Design Conditions -- The average skin temperature of people is 80°F. If the room is cooler, bodies radiate heat; if former they absorb heat. Consequently, comfort air conditioning systems are designed at 80°F in the summer, and at 60°F in the winter. This is too wide of a range for computer room applications. A computer radiates considerable heat and requires a stable temperature of 72°F - 75°F.
Sensible Heat Ratio -- People emit latent heat through normal metabolism, and the heat contains moisture. Equipment gives off dry electronic sensible heat which is moisture-free. The Sensible Heat Ration -- the amount of sensible cooling as a percent of total cooling capacity (sensible plus latent heat) is 65% - 70% of total load in a comfort system. The dry heat generated by computers requires a sensible heat ratio of 90% - 95% from the cooling equipment. This creates additional confusion when the only measure of cooling capacity is tons. A comfort air conditioning system nominally rates at 10 tons may only provide 6 or 7 tons of precision air conditioning. This resulted in unpleasant circumstances when the room cannot be cooled: There may not be enough cooling. This same concept holds true with smaller 1-3 ton requirements.
Load Density -- Because the high sensible heat, the cooling capacity in terns of BTUH per square feet it greatly increased. Office buildings, where the total load results from many people and considerable outside air, are designed for 40 to 48 BTUH per square foot. Data centers average 120 to 240 BTUH per square foot, 3 to 5 times as much as in comfort system.
Translating this to another "rule of Thumb," square feet per ton, we have the following:
Design Conditions -- The average skin temperature of people is 80°F. If the room is cooler, bodies radiate heat; if former they absorb heat. Consequently, comfort air conditioning systems are designed at 80°F in the summer, and at 60°F in the winter. This is too wide of a range for computer room applications. A computer radiates considerable heat and requires a stable temperature of 72°F - 75°F.
Sensible Heat Ratio -- People emit latent heat through normal metabolism, and the heat contains moisture. Equipment gives off dry electronic sensible heat which is moisture-free.
Load Density -- Because the high sensible heat, the cooling capacity in terns of BTUH per square feet it greatly increased. Office buildings, where the total load results from many people and considerable outside air, are designed for 40 to 48 BTUH per square foot. Data centers average 120 to 240 BTUH per square foot, 3 to 5 times as much as in comfort system. 
