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Thermostatic mixing valve recommendation - 180 degrees

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  • #31
    Originally posted by J.P.M. View Post
    I checked out the website and the OG-100 cert. prior to my first post to this thread. It seems like a fine product. I would comment however, that given the published, certified efficiency curves, which are quite similar to other very similar designs but without inert gas, I'd continue to question the benefit of such design features, i.e., the inert gas.

    My question was about the very high collector temps. shown in your graph.

    1.) I assume those are stagnation or VERY low flow rate fluid temps. or absorber plate temps. at zero or no flow. ? The efficiency curves for either of the Buderus collectors (selective or semi/higher emissivity selective surface treatments) do not allow for a fluid outlet temp. that high unless the flowrate < ~ 20-30 lbm/hr. or so - essentially stagnation. Where is the temp. sensor located, and of what type is it ?

    2.) While they are a robust looking product, cooking in the sun for several months under zero or low flow conditions probably won't increase their efficiency or service life. Because the Argon is sealed, which I'm sure it is, without some accommodation for gas expansion, the elevated temps. will increase the gas pressure, perhaps causing the gas to exchange with/leak into the environment sooner than it does anyway.

    3.) Those elevated summer temps may be a problem for any working fluid (water/glycol ?) in the collector loop.

    4.) FWIW, I'd cover all of the collectors once the heating season is over, or at least some of them if the system also provides DHW, and/or change the control logic to avoid prolonged +300 deg. F. temps. Repeated and short thermal cycling over say, a 200 deg. F temp. swing on a regular basis (if DHW summer service is involved), probably isn't a collector's best friend either.
    You are correct in your assumptions about excessive time spent under stagnation conditions.
    The sks4 panels operate at a very low flow rate normally and they utilize steam back when the load is satisfied, so yes they can be under stagnation conditions frequently during the summer month's. All systems need to be designed properly to minimize stagnation temps.
    I would not recommend installing 10 sks4 on a roof in direct sunlight for solar thermal heating or any non drainback system for that matter with out a way to handle the excess production during the summer month's. A dump zone would be required, or as is the case in the simulation that I posted 3 panels were to be mounted on the roof for domestic hot water year round. The remaining 7 panels were to be mounted under a 3 ft existing overhang on the south wall of the barn at a 75 degree inclination. The panels would be shaded during the summer month's.

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    • #32
      Originally posted by LucMan View Post
      You are correct in your assumptions about excessive time spent under stagnation conditions.
      The sks4 panels operate at a very low flow rate normally and they utilize steam back when the load is satisfied, so yes they can be under stagnation conditions frequently during the summer month's. All systems need to be designed properly to minimize stagnation temps.
      I would not recommend installing 10 sks4 on a roof in direct sunlight for solar thermal heating or any non drainback system for that matter with out a way to handle the excess production during the summer month's. A dump zone would be required, or as is the case in the simulation that I posted 3 panels were to be mounted on the roof for domestic hot water year round. The remaining 7 panels were to be mounted under a 3 ft existing overhang on the south wall of the barn at a 75 degree inclination. The panels would be shaded during the summer month's.
      It's not my system, but if it was, I'd have put all 10 panels on the roof in one spot, up the flowrate with a different series/parallel arrangement and perhaps increase eff. a bit, set the elevation at optimum winter tilt and cover some of the panels as needed in the summer. Seems like less plumbing and perhaps fewer/easier controls.

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      • #33
        Originally posted by J.P.M. View Post
        It's not my system, but if it was, I'd have put all 10 panels on the roof in one spot, up the flowrate with a different series/parallel arrangement and perhaps increase eff. a bit, set the elevation at optimum winter tilt and cover some of the panels as needed in the summer. Seems like less plumbing and perhaps fewer/easier controls.
        The manufacturers specify the flow rate range for their panels.
        Covering and uncovering panels on roofs is usually not an option for clients.

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