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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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    • CommentAuthortony
    • CommentTimeJul 28th 2022
    I read this recently about heating your home whilst using less energy:-

    Bleed your radiators. Trapped air can make your radiators less efficient, so they'll be slower to heat up. If you feel confident doing it yourself,….

    I disagree! The use of the term efficient winds me up again

    I think that they might mean, ‘Trapped air can make your radiators deliver less energy’ which it could be a good thing as bills will be lower.

    Bleeding the ‘air’ out will help them deliver more heat to the home and use more energy and cost more.

    Again the opposite of what they were saying it would do (use less energy)
    • CommentAuthorphiledge
    • CommentTimeJul 28th 2022
    If the system is sized correctly and has a room stat, surely air in the rads could cause non modulating boilers to short cycle for ever without the room stat inhibiting the boiler??
    Air or debris in the rads would make for a higher return temperature (for a given supply temp) so the boiler would condense less efficiently.

    And the heating would have to come on an extra half hour earlier, to warm the house up before everyone gets home.

    But agree with Tony that this is not very impactful advice.
    • CommentTimeJul 28th 2022
    I think it's quite useful advice. To anybody who doesn't already know it. I remember when I first learned about it and discovered lots of air trapped in our radiators. System worked a whole lot better after being bled.

    In terms of efficiency, if you define it as the fraction of rated output that the radiator is providing then it all makes sense so I can't take much issue with the use of the word. And as Phil and Will say, air in the system can easily cause the system to use more energy to achieve the same result, so it's also justified usage in that sense.
    • CommentAuthortony
    • CommentTimeJul 29th 2022
    I am wondering where the energy used is going, it must be going into the home isn’t it.

    Heating coming on half an hour earlier does not count, needing to yes.

    The whole thing is very complex with lots of variables

    Nice chat though.
    • CommentAuthorphiledge
    • CommentTimeJul 29th 2022
    If the boiler is short cycling or not condensing isnt the extra wasted enetgy is going up the flue??
    • CommentAuthorjms452
    • CommentTimeJul 30th 2022
    I've done thermal surveys where the radiators were 3/4 full of air and the comment from the householders was the heating struggled.

    At that level the efficiency decrease would be really quite considerable.
    • CommentAuthortony
    • CommentTimeJul 30th 2022
    I would have thought that the boiler control system would reduce the boiler output power to try to get the return temperature down.

    Yes the radiators won’t be so good at delivering heat to the rooms.
    Posted By: tonyI would have thought that the boiler control system would reduce the boiler output power to try to get the return temperature down.

    Yes the radiators won’t be so good at delivering heat to the rooms.

    Which means that some users will try to over come the problem by either winding up the thermostat or the temp. control on the boiler or both to mask the problem with the rads - which by doing so will lower the efficiency of the boiler = lost energy = more expense.
    • CommentAuthorSimonD
    • CommentTimeJul 31st 2022 edited
    Posted By: tonyI would have thought that the boiler control system would reduce the boiler output power to try to get the return temperature down.

    Unfortunately most boilers don't work like that even when they can modulate their output. Most systems are installed and set up with simple on/off thermostats so the boiler either runs according to the output temp set on the boiler or just off. You need something like Opentherm or other proprietary controls to get the boiler modulating properly. It would be great if the boiler could intelligently modulate flow temperature and flow rate to achieve the most desireable return temps, but it seems they still rely on the installer to set this up.

    BEAMA recently published a report on potentially achieving 10-12% energy savings by installing these better controls. The research was conducted by University of Salford (obviously caveating this with the fact that Beama is the trade association for manufacturers of these kinds of products, but the reasoning and data seem fair - https://www.beama.org.uk/static/7f5ebe31-04e1-470e-9befd249359959d9/15d07ed2-35d0-4c9f-90f958f81e9425f6/Salford-tests-on-load-and-weather-compensation.pdf)
    There's lots of discussion about blending 20% hydrogen into the gas grid (20% by volume, which is 7% by energy content). But ironically everyone would save more energy and carbon by just adjusting their flow temperature down from the default 70-80⁰C to about 60⁰C, to get the returns cool enough to condense for more of the time. That would be more carbon-saving than much of the "advice" out there and would need even less skill.

    In the course of five heating systems in three houses we lived in recently, the radiators were mostly oversized, some wildly so. Either because the installer had been generous with radiator sizing as they are pretty cheap and he didn't want callbacks, or because newer radiators were fitted to the same dimensions as older less effective ones. They have all worked fine with lower flow temperatures than default. However if someone found their house wasn't warm enough all year with flow temperature at 60⁰C, they could tweak it up during cold snaps and back down in the early spring.

    I wondered if anyone makes retrofit hi-efficiency controllers for older "dumb" boilers (IE those without variable flow temperatures) to upgrade them with load or weather compensation. I was thinking about some electronics that would hook into the wiring of the existing flow temperature probe on the boiler and provide a different apparent resistance, which would fool the boiler into adjusting its flow temperature for greater efficiency, . Bit like "re chipping" a car.
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