CSLB C-46 Solar ContractorSolar Thermal System InstallationHard
A solar thermal installer is troubleshooting a system where the collector fluid is getting excessively hot (stagnation temperatures) but the storage tank is not heating adequately. The circulating pump is confirmed to be running, and the differential controller is operating correctly. The installer also observes a significant pressure drop across the heat exchanger on the solar loop side. What is the most likely cause?
- AA faulty check valve in the domestic hot water return line
- BInsufficient glycol concentration in the solar loop
- CA dirty or fouled heat exchanger on the solar loop side
- DAn undersized expansion tank on the DHW side
Show answer & explanationAnswer & explanation
Correct answer: C. A dirty or fouled heat exchanger on the solar loop side
Excessively hot collectors with a cool tank, despite the pump running and controller working, point to a failure in heat transfer. A significant pressure drop across the heat exchanger on the solar loop side, combined with these symptoms, strongly suggests that the heat exchanger is dirty or fouled, impeding fluid flow and heat transfer within the solar loop itself.
Why the other options are wrong
- A. A faulty check valve in the DHW return line would affect the flow of potable water, not the solar loop's pressure drop or the transfer of heat from the solar fluid.
- B. Insufficient glycol concentration would reduce freeze protection and potentially heat transfer efficiency, but it wouldn't cause a significant pressure drop across the heat exchanger or directly lead to the specific symptoms of a fouled heat exchanger.
- D. An undersized expansion tank on the DHW side would cause pressure fluctuations on the potable water side, not directly impede solar heat transfer or cause a pressure drop across the solar loop heat exchanger.
Fouled Heat Exchanger
The accumulation of deposits (scale, sludge, corrosion products) on the surfaces of a heat exchanger, which reduces its efficiency and can impede fluid flow.
- Reduces heat transfer rate
- Causes increased pressure drop
- Leads to collector overheating/stagnation
- Requires cleaning or replacement
Memory trick: Collector boils, tank is cold; heat exchanger's story untold.