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can I add a zone like this?

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  • #31
    Re: can I add a zone like this?

    Just for the fun of it, let's throw a buffer tank in there, dump the primary/secondary and go with a hydronic separator with VFD pumping
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    • #32
      Re: can I add a zone like this?

      Originally posted by Kevin Jones View Post
      Exactly...and a P/S increases boiler temp return.
      No not necessarily, it depends on the primary flow rate, and the secondary(s) flow rate with its return water temp.

      Its called mixed water temp and a basic thermodynamic calculation.

      Once you know all flow rates and temps, you may calculate the mixed water temp, which allows you to calculate the return water temp

      I will use a secondary flow that exceeds primary boiler flow since it fits into our discussion, for example:

      180 degree boiler supply X 7 GPM Boiler flow + 70 degree baseboard cold start temp X 9 GPM combined zone flows = 1890

      7 GPM primary flow + 9 GPM secondary flow = 16

      1890 / 16 = 118 degrees

      So in this case the boiler supply could be as high as 180 and the return (mixed temp with secondary) is 118 degrees

      180 - 118 = 62 degree Delta T

      62 DT X 7 GPM (flow rate through boiler) x 8.33 (weight of 1 gallon) x 60min (BTUH) = 216,913 BTU Firing Rate

      I use the example above which is far fetched but it shows you that that system with its heat emitters that may be designed at a 20 degree DT with a supply flow of 9 GPM, most likely has a heat loss load in the 90,000 BTU range, 100,000- 140,000 BTU mod-con most likely installed)- (10,000 BTU's per GPM).

      So you can see in this cold start, warm house scenario, the boiler would be at its full fire rate, till the secondary returns warm up.

      So primary/secondary piping doesn't necessary warm the return water, but as mentioned before, perhaps a cast iron system that needs to hit 130-140 within 1 minute, or a residential copper tube needing to hit 100-110 with 7 GPM consistently both to avoid condensing, would certainly be a reason for P/S.

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      • #33
        Re: can I add a zone like this?

        "There are a plethora of installation errors on every type of system. Even still 10 systems installed exactly the same, will all have different issues. Every system has it's own personality."

        Systems don't have personality, and there is not one that is the same as another. Be it a change in pressure, an extra elbow, longer pipe, location of accessories, venting, lower/higher voltage, and 100 other reasons.

        If the "personality" is being troublesome or difficult its not the location, its a install issue.
        They can only function to the best of the as they are designed and installed.

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