Solar Heating System Operation and Maintenance
Solar Heating System Operation and Maintenance
O&M questions test scheduled inspection, glycol condition, freeze-point and pH testing, collector cleaning, sensor calibration, and component wear. The goal is to preserve heat output and prevent freeze, corrosion, and scald failures over a 20-year life.
Fluid and freeze protection
Test glycol annually with a refractometer and pH strips. New propylene glycol is often pH 8–9.5; a reading below 7–8 indicates inhibitor depletion and possible corrosion. Freeze point must remain below the local design low; if it has risen, replace the fluid rather than topping up with water. Glycol life is typically 5–10 years, shorter at stagnation temperatures.
Mechanical and control checks
Inspect for leaks, insulation damage, pump noise, and relief-valve discharge. Check expansion-tank precharge and bladder integrity. Verify collector and tank sensors against a calibrated thermometer; a drifting sensor causes short cycling. Clean collectors when soiling or bird droppings reduce output; do not use abrasive cleaners on selective coatings.
Worked example
A system reports low solar gain. Glycol sample shows freeze point −5°F, pH 6.5, and dark color; the design freeze point is −20°F. The fluid has degraded and is no longer protecting the loop. Replace the full charge with a premixed propylene glycol at the correct concentration, purge air, and recheck pH and freeze point. Topping up with water would raise the freeze point and dilute inhibitors.
Traps
Adding water to a glycol loop; checking pH with a pool kit only; ignoring a relief valve that drips; assuming a pump failure when the sensor is bad; and cleaning a selective absorber with an abrasive pad. Log freeze point, pH, pressures, ΔT, and flow at each visit.