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Garn System Design/Piping Questions

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by eauzonedan, Aug 16, 2013.

  1. eauzonedan

    eauzonedan Member

    Joined:
    Jan 21, 2011
    Messages:
    35
    Loc:
    Bayfield Co. Wi
    I'm trolling for thoughts on final design for a Garn system. I’ve got portions of the puzzle in place and would welcome thoughts on design/control/piping approaches. Situation to date is as follows:

    3 buildings in play: Garn Barn, 2-story existing house, 1-story shop with loft located up in northern WI.

    1.) Garn 1500 is in place in a remote insulated structure.
    2.) 150’(x 2) of 1 ½ “ PEX buried and spray foamed in a 1’ block of closed cell foam. (40% of the run is actually inside the house between the entry point and the utility room)
    3.)Lower (walk out) level of pre-existing house - in process of laying sleepers and 1 ½” of rigid over most of the uninsulated slab. This will be covered with Warmboard. Isolated areas (+/- 1/3 of the level) to have low temp rads- ideally with thermostatic valves.
    4.)Lower level of shop is tubed with 3x300’ ½” pex in slab (insulated below slab– 2” rigid/Perimiter slab - 4” rigid
    5.) 8-2” conduits run +/- 15’ between house and shop in an insulated underground chase encased with 2” of rigid - to allow feeding heat to the shop building from the utility room in the house.
    6.) Intent is to place ??? pump in Garn barn along with HX
    7.) Insulated Garn barn will have aux electric baseboard if Garn is not fed.
    8.)It is my intent to use glycol in all lines other than Garn primary loop - all of house and shop.
    9.) Lower level House Heat load +/- 30k using 2/3 Warmboard and 1/3 low temp rads
    10.)Upper level House Heat load +/- 35k up and all Warmboard
    11.) Lower level Shop Heat load +/- 20k and already tubed in the slab
    12.) Upper level Shop Heat load +/- 15k and low temp rads are intended.
    13.) I would like to run (indirect??) Domestic HW off the Garn when it is running and ??? when it is not.
    14.) I intend to include an LP fired back up boiler of the Garn is not fed.
    15.) Heat loads are preliminary and will likely be a bit lower when final.

    There is a ton of ways to skin this cat and your thoughts on control logic/design concepts/piping would be welcomed. I’m working with a local guy with a background in more conventional systems to pipe thing up, and am looking for approaches to suggest to him to assist in incorporation of the Garn into his design thought process.

    I appreciate the input form the brain trust.

    Dan

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  2. eauzonedan

    eauzonedan Member

    Joined:
    Jan 21, 2011
    Messages:
    35
    Loc:
    Bayfield Co. Wi
    I'm thinking my previous post may have cast way to broad of a net. I'll try to ask a few more specific questions.........

    Is there a practical limit to the approach temps that I should attempt to design for thru a heat exchange? I believe it would be physically possible to approach zero - if sufficient fluid was pushed thru it - or if the HX was unlimited as to size. Both cost money, either in operational pumping costs - or in initial equipment purchase. To maximize the positive impact of my storage it seems that the closer I can get the temps, the better, but that also needs to be tempered with a realistic cost effective reality. Any input as the where that sweet spot lies would be appreciated.

    Is there a practical limit to how low you can push the supply temp to a panel radiator? It looks like something in the range of 120-130 degrees is maybe a realistic number, and the de-rating of the radiator to something in the area of 1/3 to 1/4 of their standard rated condition for btu output per the mfgr design info........ At some point it seems the physical size and costs become too high to be cost effective and practical. Guidance to that "sweet spot" would be appreciated.

    Is there a maximum flow rate you would want to push thru the primary loop in the Garn to preclude mixing (and thus impact stratification)? This would appear to be a consideration in the sizing of the HX and the flow rate thru it.

    I understand that the selection of emitters with low supply temps is important in an intigrated system design, to not impact the benefits of the storage. How do you handle a situation where you have different low supply temp requirements for various emitters and domestic HW? I can see I may have a supply temp requirement to an indirect domestic HW tank at 140+ degrees, but infloor slab heat being productive down at maybe something less than 100 degrees with the rads needing something in between. All this happening while trying to maximize time between burns. Is there some fairly simple approach that would not feed (or not strip heat away from) the domestic HW while still supplying the in-floor? I was thinking maybe heat a 50 gal indirect HW heater with 140+ degree water early in the storage cycle and then block any feed water thereafter. This would create a "storage" of a set amount of domestic HW at an optimum temp. I understand you can do amazing things with electronic controlers, but have an underlying desire to also keep things as simple as possible. It also begs the question as to the lowest practical temp. I should plan to pull down my stoarage, which would control my time between firings.

    I can't see me running the Garn all summer just to produce domestic HW. I would also like to explore maybe utilizing the backup LP boiler as the heat source for an indirect HW heater without getting crazy complicated. Maybe it would just make some sense to just have an electric unit that could be spun up for the summer months?

    Hope this makes a bit more sense than my earlier "shotgun" question. Also......the shop/garage building is more accurately described as maybe a story and a half. It's a gambrel roofed structure similar to a barn with the upper level being about 2/3 the size of the lower one.
    Thanks
    Dan
  3. ewdudley

    ewdudley Minister of Fire

    Joined:
    Nov 17, 2009
    Messages:
    1,611
    Loc:
    Cayuga County NY
    Forget the glycol, it is fun and easy to prevent freezing even if you're away six weeks in the dead of winter.

    If the top of your non-pressurized boiler is higher than the shop tubes and the lower floor of the house, then use water straight from the non-pressurized boiler for those loads and just use a small plate HX for each upper story, house and barn.

    Also there is such a thing as a hanging loop that could work for the circuits higher than the non-pressurized boiler. Over the years it is possible air can accumulate so need a strategy for re-filling with water as with initial deployment.
  4. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,169
    Loc:
    Northern MN
    If you genuinely need or want the smallest approach temp on a HX, then a Garn may not have been the best choice, because you could achieve a 0F approach temp in effect with a pressurized gasification boiler and added storage. In direct answer to your question, however, an approach temp of 10F is somewhat "standard," and anything closer than that will require you to do a cost-benefit analysis. Study the approach tables and Sides A and B flow rates carefully, and pay attention to pressure drop at the various flow rates to make sure your other plumbing and circs are up to the task.

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