Garn Tank and Supply Temp ?????

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Deere3720, Jan 27, 2013.

  1. wardk

    wardk
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    Hi Heaterman, I have a similar set up as Chris ,I am adding a Lp boiler to the system for backup. On Chris's system it looks like he has a valve in the supply line to bring his oil boiler off or on line. My question is can I continuously run my supply through my backup and have it light when the supply drops to a set temp.?I am putting the back up boiler in the Garn barn and am concerned about freezing if it's off line, it only holds 3gal of water so I was thinking the BTU loss would be minimal this way. Any input would be appreciated,
     
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  2. heaterman

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    What you are proposing is certainly doable and probably advisable in your situation.
    The valve you see illustrated in the system Chris designed is a flow check used to prevent flow through the oil boiler when it's off. In your situation you would not use that.
     
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  3. Holley

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  4. Holley

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    I talked for a few minutes with the folks at Dectra and for now I think the best location for a sensor controlling a backup boiler is in a 12" deep thermowell inserted through a 2" x 3/4" x 2" iron reducing tee at the GARN supply. The sensor should provided an accurate measurement of available supply water temperature whether or not the GARN pump is running.

    Chris Supply sensor thermowell.jpg
     
  5. maple1

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    Could you just strap on an aquastat to the supply piping as close to the boiler as you could get it?
     
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  6. ewdudley

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    (Wouldn't cost enough.) Or just tape to side of tank at whatever elevation seems appropriate, nothing really time-critical going on.
     
  7. Holley

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    Yes you could but it wouldn't be as accurate. Really depends on how close you can get...You'd want to compare the temperature the aquastat was seeing with the pump running and then shut off the pump and check the temperature a half hour later, then adjust the aquastat accordingly. With a digital control like the Ranco ETC or Johnson 419 epoxying the sensor directly onto the side of the tank adjacent to the supply tapping is probably another reasonable alternative if you can get to the tank.

    On a new install I'd go with the well....(20/20 hindsight).. Like Heaterman was saying.. with a low flow rate, and particularly with cold return water from a radiant slab system, you can get some amazing stratification. Being able to use that hot top layer with a much lower average tank temperature can be equivalent to having a few hundred more gallons of storage in an un-stratified tank. The only problem is knowing how much usable energy you have left. It really requires multiple sensors. Someone needs to work out a simple readable digital "gas gauge" with maybe six sensor top to bottom.
     
  8. maple1

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    Or just circulate until the temp at the top is not hot enough?

    That's the beauty of aquastats - even if they're not accurate they can still be made to work precisely, with simple adjustment. I've got mine in wells - but I don't think it's worth the hassle to retrofit a well.

    I'm still not sure I have a firm grasp on the issue going on here - I was thinking all along why not just strap something on where it needs to go. But just figured I was missing something.

    EDIT: My gas guage has two sensors - one in the middle of each of my two stacked tanks. More would likely be more accurate, but I get a pretty good handle on how its doing with those - especially with tridicators also on supply & return at very top & bottom. One simple digital unit with multiple sensor inputs might be nice to have.
     
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