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Grumman solar system

Randys1
Randys1 Member Posts: 2
I have just installed a Grumman solar hot water system. Its a 1978 system that was never used. It has 5 panels, 85 gal storage tank with heat exchanger, I have found mixed conflicting information as to where the hot water side from the panels should attach to the heat exchanger that’s built into the tank, my question is should the hot water leaving the panels hook into the bottom of the heat exchanger at the bottom of the tank or into the top of the exchanger. The system is up and running producing 150 degree water on a sunny day. The other question I have is the solar controller is not functioning in the auto mode which I believe is because of the sensor I installed on the panels. What ohms should I have on the panels vs the tank sensor , the controller is what came mounted on the tank. Any help would be greatly appreciated . 

Comments

  • Larry Weingarten
    Larry Weingarten Member Posts: 2,785
    Hi @Randys1 , This photo might help with the plumbing question. About the sensor question, if it is an open loop system, there is a freeze sensor along with the two thermal sensors. That system uses the OL 100 module. I'll guess that they are 10K ohm sensors. The old solar tech trick is to put both sensors together in a glass of water (keeping just the copper part of the sensor in water) and then read resistance of both. If they are far apart, clearly one is bad. If not, it's not a sensor problem. That's a start.

    Yours, Larry
  • hot_rod
    hot_rod Member Posts: 18,227
    A tank with internal coil? The hot from the collector should go in the upper coil connection. This give you a counterflow exchange.
    Got a pic?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Randys1
    Randys1 Member Posts: 2
    Thanks for the help . So Iam plumbed with hot going in the bottom, will reverse and update thanks
  • hot_rod
    hot_rod Member Posts: 18,227
    Same for indirect tanks, solar tanks, any heat exchanger really.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sol_Brother
    Sol_Brother Member Posts: 10
    In all the Grumman systems I have seen the heat exchanger is in the pump module, so if it is of this type (pressurized glycol in the collector loop/potable water on the other side) your tank should not have a coil — just extra ports. Hot Rod is right that the heated return normally goes in an upper port (or mid-way up the tank if it has a built-in upper element backup), but I have always suspected that after some time pumping the tank is so destratified that it would not make any difference. And you do not want to be pulling water from the very bottom (say, a Tee off the tank drain port) because you will suck all the sediment from the tank into the heat exchanger.
    And all I have seen used controls made by Independent Energy with 10k Ohm sensors with a negative temperature-resistance coefficient. That is, the resistance is 10k at 77° and goes down as the temperature increases. You can find a chart for this at http://www.deltatcontrols.com/manuals/SAS-10-RT.pdf
    There is some testing info in the posting to this board called "Goldline GL-30".
    Another concern is that you have so many collectors for your tank size, which could lead to overheating the water and/or boiling the glycol. So unless you are guaranteed to be using hot water all day, every day or your collectors are seriously shaded you might need to cover most of them with a tarp in summer.
    Sol Brother