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General: Wood Burner with back boiler with ground source heat pump.

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    • CommentAuthorEdwin
    • CommentTimeNov 14th 2007
     
    Hello - my first post!
    I am hoping someone can advise me as to the dos and don'ts of this combination.
    I am installing an Ice Energy heat pump running underfloor heating and hot water and want to integrate
    a wood burner with back boiler to run 5-8 rads and provide hot water back-up.
    Two initial questions:
    1) Does anyone have technical plumbing information for this kind of set-up?
    2) Does anyone know if the HWAM Classic 4 stove is capable of taking a back boiler?
    I'm trying to find a boiler which is utility/contemporary in style but with the boiler option....
    I'm trying to avoid the traditional looking boiler such as the Charnworth......
    Thanks
    • CommentAuthortony
    • CommentTimeNov 14th 2007
     
    Best idea would be to have a thermal store the bigger the better for the wood burner

    Even better spend on insulation and draft sealing forget the wood burner and only pay for a small heat pump and perhaps a solar panel.
    • CommentAuthorEdwin
    • CommentTimeNov 14th 2007
     
    Thanks very much for that Tony ... thermal store is going in for the two systems yes ....the house is a new build with massive insulation etc. I want a wood burner for back-up but also as a fire focus for the open plan living area.

    Does anyone shave knowledge on the plumbing side and boiler models if possible - I'm having a hard time getting reliable information...

    Cheers
    • CommentAuthortony
    • CommentTimeNov 14th 2007
     
    If it is new build why not insulate it so that you dont need any heating?

    For sure even poorly insulated the wood burner will make you too warm.

    With the gshp you dont really need a thermal store but you can use one. Then hook it up to both heat sources. Some thermal stores heve a pair of low down tappings specially for under floor heating.

    My advice is just have the wood burner to look at!

    Have you built yet?
    • CommentAuthorEdwin
    • CommentTimeNov 14th 2007
     
    Yes we are at roof on stage but no fit/out as yet.

    Thanks for the link.

    Exactly - woodburner for aesthetic as much as heat.
    • CommentAuthortony
    • CommentTimeNov 14th 2007
     
    Up the insulation and watch like a hawk for air leakage paths, holes, gaps, naffs, omissions, ducts with no seal, conduits, etc
    • CommentAuthorEdwin
    • CommentTimeNov 15th 2007
     
    We are working with the experts in this field - KOYA construction - (they built The Straw House - 1st ever Grand Designs for what it's worth - and also The Tree House - "Diary of an Eco Builder") -
    so we are covered for all those technologies Tony - thanks though - you're right, insulation is absolute key!).

    Sorry to stress the point but I am really keen to talk to someone who has integrated GSHP and woodburner with backboiler (OR another heat input source e.g. solar) - someone
    with plumbing / tech spec knowledge. KOYA are confident and that's great but I am the kind of client who likes to keep eyes on costs and constantly changing technologies...
    This project is LIVE and avtive so if anyone out there is interested in getting involved please post.....

    ESPECIALLY on the woodburner/backbolier issue re: plumbing

    many thanks

    Ed:bigsmile:
    •  
      CommentAuthorted
    • CommentTimeNov 15th 2007
     
    The woodburner will just be a second input to the thermal store (GSHP the first) with its own coil.

    I have a GSHP but without a second input (solar is waiting for the money).

    Get a thermal store that will accommodate at least 3 inputs in total. (Why would you not want solar?)

    Get it installed by a plumber who has done it before.

    Have a look on the Navitron Forum (sorry Keith!) for plenty of advice from plumbers. http://navitron.org.uk/forum/
    • CommentAuthortony
    • CommentTimeNov 15th 2007
     
    What type of how water system were you thinking of?
    • CommentAuthorEdwin
    • CommentTimeNov 15th 2007
     
    thanks for the link ted...lots of useful plumbing advice...I'm not installing solar yet due to costs...similarly voltaics...but am providing inputs plumbing for retrofitting. Voltaics are £18K.

    Tony the HW source is heat pump.
    • CommentAuthortony
    • CommentTimeNov 15th 2007
     
    I was meaning hot cylinder? or instantaneous or from a thermal store or via a plate heat exchanger or some combination?
    • CommentAuthorEdwin
    • CommentTimeNov 16th 2007
     
    Sorry my friend...thermal store due to requirement for gshp+wd burner.

    Does anyone have any stove experiences/reccommendations?
  13.  
    Is there any point producing hot water from a GSHP? Manufacturers quote COPs of around 2 for deltaT of 60degrees C, and that's under strict laboratory conditions. I suspect that in reality the COP for water heating will approach 1. Before deciding against installing a GSHP, I searched in vain for any real measurements from a real installation. That rang alarm bells for me.

    I would keep the two separate, with the GSHP powering the underfloor heating. Wood with electric backup could be used for the hot water (and perhaps the odd radiator). Solar works well with wood for hot water as both produce water at a high temperature. Heating water with wood is not without its problems. The main issue is that you must avoid designs where the water jacket cools the fire or you end up fractionally distilling tar in your chimney.

    T
    • CommentAuthortony
    • CommentTimeNov 16th 2007
     
    Surely if GSHP can heat water to 40 or more for ufh at a reasonable COP then it must make more sense to at least start heating the water with an immersion heater from there rather than from mains temperatures?
  15.  
    I didn't realise UFH water temperatures are as high as 45-65 degrees C. If you are running at 65 degrees, then a ground source heat pump is pointless.

    T
    • CommentAuthortony
    • CommentTimeNov 16th 2007
     
    Why is a heat pump pointless?? It pumps heat from the ground and into the house the idea is that you pay for 1 kW of electricity and get 4 to 4 kW of heat.

    Does not sound pointless to me.
    • CommentAuthorIce Energy
    • CommentTimeNov 16th 2007
     
    Edwin, please give our Technical Support line a call (01865 882202 option 2) and they can discuss some of the issues around this with you.
    Regards
    David
    • CommentAuthortony
    • CommentTimeNov 16th 2007
     
    Sorry I meant to say," 3 to 4 not 4 to 4
  19.  
    Getting 4.0 to 4.5 kWh of heat from 1kWh of electricity is a nice idea, but I've only seen these figures in the marketing spin and not in reality. In reality a COP of 2.0 is more likely, which is pointless. Also if this heat is at a low temperature it's even less useful. It would be extremely easy for a heat pump company to demonstrate actual measurements for a 3 bed semi with an average sized garden and average family life, but none have since I last looked. I don't believe them, but will be easily swayed by some evidence.

    T
    • CommentAuthortony
    • CommentTimeNov 16th 2007
     
    So 2 for the price of one is not worth the effort?? Savings sound worth it to me?
    • CommentAuthorEdwin
    • CommentTimeNov 16th 2007
     
    Thanks for your comments gents. Tom - your comment about cooling the fire and tar build up is something which concerns me.
    Sounds like you have experience with this - can you recommend a brand of woodburner which overcomes this?

    Have to say though that I'm with Tony on the savings equation - and for good reason - I have researched and seen proven systems and spoken with
    the owners.

    Don't forget that UF heating needs much lower temperatures than those to heat HW supply of course....notice that Ice Energy have contributed above!
    They tell me that HW @ 55 degrees is well within capacity and UFH needs 25 degrees.

    I am aware of the fledgling nature of this market and therefore the lack of info out there - and presumably that's where Tom is coming from -
    i.e. lack of real world case history info. Koya have a good track record of installations of GSHPs to suit all types of situations and with/without
    complimentary heating technologies - simply, it works - but each individual building/situation/requirement needs tailoring to suit itself.

    Anyone plumbed a system like mine!?

    Many thanks


    :wink:
  22.  
    Hi,

    Dont forget tht the basic equation is that the heating system has to equate to the heat loss and that is true what ever the system so minimusie yor needs first then choose.
    Cheers, Mike way up north
  23.  
    There's some information about heating water with wood here:
    http://www.cosi.co.uk/prod02.htm

    A fancy stove that looks like it will work is the Rika Tavo Aqua.

    T
    •  
      CommentAuthorted
    • CommentTimeNov 17th 2007
     
    I'm the owner of a GSHP with 500 liter thermal store but I have no measurements to use to convince any prospective purchasers of the efficacy of the system. I simply don't have the equipment to automatically log all the data required nor the time to take readings manually. I suspect that pretty much all other owners are in a similar position.

    I do know that when we have the 500 liters store starting at ambient temperature (15C) it takes less time to heat this to 55C using the GSHP (with a 2.75kW input/12kW output rating and running only intermittantly) as compared to using the 3kW (running constantly) immersion back-up.

    Powered by the GSHP it takes about 3 hours to get up to 55C whereas when powered by the immersion it took over 7 hours. (Someone with all the BTU, MJ etc forumlae can hopefully confirm that this result aligns with what might be expected.)

    Other than to check that it was working OK initially I have no reason to ever want to turn the immersion on.
  25.  
    So, your heat pump has a COP of ~2.5.

    T
    • CommentAuthortony
    • CommentTimeNov 17th 2007
     
    Greater than 2.5 but how much greater will depend on how intermittently it was running could easily be 4 or more
  27.  
    The evidence points to 2.5, which ties in with the graphs on this page very nicely: http://www.heatpumps.co.uk/graphs.htm

    T
    • CommentAuthorEdwin
    • CommentTimeNov 17th 2007
     
    Thanks again fellas. Anyone had experience of plumbing this particular combination?


    :bigsmile:
  29.  
    I think the more important question is why?

    T
    • CommentAuthorEdwin
    • CommentTimeNov 17th 2007
     
    Because I want to install it! Heat pump + wood burner is a practicle modern system in my situation.

    And that .. surely .. is the point .. that all these emerging technologies need to be applied according to the
    specific case.

    Hi Tony - have you read my information above about my build or are you just preaching? I'm genuinely asking for advice not a total re-plan!

    Thanks again.


    :confused:

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