I'm a new board member at a condominium association in the Los Angeles area. The complex has an outdoor spa with two heating systems: natural gas and solar. That's where I can use some help figuring things out.
First issue: the control system design puzzles me. The two systems' temp. sensors and controllers are independent of each other. The main spa pump works on a timer, running steadily from 6 am to 10 pm. It circulates water through the gas heater but not (or only a little) through the solar collectors. Each morning, by the time that the sun is high enough to heat the collectors, the gas heater has long since heated up the water to its service temperature.
So here's the control system design issue: Logically, because the gas heater's thermostat will maintain the proper water temperature regardless of what the solar system does, this suggests that the solar system's controller will hardly ever find that the water temp. is cool enough to warrant turning on the solar pump in order to contribute hot water from the collectors, even during midday sunny conditions. (Occasional observation indeed suggests that the solar pump is hardly ever running during midday.)
Am I missing something? Is this really the optimal way to supply solar energy to a spa?