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Data and monitoring: Monitoring DHW Cold-Death Alerts...

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  1.  
    • CommentAuthorgyrogear
    • CommentTimeMay 2nd 2016 edited
     
    With kids away, our DHW usage has dropped drastically; we (obviously) still have the same 250-liter immersion tank, on off-peak tariff.

    With tank full and hot, it drips hot water to drain, via the safety valve.
    I considered this “waste” but my electrician said, “no it is normal, and fortunately so…”

    Being that way out, I then asked the electric co. They said, “Yes, it is OK to switch it off a couple of times a week if it is not in full use”. (did not mention this to wife, of course…).

    So I started doing my Green Bit, several months back. Obviously, the inevitable happened, and tdy we ended up with a tankful of tepid water, OH being highly impressed, of course…(read, “IDT”) (or “NFM” if you’re from the West Riding)…

    Soooo, once recovered, I wired my IR external temperature sensor to the takeoff pipe, thinking that this would record the temperature, which I could then read on my weather station… (even if means sacrificing a channel to gain one, but can’t have everything…).

    Of course all that turned out pretty naff, due to hysteresis etc. And also need to run HW to get a reading etc. (which in fact eats up more brain power than remembering to check the switch in any case…).

    I then discovered this site… http://board.homeseer.com/showthread.php?t=161028

    So I have now decided the best solution is to use a wake-up ringtone on my cellphone, each time I touch the Death Breaker…

    (My main worry now being, what happens when both the DHW tank AND the cellphone are out of charge…).

    gg

    (this is what happens when you live in France and omit the "muguet" on 1st May...):sad:
  2.  
    Well, It damn well should not drip out of the safety vale - that is NOT normal
    Personally I always have my DHW on a timer - Heat it up, use it. When its gone, its gone.
    I cannot believe that people still recommend leaving it on "on the thermostat" all the time - it is SO wasteful
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 2nd 2016
     
    Posted By: dimengineerPersonally I always have my DHW on a timer - Heat it up, use it. When its gone, its gone.
    What I do too, works well, but I have occasionally had a lukewarm bath.

    I actually limit the amount of time that the E7 can charge the cylinder. My E7 timings are 23PM to 00AM, 01AM to 07AM.
    So limited it to 4:30AM to 07AM.
    I could, it I wanted to get some more kit and write a bit of code, set it up so that it 'counts back' on thee time depending on the starting temperature within the cylinder. So say for every 1°C below the maximum temperature (50°C in my case) takes 5 minutes heating.
    If at the end of the day the temperature is 35°, then I would need 100 minutes heating, so that would then start to heat at 5:20AM.

    Have you checked for your thermal losses though. These can easily be greater than your usage. Mine still are and I have added extra insulation.
    • CommentAuthorDantenz
    • CommentTimeMay 2nd 2016
     
    Depends which country you live in as to whether normal or not. In OZ & NZ I know this is what happens as they don't include expansion vessels however, in the UK definately not right.
    • CommentAuthorgyrogear
    • CommentTimeMay 2nd 2016
     
    Posted By: SteamyTeaHave you checked for your thermal losses though. These can easily be greater than your usage. Mine still are and I have added extra insulation.


    Well, the DHW certainly leaks heat, as it seems to be warming the basement room that it's in (16.5 cubic meters), 2°C more than the next-door room (27 m3). Afraid I cannot crunch the numbers any better than that; my perception is that the DWH is Certainly Warming the Room. The tank has a rigid insulated jacket, no idea what is inside it, I suspect 30 mm of PU foam or something...

    gg
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 2nd 2016 edited
     
    The quick and easy way to monitor the losses is to not use it for a couple of days i.e go away. Then read see what the meter says. It does depend on what else is being used, but you could turn most things off, a fridge and a freezer don't use that much these days, assuming they are fairly new.
    The other way is to measure the temperature at the hot tap at the end of the day and then first thing in the morning. As you know the volume, you can work out the expected energy stored, then don' use it till the evening i.e go smelly, then see what the tap temperature is.
    • CommentAuthorgyrogear
    • CommentTimeMay 2nd 2016
     
    ST, thanks for that, I shall give it a try as soon as my bruises are healed :shamed:

    gg
  8.  
    whether the safety valves drip will depend upon the type of DHW tank you have. Over here DHW tanks are mains pressure and have no expansion vessel - so when the water is heated the resultant expansion is relieved through the over pressure valve - causing the valve to drip. If your valve is dripping check the type of installation you have and check that the expansion vessel is working (correct pressure and no punctured diaphragm) or if open vented system mace sure it is open! - then fix the pressure valve!

    For the DHW control surely the simple solution is to put an alternative thermostat near the top of the cylinder at a location that gives your daily usage plus a bit so that your daily usage only is heated. Easy enough to do, break into the insulation so that the thermostat sensor can be placed on the bare tank surface and wire the thermostat into the controls, then repair the insulation - then add a bit more insulation over the whole tank (to cut down the standing losses). With a bit more wiring you could put in a change over switch so that you can revert to a full tank when the kids turn up
    • CommentAuthorgyrogear
    • CommentTimeMay 2nd 2016 edited
     
    Per electrician, who installed the thing, the dripping is normal operation (to relieve pressure).

    Posted By: Peter_in_Hungaryyou could put in a change over switch so that you can revert to a full tank when the kids turn up


    Excellent suggestion, PIH, many thanks -- I'm sure the "électricien" will not only be very impressed, but glad to do the job & keep me happy !

    gg
  10.  
    I'm always deeply suspicious of using the PRV to relieve the pressure as a normal operation - unless there is a seperate high pressure safety valve as back up. The problem is that the PRV will eventually scale up and fail. I've destroyed a pressure vessel in the past doing this. It isn't particularly a safety issue - you'd have to be unspeakably unlucky to get an explosive situaiton, but it would be expensive and inconvenient.
    • CommentAuthorgyrogear
    • CommentTimeMay 3rd 2016 edited
     
    well, this is France (part of Old Europe...) (still...)
    so quoting from Wiki...

    "Immersion Tank Safety Valve: designed to maintain the pressure below 7 bar.
    Also allows water discharge as water expands during heat cycle, thus preventing tank over-pressure.

    Valve is calibrated to open at a certain pressure. The daily quantity of lost water would not exceed 3 % of the tank contents.

    Safety valve also allows cutting the cold water feed, such as when tank needs to be drained.

    Third and final function is to prevent hot water reaching the cold water network when the tank is heating (through pressure increase due to expansion of hot water)".

    gg
  12.  
    Posted By: gyrogearwell, this is France (part of Old Europe...) (still...)
    so quoting from Wiki...

    "Immersion Tank Safety Valve: designed to maintain the pressure below 7 bar.
    Also allows water discharge as water expands during heat cycle, thus preventing tank over-pressure.

    Valve is calibrated to open at a certain pressure. The daily quantity of lost water would not exceed 3 % of the tank contents.

    Safety valve also allows cutting the cold water feed, such as when tank needs to be drained.

    Third and final function is to prevent hot water reaching the cold water network when the tank is heating (through pressure increase due to expansion of hot water)".

    gg

    Sounds exactly like the sort that is in common use here!!

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