CSLB C-46 Solar ContractorSolar Thermal System InstallationMedium
A solar thermal installer is troubleshooting a closed-loop glycol system that is experiencing frequent overheating and stagnation, even with adequate solar radiation. The differential controller appears to be functioning correctly, but the pump is not circulating fluid as expected. What is the MOST likely cause of this issue?
- AAir is trapped in the collector loop, causing air binding.
- BThe storage tank thermostat is set too low.
- CThe glycol concentration is too high, increasing viscosity.
- DThe collector temperature sensor is faulty, giving false readings.
Show answer & explanationAnswer & explanation
Correct answer: A. Air is trapped in the collector loop, causing air binding.
Air trapped in the collector loop can cause 'air binding,' preventing the circulation pump from effectively moving the heat transfer fluid. This leads to stagnation and overheating in the collectors, despite the pump attempting to run.
Why the other options are wrong
- B. A low thermostat setting would cause the pump to run more frequently, not less, leading to cooler tank temperatures.
- C. While high viscosity can reduce flow, air binding is a more common and severe cause of complete circulation failure.
- D. If the sensor were faulty, the controller would either not turn on the pump (if reading low) or turn it on unnecessarily (if reading high), but not directly cause a circulation block when the pump is 'not circulating as expected'.
Air Binding
A condition in hydronic systems where trapped air prevents the circulation of fluid, leading to system failure or reduced performance.
- Common in collector loops due to high points where air can accumulate.
- Prevents heat transfer and can lead to collector overheating/stagnation.
- Resolved by proper air purging during installation and maintenance.
Memory trick: When the solar fluid won't flow, trapped air is often the foe.