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Building Regulations and Standards: Hot water temperature

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    • CommentAuthorgreenman
    • CommentTimeJul 9th 2010
     
    I've seen several references recently (in this forum) to regulations regarding the temperature of domestic hot water supplied to taps, but can't see anything that sets out how systems with solid fuel boilers can comply with the regulations.

    If (like me) you have a solid fuel rayburn, with very primative controls, and no thermostat, it keeps on heating the water in the cylinder for as long as convection continues to cause it to circulate. At the moment, this isn't an issue for me (as I assume that any regulations only apply if you install a new system, or make modifications?), but if I wanted to make any changes to my setup (such as to incorporate an additional heat source, and/or to change my cylinder for a heat store, then what would the position be?
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      CommentAuthorjoe90
    • CommentTimeJul 9th 2010
     
    What you need is a mixing valve (seen in schools and hospitals for example ). You can then set it to the max temp you want at the taps etc and if the water is above this temp it mixes cold to achieve the result you want. I certainly will be installing one of these when I have solar and a wood stove so accidents cant happen after a sunny day or a chilly one.
    • CommentAuthorgreenman
    • CommentTimeJul 9th 2010
     
    Thanks Joe90. Is that an entirely mechanical solution, or does the valve incorporate some electronics (thermostat, solenoid/motor, etc)? Presumably, unless you include a non-return valve on the hot water supply, for such a valve to operate effectively, the input water pressures have to be comparable, (i.e. you can't mix gravity fed hot water with mains water)?
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      CommentAuthordjh
    • CommentTimeJul 9th 2010
     
    There's an article in the latest green building mag.

    Under the latest Part G regs you need a 60 C TMV on the cylinder and a 48 C TMV (or equivalent) on the bath taps
    • CommentAuthorcontadino
    • CommentTimeJul 9th 2010
     
    They're entirely mechanical. Well worth the cost.
    • CommentAuthorgreenman
    • CommentTimeJul 9th 2010
     
    You have to have a valve on the cylinder as well? Presumably that is to restrict the temperature of output to 60 C?
    • CommentAuthorcontadino
    • CommentTimeJul 10th 2010
     
    I have a variable one for the kitchen, which controls the water for the whole room. It's so that the washing machine/dishwasher can have either 60 or 40 degree feeds.

    When I redo the bathroom, it'll have a (probably fixed TMV) on the hot feed after the branch to the kitchen, so that water to all the hot feeds in there is restricted to 60 degrees.

    I hope that makes sense.
    • CommentAuthorCWatters
    • CommentTimeJul 10th 2010
     
    Posted By: djhThere's an article in the latest green building mag.

    Under the latest Part G regs you need a 60 C TMV on the cylinder and a 48 C TMV (or equivalent) on the bath taps


    That seems rather unnecessary. I have one on my thermal store that limits all the water it supplies to the whole house so no tap, shower or bath gets anything hotter. Seems to work fine.
    • CommentAuthorcrusoe
    • CommentTimeJul 10th 2010 edited
     
    greenman - your current problem with fitting a TMV may be that, despite the claims of mfrs, they don't work well on gravity (tank fed) systems, which you should have with a SF Rayburn. OK on pressurised/mains fed systems though, if somewhat unnecessary in 95% of cases....

    If water is far too hot, add an extra heat leak rad on gravity to dissipate, and have warmer towels to boot! Ideally, a Rayburn with TS is bees knees.
    • CommentAuthorevan
    • CommentTimeJul 10th 2010 edited
     
    Posted By: CWatters
    Posted By: djhThere's an article in the latest green building mag.

    Under the latest Part G regs you need a 60 C TMV on the cylinder and a 48 C TMV (or equivalent) on the bath taps


    That seems rather unnecessary. I have one on my thermal store that limits all the water it supplies to the whole house so no tap, shower or bath gets anything hotter. Seems to work fine.


    "Guidance to the Water Byelaws recommends that, to prevent the development of Legionella or similar pathogens, hot water within a storage vessel should be stored at a temperature of not less than 60o C and distributed at a temperature of not less than 55o C."

    So apparently you shouldn't distribute the water less than 55C, which is a problem if you have the TMV on the tank set to 48 to comply with the other regulation!

    Only if you actually care, obviously. I'm not sure I do.

    However I can't see in the Scottish regs anything about a "60 C TMV on the cylinder", is that something specific to England or a mis-reading? I can understand the concern over 90C solar hot water coming out of any tap, not just the bath.

    There was a thread somewhere about makes of TMV which work tolerably with gravity fed systems, will need to dig it out (or buy a boost pump..)
    • CommentAuthorgreenman
    • CommentTimeJul 12th 2010
     
    Crusoe - actually, I don't actually have a problem, I was just concerned that when I alter my current system (dual coil cylinder fed by s/f Rayburn and gas boiler, hoping to change to Thermal Store, with additional solar h/w feed), I might find that some new regulation has been introduced that it might be impossible for me to comply with!

    Doesn't sound as though that's the case though, so thanks everyone (although if the TMVs don't work well with gravity fed systems then that could still be a problem...)
    • CommentAuthorwookey
    • CommentTimeJul 13th 2010
     
    Thorne work OK with gravity systems.

    The problem with TMVs is that they always add some cold, so having one at all prevents you getting an acceptable shower (say 42C) unless your water is 47C or more (57C with some brands). That's a problem with solar thermal water in the shoulder seasons and winter. If I fitted one I'd add a bypass to disable it in winter, but it's dull having to change this twice a year. The regs make no allowance for any of this and simply enforce the extra energy use: heating up to 60 every week, having to heat water to be 5-15C hotter than use temp. I don't like that tradeoff, but it would be useful to quantify just how much extra energy per year it will take to comply with said regs; None in some houses, a great deal (at least in percentage terms) in others.
    • CommentAuthorbrig001
    • CommentTimeJul 14th 2010
     
    Out of interest, we loose 4 degrees C across the two TMVs we have - one on the store and one on the shower. So, not too bad, but still means we have to keep water hotter than we need, so waste more energy. To put this into context though, it means our standing losses are 20% higher, so not a big loss, but a bigger problem if your hot water is solar.
    • CommentAuthorCWatters
    • CommentTimeJul 14th 2010
     
    Are you sure? A 4 degree drop at a flow rate of say 10L/min would be a power loss of 2800W/2.8kW. Sounds a lot. I suspect what's happening is that some cold water is being added even when the mixer is set to 100% hot.
    • CommentAuthorbrig001
    • CommentTimeJul 14th 2010
     
    Yes, as Wookey says, they always add some cold. I read Wookey's post and decided to measure it - just out of interest and to give some real world numbers to it. There was a longish debate about this here: http://www.navitron.org.uk/forum/index.php/topic,9570.0.html and I was surprised that our temperature drop is so low especially since the one on the store is a Screwfix special.

    After four showers, we were getting 43 degrees C out of the store itself and could get 39 degrees C at the shower - hot enough for me anyway. I should have measured the outlet of the first TMV too, but with only 4 degrees C it didn't seem worth it.
    • CommentAuthorgreenman
    • CommentTimeJul 16th 2010
     
    This all sounds very interesting. I like the idea of a by-pass for use in colder conditions, but surely this wouldn't meet the regulations would it? And if you're not going to meet the regs then you might as well not bother with the TMVs...?
    • CommentAuthorGavin_A
    • CommentTimeJul 16th 2010 edited
     
    just put an isolation valve on the cold feed to the tmv for maintenance purposes... ;)

    turn the valve part way off as well to partially restrict the flow to the tmv and reduce the minimum amount of cold that get's added to the hot for warmer water from lower tank temps, while still maintaining enough tmv functionality to fullfil the safety function (tmv would need to be set slightly lower to compensate).
    •  
      CommentAuthorjoe90
    • CommentTimeJul 17th 2010
     
    I am suprised that a TMV seems unable to supply only hot water but on thinking about it perhaps the TMV has shut off the cold water completely but its proximity to the hot allows a "cold bridge" within the TMV giving a reduction of the 4degrees mentioned above. Just a thought!!!!
    • CommentAuthorGavin_A
    • CommentTimeJul 17th 2010
     
    Posted By: joe90I am suprised that a TMV seems unable to supply only hot water but on thinking about it perhaps the TMV has shut off the cold water completely but its proximity to the hot allows a "cold bridge" within the TMV giving a reduction of the 4degrees mentioned above. Just a thought!!!!

    no, it's a deliberate safety feature - the tmv's are fail safe, so if it fails in the cold closed position when the tank is at silly hot temperatures it will at least still mix in some cold to reduce the severity of any scalding even if it can't still mix it down to the correct temperature.

    it also means that the tmv always mixes in some cold from the point the tap is opened, rather than there being a delay while the heated water opens the tmv valve, which could lead to a short period of unmixed scalding water coming out of the taps before the tmv opened.
    • CommentAuthorEd Davies
    • CommentTimeMar 4th 2012
     
    Blog post about a TMV which appears not to mix in cold:

    http://blog.energysmiths.com/2012/03/getting-into-hot-water-part-3.html
    • CommentAuthorborpin
    • CommentTimeMar 4th 2012
     
    Ages ago someone pointed out these folk http://www.termomix.co.uk/index.html as alternatives to Laddomat, but they also do various flavours of mixing valves.

    Does the new part G insist on the storage being at least 60C? Personally I intend to boost the DHW on demand using a Fastflow gas heater for the Solar system.

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