I’m continuing to learn more about my DHW solar thermal system that came with my house. It’s got two Steibel Eltron Sol 25 Plus collectors on the roof and a SBB-300 Plus tank in the basement and has been operating pretty much fine for the past 7+ years. However, the controller (Goldline TL-30) shuts off the circulator when the tank temperature reaches about 145 deg F (measured on the hot water pipe leaving the tank, well before the mixing valve). I’ve got the TL-30 high limit dialed to its max (supposedly 220 deg F). So two questions: In general, what’s an appropriate high temperature limit for the storage tank? And, why might the TL-30 high limit shutoff be kicking in at such a low temperature?
One important detail - the storage tank sensor (a GLSB-10k best as I can tell) is not in the lower thermal well as expected, but rather simply taped to the metal cleanout port cover near the bottom of the storage tank. This port is covered with a cap with 2” of foam insulation, so it seems like the sensor should be getting a decent temperature reading from the lower part of the storage tank. If anything, I think the sensor would be underestimating the temperature in the storage tank and therefore allowing the tank to reach a higher temperature before the controller’s high limit kicks in. I’ve made a few quick measurements and the 10k sensor changes resistance with temperature roughly as expected. Could the precise temperature-resistance response of the sensor degrade over time?
One important detail - the storage tank sensor (a GLSB-10k best as I can tell) is not in the lower thermal well as expected, but rather simply taped to the metal cleanout port cover near the bottom of the storage tank. This port is covered with a cap with 2” of foam insulation, so it seems like the sensor should be getting a decent temperature reading from the lower part of the storage tank. If anything, I think the sensor would be underestimating the temperature in the storage tank and therefore allowing the tank to reach a higher temperature before the controller’s high limit kicks in. I’ve made a few quick measurements and the 10k sensor changes resistance with temperature roughly as expected. Could the precise temperature-resistance response of the sensor degrade over time?
Comment