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ASHRAE Design Wet-Bulb Temperatures — Major Canadian Cities
Values at 1% summer design condition (ASHRAE Fundamentals 2021). Use for cooling tower and evaporative equipment sizing.
| City | DB 1% (°C) | WB 1% (°C) | DB 1% (°F) | WB 1% (°F) | Elevation (m) |
|---|---|---|---|---|---|
| Toronto, ON | 33 | 23 | 91 | 73 | 173 |
| Vancouver, BC | 27 | 20 | 81 | 68 | 4 |
| Calgary, AB | 29 | 18 | 84 | 64 | 1045 |
| Edmonton, AB | 29 | 19 | 84 | 66 | 671 |
| Montreal, QC | 31 | 23 | 88 | 73 | 57 |
| Ottawa, ON | 31 | 23 | 88 | 73 | 79 |
| Winnipeg, MB | 31 | 22 | 88 | 72 | 239 |
| Halifax, NS | 28 | 21 | 82 | 70 | 28 |
| Regina, SK | 33 | 21 | 91 | 70 | 577 |
| Quebec City, QC | 29 | 22 | 84 | 72 | 73 |
Wet-bulb temperature in HVAC design
Wet-bulb temperature is the temperature a parcel of air reaches when water evaporates into it at constant pressure until saturation. It is always lower than or equal to the dry-bulb temperature. The wet-bulb depression — the difference between dry-bulb and wet-bulb — is a direct indicator of how much evaporative cooling potential exists in the air. Dry prairie air in Calgary with a 10°C wet-bulb depression has far more evaporative cooling capacity than humid Toronto air with a 2°C depression.
In HVAC, wet-bulb temperature governs the performance of any water-evaporating system. Cooling towers, evaporative condensers, and indirect evaporative coolers all approach the outdoor wet-bulb temperature as their thermodynamic limit. A cooling tower cannot cool water below the outdoor wet-bulb — the closer the leaving water temperature is to wet-bulb, the larger and more expensive the tower required to achieve that approach.
Cooling tower approach and range
Cooling tower approach is the difference between leaving cold water temperature and the entering wet-bulb temperature. A 5°C approach means the tower cools water to within 5°C of the outdoor wet-bulb. Range is the temperature drop of the water across the tower — the difference between entering hot water and leaving cold water. A tower with a 10°C range and 5°C approach operating at 22°C wet-bulb produces water at 27°C and returns it at 37°C. Enter your hot and cold water temperatures above to calculate approach and range for your site conditions.
Fixed-orifice AC charging and wet-bulb
For residential AC charging, fixed-orifice (piston and cap tube) systems use a charging chart that requires both outdoor dry-bulb and indoor wet-bulb temperature to determine target superheat. Indoor wet-bulb measures the combined effect of temperature and humidity on the evaporator load. Use this calculator to find indoor wet-bulb from your dry-bulb and RH measurements, then feed the value to the superheat calculator for precise charge verification.
Frequently Asked Questions
Wet-bulb temperature is the lowest temperature air can reach through evaporative cooling. It equals dry-bulb only at 100% RH. In HVAC, wet-bulb is critical for cooling tower sizing — a tower can only cool water to the outdoor wet-bulb, never below it. The difference between cooled water temperature and wet-bulb is the approach temperature. Wet-bulb also determines fixed-orifice AC superheat targets and evaporative cooler performance. Use the psychrometric calculator for all associated air properties at the same conditions.
ASHRAE 1% summer design wet-bulb temperatures: Toronto 23°C (73°F), Vancouver 20°C (68°F), Calgary 18°C (64°F), Edmonton 19°C (66°F), Montreal 23°C (73°F), Winnipeg 22°C (72°F), Halifax 21°C (70°F). Calgary and Vancouver's lower wet-bulb temperatures make evaporative cooling more effective in western Canada. Always use the full ASHRAE Fundamentals climate data for your specific city and design percentile for equipment sizing. See the table above for a complete city reference.