92. Methods for hygienic investigation and evaluation of main physical factors of the air – air temperature and air humidity.

9) Methods for hygienic investigation and evaluation of main physical factors of the air – temperature and humidity; air velocity and IR radiation

• -microclimate is defined as the common thermal setting of a room, house, office etc.
• -general influenced by its physical parameters (air temp, relative humidity, velocity of air movement, heat/IR radiation)
• Thermal balance/misbalance is determined by: metabolic activity and heat protection (clothing)
• -all factors are included in one equation to determine the heat balance:

• Q: total rate of lost heat
• M: metabolic rate
• C: dry heat exchange via convection
• R: dry heat exchange via radiation
• E: evaporation heat loss from skin

AIR TEMPERATURE

• -is the amount of thermal energy in a unit volume of air
• -measurement by a thermometer (air should have free access to the bulb of the thermometer; thermometer should be protected against radiant heat)
• -different kinds: maximum thermometer (mercury, to measure highest temperature for a given time/interval), minimum thermometer (alcohol, to measure lowest temperature for a given time/interval), Six’s maximum and minimum thermometer (combination of both), dry bulb thermometer (like Assmann psychrometer), globe thermometer (for direct heat radiant temp of the surrounding, hollow copper bulb coated with matt black paint outside, inside a specially mercury thermometer, registers higher air temperature -> is affected by air temperature and radiant heat and influenced by air velocity)
• air temperature should be in between 16-25°C if humidity is 30-60% and air velocity is 0,2-0,4 m/s
• -horizontal thermal gradient: difference between temperature of 0,5m of the window and close to the opposite wall -> no more than 2°C
• -vertical thermal gradient: difference between temperature at 0,2m and 1,5m over the floor
• -difference between maximal and minimal values of ambient temperatures for 24h -> no more than 3°C for central heating system and no more than 5°C at local heating system
• -> measured by thermos hygrometer/anemometer or special thermos hygrographs (registration of temp and relative humidity)

HUMIDITY

• -water vapor content of the air
• -absolute humidity: weight of H₂O vapor in a unit volume of air (g/m³ or Pa)
• -maximal humidity (MH): excessive amount of water vapor in the air for a particular temperature without complete saturation (MH has permanent value for this temperature)
• -dew point: temperature at which air can exist saturated with water vapor