed to function at about 75C with the outlet dhw temp regulated by a thermostatic mixing valve.
    ....
    Like I've said before, this stuff is all a question of balance and context of use.

    All good points! My thermal store is set to 52C when the boiler has to heat it, and for solar it goes up to 70+ deg C. I have removed the mixing valve and put a thermostatic valve in the primary circuit with the sensor at the DHW output so that the pump gets pinched off when DHW temperature is reached.
    With this setup I can run it at lower T, reducing standing losses when energy is not 'free'. The boiler T sensor sits in the lower half of the tank so that it jumps in before the store is depleted. It was a bit of trial and error to get it to work properly I must admit.


    That's really interesting. I am trying to decide whether to use a UVC or a TS and the only thing putting me off a TS was having to heat it to 70C plus with the boiler in winter. Do you have a schematic of your plumbing setup that you are willing to share as it would be very useful.
  2.  
    Hi Borpin, have you also looked at the Steibel Eltron DCE instantaneous water heaters?

    The purpose of the store is to swing in temperature (that's how it stores and releases heat), so the more ⁰C it swings up and down by each time, the more kWh it stores. Swinging 200litres from 50⁰ to 75⁰ and back, stores ~6kWh which is enough for three baths.

    But how many kWh of heat do you actually need to store, if you have nearly-instantaneous boiler heat available, and are not storing up solar?

    We store heat at much lower temperature than we used to, because the boiler can reheat pretty fast, so we don't need to store up lots of kWh in reserve. The lower the storage temperature, the less standing losses, and the better the boiler condenses during the reheat.



    One option could be to bypass the store and flow CH direct to the radiators at a lower flow temperature, which could be fixed or controlled to maximize condensing. Would need checking that the cooler rads could dissipate all the boiler heat without using the storage.

    Another option is to maintain just the top of the TS at a high temperatures for DHW, but allow the bottom to drop whilst the CH is running at a lower temperature.

    Another option is to reduce the DHW temperature - a TS has fewer issues with sterilisation. Some people go down to 40⁰ DHW which (to me) is fine for showering but too cold for dishwashing.


    It is true that losses from the store help to heat the room, but that's the same argument for incandescent lightbulbs - you might not want that room heated all of the time.
  3.  
    Posted By: DJHDS18B20 temperature sensor? Solid-state relay or contactor? Plus a small computer - pi or arduino?

    The advantage (and disadvantage) of Pi and Arduino for any DIY project such as an advanced heating controller, is that ~1001 other people have already done it, and published their projects in various levels of detail and duffer-friendliness. So far I have read through ~101 of them!

    There seems a consensus to control the boiler by on/off switching the call-for-heat wiring, rather than interfacing with the control bus, although some have done that, and somebody wired logic to take over the digital bit of their existing CH timeswitch.

    There is less consensus about how to collect the various temperature measurements together, using wired sensors or by using lots of Pies or microcontrollers networked in various ways. People have added buttons and LCD displays and/or logged in remotely over the internet.

    Some of the better write-ups:

    Raspberry Pi Central Heating Controller
    https://www.instructables.com/Raspberry-Pi-Home-Heating-Controller/

    Raspberry Pi Weather Compensated Heating Controller
    http://hacks.slashdirt.org/hw/rwchc/
    (extraordinarily comprehensive)

    DIY Open Source PiHome Smart Heating Control
    https://forums.raspberrypi.com/viewtopic.php?t=197806

    Pi Central Heating
    https://github.com/davegreen/PiCH


    Raspberry Pies (Pi's?) are hard to obtain at the moment so I'm off now to learn about arduino/pico. Any pointers to more relevant discussion threads, gratefully received!
    • CommentAuthorbhommels
    • CommentTimeOct 22nd 2022 edited
     
    Posted By: PeterStarck
    That's really interesting. I am trying to decide whether to use a UVC or a TS and the only thing putting me off a TS was having to heat it to 70C plus with the boiler in winter. Do you have a schematic of your plumbing setup that you are willing to share as it would be very useful.

    Let's see if I can attach a drawing... The people at DFS, the heatbank manufacturers, were very helpful and pointed me to the right parts. Initially I thought a 15mm bypass would be needed to save the pump in case the valve would fully close, the DFS expert pointed out that for this application the RAVK/VMV combo will never shut and a bypass is not needed. It has worked great so far after finding the right temperature set point.
  4.  
    Posted By: bhommels
    Let's see if I can attach a drawing...


    That's great, many thanks.
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