Unit 35 Comfort and Pyschrometrics

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.

perspiration cools the body by

Latent heat removal through perspiration evaporation.

lower room temperatures can be off set in winter by

Raising the relative humidity

Air that contains all of the moisture that is can hold is know as

Saturated

Relative humidity is measured using a

Sling pyschrometer

Name the four comfort factors

Temperature, Humidity, Air movement, & Air cleanliness.

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%

In order for an air-conditioning coil to remove moisture from the air, it must be below the _______ _____ temperature of the air.

Dew Point

Describe why fresh air is important in a house

Fresh air dilutes any pollutants that may be in the house from furniture, carpet, cleaning supplies, and other indoor pollutants.

Name the two unknowns that are easiest to obtain for making pots on the psychrometric chart

wet-bulb and dry-bulb temperatures

With a dry-bulb reading of 70°F and a wet-bulb reading of 61°F, the dew point temperature is __________°F

27

If the fresh-air requirements for the house in question 13 were to be 0.4 air changes per hour, how much fresh air must be taken in per minute?

31,500 cu.ft. x 0.4 = 12,600 cu.ft./hr. ÷ 60 min. = 210 cubic feet per minute

A house has 3500 ft2 of floor space and a 9-ft ceiling. What is the cubic volume of the house?

3500sq.ft. x 9ft. = 31,500 cu.ft.

Relative humidity in question 10 is __________%.

60

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

For a room to be comfortable the following conditions are considered average:_________*F dry bulb and _________ % relative humidity

75 *F and 50%

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

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.

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

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

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

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.

state three ways the body gives off heat

Conduction, Convection, Radiation, and perspiration evaporation.

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.

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.

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

A gas furnace has an output of 60,000 Btu/h. The return air temperature is 72°F, and the temperature out of the furnace is 130°F. Disregarding the heat the fan motor may add to the airstream, how much air is the furnace handling?

60,000/58∆T x 1.08 = 957.8 cfm

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.

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.

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.