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Course 711 - Introduction to Ergonomics

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Temperature and Humidity

Recommendations

Set room temperature controls to maintain thermal comfort (sufficient cooling and ventilation). Avoid overcrowding Computer work areas. Provide a fairly constant relative humidity level (30-70 percent is recommended). Do not direct warm air units from central processing units (CPUs) and disk and diskette drives toward operators.

Table 1 presents the values from the Canadian Standards Association (CSA) International's Standard CAN/CSA Z412-00 - "Office Ergonomics" which gives temperature and relative humidity requirements for offices in Canada. These values are based on the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 55 - 2004 "Thermal Environmental Conditions for Human Occupancy". These values are designed to meet the needs of 80% of individuals which means a few people will feel uncomfortable even if these values are met. Additional measures may be required. ASHRAE Standard 55 recommends a range of temperature and humidity values for thermal comfort in office work.

Table 1
Temperature and Humidity of an Office Environment
CSA Z412-00
x
Temperature
% Relative Humidity
Heating Season
20-23.5C°
68-75F°
50%
Cooling Season
23-26C°
73-79F°
50%

*Acceptable temperature for people with typical winter and summer clothing doing secretary work at 50% relative humidity and mean air speed less than 0.15 metres/second (30 feet/minute).

ASHRAE recommends that relative humidity be maintained below 60%. There is no recommended lower level of humidity for achieving thermal comfort, but very low humidity can lead to increased static electricity and health problems, such as skin irritation. The relative humidity should be greater than 30%.

Table2 shows ASHRAE's acceptable ranges of operative temperature (a combination of air and radiant temperatures) for relative humidity levels of 30% and 60%.

Table 2
Examples of acceptable operative temperature ranges based on comfort zone diagrams in
ASHRAE Standard-55-2004
ConditionsAcceptable operative temperatures
x°C°F
Summer (clothing insulation = 0.5 clo)
Relative humidity 30%24.5 - 2876 - 82
Relative humidity 60%23 - 25.574 - 78
Winter (clothing insulation = 1.0 clo)
Relative humidity 30%20.5 - 25.569 - 78
Relative humidity 60%20 - 2468 - 75

Source: National Research Council (Canada) Indoor Air Quality and Thermal Comfort in Open-Plan Offices, Construction Technology Update No. 64 , October 2005 PDF Copy