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UNIT 42 REVIEW QUESTIONS ANSWER KEY GO BACK TO INDEX
42-1) What three environmental conditions have the most effect on comfort?
42-2) List four ways the human body expels heat?
42-3) Why does the air’s relative humidity affect comfort?
42-4) How is the air volume affected by temperature?
42-5) What is the relationship between air volume and air weight (density)?
42-6) What are grains and what air property is measured in grains?
42-7) In general, which is heavier humid air or dry air?
42-8) What is a wet bulb temperature reading?
42-9) How is relative humidity measured?
42-10) What is the dew point temperature?
42-11) What is the difference between specific humidity and relative humidity?
42-12) What is a psychrometric chart?
42-13) List the air properties that are plotted on a psychrometric chart and give a brief
description of each.
Dry bulb temperature – the normal air temperature in degrees Fahrenheit
Wet bulb temperature – the temperature of a thermometer with a wet bulb
42-14) What would the mixed air temperature be for a system with 20% outdoor air if the
outdoor temperature is 10°F and the return air temperature is 75°F?
42-15) Identify the scales represented by the lines on Figure 42-49.
A –% Relative humidity
B – dry bulb temperature
42-16) Use the psychrometric chart in Figure 41-1 to look up the missing data in this
table.
Dry
Wet
Relative
Dew
Specific
Volume Enthalpy
3
87.5°F 62°F 23% 45 44 grains 14 ft
3
28 BTU/lb
3
42-17) What pressure units are used for measuring duct pressures?
42-18) What two pressures are created by air moving through the duct system?
42-19) What instruments are used for measuring duct pressure?
42-20) Explain how to take a static pressure reading on a duct system.
42-21) Explain how to take a velocity pressure reading on a duct system.
Insert one pressure probe facing the airflow to read total pressure and
42-22) What units are used to measure air velocity?
42-23) What tools are used to measure air velocity?
150
42-24) What units are used to measure air volume?
42-25) What is the airflow through a register with a free area of 72 square inches if the
air velocity is 300 feet per minute?
42-26) How does a flowhood measure airflow?
42-27) What is the velocity of the air in a duct with a total pressure of 0.15 inches wc and
a static pressure of 0.1 inches wc?
42-28) What is the airflow in CFM through a 10 inch by 20 inch duct with a total
pressure of 0.15 inches wc and a static pressure of 0.1 inches wc?
42-29) What is the typical airflow per ton of residential air conditioning equipment?
