SHI Solar Thermal System Design & Components 2 — Questions and Answers
Question 1: What is the primary function of an expansion tank in a closed-loop solar thermal system?
- To increase system flow rate
- To accommodate fluid volume changes due to temperature fluctuations (Correct answer)
- To filter debris from the heat transfer fluid
- To regulate collector inlet temperature
Correct answer: To accommodate fluid volume changes due to temperature fluctuations
An expansion tank absorbs the increased volume of heat transfer fluid as it expands when heated, preventing dangerous pressure spikes in a closed-loop system.
Question 2: Which type of collector is best suited for high-temperature applications above 180°F (82°C)?
- Unglazed flat plate collector
- Evacuated tube collector (Correct answer)
- Polymer pool collector
- Single-glazed flat plate collector
Correct answer: Evacuated tube collector
Evacuated tube collectors maintain high efficiency at elevated temperatures because the vacuum insulation minimizes heat loss to the environment.
Question 3: In a drainback solar thermal system, what prevents collector freeze damage when the pump shuts off?
- Antifreeze fluid circulates continuously
- Water drains back to a reservoir by gravity (Correct answer)
- A heat trace cable warms the collectors
- The check valve holds fluid in the collectors
Correct answer: Water drains back to a reservoir by gravity
Drainback systems rely on gravity to drain all water from the collectors into a reservoir when the pump stops, leaving no fluid to freeze.
Question 4: What is the recommended minimum tilt angle for a solar thermal collector installed primarily for domestic hot water in the continental US?
- 5 degrees
- 10 degrees
- Latitude minus 15 degrees
- Latitude plus 5 degrees (Correct answer)
Correct answer: Latitude plus 5 degrees
For year-round domestic hot water, collectors are typically tilted at latitude plus 5 to 15 degrees to optimize winter solar gain and maximize annual output.
Question 5: A differential temperature controller in a solar thermal system typically activates the pump when collector temperature exceeds storage temperature by:
- 1–2°F (0.5–1°C)
- 5–10°F (3–6°C) (Correct answer)
- 20–30°F (11–17°C)
- 50°F (28°C)
Correct answer: 5–10°F (3–6°C)
Most differential controllers are set to turn the pump on when the collector is 5–10°F warmer than storage and off when the difference drops to about 2–5°F.
Question 6: Which component in a solar thermal system protects against excessive pressure buildup and is required by code?
- Pressure-reducing valve
- Temperature and pressure (T&P) relief valve (Correct answer)
- Backflow preventer
- Air vent
Correct answer: Temperature and pressure (T&P) relief valve
A T&P relief valve is mandatory on solar storage tanks and opens automatically to discharge fluid if pressure or temperature exceeds safe limits.
Question 7: What is the purpose of the heat exchanger in an indirect solar thermal system?
- To measure heat output of the collectors
- To transfer heat from the collector loop fluid to the potable water without mixing them (Correct answer)
- To remove air from the collector loop
- To regulate collector inlet pressure
Correct answer: To transfer heat from the collector loop fluid to the potable water without mixing them
The heat exchanger separates the collector fluid (which may contain antifreeze or be non-potable) from the domestic water supply while allowing thermal energy to transfer between them.
SHI Solar Thermal System Design & Components 2
What is the primary function of an expansion tank in a closed-loop solar thermal system?