SHI Case Analysis & Practical Application 3 — Questions and Answers
Question 1: A flat-plate collector system installed at 35° latitude is being evaluated for year-round performance. The owner wants to maximize annual output. What tilt angle should be recommended?
- Equal to the latitude angle (35°) (Correct answer)
- Latitude minus 15° for summer bias
- Latitude plus 15° for winter bias
- 90° (vertical) to shed snow
Correct answer: Equal to the latitude angle (35°)
Tilting collectors at the site latitude optimizes annual energy collection by balancing summer and winter sun angles.
Question 2: A solar pool heating system in Florida runs the pool pump but the water temperature is not rising. The installer measures no flow through the unglazed collectors. What is the most likely cause?
- Collectors are tilted at wrong angle
- Diverter valve has failed in bypass position (Correct answer)
- Pool pump is undersized for solar loop
- Collectors need cleaning
Correct answer: Diverter valve has failed in bypass position
A failed or stuck diverter (actuator) valve that remains in bypass position will circulate pool water without routing it through the solar collectors.
Question 3: During a site assessment for a solar thermal retrofit, the installer finds existing 3/4" copper supply lines to the water heater. The solar system design calls for a 40 GPH flow rate through the heat exchanger. What should the installer verify?
- That 3/4" copper can handle the required flow without excessive pressure drop (Correct answer)
- That the pipe must be replaced with 1" diameter to meet code
- That PEX is substituted for all copper piping
- That flow rate is reduced to 20 GPH regardless of pipe size
Correct answer: That 3/4" copper can handle the required flow without excessive pressure drop
The installer must verify that existing 3/4" copper piping can handle the design flow rate within acceptable pressure drop limits before reusing it.
Question 4: A homeowner in Minnesota wants a solar space heating system. The installer recommends a solar combisystem. What distinguishes a combisystem from a standard solar DHW system?
- It uses evacuated tube collectors exclusively
- It provides both domestic hot water and space heating from a single solar array and storage (Correct answer)
- It requires a separate storage tank for each application
- It operates only during summer months
Correct answer: It provides both domestic hot water and space heating from a single solar array and storage
A solar combisystem integrates domestic hot water and space heating loads, using a single collector array and thermal storage to serve both needs.
Question 5: An evacuated tube collector system is installed in a cold climate. After a heavy snowfall, the owner notices the evacuated tubes shed snow faster than neighboring flat-plate collectors. What property causes this?
- Higher absorber temperature melts snow from the tube surface
- Round tube geometry presents less surface area to accumulated snow (Correct answer)
- Evacuated tubes have hydrophobic coatings
- Evacuated tubes operate at lower temperatures
Correct answer: Round tube geometry presents less surface area to accumulated snow
The cylindrical shape of evacuated tubes provides minimal horizontal surface for snow accumulation, and any snow tends to slide off more readily than from flat-plate surfaces.
Question 6: A contractor is proposing a solar water heating system with a solar fraction of 70% for a commercial kitchen. The owner asks what 'solar fraction' means in practical terms. How should the installer explain it?
- 70% of the roof area is covered with solar collectors
- 70% of the annual water heating energy demand is supplied by the solar system (Correct answer)
- The system operates at 70% efficiency on average
- 70% of the cost is offset by tax credits
Correct answer: 70% of the annual water heating energy demand is supplied by the solar system
Solar fraction is the percentage of the total annual energy demand for water heating that is met by the solar energy system, with the remaining 30% supplied by the backup heater.
Question 7: A glycol-based solar thermal system has been operating for 8 years. A technician tests the fluid and finds pH of 5.8 and freeze protection only to 15°F. The system is located in Colorado. What is the correct action?
- Add more glycol concentrate to restore freeze protection only
- Flush and replace the glycol solution with fresh properly inhibited fluid (Correct answer)
- Neutralize the acid with baking soda and continue operation
- Add pH buffer and retest in one year
Correct answer: Flush and replace the glycol solution with fresh properly inhibited fluid
Acidic glycol with degraded inhibitors must be fully replaced — partial corrections are unreliable and acidic fluid will continue to corrode system components.
SHI Case Analysis & Practical Application 3
A flat-plate collector system installed at 35° latitude is being evaluated for year-round performance.
The owner wants to maximize annual output.
What tilt angle should be recommended?