4B Older Practice Questions Air Conditioning

Question 1

Air is approximately what composition by volume:

a. 79% N2 and 21% CO2.
b. 79% O2 and 21% N2.
c. 79% N2 and 21% O2.
d. 79% CO2 and 21% O2.
e. 79% H2 and 21% Water vapour

Answer 1

c. 79% N2 and 21% O2.

Question 2

To find various properties of air _____ chart is used.

a. A Psychrometric.
b. A Ringleman.
c. A Mollier.
d. A Dew point.
e. An Enthalpy

Answer 2

a. A Psychrometric

Question 3

The heat content of air is called the _____ of the air.

a. Temperature.
b. Humidity.
c. Enthalpy.
d. Psychrometry.
e. Entropy.

Answer 3

c. Enthalpy

Question 4

The relative humidity is plotted on a psychrometric chart along the:

a. Lines curved upwards from the lower left to the upper right side of the chart.
b. Horizontal axis on the bottom of the chart.
c. Vertical lines and read along the horizontal scale at the bottom of the chart.
d. Saturation line and plotted along the horizontal lines.
e. Horizontal lines and read along the left side scale.

Answer 4

a. Lines curved upwards from the lower left to the upper right side of the chart.

Question 5

Which of the following instruments use a battery operated fan to draw air over the thermometer bulbs?

a. Hydrometer.
b. Aspirating psychrometer.
c. Sling psychrometer.
d. Dry psychrometer.
e. Potentiometer.

Answer 5

b. Aspirating psychrometer

Question 6

The wet-bulb temperature scale is read on a psychrometric chart along the:

a. Right vertical axis.
b. Left vertical axis.
c. Saturation line and sloping downward to the right.
d. Horizontal axis on the bottom of the chart.
e. Top horizontal axis.

Answer 6

c. Saturation line and sloping downward to the right.

Question 7

Dalton’s Law of partial pressure states that:

a. The sum of the mass of air and water vapour in a vessel is equal to the total pressure.
b. In a mixture of two or more gases each will exert a partial pressure that is equal to the pressure that it would exert if it filled that space alone.
c. The pressure exerted by two or more gases on the walls of the containing vessel is equal to a constant.
d. Water vapour must be included when calculating air pressures.
e. For every pressure there is an equal and opposite pressure.

Answer 7

b. In a mixture of two or more gases each will exert a partial pressure that is equal to the pressure that it would exert if it filled that space alone.

Question 8

Relative humidity is:

a. The ratio of water vapour in the air compared to the total amount water vapour the air could contain at a given temperature.
b. Equal to the dry bulb temperature divided by the wet bulb temperature.
c. Equal to the wet bulb temperature divided by the dry bulb temperature.
d. The ratio of the mass of water vapour divided by the mass of dry air.
e. The ratio of the mass of water vapour divided by the mass of wet air.

Answer 8

a. The ratio of water vapour in the air compared to the total amount water vapour the air could contain at a given temperature

Question 9

Absolute or specific humidity is:

a. The actual mass of moisture present in a specific amount of air.
b. The maximum mass of moisture that a specific amount of air can hold.
c. The ratio of the mass of moisture contained in a specific amount of air to the maximum amount of moisture this specific amount of air can contain.
d. The mass of moisture present in a specific amount of air at that absolute temperature.
e. A specific amount of air saturated with moisture

Answer 9

a. The actual mass of moisture present in a specific amount of air.

Question 10

Air conditioning involves:

a. Only the cooling of the air in a conditioned space.
b. The control of the air temperature, humidity, air circulation, and removal of contaminants.
c. Only the control of air temperature.
d. Only the control of humidity and temperature.
e. Only air purification.

Answer 10

b. The control of the air temperature, humidity, air circulation, and removal of contaminants

Question 11

A device for measuring relative humidity is called:

a. A dew point tester.
b. An R. H. gauge.
c. An aspirating gauge.
d. A psychrometer.
e. A chronometer

Answer 11

d. A psychrometer

Question 12

The composition of dry air is generally taken to be:

a. 23.2% oxygen and 76.8% nitrogen by volume.
b. 21% oxygen and 79% nitrogen by weight.
c. 23.2% oxygen and 76.8% nitrogen by weight.
d. 24% oxygen and 76% nitrogen by volume.
e. 21% oxygen and 79% carbon dioxide by volume.

Answer 12

c. 23.2% oxygen and 76.8% nitrogen by weight.

Question 13

In the S.I. (metric) system the enthalpy of air is measured in:

a. °C.
b. %.
c. BTU’s/kg of dry air.
d. kJ/kg of dry air.
e. kW/kg of dry air

Answer 13

d. kJ/kg of dry air.

Question 14

The dry-bulb temperature scale is read on a psychrometric chart along the:

a. Left vertical axis.
b. Right vertical axis.
c. Saturation line and sloping downward to the right.
d. Top horizontal axis.
e. Horizontal axis on the bottom of the chart.

Answer 14

e. Horizontal axis on the bottom of the chart.

Question 15

The specific volume of air is the volume of:

a. 1 kg of air at atmospheric pressure in cm3.
b. 1 g of air at atmospheric pressure in m3.
c. 1 kg of air at atmospheric pressure in m3.
d. 1 g of air occupied at any temperature and pressure.
e. 1 kg of air at any pressure

Answer 15

c. 1 kg of air at atmospheric pressure in m3.

Question 16

The enthalpy values are found on a psychrometric chart by:

a. Plotting a line through the required point on the chart parallel to the lines of the two, enthalpy scales, one on the left side and the other on the right side of the chart.
b. Plotting a horizontal line from one of the enthalpy scales.
c. Plotting a vertical line from one of the enthalpy scales.
d. Simply reading values on one of the enthalpy scales.
e. Plotting a line from one of the enthalpy scales

Answer 16

a. Plotting a line through the required point on the chart parallel to the lines of the two, enthalpy scales, one on the left side and the other on the right side of the chart.

Question 17

The dew point is the:

a. Temperature at which dew forms on the grass.
b. Temperature at which water vapour will start to be absorbed into the air.
c. Temperature below which water vapour will start to condense out of the air.
d. Pressure below which water vapour will start to condense out of the air.
e. Temperature at which water will start to evaporate.

Answer 17

c. Temperature below which water vapour will start to condense out of the air

Question 18

Relative humidity is:

a. The actual mass of moisture present in a specific amount of air.
b. The ratio of the mass of moisture contained in a specific amount of air to the maximum amount of moisture this specific amount of air can contain.
c. The maximum mass of moisture that a specific amount of air can contain.
d. The ratio of the mass of air contained in a specific amount of moisture to the maximum amount of air this specific amount of moisture can contain.
e. A specific amount of air saturated with moisture

Answer 18

b. The ratio of the mass of moisture contained in a specific amount of air to the maximum amount of moisture this specific amount of air can contain.

Question 19

The specific volume on a psychrometric chart:

a. Is plotted on vertical lines and read on the horizontal scale at the bottom of the chart.
b. Is plotted on horizontal lines and read on the vertical scale on the left side of the chart.
c. Is plotted on horizontal lines and read on the vertical scale on the right side of the chart.
d. Has its lines originate on the volume scale along the saturation line and they slope steeply down to the right of the chart.
e. Is plotted on vertical lines and read on the horizontal scale at the top of the chart.

Answer 19

d. Has its lines originate on the volume scale along the saturation line and they slope steeply down to the right of the chart.

Question 20

The term “relative humidity” applies to the:

a. Percentage of moisture in the air as compared to the amount of moisture the air can hold at a specific temperature.
b. Weight of moisture in the air.
c. Dryness fraction of the air.
d. Amount of moisture in the air.
e. Amount of humidity in the air.

Answer 20

a. Percentage of moisture in the air as compared to the amount of moisture the air can hold at a specific temperature

Question 21

Dew point can be best defined as the:

a. Absolute temperature at which air, upon heating, will evaporate moisture.
b. Absolute temperature at which air, upon cooling, will vaporize moisture.
c. Temperature that air will begin to evaporate moisture.
d. Temperature at which air, upon cooling, becomes saturated and will begin to condense out water vapour below this temperature.
e. Atmospheric pressure at which air will condense moisture.

Answer 21

d. Temperature at which air, upon cooling, becomes saturated and will begin to condense out water vapour below this temperature.

Question 22

Psychrometers are:

a. Instruments used to determine the purity of air.
b. Instruments used to determine the relative humidity of air.
c. Meters used to measure the density of air.
d. Instruments used to measure atmospheric pressure.
e. Meters used to measure air speed

Answer 22

b. Instruments used to determine the relative humidity of air.

Question 23

Dry-bulb temperature is:

a. The absolute temperature corresponding to the atmospheric pressure.
b. The same as the wet-bulb temperature if the relative humidity is less than 100%.
c. Not required to find the relative humidity.
d. The temperature of the air measured with an ordinary thermometer.
e. The dew point temperature.

Answer 23

d. The temperature of the air measured with an ordinary thermometer.

Question 24

Which law describes the existence of moisture in the air in vapour or evaporated state?

a. Newton’s laws of gravity.
b. 1st Law of Thermodynamics.
c. Dalton’s Law of Partial Pressures.
d. 2nd Law of Thermodynamics.
e. Boyle’s Ideal Gas Law.

Answer 24

c. Dalton’s Law of Partial Pressures

Question 25

Standard air is the:

a. Mass of 1 cubic meter of dry air at 20° C and atmospheric pressure.
b. Mass of a cubic meter of air at atmospheric conditions.
c. Volume of air at ambient temperature and atmospheric pressure.
d. Volume of 1 kg of dry air at 21° C and atmospheric pressure at sea level or 101.325 kPa.
e. Volume of 1 kg of air at 15° C and 100 kPa

Answer 25

d. Volume of 1 kg of dry air at 21° C and atmospheric pressure at sea level or 101.325 kPa.

Question 26

Specific humidity is the:

a. Ratio of the actual amount of water vapour present in the air to the amount of water vapour the air can contain when it is saturated.
b. Same as specific volume of humid air.
c. Actual moisture content of air expressed as kg of moisture per kg of dry air.
d. Ratio of dry air to moisture.
e. Moisture content of air of 100% relative humidity

Answer 26

c. Actual moisture content of air expressed as kg of moisture per kg of dry air.

Question 27

Enthalpy of air depends on the:

a. Pressure, temperature and relative humidity of the air.
b. Relative humidity of the air only.
c. Pressure and temperature of the air only.
d. Air velocity.
e. Temperature of the air only.

Answer 27

a. Pressure, temperature and relative humidity of the air

Question 28

Psychrometry is the study of the behaviour of:

a. People.
b. Air.
c. Water vapour.
d. Mixtures of air and water.
e. Ideal gases.

Answer 28

d. Mixtures of air and water

Question 29

Wet-bulb temperature is:

a. The temperature indicated by a thermometer having it’s bulb covered by a water-wetted wick or cloth and the bulb is exposed to a rapidly moving stream of air.
b. The same as the dry-bulb temperature if the relative humidity is less than 100%.
c. The dew point temperature.
d. Always less than the dry-bulb temperature.
e. Not required to find the relative humidity

Answer 29

a. The temperature indicated by a thermometer having it’s bulb covered by a water-wetted wick or cloth and the bulb is exposed to a rapidly moving stream of air.

Question 30

30. The volume of standard air is _____ m3/kg of dry air.
    a. 0.533
    b. 0.633
    c. 0.733
    d. 0.833
    e. 0.933.

Answer 30

d. 0.833

Question 31

The dew point temperature scale is read on a psychrometric chart along the:

a. Top horizontal axis.
b. Saturation line, using the same scale as wet-bulb temperature, but is plotted along the horizontal axis.
c. Horizontal axis on the bottom of the chart.
d. Right vertical axis.
e. Left vertical axis

Answer 31

b. Saturation line, using the same scale as wet-bulb temperature, but is plotted along the horizontal axis.

Question 32

The difference between the wet and dry bulb readings is called the:

a. Wet bulb depression.
b. Relative humidity.
c. Dew point.
d. Correction factor.
e. Dry bulb depression

Answer 32

a. Wet bulb depression

Question 33

Air that is fully saturated has a relative humidity of:

a. 90%
b. 96.8%
c. 100%
d. 101%
e. 10%.

Answer 33

c. 100%

Question 34

What is wet-bulb depression?

a. Lowering the thermometer bulb into water.
b. The sum of the wet-bulb temperature and the dry-bulb temperature.
c. Decrease in relative humidity.
d. The difference between the dry-bulb temperature and the wet-bulb temperature.
e. Decrease in absolute humidity.

Answer 34

d. The difference between the dry-bulb temperature and the wet-bulb temperature

Question 35

The specific humidity scale on a psychrometric chart is along the:

a. Horizontal axis on the bottom of the chart.
b. Vertical axis and right side.
c. Horizontal axis at the top of the chart.
d. Left saturation line.
e. Vertical axis and left side.

Answer 35

b. The sum of the wet-bulb temperature and the dry-bulb temperature.

Question 36

Using the psychrometric chart, find the specific volume if the dry bulb temperature is 20° C and the wet bulb temperature is 15° C.

a. 0.859 m3/kg
b. 0.842 m3/kg
c. 0.90 m3/kg
d. 0.80 m3/kg
e. 0.87 m3/kg.

Answer 36

b. 0.842 m3/kg

Question 37

The intersection between the line running vertically from the point on the dry bulb scale and the downward diagonally running line from the wet bulb scale is defined as the:

a. Dew point temperature.
b. Partial pressure.
c. Reference point.
d. Specific volume.
e. Relative humidity

Answer 37

c. Reference point

Question 38

An increase in air, flow increases heat loss of the body by which of the following methods:

1. Convection
2. Conduction
3. Evaporation
4. Radiation
   a. 1, 4
   b. 2
   c. 1, 3, 4
   d. 1, 3
   e. 1, 2, 3.

Answer 38

e. 1, 2, 3.

Question 39

If 5.0 cubic meters per second of air enters a heating coil at 20° C dry bulb and 15° C wet bulb, and leaves the heating coil at 30° C dry bulb, what is the change in enthalpy?

a. 52 kW
b. 59.4 kW
c. 42 kW
d. 65.2 kW
e. 51.7 kW.

Answer 39

b. 59.4 kW

Question 40

Which of the following statements about cooling and
dehumidification is false?
a. Air washers are used to dehumidify air.
b. When air leaves the washer it will be close to 100% relative
humidity.
c. The spray water carries off the latent heat of condensation of the water vapour in the air.
d. Dry bulb temperatures are increased.
e. Dew point temperatures are lowered.

Answer 40

d. Dry bulb temperatures are increased

Question 41

Which of the following properties cannot be found of the psychrometric chart?

a. The dew point temperature.
b. The partial pressure.
c. The specific humidity.
d. The enthalpy.
e. The relative humidity.

Answer 41

b. The partial pressure.

Question 42

An average effective temperature chart can be applicable under the following conditions except when:

a. Customary indoor clothing is worn.
b. The heating method is warm air.
c. Activity is high or heavy muscular work.
d. The heating method is steam.
e. The heating method is hot water.

Answer 42

c. Activity is high or heavy muscular work.

Question 43

Using the psychrometric chart, find the relative humidity if the dry bulb temperature is 25° C and the wet bulb temperature is 25° C.

a. 50%
b. 90%
c. 100%
d. 95%
e. 60%.

Answer 43

c. 100%

Question 44

Which of the following statements about effective temperature is true?

a. Charts with metric units cannot be used for making adjustments in SI units.
b. Relative humidity does not affect the relative temperature.
c. For each combination air velocity remains constant.
d. The test involves people all dressed in different amounts of clothing for each combination.
e. It can be easily determined by using a thermometer

Answer 44

c. For each combination air velocity remains constant.

Question 45

The comfort of human beings is affected by the atmospheric conditions that surround them, which of the following is not an atmospheric condition that affects comfort?

a. Temperature.
b. Relative humidity.
c. Saturation temperature.
d. Air movement.
e. Air cleanliness

Answer 45

c. Saturation temperature

Question 46

If 5.0 cubic meters per second of air enters a heating coil at 20° C dry bulb and 15° C wet bulb, and leaves the heating coil at 30° C dry bulb, what is the volume of air leaving the coil?

a. 5.94 m3/s
b. 5.0 m3/s
c. 5.17 m3/s
d. 4.2 m3/s
e. 5.72 m3/s

Answer 46

c. 5.17 m3/s

Question 47

If 5.0 cubic meters per second of air enters a heating coil at 20° C dry bulb and 15° C wet bulb, and leaves the heating coil at 30° C dry bulb, what is the mass of air flowing?

a. 5.94 kg/s
b. 6.84 kg/s
c. 5.0 kg/s
d. 6.2 kg/s
e. 5.4 kg/s.

Answer 47

a. 5.94 kg/s

Question 48

Using the psychrometric chart, find the enthalpy if the dry bulb temperature is 20° C and the wet bulb temperature is 15° C.

a. 40 kJ/kg
b. 45 kJ/kg
c. 55 kJ/kg
d. 50.5 kJ/kg
e. 42 kJ/kg

Answer 48

e. 42 kJ/kg

Question 49

The body needs considerable time to adjust when moving from one space to another when temperature and humidity conditions vary widely. This may be described as what?

a. Shock effect.
b. Comfort zone.
c. Comfort condition.
d. Effective temperature.
e. Air/Motion effect

Answer 49

a. Shock effect

Question 50

Evaporative cooling is:

a. Heating and humidification of the air.
b. Heating and dehumidification of the air.
c. Cooling and humidification of the air.
d. Cooling and dehumidification of the air.
e. Cooling of air only.

Answer 50

c. Cooling and humidification of the air.

Question 51

The comfort of human beings is affected by:

a. Temperature
b. Relative humidity
c. Air cleanliness
d. Air movement
e. All of the above.

Answer 51

e. All of the above

Question 52

Using the psychrometric chart, find the specific volume if the dry bulb temperature is 25° C and the wet bulb temperature is 20° C.

a. 0.84 m3/kg
b. 0.852 kg/m3
c. 0.85 m3/kg
d. 0.90 m3/kg
e. 0.862 m3/kg.

Answer 52

e. 0.862 m3/kg.

Question 53

Using the psychrometric chart, find the dewpoint temperature at a dry bulb temperature of 25° C and a wet bulb temperature of 20° C.

a. 17.5°C
b. 14°C
c. 20°C
d. 16°C
e. 19°C.

Answer 53

a. 17.5°C

Question 54

During sensible heating, only the:

a. Relative humidity remains unchanged.
b. Relative humidity increases.
c. Dew point temperature increases.
d. Specific volume decreases.
e. Relative humidity decreases

Answer 54

e. Relative humidity decreases

Question 55

If 5.0 cubic meters per second of air enters a heating coil at 20° C dry bulb and 15° C wet bulb, and leaves the heating coil at 30° C dry bulb, what is the change in enthalpy?

a. 52 kJ/kg
b. 42 kJ/kg
c. 15 kJ/kg
d. 20 kJ/kg
e. 10 kJ/kg.

Answer 55

e. 10 kJ/kg.

Question 56

A measure of comfort that involves the combined effects of the dry bulb temperature, relative humidity and air movement is defined as:

a. Comfort zone.
b. Effective temperature.
c. Comfort condition.
d. Shock effect.
e. Psychrometric climate

Answer 56

b. Effective temperature.

Question 57

During sensible heating which of the following results is true?

a. Dry bulb temperature lowers.
b. Wet bulb temperature remains constant.
c. Relative humidity increases.
d. Enthalpy remains constant.
e. None of the above.

Answer 57

e. None of the above.

Question 58

During sensible heating the dry bulb temperature and the wet bulb temperature are raised, and the:

a. Dew point remains unchanged.
b. Specific humidity is increased.
c. Specific humidity is decreased.
d. Dew point temperature increases.
e. Dew point temperature decreases

Answer 58

a. Dew point remains unchanged

Question 59

During the winter, the majority of people feel comfortable when the effective temperature is between:

a. 15 and 19° C
b. 20.5 and 24° C
c. 19 and 24° C
d. 17.2 and 21.7° C
e. 16 and 19.5° C

Answer 59

d. 17.2 and 21.7° C

Question 60

Using the psychrometric chart, find the specific humidity if the dry bulb temperature is 20° C and the wet bulb temperature is 15° C.

a. 0.009 kg of water vapour per kg of dry air.
b. 0.008 kg of water vapour per kg of dry air.
c. 0.010 kg of water vapour per kg of dry air.
d. 0.0085 kg of water vapour per kg of dry air.
e. 0.0085 kg of dry air per kg of water vapour

Answer 60

d. 0.0085 kg of water vapour per kg of dry air.

Question 61

Using the psychrometric chart, find the relative humidity if the dry bulb temperature is 20° C and the wet bulb temperature is 15° C.

a. 50%
b. 58%
c. 52%
d. 68%
e. 62%.

Answer 61

b. 58%

Question 62

During the summer, the majority of people feel comfortable when the effective temperature is between:

a. 15 and 19° C
b. 20.5 and 24° C
c. 19 and 24° C
d. 17.2 and 21.7° C
e. 16 and 19.5° C

Answer 62

c. 19 and 24° C

Question 63

Using the psychrometric chart, find the dew point temperature at a dry bulb temperature of 20° C and a wet bulb temperature of 15° C.

a. 20° C
b. 14° C
c. 11.5° C
d. 10° C
e. 16° C.

Answer 63

c. 11.5° C

Question 64

Using the psychrometric chart, find the enthalpy if the dry bulb temperature is 25° C and the wet bulb temperature is 20° C.

a. 55 kJ/kg
b. 57 kJ/kg
c. 60 kJ/kg
d. 50 kJ/kg
e. 65 kJ/kg.

Answer 64

b. 57 kJ/kg

Question 65

Shock effect is:

a. A constant dry bulb temperature of 25° C.
b. A constant effective temperature of 15° C.
c. The discomfort felt when a person moves from a much hotter space to a much cooler place or vice versa.
d. More apparent in the winter.
e. A constant wet bulb temperature of 25° C.

Answer 65

c. The discomfort felt when a person moves from a much hotter space to a much cooler place or vice versa.

Question 66

Using the psychrometric chart, find the specific humidity if the dry bulb temperature is 25° C and the wet bulb temperature is 20° C.

a. 0.12 kg of water vapour per kg of dry air.
b. 0.012 kg of water vapour per kg of dry air.
c. 0.0125 kg of water vapour per kg of dry air.
d. 0.013 kg of water vapour per kg of dry air.
e. 0.0115 kg of water vapour per kg of dry air.

Answer 66

c. 0.0125 kg of water vapour per kg of dry air.

Question 67

Air used for ventilating purposes in an office building should be kept within a certain range of relative humidity as indicated below:

a. 30 to 50%
b. 30 to 70%
c. 40 to 50%
d. 50 to 60%
e. 10 to 30%.

Answer 67

b. 30 to 70%

Question 68

Using the psychrometric chart, find the relative humidity if the dry bulb temperature is 25° C and the wet bulb temperature is 20° C.

a. 62%
b. 70%
c. 52%
d. 72%
e. 75%.

Answer 68

a. 62%

Question 69

Effective temperature is defined as a measure of comfort that involves:

a. The effects of relative humidity.
b. The effects of air movement.
c. The effects of dry bulb temperature.
d. The effects of wet bulb temperature.
e. All of the above

Answer 69

e. All of the above