Exam (elaborations)
HVAC MIDTERM EXAM
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Exam of 8 pages for the course HVAC at HVAC (HVAC MIDTERM EXAM)
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HVAC MIDTERM EXAMOne watt (1 W) of electrical energy is equivalent to ________ Btu's of heat energy. -
Answers-3.413 Btus
Latent heat is also know as.
A. Heat quantity
B. Heat Intensity
C. Hidden Heat
D. Specific Heat - Answers-C. Hidden Heat
Why does a heat pump require three-function control? - Answers-Because a heat pump
performs three functions-it provides cooling, it provides heating, and it must defrost the
outdoor coil when ice forms on it.
What is the coefficient of performance (COP) of a heat pump? - Answers-A comparison
of how much heat the heat pump is producing compared to how much heat an electric
furnace would produce using the same amount of electricity.
What three types of compressors are used in residential heat pump applications? -
Answers-Reciprocating, scroll, and rotary.
Name two problems that occur when flash gas enters a TEV while a system is
operating? - Answers-The valve operates inefficiently, the system
loses capacity, and superheat increases.
Typical superheat values measured at the evaporator outlet of a properly operating heat
pump system is about how many degrees? - Answers-10 to 12 degrees
((Ref: 124/2))
TEVs that limit the pressure created by an expanding bulb charge are called what? -
Answers-Maximum operating pressure (MOP)
If a system operates correctly in one cycle and pumps down when switched to the other
cycle, what problem is indicated? - Answers-A defective TEV (in such cases, the power
element could be defective) or a stuck check valve.
How can you inspect ball-type check valves for free movement of the ball? - Answers-
Valves of this type may be checked for free movement with a magnet when the system
is not running.
, Why are suction-line accumulators used in heat pump systems? - Answers-To protect
the compressor from liquid refrigerant.
Where in the refrigerant circuit is an accumulator located? - Answers-Between the
reversing valve and the compressor inlet.
How does the oil return to the compressor in a heat pump system that is equipped with
a suction-line accumulator? - Answers-Through the small hole drilled in the lower
portion of the U-tube.
What is superheat?
A. A vapor with a temperature above its saturation temperature.
B. The temperature of refrigerant leaving the evaporator
C. The temperature of refrigerant entering the compressor.
D. None of the above - Answers-A. A vapor with a temperature above its saturation
temperature.
The indoor coil of a heat pump system serves as the _____ during the cooling season,
and as the _____ during the heating season. - Answers-evaporator, condenser
In which component of a refrigeration system is heat removed? - Answers-The
Condenser
What is the most common type of heat pump used in residential applications? -
Answers-Air-to-air split system
What indoor air volume (expressed in cfm) would be required for a heating unit that has
a 50°F temperature rise and an output of 80,000 Btuh?
* See formula page - Answers-1481 cfm
How much auxiliary heat will be required on a design day when a home's heat loss is
35,600 Btuh and the heat pump output is 17,200 Btuh?
* See formula page - Answers-5.39 kW or 5,390 watts
Why does the indoor coil of a heat pump need more area than the indoor coil of a
cooling-only unit? - Answers-To prevent the condensing temperatures and
corresponding head pressures from becoming too high during the heating cycle.
Describe the method used to free up a sticky main valve slide. - Answers-With the
system operating at normal operating pressures, rapidly energize and deenergize the
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