CSLB C-46 Solar ContractorSolar Thermal System InstallationMedium
A solar thermal installer is commissioning a new closed-loop glycol system. During the startup, the installer notices that the pump runs continuously, but the collector outlet temperature is consistently much lower than expected, even on a sunny day. The storage tank temperature is also not rising significantly. Which of the following is the most likely cause?
- AThe system is air-bound, preventing proper fluid circulation.
- BThe differential controller's 'on' temperature setting is too low.
- CThe check valve in the collector loop is installed backward.
- DThe expansion tank is undersized for the system volume.
Show answer & explanationAnswer & explanation
Correct answer: A. The system is air-bound, preventing proper fluid circulation.
If the pump is running but no significant heat transfer is occurring and collector temperatures are low, an airlock in the piping is a common cause. Air pockets prevent the fluid from circulating effectively, leading to poor heat transfer.
Why the other options are wrong
- B. A low 'on' setting would cause frequent pump cycling, not continuous running with low heat transfer.
- C. A backward check valve would prevent flow entirely or cause resistance, but the question implies the pump is running continuously, which might not happen if flow was completely blocked.
- D. An undersized expansion tank would typically lead to pressure issues, not a lack of heat transfer.
Air Binding in Solar Thermal
Air binding occurs when air pockets become trapped in the solar thermal piping, preventing the circulation of heat transfer fluid and severely reducing system efficiency.
- Common during initial fill or after maintenance.
- Symptoms include pump running with little or no heat transfer and low collector temperatures.
- Requires proper purging procedures to resolve.
Memory trick: Air in the pipes, heat takes a hike.