CSLB C-46 Solar ContractorSolar Thermal System InstallationMedium
A homeowner reports that their closed-loop glycol solar thermal system is no longer providing adequate hot water, even on sunny days. The installer checks the system and finds the collector outlet temperature to be 180°F and the storage tank inlet temperature to be 100°F, while the pump is running normally. The glycol solution appears dark brown and smells burnt. What is the most likely cause of this performance degradation?
- AA blockage in the cold water supply to the tank
- BA faulty differential controller
- CGlycol degradation due to overheating
- DInsufficient glycol concentration causing freezing
Show answer & explanationAnswer & explanation
Correct answer: C. Glycol degradation due to overheating
The symptoms of dark brown, burnt-smelling glycol, coupled with a high collector temperature and a noticeable temperature difference between collector and tank inlet, strongly indicate that the glycol has degraded due to prolonged overheating. Degraded glycol loses its heat transfer properties and can become acidic, damaging the system.
Why the other options are wrong
- A. A blockage in the cold water supply would primarily affect the availability of cold water to the tank, not the heat transfer fluid's condition or the collector's high temperature.
- B. A faulty differential controller might cause the pump to not run at all or run at inappropriate times, but it wouldn't directly cause the glycol to degrade and change color/smell.
- D. Insufficient glycol concentration would primarily lead to freezing damage, not necessarily dark, burnt-smelling fluid, and the collector temperature would likely not reach 180°F if flow was completely stopped by ice.
Glycol Degradation
The breakdown of propylene or ethylene glycol in solar thermal systems due to prolonged exposure to high temperatures, leading to reduced heat transfer efficiency and system damage.
- Causes fluid to turn dark brown/black
- Produces a burnt odor
- Forms acidic byproducts and sludge
- Reduces heat transfer effectiveness
Memory trick: Brown and burnt, a high temp fright; glycol's broken, lost its light.