Picbasic-l Solar Pool Heating

Q: Just a thought about your pool heater -- I agree that timing might not be a needed complication. What you are interested in, really, is that there is some heat gain going on. That means that even with the pump running the outlet temperature must, by definition, be greater than the inlet temperature. The difference might be small, but if it is not there -- then you are radiating heat rather than absorbing it. Remember that heat always flows "downhill" so if the pipe is hotter than the air plus sun it will radiate just as well as it absorbs when the temp is the other way around. I suggest that you use three sensors, one shaded air temp, one inlet to the absorber and one on the outlet from the absorber. Turn the pump on when the outlet temp is some amount larger than the air temp. Then switch to measuring the outlet-inlet temp. Turn the pump off only when that number goes to zero or negative for some period of time. The time is relative so a simple delay loop is good enough. If you want it to wait for first turn on until mid-day I would vote for the CdS light sensor plus the timing loop rather than RTC. If you go RTC you would have to adjust for sunrise/sunset times, daylight savings time, etc. A lot of unnecessary bother.

A: let's get really off topic. Here in Las Vegas I have your basic palm-lined swimming pool, but because of the low humidity the water temperature is always well below 20 deg C even when the air temperature is > 45 deg C. Heating would be nice but the commercial outfits are expensive. The propane heating system is prohibitive for anything but the spa. Others in the list are probably in the same predicament. Just how are you arranging your solar heater and what kind of tubing are you using? How are you orienting it? Are you operating the tubing in series or series parallel? Are you using the main pool pump and then diverting flow via a solenoid system, or are you using a separate pump, and if so, why? Why not use a photovoltaic cell in max current generating mode (operating into a low resistance, so that I*R voltage is proportional to insolation intensity) with a 16F876 10-bit A/D and use a math model to predict optimal turn-on/turn-off times (back to PICs again)? Inquiring minds want to know.

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