Lesson 2
Answers

1. Briefly describe the two main types of active solar water-heating systems?

Answer: A direct system circulates the potable water from storage through the collectors. An indirect system circulates a heat transfer fluid through the collectors and a heat exchanger. The potable water is heated by the heat exchanger.

2. In passive solar water heating systems, what drives the fluidís circulation from the collector(s) to the storage tank?

Answer: As solar energy heats the fluid it becomes less dense and it to rises (floats) up through the collector.

3. What is the most common solar collector type?

Answer: A flat-plate design

4. When is a double-walled heat exchanger required in a solar water-heating system?

Answer: When the heat transfer fluid is toxic, such as ethylene glycol and when the plumbing codes say that a double-walled heat exchanger is required.

5. Why are refrigerant heat transfer fluids, such as chlorofluorocarbon, being phased out of solar heating systems?

Answer: They have a negative effect on the ozone layer of the atmosphere.

6. In a typical residential, closed-loop solar water heating system what type of pump is commonly used?

Answer: A cast-iron, centrifugal pump

7. What is the difference between static head and dynamic head?

Answer: Static head is the pressure resulting from the height and weight of the column of the fluid in the system. Dynamic head is the pressure needed to overcome the friction losses in the plumbing system.

8. Where should the controllerís sensors be placed in a solar water-heating system?

Answer: At the collector outlet and at the bottom of the storage tank.

9. Why should a check valve be installed on a solar water-heating system? Where should a spring-type check valve be installed?

Answer: To prevent reverse thermosyphon, nighttime heat losses through the collector, the spring-type check valve should be installed in the plumbing line between the collector outlet and the storage tank.

10. What is the main function of the expansion tank in a closed-loop system?

Answer: To allow thermal expansion of the heat transfer fluid without rupturing the pipes in the system.

11. Where should temperature gauges be installed to indicate how the system is functioning in an open-loop and in a closed-loop solar water heating system?

Answer: In an open-loop systemís collector loop, one gauge should be installed in the line from the collector and one in the line from storage to the collector. In a closed-loop systemís collector loop, one gauge should be installed at the inlet and one at the outlet of the heat exchanger. In both the open- and closed-loop systems, a gauge should be installed to indicate the temperature of the water leaving storage going to the conventional hot water heater.