Outdoor design temperatures come from long-term climate data: a cooling design dry bulb exceeded only about 1 percent of hours, with its matching wet bulb, and a heating design temperature exceeded 99 percent of hours. Indoor design is commonly 75 degrees F at 50 percent RH for cooling and 70 degrees F for heating. Picking extreme record temperatures instead leads to oversized, short-cycling equipment.
Design conditions here are 94 over 75 for cooling and 8 for heating, so don't let the owner size it for the one-day record.
Also heard as
- design temperatures
- design temps
Related terms
Cooling load
How much heat and moisture a cooling system has to pull out of a space each hour to keep it at design conditions.
Dry bulb
Plain air temperature as an ordinary thermometer reads it, kept dry and out of direct sun.
Wet bulb
The temperature a wet-wicked thermometer reads in moving air, lowered by evaporation in proportion to how dry the air is.
Ton
A unit of cooling capacity equal to 12,000 Btu per hour, the heat needed to melt a ton of ice in a day.