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Flow sensor for closed loop?

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  • Flow sensor for closed loop?

    Hi all,
    I'm seeking recommendations for devices that can measure flow rate (i.e., in-line flow meter) that can handle the glycol solution and 180 deg F temperatures in a solar thermal closed loop. I've got a nice solar thermal system that's been working fine for 6+ years (2 Steibel Eltron Sol 25 Plus collectors on the roof and a SBB-300 Plus tank in the basement). I've got it wired so I can monitor temperatures in all parts of the system, and now I'm interested in monitoring flow rate through the closed loop. A device that outputs a digital pulse would be ideal. Any suggestions? Thanks

  • #2
    Originally posted by sroof View Post
    Hi all,
    I'm seeking recommendations for devices that can measure flow rate (i.e., in-line flow meter) that can handle the glycol solution and 180 deg F temperatures in a solar thermal closed loop. I've got a nice solar thermal system that's been working fine for 6+ years (2 Steibel Eltron Sol 25 Plus collectors on the roof and a SBB-300 Plus tank in the basement). I've got it wired so I can monitor temperatures in all parts of the system, and now I'm interested in monitoring flow rate through the closed loop. A device that outputs a digital pulse would be ideal. Any suggestions? Thanks
    Industrial flow meters will work - magnetic, ultrasound, other types. They are all over the net and can be quite costly, especially if not OEM pricing.

    This is probably not applicable to your situation, but FYI, Pentair peddles a line of rotameters that are good to +240F. and 150 PSI if purchased w/NPT fittings. They cost about $100 or so. I have 2 of them but my system is single loop and domestic H2O circulates directly thorough the collectors. Don't know availability or, more importantly, suitability of rotameters for glycol given the different sp. gr, viscosity and other transport prop. of glycol etc., and the greater variability of those prop. as f(temp.). They do work quite well and are surprisingly accurate (to me anyway) for H2O.

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    • #3
      Perhaps I don't need a permanent flow sensor, but I would like to get a decent estimate of the flow rate through my closed loop. Any clever suggestions for determining flow rate in a closed loop? My loop is 3/4 copper and fairly long (maybe 200 ft roundtrip) with lots of bends as it winds across the roof and down to the basement. The circulator is a standard Taco 007-5F. My only idea is to measure the pipe length carefully and calc its volume, then time how long it takes hot water water to travel from the collectors to the storage tank when the pump turns on after being off for a while. Anybody have another way of determining flow rates in pipes?

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      • #4
        If you know the fluid temperatures accurately at the point of the sensor, you can calculate the flow rate from the equilibrium temperature of a self-heated sensor which is exposed to the flow. Not a simple analog meter, but a calculation done with a PLC, embedded controller, or external PC.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          There are numerous available for hot water system - typically pulse generators. If you search you should find them. I don't have the right hard drive connected right now but maybe later on today. The type I am talking about were not all that expensive.
          [SIGPIC][/SIGPIC]

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          • #6
            Originally posted by sroof View Post
            Perhaps I don't need a permanent flow sensor, but I would like to get a decent estimate of the flow rate through my closed loop. Any clever suggestions for determining flow rate in a closed loop? My loop is 3/4 copper and fairly long (maybe 200 ft roundtrip) with lots of bends as it winds across the roof and down to the basement. The circulator is a standard Taco 007-5F. My only idea is to measure the pipe length carefully and calc its volume, then time how long it takes hot water water to travel from the collectors to the storage tank when the pump turns on after being off for a while. Anybody have another way of determining flow rates in pipes?
            Correcting my brain fart from yesterday: A direct reading rotameter of the type I wrote about on this thread will work. Cost to me was $95 for the meter and costs for the fittings and time, but that was 6 + yrs. ago. Still running trouble free BTW.
            You will still need a correction factor for the specific gravity of the glycol sol. you are using at the fluid temp - a fairly straight forward calc., and a table or correlation for the sp. gravity of the solution as f(temp.). Sounds like you're doing a lot of the same stuff I got involved in after retirement and still monkey with in my spare time.

            I apologize for the mental lapse.

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            • #7
              I have been using Blue-White Industries flow meters, reasonably priced and no problems so far.

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