Risk Assessment & Mitigation Flashcards

Which property of propylene glycol heat transfer fluid makes it preferable over ethylene glycol in solar thermal systems?

Answer: Lower toxicity if leaked

Propylene glycol is preferred because it is non-toxic, making incidental contact with potable water or skin far safer than toxic ethylene glycol.

A solar collector reaches stagnation temperature on a hot summer day. What is the PRIMARY risk this creates in a glycol-filled system?

Answer: Glycol degradation producing acidic compounds

Stagnation temperatures can exceed 200°C, causing glycol to break down into acidic byproducts that corrode system components.

When pressure-testing a newly installed solar thermal loop, what fluid should be used to safely detect leaks before commissioning?

Answer: Compressed nitrogen

Nitrogen is inert, dry, and non-damaging, making it the safest medium for pressure testing solar thermal piping before fluid fill.

An installer notices the expansion vessel pre-charge pressure is lower than the system static head. What risk does this create?

Answer: The bladder will not compress, leading to pressure spikes that open the relief valve

If pre-charge pressure is less than static head, the bladder stays fully compressed and cannot absorb thermal expansion, causing the pressure relief valve to discharge repeatedly.

What is the correct response when an installer finds that a pressure relief valve on a solar thermal system is weeping continuously?

Answer: Replace the relief valve and investigate the cause of overpressure

A weeping relief valve signals a real overpressure condition; the valve must be replaced (it may be damaged) and the root cause—such as undersized expansion vessel—must be corrected.

Which chemical hazard is specifically associated with draining a solar thermal system that has been in service for several years without fluid maintenance?

Answer: Exposure to acidic, degraded glycol with low pH

Long-service glycol degrades into organic acids with pH as low as 4–5, which can cause skin and eye irritation during draining.

A solar domestic hot water system is set to deliver water at 60°C (140°F) to prevent Legionella growth. What additional risk does this temperature introduce?

Answer: Scalding hazard at fixtures, requiring thermostatic mixing valves

Water stored or delivered at 60°C can cause rapid scalding; thermostatic mixing valves at point of use are required to blend water down to a safe delivery temperature.