Optimal System Design To Supply Solar Energy To A Spa?

[David Stein]

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?

[LBuehler]

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?

I have plumbed solar into my spa. I have yet to install the panels and utilize the motor and controls. During the winter of course their is no solar gain so it is off and winterized. During the summer I will bypass my heaterall together and just let the solar do its thing. Usually 85 - 95 is a good temp. during a warm day. If at night i want it hotter I will open the bypass valves to my heater.

[chem geek]

Ideally, the two systems would be tied to a more intelligent controller that can do a priority so that solar is used when it can (i.e. when the temperature in the panels exceeds that in the spa water by some minimum amount) while the gas is used when the solar cannot. My IntelliTouch controller for my pool has such a priority option called "Solar Preferred".