I've built a solar hot water collector using glycol as the heating transmission fluid. When the collector is 8 degrees hotter than the hot tub water, the collector's circulation pump turns on and runs the hot glycol through a heat exchanger mounted in the hot tub enclosure. The Gatsby spa I have runs a circulation pump constantly, so I took advantage of this, and put the heat exchanger in the circulation path. Before I put in the heat exchanger, the path was: Filter -> Circulation Pump -> Heater -> Tub Interior. Now the path is Filter -> Heat Exchanger -> Circulation Pump -> Heater -> Tub Interior.
I set the tub thermostat to 95, thinking that the solar would boost the temperature up to 104 or so. I figured that this would keep the tub at a warm minimum temperature, and it would only take about 90 minutes to bring it up to temperature with the tub's heater if it had been a cloudy day.
Everything seemed fine when I first turned it all on. I was concerned that the addition of the heat exchanger and the extra piping involved might slow the flow down enough to register as a clogged filter, but no problem.
The first problem arose when the collector started working and circulating hot water through the exchanger. The spa shut down with the error message Oht, meaning that it sensed an overheating condition. The manual says that this will trigger when the tub temperature is 120 F or if the heater enclosure temp is 125 F. Since the heater is downstream of the heat exchanger, I figured that the hot water circulating through the heater was triggering this error. The tub was only at 98, so it wasn't the first condition.
My crude fix was to simply remove the temperature sensor that's wing-nutted to the heater enclosure. Since then, what happens when it's sunny is that the the tub gets up to 99 or so, and then the circulation pump just stops. No error codes. It will start up again if I press the temperature adjust buttons, or cycle the tub power.
Any idea what's going on? I'm wondering:
-Could the heater enclosure temperature sensor just reading the air temp inside the enclosure be a problem?
-Could the fact that the tub's temp is rising above the thermostat setting be triggering some kind of unreported error?
It's a head scratcher. I may have to resort to creating an independent circulation system that will run just when the solar is heating but it seemed so great to have this automatic circulation system running all the time and I'd love to take advantage of it.
Thanks for your thoughts,
Tom
-- Edited by tomasaur on Monday 16th of May 2016 09:03:40 PM
-- Edited by tomasaur on Monday 16th of May 2016 09:04:54 PM
