DWH- indirect- storage thoughts

TCaldwell Posted By TCaldwell, Feb 10, 2018 at 10:54 AM

  1. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    917
    93
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    I think I’ve pigeonholed myself in this aspect, Garn And flat plate are in the barn 75ft from house, primary odr mix valve is between the Garn and flat plate. The thought is to limit the exposure of high temp water in the insulated pex underground. The Tekmar controller on a dwh call will temporarily raise the temp beyond the odr mix temp to satisfy the demand and resume mix temp after, it also looks at the oil boiler temp, if wood won’t cut it after a set time it the ob satisfies and will resume to wood after.
    This all works but there are a few caveats, 1. The default dwh oil temp is the max limit for the oil boiler, which is recommend to be 10 deg above the max odr temp. So if your max odr temp is 145, the max ob temp is 155, this is based upon not short cycling the oil boiler, makes sense from that standpoint but kind of overkill to satisfy a indirect tank with a 127 setting with a 3 deg cut in differential.
    2. That dwh temp really disrupts a odr curve for the rest of the system on a regular basis.
    I realize this is splitting hairs but why take 155 deg storage water that could go along way to house heating at much lower temps to heat a indirect tank with its own losses to eventually supply a 103 deg shower.
    So I’m monitoring the time with a old analog clock that the dwh circ currently runs over a 2 week period.
    I’m not changing the odr mix temp setup to bring storage water temp to the house and pull dwh from there, I’m thinking of taking dwh out of the wood equation all together with a wall hung tankless gas unit. I already have gas in the house, and the analog clock will give a indication as to how much farther storage could go to house heating. What am I overlooking?
     
  2. maple1

    maple1
    Minister of Fire 2.
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    Sep 15, 2011
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    How do you heat DHW in the summer?
     
  3. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    917
    93
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    Tekmar sees wood temp too low, fires ob to heat indirect tank
     
  4. maple1

    maple1
    Minister of Fire 2.
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    Sep 15, 2011
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    So you burn wood all summer?

    Not sure this is on your radar, but if I had gas to my house I would be very tempted to get rid of all oil stuff I had. Maybe a new gas unit for dhw and back up heat? I sure don't miss our oil tank.
     
  5. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    917
    93
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    The thought crossed my mind but the ob is old but in good shape, unfortunately still good for a intermittent backup
     
  6. Bad LP

    Bad LP
    Minister of Fire 2.
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    Nov 28, 2014
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    Northern Maine
    Interesting. I'm finding that heating the indirect DHW off the wood boiler is a waste. The DHW will not get satisfied with lower water temps and only acts as a heat sink sucking hot water and cooling it within the full system.

    I seriously think it's going to get cut away from the wood boiler and be dedicated to the System 2000.

    My shower flow is much too high for any wall hung unit and personally don't care for them anyway.
     
  7. TCaldwell

    TCaldwell
    Minister of Fire 2.
    NULL
    

    Oct 26, 2007
    917
    93
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    So I’m not alone with this thought, 90% of the time it’s just the wife and I.
     
  8. Bad LP

    Bad LP
    Minister of Fire 2.
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    Nov 28, 2014
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    Just the two of us as well. Now add in that this boiler is in a 2nd home and used about 2 long weekends a month but it was built to be a primary home.

    My DHW zone valve rarely closes. Hard to make 170+ degree water with 150 degrees. If I had another flue a stand alone would be installed. No interest in a side wall vented unit at this time.
     
  9. gfirkus

    gfirkus
    Member 2.
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    Nov 28, 2014
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    Loc:
    central wisconsin
    I have my dhw run thru a coil in the top of my boiler, then to the lp water heater. It serves as a preheat. I can valve it out to run normally in summertime. The only issue I have is the amount of lp wasted on pilot light for 90% of heating season. I shut down water heater and only used as storage tank , but that didn’t last long when temps got to low mama wasn’t happy. So I’ll leave heater on and ready for when needed
     
  10. maple1

    maple1
    Minister of Fire 2.
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    Sep 15, 2011
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    I don't think there would be one clear answer to this - you have a few ways you could go.

    I was very happy to send our oil burner down the road & the oil tank to the scrap heap, even though the burner was still burning. It's kind of a big leap but after all said & done I am very comfortable in not having an oil tank now & all the associated liability potentials. And I did get a few hundred out of the old boiler & burner - which helped.

    I also eventually decided it wasn't worth burning in the summer for DHW, unless maybe I had junky wood to get rid of. But before I got to that point I also realized that without a capable flat plate HX, heating DHW from storage in the summer wasn't making good use of my storage at all. Stratification got messed up and I was having to burn again way too soon - the old sidearm wasn't much good when supply got below the 140-150 range. An indirect is likely better than a sidearm, but not as good as a good sized plate. My plate circulates to an 80 gallon electric DHW tank. Slowly. So that could be another way to go - I can now go a week (just) between burns for summer DHW with wood. Then you'd be able to heat either with or without wood. If you go to all gas, you won't be able to utilize wood to heat your DHW at all - unless you do a tank type DHW heater.

    How big is your indirect? Could you add a flat plate to it somehow? Getting the most DHW mileage you can from storage also depends I think on having a fairly big reserve in your DHW tank/heater - allowing you to heat the reserve to capacity slowly with bigger dTs while preserving stratification, while giving enough DHW reserve that you won't run out of DHW before or while the tank is heating again.

    Lots of factors, but if I was contemplating removing my indirect & replacing with a gas heater, I would also bring my entire oil burning setup into bigger picture considerations - prime time for wholesale assessments. :)
     
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  11. JohnDolz

    JohnDolz
    Feeling the Heat 2.
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    Dec 29, 2015
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    Loc:
    Burlington, CT
    I understand you are splitting hairs and striving for utopia so have you given thought to running a 2nd set of pipes from the Garn Barn? You can add a 2nd mixing valve exclusive for DHW. I imagine your Tekmar Controller gives you the ability to do DHW Priority so you can shut down all of your Heating Zones while you meet DHW call therefore focusing the higher temperature water only on the DHW call. It is worth doing, that is not the question you asked:).
     

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