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29 Cards in this Set
- Front
- Back
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What is Psychrometrics ?
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(1) Psychrometrics is the study of the physical principles governing the behavior of moist air.
(2) Psychrometrics is the measurement of water vapor and heat in an air sample. It is used in the refrigeration industry, the design of clean rooms, certain manufacturing processes, and for theoretical applications. |
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Name the four comfort factors.
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(1) Temperature
(2) Humidity (3) Air movement (4) Air cleanliness |
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State three ways the body gives off heat.
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Conduction, Convection, Radiation, and perspiration evaporation.
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Lower room temperatures can be offset in the winter by:
A. lower the relative humidity. B. being very still. C. activity. D. raising the relative humidity. |
D. raising the relative humidity.
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Perspiration cools the body by ________.
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Latent heat removal through perspiration evaporation.
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Relative humidty is measured using a:
A. Thermotyporiter B. sling psychromter C. dry-bulb thermometer D. volt-ohmmeter |
B. sling psychromter
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Name the two unknowns that are easiest to obtain for making plots on the pychrometric charts.
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Wet-bulb and dry-bulb temperatures.
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Air that contains all the moisture that it can hold is known as _________.
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saturated
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In order for an air-conditioner coil to remove moisture from the air, it must be below the _____ temperature of the air.
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Dew point
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For a room to be comfortable, the following conditions are considered average: _____ °F dry-bulb and _____ % relative humidity.
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75°F & 50% relative humidity.
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A gas furnace has an output of 60,000 Btu/h. The return air temperature is 72°F, and the temperature out of furnace is 130°F. Disregarding the heat the fan motor may add to the airstream, how much air is the furnace handling?
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60,000/58∆T x 1.08 = 957.8 cfm
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A house has 3500 Sq.Ft. of floor space and a 9-ft. ceiling. What is the cubic volume of the house?
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3500sq.ft. x 9ft. = 31,500 cu.ft.
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If the fresh air requirements for the proceeding house (Q. #12) were to be 0.4 air changes per hour, how much fresh air must be taken in per minute?
(Q. #12) A house has 3500 Sq.Ft. of floor space and a 9-ft. ceiling. What is the cubic volume of the house? |
31,500 cu.ft. x 0.4 = 12,600 cu.ft./hr. ÷ 60 min. = 210 cubic feet per minute.
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Describe why fresh air is important for a house.
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Fresh air dilutes any pollutants that may be in the house from furniture, carpet, cleaning supplies, and other indoor pollutants.
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The human body is comfortable when:
A. heat is transferring from the surroundings to the body at the correct rate. B. heat is transferring from the body to the surroundings at the correct rate. |
B. heat is transferring from the body to the surroundings at the correct rate.
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To be comfortable in winter, lower temperatures can be offset by:
A. lower humidity. B. higher humidity. C. more air movement. D. less activity. |
B. higher humidity.
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The generalized comfort chart can be used as a basis to:
A. determine combinations of temperature and humidity to produce comfort in summer and winter. B. study air and its properties. C. determine the amount of fresh-air makeup necessary for comfort. D. compare ventilation with infiltration. |
A. determine combinations of temperature and humidity to produce comfort in summer and winter.
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The density of air is the:
A. amount of moisture in the air. B. amount of movement in the air per cubic foot. C. weight of the air per unit of volume. D. combination of the temperature and pressure of the air. |
C. weight of the air per unit of volume.
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Air is made up of primarily:
A. oxygen and carbon dioxide. B. nitrogen and carbon dioxide. C. oxygen and ozone. D. nitrogen and oxygen. |
D. nitrogen and oxygen.
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The dry-bulb temperature is the:
A. same as the wet-bulb depression. B. total of the sensible and latent heat. C. sensible heat temperature. D. sensible heat less and humidity. |
C. sensible heat temperature.
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The wet-bulb temperature:
A. is the same as the wet-bulb depression. B. is the total of the sensible and latent heat. C. takes into account the humidity. D. is always higher than the dry-bulb temperature. |
Both B & C
B. is the total of the sensible and latent heat. C. takes into account the humidity. |
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The wet-bulb depression is:
A. the difference between the dry-bulb and the wet-bulb temperature. B. the same as the wet-bulb temperature. C. the same as the dry-bulb temperature. D. when the air is saturated with moisture. |
A. the difference between the dry-bulb and the wet-bulb temperature.
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The dew point temperature is the:
A. temperature when the air is saturated with moisture. B. temperature when the moisture begins to condense out of the air. C. difference between the dry-bulb and the wet-bulb temperature. D. temperature at which the relative humidity is 50%. |
B. temperature when the moisture begins to condense out of the air.
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If the dry-bulb temperature is 76°F and the wet-bulb temperature is 68°F, the wet-bulb depression is _____°F.
A. 6 B. 8 C. 10 D. 12 |
B. 8°F
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Fresh-air intake is necessary to keep the indoor air from becoming:
A. too humid. B. superheated. C. oxygen starved and stagnant. D. too dry. |
C. oxygen starved and stagnant.
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Infiltration is the term used when air comes into a structure:
A. through an air makeup vent. B. around windows and doors. C. through a ventilator. |
B. around windows and doors.
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Using a sling psychrometer and the wet-bulb depression chart, a technician finds a dry-bulb temperature of 80°F and a wet-bulb temperature of 65°F. The relative humidity is:
A. 44% B. 28% C. 52% D. 60% |
The relative humidity is: (A) 44%
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Using a psychrometric chart, the total heat for a wet-bulb reading of 41°F and a dry-bulb reading of 62°F is:
A. 16.9 Btu/lb. B. 14.6 Btu/lb. C. 18.6 Btu/lb. D. 15.7 Btu/lb. |
D. 15.7 Btu/lb.
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A furnace puts out 122,000 Btu/h sensible heat and the air temperature rise across the furnace is 55°F. The airflow across the furnace is:
A. 2,062 cfm. B. 1,850 cfm. C. 2,525 cfm. D. 1,750 cfm. |
A. 2,062 cfm.
122,500 btu/h ÷ 1.08 = 113425.93 ÷ 55°F = 2062.28 cfm |
