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solar tank sensor placement

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mark schofield
mark schofield Member Posts: 153
in Solar
What would be the optimum placement for the tank sensor in a solar system?. If it is up top, the system will shut down too soon with the water at the bottom staying cold. But with the sensor nearer the bottom, The circulator will com on in the evening when cold street water enters the tank and it seems some of the days gain will be pumped back to the panels and actually loose temperature. My system is an older Grumman Sunstream, wall mounted HX with 2 pumps. The controller has a set differential (4 deg) with no option to shut the system down when the panels/glycol drop below a user set temperatures. A 30 year system that continues to work perfectly. Except for possibly dumping heat back out under certain conditions. Thanks for any thoughts.   Mark S

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  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
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    Differential controller

    Your differential controller has a delta-t "on" (probably 10 to 20F), and a delta-t "off" (+4F).



    The pump will shut off when the collectors are 4 degrees hotter than the bottom of the storage tank.





    These settings will prevent the heat wasting you are worried about, assuming that the pump is pulling water from the bottom of the tank.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • ABSolar
    ABSolar Member Posts: 41
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    sensor placement

    Sensor on the tank goes down on the bottom to read "coldest water temp available".  Always.  IF the controller is working correctly, then it should NOT operate the circulator UNLESS the collector is hotter than the storage tank bottom temperature.  I think your controller is a goldline C-30 or independant C-100.  They were susceptable to large static shocks that would disable them.  If you have to replace your controller, you can disconnect and remove the old unit, and either (space permitting) replace with a new modern controller or install a new controller on the wall nearby and install longer line voltage cable from the controller to your existing (2) pumps.  You can splice additional length of low voltage (18-2) sensor cable if need be (but don't splice the 120 volt cables to the pumps - use new cable direct from controller to pumps!) 
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