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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorringi
    • CommentTimeOct 22nd 2014
    I have been thinking and dreaming….

    I know that a heap pump gives a better COP if the “output” temperature is as close to possible to the temperature of the water it is taking heat from. A better COP leads to a lot better government payment. I also understand that a big issue with water based solar inter seasonal store is the insulation and that having lot of luke warm water is not of much value.

    So why not combine the two?

    Use the inter seasonal store for UFH while it is still warm enough.
    Then use the inter seasonal store as the “input” to the heat pump while it is still warmer then the ground
    Then use the ground loop.

    However the few heat pumps I have looked at in passing having a max input temperature of 15c that is too low.
    • CommentAuthortony
    • CommentTimeOct 22nd 2014
    Getting close to thermodynamic system

    Yo need to look at heat demands as the window of opportunity will be small for being able to use solar for heating making it uneconomic

    gshp can have nice high CoP so if you must go for it use that

    I designed out heating using insulation, 3g, air tight, interseasonal storage.
    Inter-seasonal storage in water just isn't viable on a single dwelling level. The installation costs and standing losses are just too high at that scale.

    Paul in Montreal has previously posted links to a district based system in Canada which from memory performs on the margins of viability and there are currently two EU funded research projects at district level, one in Poland and one in Spain part of the objectives of which is to develop a suitable heat pump system for extracting higher grade energy from the store.

    The EU systems are funded by the "EinStein project" but it has only been running for a little over two years now and has yet to report.
    • CommentAuthortony
    • CommentTimeOct 23rd 2014
    Canada where it is -30 in winter is performing well:-

    "The solar energy system is currently surpassing its 5 year performance goal of 90% solar fraction.
    The final construction of the 52 homes was complete in August, 2007 See dlsc.ca not marging of viability, imagine how well it would work here!

    Mine is stores heat under my house in the substrata, temperature at the end of March in my basement was 19C -- I have no formal heating - do have a 65W warming system.

    The ISHS system does not work well but it does work a bit.
    • CommentAuthorEd Davies
    • CommentTimeOct 23rd 2014
    The system in Canada that Crispy is probably referencing is Drake Landing: http://www.dlsc.ca/

    There's another district store in Europe (closer to him is southern Sweden) on a Danish island: http://www.solarge.org/index.php?id=1235&

    Still, I really hope he's wrong about single domestic interseasonal storage: http://edavies.me.uk/2014/07/energy-budget/
    Thanks Ed, yes Drake Landing was the one I was thinking off.

    I see from their website that they only have short term storage in water, longer term storage is via boreholes in rock.

    The details on the Danish scheme are rather scant but it seems to be via a gravel/water mix in an underground pit.

    I see from their website that the latest phase of their district heating system is 60% solar 40% biomass (willow) which doesn't indicate to me a ringing endorsement of their inter-seasonal store.

    In any case these are all large scale projects rather than single dwellings.


    I don't see from your link details of your store Ed?

    I do think that you probably have a greater chance than most if you have input from a wind turbine throughout the heating season, unfortunately that's not an option open to many of us.

    Also looking at your figures if I have read them correctly then thanks to the input of the wind turbine you are only looking to store about 270kWhrs over a 6 or 7 week period which is quite a difference to a typical 150m² passive house which would more likely require about 2,000kWhrs over a 3-4 month period.

    A small increase in the size of your wind turbine should ensure that your store only has to act as a buffer for calm days rather than as any type of inter-seasonal store.
    • CommentAuthorEd Davies
    • CommentTimeOct 23rd 2014 edited
    Posted By: Chris P BaconI don't see from your link details of your store Ed?
    It'll be 10 tonnes or so of water. Long narrow tanks along the north side of the house within the insulated envelope so all “losses” are just heating. I'll see how it goes but there might not be any need for additional radiators - just leakage from the store ought to be enough.

    A small increase in the size of your wind turbine should ensure that your store only has to act as a buffer for calm days rather than as any type of inter-seasonal store.
    Indeed, it's a fine line between interseasonal and “just” a buffer for dull/calm days. Still, I think you'll wind up over-engineering things if you design for the run of short days lasting forever.

    Getting back to ringi's original point: a small heat pump for, e.g., DHW would allow use of a wider range of temperatures in the heat store and would allow the solar collectors to operate more efficiently because they'd be a lower temperature which is important even for evacuated tube collectors when there's not a lot of sunshine; 1 hour at 200 W/m² is much the same as 2 hours at 100 W/m² for PV (not quite, but almost) whereas the 100 W/m² is worth a lot less with solar thermal. As tony said it's getting close to so-called thermodynamic systems, just with a lot more buffering between the heat pump and the panels.

    The question, it seems to me, is whether the cost and extra complexity of such a heat pump is worthwhile. It depends a lot on circumstances but basically you've got to weigh up the cost of the heat pump vs just having more PV and then heating the output directly with resistance heating.
    • CommentAuthortony
    • CommentTimeOct 23rd 2014
    There is also a danger of freezing the water in the stores as heat pumps are pretty aggressive at removing heat from things
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