SHI System Maintenance & Troubleshooting 2 — Questions and Answers
Question 1: A solar thermal system shows a significant drop in flow rate over time. Which component is most likely causing this restriction?
- Expansion tank
- Scale buildup in heat exchanger (Correct answer)
- Pressure relief valve
- Air vent valve
Correct answer: Scale buildup in heat exchanger
Mineral scale deposits inside the heat exchanger restrict flow over time, especially in hard-water areas.
Question 2: When inspecting a solar collector during a maintenance visit, you notice the glazing has turned yellowish and opaque. What is the most appropriate corrective action?
- Clean the glazing with acetone
- Replace the glazing material (Correct answer)
- Apply a UV-protective coating
- Increase the collector tilt angle
Correct answer: Replace the glazing material
Yellowed, opaque glazing indicates UV degradation and loss of transmittance, requiring replacement to restore system efficiency.
Question 3: A differential temperature controller is cycling the pump on and off every few seconds. Which condition is the most likely cause?
- Controller set points are too wide apart
- Sensor is correctly reading marginal solar gain
- The on/off differential is set too narrow (Correct answer)
- The heat exchanger is undersized
Correct answer: The on/off differential is set too narrow
A very narrow differential between on and off set points causes rapid cycling; widening the differential stabilizes pump operation.
Question 4: During a pressure test of a closed-loop solar system, pressure drops steadily over 30 minutes with no visible leaks. Where should you check next?
- Pump impeller seal
- Expansion tank bladder or diaphragm (Correct answer)
- Collector absorber plate
- Differential controller wiring
Correct answer: Expansion tank bladder or diaphragm
A failed expansion tank bladder or diaphragm allows fluid to fill the tank completely, causing pressure loss without an external leak.
Question 5: What is the purpose of performing a glycol concentration check during annual maintenance of a drainback-type solar system?
- Glycol concentration controls collector stagnation temperature
- Drainback systems use glycol as the primary heat transfer fluid
- Some drainback systems use dilute glycol; concentration affects freeze protection (Correct answer)
- Glycol prevents scale formation on the absorber
Correct answer: Some drainback systems use dilute glycol; concentration affects freeze protection
While many drainback systems use water only, some use dilute glycol solutions, and annual concentration checks ensure adequate freeze protection.
Question 6: A solar water heating system produces hot water in the morning but the storage tank temperature stops rising by noon on clear days. What is the most probable cause?
- Collector is undersized for the load
- Tempering valve is mixing in cold water prematurely
- High-limit aquastat is shutting down the pump (Correct answer)
- Insulation on storage tank is inadequate
Correct answer: High-limit aquastat is shutting down the pump
A high-limit aquastat or controller cutoff stops the circulation pump when the tank reaches a set maximum temperature to prevent scalding.
Question 7: Which maintenance task is specifically required to preserve the performance of a selective absorber coating on a flat-plate collector?
- Annual repainting with high-temperature black paint
- Keeping the collector glazing clean to prevent moisture ingress
- Avoiding harsh chemical cleaners when washing the glazing (Correct answer)
- Draining the collector seasonally to prevent coating oxidation
Correct answer: Avoiding harsh chemical cleaners when washing the glazing
Selective absorber coatings can be damaged by harsh chemicals that might contact them if glazing seals fail; using mild cleaners on glazing protects the coating.
SHI System Maintenance & Troubleshooting 2
A solar thermal system shows a significant drop in flow rate over time.
Which component is most likely causing this restriction?