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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    •  
      CommentAuthorJustin
    • CommentTimeJun 4th 2018
     
    Hi all.

    I've been too busy to haunt this place for ages. Hello again. Here's something though.

    https://www.viessmann.co.uk/en/residential-buildings/combined-heat-and-power-generation/micro-chp-unit-based-on-a-fuel-cell/vitovalor-300-p1.html

    I'd like to comment in a learned way about this device which one of my customers is looking at. (I'm not actually in this business, more the electrical line).

    From a first early look, my head is swimming with potential technical issues and pitfalls.

    So this "burns" natural gas (reforming it to hydrogen plus CO2 Plus CO along the way), providing up to 750 watts electrical output (at just 37% efficiency) with I guess a grid-tied inverter (manufacturer is vague on that one in the details). The "spare" heat from the fuel cell is for DHW and ups the overall energy efficiency to (claimed) 90%. DHW/heat output is also (only) 1KW. It then has a tag-on 25KW condensing boiler on the back end.

    The way I see this is it's adding massive amount of complexity to achieve a modest total efficiency whilst still being as carbon intensive as a home heated with gas and wired from a gas fired power station. They claim "spare" electricity can be exported, but that's probably not likely to be done much during heating season, and at 37% that's well below a thermal power station.

    The particular house in mind is a 1950's four bed detached, fairly inefficient at best, currently running on a standard 25-30KW gas boiler. Hence the modest performance of this device won't make much of an impact on a cold winter day and I can see the integrated boiler doing much of the work.

    The approach is very far away from where I'd be going, and I've already advised a thermal efficiency makeover as an essential starting point, however it's the normal case of a established property, appearance, space, little practical chance of this happening.

    Even ASHP which at it's worst performance (thermal gas power plant at 60%, low air and high water temperature) I believe would probably beat this in total efficiency. Then PV (There are good south and west unshaded roofs, I'd estimate would take 3KWp and easily plenty of solar thermal), - only they don't like PV or anything that looks a bit like it).

    I think the "Government subsidies up to £6K" has piqued the interest, perhaps overly so.

    I'd be interested in other's takes on this device.
    •  
      CommentAuthordjh
    • CommentTimeJun 4th 2018
     
    Posted By: JustinSo this "burns" natural gas (reforming it to hydrogen plus CO2 Plus CO along the way), providing up to 750 watts electrical output (at just 37% efficiency)

    I thought one of the main practical problems with fuel cells was their inability to deal with impurities in their fuel source without poisoning the fuel cell. So I'm very impressed if this device can deal with normal mains supply gas without problems.

    It seems to be way too high-powered for a typical single dwelling, unless the dwelling is so old-fashioned that they should be spending money on insulation instead.

    As I understand it, it's best to regard a CHP device as a heater that provides some additional electrical power. That is, the heating power is controllable but the electrical power is not.

    So I'd agree with your assessment that a better plan is insulation, insulation, insulation (plus airtightness). It's a bit worrying that the most prominent thing on the web page is a claim of government subsidies :cry:
  1.  
    I looked at a similar product to this a while back. The gas isn't burned as such, a chemical reaction takes place that creates electricity and heat. We have a two family home with a baseload of around 300 - 400w. I was looking at one of these units coupled to our 350l thermal store and a battery. The fit payments effectively pay for the unit, but I was put off by the amount of regular maintenance they required. They're not 'fit and forget' like solar (though they do generate 24hrs a day).
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