Boiler return temp protection

3fordasho Posted By 3fordasho, Mar 15, 2019 at 1:38 PM

  1. 3fordasho

    3fordasho
    Minister of Fire 2.
    NULL
    

    Jul 20, 2007
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    Loc:
    South Central Minnesota
    Planning a system based on a 40-45kw euro style downdraft gasser (cordwood) and 1000g storage.

    A loading unit (LK810 or similar) looks to be the least complicated plumbing wise to accomplish return protection - however a LK823 thermovar or danfoss VTC with separate ECM circulator seems to have the advantage of lower overall cost and lower power consumption. The loading unit has a built in swing check which allows some thermosiphon action during power outage, but other than that is there any down side to the separate circulator / LK823 or Danfoss set up?
     
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  2. Woodman1

    Woodman1
    New Member 2.
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    Jan 15, 2018
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    Loc:
    Michigan
    My 1000 gallons of storage is right next to my boiler. All storage plumbing is 1.5". I have a danfoss between the boiler return and the bottom of storage. I think it is an older style danfoss because I can use automotive style thermostats. A taco 0010 between danfoss and boiler with the bypass loop and throttling valve tying into the top of the danfoss. I never have to touch the throttling valve and at peak burn I can see a 30 degree delta t through the boiler. Usually it holds at 20 through the majority of the burn. Very simple layout and works extremely well. My boiler never idles during a burn and with the 160 thermostat I can have 180 degree water going to house within 20 minutes of a start up even with depleted storage. There are fancier and probably better ways to load storage but this works very well for me
     
  3. salecker

    salecker
    Minister of Fire 2.
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    Aug 22, 2010
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    Loc:
    Northern Canada
    I have an Econoburn 200 with 1000 gallons storage.
    I used the near boiler pump that Econoburn recommends.
    No fancy valving to go bad like so many come on here to diagnose and replace what has been installed.
    Plus if need be i can rob the near boiler pump to replace a bad pump.
     
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  4. Marshy

    Marshy
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    Dec 29, 2016
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    Loc:
    NY
    I have a froling and storage. Tarm Biomass provided the system schematic and they have two options for the return temp protection. They recommend, and I opted for the ThermoVar LK823 valve and separate Grundfos circulator. The froling controls activate the circulator to siphon off the boiler jacket after it is done heating and as your storage temp declines. My system has a ThermoVar LK821 it uses to divert water either back to the storage or boiler if it is below 165F or it keeps it circulating in the zone when its above 165F.

    Both the LK821 and LK823 have optional internals to change their temperature settings.
    20190317_110518.jpg 20190317_110530.jpg
     
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  5. Chris Hoskin

    Chris Hoskin
    TarmSalesGuy 2.
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    Aug 29, 2008
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    Loc:
    Lyme, NH
    The loading unit incorporates a Grundfos 15-58 pump and should be fine for a 40kW boiler. Normally the reason to choose the LK823 valve instead is that it allows you to use a larger pump. A larger pump might be necessary if you have a larger boiler and/or longer pipe runs from the boiler to the distribution and/or thermal storage. For example, if the boiler and thermal storage are in a detached garage 50' from the house, it is most likely that a 15-58 would not be big enough for even a 40kW boiler. Another example where you might have high pumping resistance is if you are using an unpressurized thermal storage tank (lots of linear feet in those coils!). Lastly, the LK823 with separate pump is less expensive than the Loading Unit option, but that is offset a bit with higher installation cost (labor).
     
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