Ballast: Chapter 16 - Human Comfort and Mechanical System Fundamentals

Question 1

What 8 factors are human comfort based on?

Answer 1

1. Temperature
2. Humidity
3. Air movement
4. Temperature radiation to and from surrounding surfaces
5. Air quality
6. Sounds
7. Vibration
8. Light

Question 2

What is the standard range of comfortable temperatures for humans?

Answer 2

69 - 80 degrees (60-85 degrees tolerable)

Question 3

Dry-Bulb Temperature

Answer 3

Derived from a standard thermometer

Question 4

Wet-Bulb Temperature

Answer 4

Measured using a sling psychrometer, a thermometer with a moist cloth wrapped around the bulb.

It is swung around, causing the water to evaporate. In dry air, the moisture evaporates rapidly and acquires latent heat, which produces a low wet-bulb temperature. A large difference in the dry- and wet-bulb temperatures means low relative humidity.

Question 5

Relative Humidity

Answer 5

The ratio of the percentage of moisture in the air to the maximum amount that the air can hold at a given temperature without condensing.

Question 6

What is the standard range of comfortable relative humidity for humans?

Answer 6

30 - 65% (20 - 70% tolerable)

Question 7

What is the acceptable range for wind speed before becoming drafty?

Answer 7

50 ft/min - 200 ft/min

Question 8

Emissivity

Answer 8

Measure of an objects ability to absorb and radiate heat

Question 9

Emitance

Answer 9

Ratio of the radiation emitted from an object compared to that of a black body at the same temperature

Question 10

Mean Radiant Temperature (MRT)

Answer 10

Weighted average of the various surface temperatures in a room and the angle of exposure of the occupant to the surfaces

Question 11

Operative Temperature

Answer 11

The average of the air temperature and the Mean Radiant Temperature (MRT) of a space. This is used to account for human comfort within a space.

Question 12

What are the 5 reasons for providing ventilation?

Answer 12

1. Provide oxygen
2. Remove carbon dioxide
3. Remove Odors
4. Carry away contaminants
5. Remove unwanted moisture

Question 13

What spaces, according to the International Mechanical Code, require an separate exhaust system from the main ventilation system?

Answer 13

Toilet rooms, clothes dryers, cooking appliances, refuse conveyor systems, and laboratories

Question 14

When natural ventilation is required, what percentage of the room’s floor area must be provided as ventilated area (the area of an operable window e.g.)?

Answer 14

4% of the floor area

Question 15

British thermal unit (BTU)

Answer 15

The amount of hear required to raise the temperature of 1 lbm water by 1 degree

Question 16

Coefficient of heat transmission (U)

Answer 16

The overall rate of heat flow through any combination of materials, including air spaces and air layers on the interior and exterior of a building assembly. It is the reciprocal of the sum of all the resistances in a building assembly

Question 17

Conductance (C)

Answer 17

The number of British thermal units (BTU) per hour that pass through 1 sq.ft. of homogeneous material of a given thickness when the temperature differential is 1 degree F

Question 18

Conductivity (k)

Answer 18

The number of British thermal units per hour that pass through 1 sq.ft. of homogeneous material 1 in thick when the temperature differential is 1 degree F

Question 19

Dew Point

Answer 19

The temperature at which water vapor in the air becomes saturated and begins to condense into drops of water

Question 20

Dry-bulb Temperature

Answer 20

The temperature of the air-water mixture as measured with a standard dry-bulb thermometer

Question 21

Enthalpy

Answer 21

The total heat in a substance, including latent heat and sensible heat

Question 22

Latent Heat

Answer 22

Heat that causes a change in state of a substance, such as the heat required to change water into steam. The amount of heat required to change the state of a substance is much greater than the heat required to raise the temperature of a substance (sensible heat). The average value of latent heat per pound of moisture is 1061 Btu

Question 23

Resistance

Answer 23

The number of hours needed for 1 Btu to pass through 1 sq.ft. of material or assembly of a given thickness when the temperature differential is 1 degree F. It is the reciprocal of conductance.

Question 24

Sensible Heat

Answer 24

Heat that causes a change in temperature of a substance but not a change in state. For example, the sensible heat needed to raise the temperature of 1 lbm of water from 50 to 100 degrees F is 50 Btu. In contrast, the latent heat needed to change liquid water at 212 degrees F to steam at 212 degrees F is 1061 Btu

Question 25

Specific Heat

Answer 25

The number of Btus required to raise the temperature of a specific material by 1 degree F. Specific heat is a measure of a material’s capacity to store heat as compared with the storage capacity of water

Question 26

Wet-Bulb Temperature

Answer 26

The temperature of the air as measured with a sling psychrometer. The wet-bulb temperature is a more critical measure of heat in high humidity because it is an indicator of physical stress caused when the human body is near the upper limits of temperature regulation by perspiration.