Indoor Air Quality: Comfort and Health

1. Human Comfort

1.1 Comfort Factors

(1) Activity(metabolic heat generation) (2) Clothing (3) Temperature of surrounding air (4) Humidity of surrounding air (5) Relative velocity of surrounding air (6) Radiation

Activity

Metabolism: heat generation rate at which energy is converted from chemical to thermal form within the body.

Blood circulation near the skin surface: heat transfer rate at which the thermal energy if carried to the skin surface.

Respiration: air is taken in at ambient condition but leaves saturated with moisture at the body temperature.

Sweating: evaporative heat transfer from skin.

Standard unit: metabolic rate of a sedentary (seated and quiet) person.

1 met = 18.4 Btu/hr-ft2 = 58.2 W/m2.

Clothing

Clothing insulation: single equivalent uniform layer of the whole body.

1 col = 0.880 F-ft2-hr/Btu = 0.155 m2-K/W Radiation

Thermal radiation between a person and the surroundings, determined by Mean Radiant Temperature.

4 4 1/2 Tmrt = Tg + CV (Tg – T)

Tg: globe temperature (from Vernon’s globe thermometer).

V: air velocity

C = 0.103  109 (IP) = 0.247  109 (SI)

1.2 Comfort Zones and Design Conditions

Effective Temperature (ET*): temperature of an environment at RH=50% that results in the same total heat loss from the skin as in the actual environment.

Standard Effective Temperature (SET) is defined under typical indoor conditions:

0.6 clo; 1.0 met; V < 20 fpm; T = Tmrt; and moisture permeability index = 0.4

Acceptable operative temperature for active persons (for 1.2 < met < 3)

Tactive(F) = Tsedentary(F) – 5.4 (1 + clo)(met – 1.2) or

Tactive(C) = Tsedentary(C) – 3.0 (1 + clo)(met – 1.2)

2. Common Contaminants

2.1 Gaseous contaminants

CO2, CO, SO2, NOx, Radon, VOCs (volatile organic compounds)

Resources: fuel combustion, pesticides, building materials, paints, etc.

2.2 Suspended particulate (aerosol)

Soot, smoke, dust/fine powder (e.g., cement), mist spray (e.g., perfume)

2.3 Ways of control

(1) Source elimination (2) Air cleaning or treatment (filtration) (3) Dilution with outdoor air

3. Air Cleaning or Treatment

3.1 Gas contaminants

Adsorption: Coating of activated carbonate on filters Chemical/physical absorption column Spray of liquids (wet scrubber)

3.2 Particulate contaminants

(1) filtration (cake or in-depth) (2) cyclone (3) electrostatic precipitator (4) gravity sedimentation (5) wet scrubber 4. Dilution with Outdoor Air

5. Pressure Drop and Filter Selection