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setting the difference setpoint controller

ecletrical Member Posts: 22
I'm pumping from 8 flat plates into a 1500 sq ft slab - no heat exchanger (there is diversion to an indirect should the temp go to high). I'd like suggestions on setting the delta t target to start pumping considering the massive size of the "heat exchanger" (tubing to concrete)


  • hot_rod
    hot_rod Member Posts: 22,262
    Is there any tank

    in the circuit between the collectors and heat loops? Where is sensor 2 located?

    The default setting on solar controllers is often 12 on 8 off. They are adjustable of course, but you want to prevent short cycling so it is a balancing act.

    Also, most of the newer solar controls have variable speed functions, that can help with the cycling and might allow you to tighten up the on/ off settings.

    I don't know that there is an ideal, one size fits all, setting, ideally you would have a data logger to record the operation of the system, watching the pump cycles, temperature swings, etc after you make adjustments.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ecletrical
    ecletrical Member Posts: 22
    no tank

    no tank between collector and heat loops - directly into slab. However there is a 2nd circ which pumps to an indirect - this diverts flow to the tank based on the temperature of the supply line from the collector, etc.(the two circulators never operate at the same time). Otherwise it always goes to the slab. To answer your question - the 2nd sensor is in the tank, no sensor in the slab. The slab will never over heat. When the heating season is over a switch will divert all flow to the tank.

    The tank will be kept at some minimum temp during the heating season - say 42F, after that all heat will go to the slab. This is not a temperature controlled space - it is an equipment shed for a dairy farm; the purpose to minimize condensation on equipment.

    Thanks for the suggestion, I will datalog cycling. Then maybe I can fine tune.
  • Fortunat
    Fortunat Member Posts: 103
    add a sensor in the slab

    If you can still do it, I'd add a sensor in the slab as S2 and then probably  just use the delta's that Rod suggested (12 and 8).

    If the pipe run from the collectors is very long, maybe wind them up to 17 and 12 or something like that.

    Finally, if your controller supports variable speed pumping, I'd definitely enable it here. When pumping to a low temperature load (like a direct slab is likely to be), we find variable speed control extends the solar day by close to an hour at each end compared to a fixed speed pump which is optimized for the high insolation periods.

    best of luck


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