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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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    • CommentAuthormikrt
    • CommentTimeDec 10th 2016
     
    Can anyone please tell me, is there such a thing as a cylinder stat with a wider than standard temperature range?

    I have a bog standard one now which holds temperature to (I guess about) +/- 5 oC from set point. I'd like one that has maybe a 20 oC range, so it comes on at 50 oC and off at 70 oC.

    The reason for this is that it calls on my wood pellet boiler to fire too often and I figure this would significantly reduce the start-ups, and 50 oC is ample for my needs.

    Thanks in advance.
    •  
      CommentAuthordjh
    • CommentTimeDec 10th 2016
     
    I did a quick search for 'thermostat adjustable hysteresis' (without the quotes). It looks like there may be a few possibilities but to get such a wide range, you may have to build a circuit. There are apparently also devices that limit the number of operations per hour, but I don't know how they work.
    • CommentAuthormikrt
    • CommentTimeDec 10th 2016
     
    Thank djh, that seems to be the sort of thing I need.

    I've not heard of that term before. I've only had a quick search, but cannot find anything that seems to work straigh out of the box. I'd have thought there would be a market for it though.
  1.  
    If you can fit 2 cylinder stats (one for the low temp and one for the high temp) it's easy enough to build a circuit with a couple of relays.
    • CommentAuthorringi
    • CommentTimeDec 10th 2016
     
    Also put the stat that turns the boiler on near the top of of the cylinder and the stat that turn the boiler off near the bottom.
  2.  
    And if, like me, being told it is easy to build a circuit with relays and soldering up a PCB what have you reminds you when you were behind everybody else in class at school then REUK will build the thing for you for peanuts (about what it would cost you to buy the parts and a soldering iron). No connection with REUK other than a satisfied customer (and I couldn't find anyone else to do bespoke work!)
    • CommentAuthorJonG
    • CommentTimeDec 11th 2016
     
    Have you got a schematic for the hydraulics, size of the boiler, size of the cylinder, size of any buffer and the heat loss for the property.

    Stats, maybe the answer or they may be just a patch to cover up a more significant issue.
    • CommentAuthormikrt
    • CommentTimeDec 11th 2016
     
    There is no significant issue, other than as it's a biomass boiler, I don't want it starting as much as it does. I guess this is something other biomass users will find.

    Not only is it inefficient, I am using up one igniter every 10 months or so, and it's a pain I thought would be easily overcome, not so though.

    I have purchased off an auction site, a temperature controller with an adjustable hysteresis, I had to buy a 240v/12v transformer also.

    Once I receive it, and fit it, and then work out the settings I will post back with results.

    Thanks all for advice.
    • CommentAuthorJonG
    • CommentTimeDec 11th 2016
     
    The thing is mikrt that either the design or the boiler software or a combination of the 2 should ensure that boiler is not cycling, it is as you say very inefficient for biomass to work in this way because of the time it takes to bring the castings to temp, plus at the end of a burn you need somewhere for the heat to dissipate to while all the fuel is burnt off the grate. The thermal stress as you have found also leads to premature failure.

    I just wonder if there is something amiss, we have fitted a large number of chip and pellet boilers from 20kw up to 350kw cascades and cycling is something we try to avoid through the design process.

    Often the issue is over sizing of the boiler and under sizing or omission of a buffer and routing of the cylinder return to the base of the buffer, as the cylinder return is often hotter than the base of the buffer, it mixes the contents through destratification and the boiler has to re-fire.
    • CommentAuthorringi
    • CommentTimeDec 12th 2016
     
    @mikrt

    Do not overlook having a simple time switch so your cylinder is only heated just before you need the hot water, e.g. 6am and 4pm for an hour each, the better programmers have a button you can press any any time to give an additional hr if you need hot water when not expected.
    • CommentAuthormikrt
    • CommentTimeDec 12th 2016
     
    Thanks again all,

    JonG, I really do appreciate you're trying to help me, but there's nothing actually wrong or broken. All I want to do is to reduce the amount of "start-ups" my boiler performs. It's running fully as designed now, I just want to get it better.

    ringi, The boiler timer disabled and is run by an external timer and it has a boost button function which is used, but @ weekends the boiler is on constant.

    The boiler is a Woodpecker 24 kw and It heats my only tank, a Gledhill torrent greenheat 350 and that directly supplies downstairs UFH, upstairs towel rails & indirectly DHW via a small heat exchanger on the side of the cylinder, so I'm happy for the tank to fall to 50 oC. the DHW is mixed down to 50 oC.

    The boiler is set to 80 oC and on power 1 (of 1 to 5) and tank set to 70 oC. I've already fitted an over-run timer to the boiler recirc pump, so when tank is satisfied @ 70 oC, the pump coninues for about 15 mins.

    I'm really happy with the boiler and haven't had any issues with it apart from changing the igniters and the timer playing up from new (now external timer).
    • CommentAuthormikrt
    • CommentTimeJan 6th 2017
     
    Just some feedback on the controller I bought last month.

    It works a treat, I have the set point @ 78 oC with the hysteresis @ 25 oC and it does what it says.

    Only problem with it was the probe/sensor wire was too short for my positioning so had to extend it with some screened wire. And I need to get hold of a solid state relay as it also now controls my 3 speed boiler pump and may be drawing too much current over the long term.
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