Outdoor design conditions

CoolCalc Manual J automatically selects the nearest ACCA weather station and outdoor design conditions for each project. If you believe the design conditions of another nearby weather station are more appropriate for the home, you can select a different weather station on the "Design Conditions" screen.

Heating and cooling design temperatures are not the most extreme temperatures that may occur in your area but rather represent high and low temperatures that occur 99% of the time over a 5 year sample period. You may override ACCA design temperatures only if local building code allows.

In addition to summer and winter design temperatures the underlying ACCA tables include additional climate data such as “design grains” and “daily range” which are used in the MJ8 procedure. These values are listed on the MJ8 report but are not user-editable.

“Design grains” represents the difference between the humidity of the outdoor air and the humidity of the indoor air in cooling season. Grains difference values are used to estimate the latent infiltration and engineered ventilation loads for the cooling season.

“Daily range” represents the average difference between the daily high and low dry-bulb temperatures at a particular location. High daily range values characterize arid climates and high altitude locations. A low daily range is associated with locations near a large body of water.