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chapter 11
Copyright Cengage Learning. Powered by Cognero.
Page 1
Indicate whether the statement is true or false.
1. The use of drainback protection (rather than antifreeze protection) involves a thermal penalty associated with the use of
a heat exchanger.
a.
True
b.
False
2. Once a siphon is established, it is important to maintain it for the duration of the solar energy collection cycle.
a.
True
b.
False
3. The collector temperature sensor should be mounted on the piping outside the collector housing.
a.
True
b.
False
4. Maximum head loss is generally independent of flow rate.
a.
True
b.
False
5. Drainback systems can use either unpressurized or pressurized thermal storage tanks.
a.
True
b.
False
Indicate the answer choice that best completes the statement or answers the question.
6. What could occur if system installers fail to compensate for roof sags?
a.
The increased average weight of the system may cause the roof to fail.
b.
The drainback system will not operate.
c.
The system could have a steeper pitch than required.
d.
Low points are created where freezing water may occur.
7. Which is a benefit of a closed-loop drainback system?
a.
Its components last longer because they must be made of non-corroding materials.
b.
It can be connected directly to a space heating distribution system.
c.
It can be operated at a slight negative pressure.
d.
It does not need to accommodate the thermal expansion of system water.
8. What is the most typical function of a sight tube in a drainback system?
a.
to determine the proper water level in the tank
b.
to determine whether the circulator is functioning at capacity
c.
to view the collector temperature sensor
d.
to accommodate the increased volume of water as temperatures increase
9. What is different about the collector circulator for drainback-protected systems as compared with that of antifreeze-
protected systems?
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chapter 11
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Page 2
a.
It only needs a single circulator as opposed to two circulators.
b.
It must not allow air bubbles to be entrained in the return piping.
c.
It must lift water from the static water level in the tank to the top of the collector array.
d.
It must have potential for overcoming increased frictional head loss in the collector piping.
10. What are the two primary factors in sizing the air space in pressurized drainback systems?
a.
the average temperature of the outside air and the pitch of the collector piping
b.
the number of circulators and the system pressure
c.
the pitch of the collector piping and the system pressure
d.
the amount of water that drains back and the increased volume of system water with temperature
11. What results when two identical circulators are installed in series?
a.
Twice the head is produced at a given flow rate.
b.
Half the head is produced at a given flow rate.
c.
The head does not change, but the flow rate is cut in half.
d.
Less heat is lost from the system.
12. What is the recommended minimum downward pitch for drainback-protected solar collector tubes?
a.
¼ inch per foot of horizontal travel
b.
½ inch per foot of horizontal travel
c.
¾ inch per foot of horizontal travel
d.
1 inch per foot of horizontal travel
13. What is the minimum recommended insulation value for piping and components in a drainback system?
a.
R-2
b.
R-3
c.
R-10
d.
R-12
14. What happens if the water velocity reaching the top of the collector array is too low?
a.
It will entrain many air bubbles.
b.
It will not entrain all the air.
c.
The siphon will be maintained.
d.
The return piping will fill completely with water.
15. Which statement is NOT true of drainback-protected solar combisystem designs?
a.
They must have sufficient pitch to allow water to drain back.
b.
They have more than one operating mode.
c.
They must have make up water systems.
d.
Their electrical schematics will vary.
16. Which freeze protection design can be used on domestic water heating systems?
a.
antifreeze-protection only
b.
drainback-protection only
Name:
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chapter 11
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Page 3
c.
either antifreeze- or drainback-protection
d.
neither antifreeze- or drainback-protection
17. How can maximum siphon height be increased within a closed-loop drainback system?
a.
increasing the water temperature
b.
decreasing the pressure
c.
increasing the pressure
d.
increasing water levels
18. What is the recommended flow velocity for establishing a siphon?
a.
1 foot per second
b.
2 feet per second
c.
3 feet per second
d.
5 feet per second
Name:
Class:
Date:
chapter 11
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Page 4
Answer Key
1. False
2. True
3. False
4. False
5. True
6. d
7. b
8. a
9. c
10. d
11. a
12. a
13. b
14. b
15. c
16. c
17. c
18. b
