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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.

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  1.  
    pmcc

    We are not at pre publicity it is tried and tested technology just that in the UK we are 20 years behind our European neighbours. The town of Lienz in Austria came on stream in 2001 see link below.

    http://www.energie-cites.org/db/lienz_140_en.pdf
    • CommentAuthorjon
    • CommentTimeJul 8th 2009
     
    I'm having difficulty following this: What is tried and tested? (sorry for being dense)
    • CommentAuthorpmcc
    • CommentTimeJul 8th 2009
     
    John, it's a good story but doesn't have any information about solar. Can you point at anything else?

    Unfortunately we don't have enough wood per person in the UK to follow the Austrian example on a large scale. The sun does shine (sometimes) on every roof in the land, though, so it's interesting to look at the contribution to domestic power and heat which could be made by current and next generation solar technology.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 9th 2009
     
    Slowly working my way through MacKays book and so far I have not seen anything amiss with his methodology or assumptions (which he states clearly).

    Fostertom mentioned exergy (though if he was one of my students he would get a big red mark for using wikipedia as a reference :bigsmile: ). The way I think of exergy is as 'efficiency of use'. It is all very well producing 2kh of home grown electricity but if you cannot use it there and then it is irrelevant, efficiency is therefore zero. This issue frequently crops up with first year renewable energy students and takes another year to beat it out of them and is sadly the reason why we use centralised generation.

    A friend of mine was asked to help make a cafe 'eco', the owners imagined a small wind turbine or some PV on the roof, he pointed out that removing the 2.8kW hand dryers would have more impact, he did not get the job (heard on Today the there is yet another website (energy saving trust I think) that tells us how 'well' wind can generate electricity).

    Mackay quotes Richard Feynman "Nature cannot be fooled" ({he also quotes Markus Brigstock which makes me smile, he must be a Radio 4 listener). Physicists (and mathematicians) have their own language to describe the environment and it does not always translate perfectly into English, remember this when reading technical stuff.

    If I do have a criticism of his book (apart from small print as I am half blind) it is the way that he jumps from production to use, personally I would prefer to get one or the other covered in a single block before moving on, but I have only read the first third so will not hold that against him till I have finished.

    Nick
  2.  
    Posted By: jonI'm having difficulty following this: What is tried and tested? (sorry for being dense)


    Using thermal oil for the generation of electricity is tried and tested. How you heat that thermal oil from a renewable source such as woodchip or solar is the point of innovation. Our plant is co-fired using both woodchip and solar.
    • CommentAuthorjon
    • CommentTimeJul 9th 2009
     
    Thanks

    What temperature differential (and thus technology) are you using for generation?
  3.  
    Posted By: pmccJohn, it's a good story but doesn't have any information about solar. Can you point at anything else?

    Unfortunately we don't have enough wood per person in the UK to follow the Austrian example on a large scale. The sun does shine (sometimes) on every roof in the land, though, so it's interesting to look at the contribution to domestic power and heat which could be made by current and next generation solar technology.


    pmcc
    http://www.bios-bioenergy.at/en/references/all-projects/lienz.html

    Their system puts solar direct into the district heating circuit. Ours feeds into the thermal oil circuit

    I will comment later regarding the wood supply as my comments have been rejected twice. At least you may understand the system better
  4.  
    Posted By: jonThanks

    What temperature differential (and thus technology) are you using for generation?


    jon

    Thermal oil 250C-300C with steam evaporator to produce conventional steam upto 30 bar.
    • CommentAuthorjon
    • CommentTimeJul 9th 2009
     
    Sounds interesting: Do you have efficiency rates yet?

    Would be interested to know your loss rates when you get round to it:

    Area of capture >> Oil (assuming you're capturing in-plane)
    Oil> Steam (very low?)
    Steam > electricity
  5.  
    Posted By: jonSounds interesting: Do you have efficiency rates yet?

    Would be interested to know your loss rates when you get round to it:

    Area of capture >> Oil (assuming you're capturing in-plane)
    Oil> Steam (very low?)
    Steam > electricity


    Jon

    As a guide 4000 m2 of solar panels generates 300kw of electric however this will improve when the engines are replaced by screw expanders
  6.  
    Posted By: renewablejohnAs a guide 4000 m2 of solar panels generates 300kw of electric
    So that's about 75W/m2 - so about 7.5% of peak incident power. I guess this is of the same order of efficiency as bulk PV (which are around 10%). Wonder if you could do CHP with such a setup? I'm sure you have a lot of heat "left over" that's not converted to electricity.

    Paul in Montreal.
    • CommentAuthorjon
    • CommentTimeJul 9th 2009 edited
     
    That's not bad: What sort of % increase do you expect with screw expanders?

    Given your 250k ambient differential, at the oil delivery point, what is your peak measured energy collection rate per in-beam unit area?

    And, what is your expected all-in production cost per sqm of collection area?

    Edit, and assuming the oil line divides sun-side kit from generation-side kit, what is the percentage cost ratio between these two?
  7.  
    Posted By: Paul in Montreal
    Posted By: renewablejohnAs a guide 4000 m2 of solar panels generates 300kw of electric
    So that's about 75W/m2 - so about 7.5% of peak incident power. I guess this is of the same order of efficiency as bulk PV (which are around 10%). Wonder if you could do CHP with such a setup? I'm sure you have a lot of heat "left over" that's not converted to electricity.

    Paul in Montreal.


    Paul

    District heating is approx 1.2 Mw
    • CommentAuthorjon
    • CommentTimeJul 9th 2009
     
    Sounds interesting. When do you think you will have information compiled to let it be evaluated?
  8.  
    Posted By: renewablejohnDistrict heating is approx 1.2 Mw
    The sounds more like it - I presume this is averaged over 24 hours? That would indicate something like 750W/m2 peak or 375W/m2 over 24 hours! Pretty good I'd say!

    Paul.
    • CommentAuthorpmcc
    • CommentTimeJul 9th 2009
     
    "That would indicate something like 750W/m2 peak or 375W/m2 over 24 hours! Pretty good I'd say!"

    I'd say magic, if it's all coming from solar :). Presumably most of the heat (& electric) comes from the wood rather than sun. The figure we don't know yet is how much wood is burned to achieve that output.

    "Their system puts solar direct into the district heating circuit. Ours feeds into the thermal oil circuit"

    If I read this right your current priority is engineering process improvement to maximise electricity production for a given input together with minimising unrecovered heat loss. Taking a step back, it would be very interesting to have an overall view on your efficiency targets (% of energy converted) for:

    1. Electricity generating efficiency, for both solar and wood
    2. Recovered heat which will be routed to district heating

    "I will comment later regarding the wood supply as my comments have been rejected twice. At least you may understand the system better"

    Look forward to it. I can't think where all the wood can come from in the UK. If you have identified a biomass source that can be used on a large scale then that could be where the MacKay book is wrong!
    • CommentAuthorpmcc
    • CommentTimeJul 9th 2009 edited
     
    "Sounds like a fresnel type array?"

    Yes indeed Jon, my mistake. I've been so busy thinking about roof-mounted kit that I was caught out by the switch in topic to generating plant. Looks like the fresnel approach is much cheaper than parabolic reflectors due to much lower cost of reflectors and easier deployment.
    • CommentAuthorbrig001
    • CommentTimeJul 10th 2009 edited
     
    It seems like a good book to me, but he vastly underestimates the use of demand management of fridges. Earlier he quotes 18W average running power and 100W when running the compressor, then says you can save 18W per fridge as part of a demand management scheme. The actual figure is 100 - 18 - 82W (ie. the compressor power), making the total figure 2.46GW easily coping with the 0.6 to 0.8GW increase caused by kettles during commercial breaks and 2GW during football matches - presumably at half/full time.
    Edit: He doesn't even consider commercial fridges/freezers.
    Edit: I've spotted it now, 82W is possible, but on average, he's right at 18W.

    Oh, and you can't have a vegetarian cat (P78).

    Bri.
    • CommentAuthorjon
    • CommentTimeJul 10th 2009 edited
     
    Posted By: Paul in MontrealThe sounds more like it - I presume this is averaged over 24 hours? That would indicate something like 750W/m2 peak or 375W/m2 over 24 hours! Pretty good I'd say!


    Exceptionally good. Over 24 hours in the UK in Summer on a really good day given atmospheric extinction and assuming perfect tracking, that's nearly a 100% capture rate.

    Unless 1.2 is peak? In which case it's OK but will it be cost effective?

    It will be interesting to see how it works. I haven't come across screws that can do better than 12% so I'm struggling to see how one can get 75 out of 375.. but may be it is 750 peak?.

    All a bit too vague for me.
  9.  
    <blockquote><cite>Posted By: Paul in Montreal</cite><blockquote><cite>Posted By: renewablejohn</cite>District heating is approx 1.2 Mw</blockquote>The sounds more like it - I presume this is averaged over 24 hours? That would indicate something like 750W/m2 peak or 375W/m2 over 24 hours! Pretty good I'd say!

    Paul.</blockquote>

    Sorry Paul divide by 2 for a 24 hr solar basis. ie 8hrs direct solar 4hrs stored solar 12 hours woodchip
  10.  
    <blockquote><cite>Posted By: Paul in Montreal</cite>District</blockquote>

    Sorry Paul divide by 2 for 24hr solar basis ie 8hrs direct solar 4hrs stored solar 12 hrs woodchip
  11.  
    <blockquote><cite>Posted By: jon</cite><blockquote><cite>Posted By: Paul in Montreal</cite>The sounds more like it - I presume this is averaged over 24 hours? That would indicate something like 750W/m2 peak or 375W/m2 over 24 hours! Pretty good I'd say!</blockquote>

    Exceptionally good. Over 24 hours in the UK in Summer on a really good day given atmospheric extinction and assuming perfect tracking, that's nearly a 100% capture rate.

    Unless 1.2 is peak? In which case it's OK but will it be cost effective?

    It will be interesting to see how it works. I haven't come across screws that can do better than 12% so I'm struggling to see how one can get 75 out of 375.. but may be it is 750 peak?.

    All a bit too vague for me.</blockquote>

    Jon

    I have been quoted a screw expander with efficiency in excess of 30% but like you I am sceptical of anything in excess of 15% and will need to have it demonstrated before purchase.
    See comment to Paul regarding numbers
    • CommentAuthorjon
    • CommentTimeJul 10th 2009
     
    Thanks

    Will be very interested to see what you've done when you're able to share the information
  12.  
    Although there are a few instances in this book where his figures are open to some discussion the central point is that he has stripped away a lot of the spin to show the areas where we should be focussing our efforts. By showing his sums if we disagree with any figures (say collector efficiency) we can redo the working to get a new answer and see if it has an effect on the overall stack.

    He was good at highlighting the methods used by both sides of the argument to "spin" their positions.

    Another good point was the exposure of the "if everyone does a little we achieve a lot" thinking as more appropriately "if everyone does a little we achieve a little".

    A thought occurred to me: the main criticisms I have seen on this forum are that he has not got specific figures correct, e.g. his estimates for solar radiation on the earth's surface are wrong or collector efficiencies are two low). However no one has questioned the mathematics he uses (i.e. the formula he uses).

    If his book could be converted into a spreadsheet, then if anyone has issue with the figures they can plug their own numbers in and see the result. If the difference between his assumed collector efficiency and the efficiency of someone's pet system makes no difference to the overall stacks then his arguments stand up.

    It would seem to me that this is the essence of his book, to allow you to see if a given approach (say everyone getting rid of gas boilers and switching to biomass) would be feasible on a country wide scale.

    I'm up for doing a bit of Excel work! anyone else?:bigsmile:
    • CommentAuthormenzies
    • CommentTimeAug 2nd 2009 edited
     
    Yes. Let me know how you wish to proceed.
  13.  
    I must point out that he seems to get his thermodynamics wrong or at least muddled. This is in comparing CHP and heat pumps.

    He fairly quickly dismisses CHP. He seems not to realise that this is thermodynamically equivalent to a large heat pump; see Wikipedia for more or the analysis on energypolicy.co.uk.

    CHP systems don't have as many heat exchangers as electric heat pumps. Heat exchangers mean extra temperature drops, meaning reduced efficiency. Nor do they threaten to freeze part of the garden. He shows this is a risk in the book.

    Small house-sized electric heat pumps will never have the energy efficiency of larger machines such as town-sized CHP plants. That's another fundamental difference he doesn't pick up.

    As far as I can see, heat pumps make more sense in low-density rural areas, assuming a reasonable COP.
    • CommentAuthorjon
    • CommentTimeSep 23rd 2009 edited
     
    I finally got round to start reading this. It's very accessible but I wonder where the starting assumption (1kWh=1KWh regardless) will lead the book.
    • CommentAuthorbiffvernon
    • CommentTimeSep 23rd 2009
     
    Since most of this thread was written, MacKay has been appointed Chief Scientific Adviser to the Department of Energy and Climate Change (DECC).
    • CommentAuthorjon
    • CommentTimeSep 23rd 2009
     
    Thanks Biff

    I didn't know that. I also was a bit niggled by some of the starting policy comparisons. Haven't read it yet so these might just be turned round later in the book.
    • CommentAuthorjon
    • CommentTimeSep 23rd 2009 edited
     
    David

    Unfortunate that he seems to have muddled this; He seems to be comparing apples with oranges. If your purpose is to produce heat and you can theoretically at least get say 200% out of a 50% efficient centralised system at a COP of 4 (but then you can get say 50% + 25% electrical out of CHP). If your choice is to produce heat from CHP then you could use the electricity with a heat pump to get 150% (50 +4x25) out of a combined system so they're similar (0.75 ratio)

    If your choice is to provide 50% heat and 25% electricity for 1 unit of fuel then the best that a heat pump/power can do given 50% theoretical efficiency and COP=4 is 0.5 units of fuel (elec) plus 0.25 units (heat) giving again a total 0.75.

    But the central electrical efficiency quoted ignores distribution losses. And I'm not sure I believe the COPs when all embodied costs are accounted for. So, actually (as you've noted) they're more or less similar and CHP may even be better at the margins (particularly industrial)
   
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