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Direct evaporative cooling for dry Canadian climates
Direct evaporative cooling works by passing air through water-saturated media. As water evaporates into the air, it absorbs latent heat from the air itself, dropping the dry-bulb temperature while raising humidity ratio. The process follows a constant wet-bulb line on the psychrometric chart — total enthalpy stays nearly constant (a small amount of pump and fan energy is added), but sensible heat converts to latent heat.
This makes evaporative cooling fundamentally different from mechanical refrigeration cooling, which removes total heat from the air. Evaporative cooling can only bring dry-bulb temperature down toward the wet-bulb temperature, never below it. In humid climates, wet-bulb temperature is close to dry-bulb, so there's little room for cooling. In dry climates, wet-bulb depression is large, giving evaporative cooling significant cooling potential at a fraction of the energy cost of refrigeration.
Saturation efficiency and leaving air temperature
Saturation efficiency measures how closely the leaving air approaches the entering wet-bulb temperature. Rigid media (cellulose or fiberglass pad) coolers typically achieve 80-90% efficiency. Simple spray pad systems achieve 50-70%. The formula is: T_leaving = T_entering − Efficiency × (T_entering − T_wetbulb). At 95°F entering dry-bulb, 20% RH (wet-bulb around 65°F), and 85% efficiency, leaving temperature drops to about 69.5°F — a 25.5°F drop, achieved using only the energy needed to run a fan and circulation pump.
Where evaporative cooling works in Canada
The Okanagan Valley in British Columbia (Kelowna, Penticton, Osoyoos) has hot, dry summers with low afternoon humidity, making it one of the few regions in Canada where evaporative cooling is genuinely effective for comfort applications. Parts of southern Alberta and Saskatchewan also see dry summer conditions suitable for evaporative cooling, particularly for industrial and agricultural applications like greenhouse cooling and livestock barn ventilation.
In humid regions — southern Ontario, Quebec, the Maritimes, and coastal BC in summer — wet-bulb temperatures stay close to dry-bulb, severely limiting cooling potential while adding unwanted humidity to already-humid air. Always check your local summer design wet-bulb temperature using the wet-bulb calculator before specifying evaporative cooling equipment for any Canadian application outside dry interior regions.
Water consumption considerations
Evaporative coolers consume water continuously during operation — typically 3-10 gallons (11-38 L) per hour for residential-scale units, scaling with airflow and humidity difference. In water-scarce regions or where water costs are significant, this ongoing consumption must be weighed against the substantial energy savings versus mechanical cooling. Bleed-off water for mineral control adds 10-20% to base consumption in hard water areas.
Frequently Asked Questions
T_leaving = T_entering − Efficiency × (T_entering − T_wetbulb). Rigid media coolers achieve 80-90% efficiency. At 35°C entering, 18°C wet-bulb, and 85% efficiency: 35 − 0.85×(35−18) = 20.55°C leaving temperature. The process follows a constant wet-bulb line — humidity ratio rises while enthalpy stays nearly constant. Use the wet-bulb calculator to find your design wet-bulb temperature first.
Evaporative cooling works best with large wet-bulb depression — hot, dry conditions. The Okanagan Valley (Kelowna, Penticton, Osoyoos) and parts of southern Alberta and Saskatchewan during summer have low enough humidity for meaningful cooling. In humid regions like southern Ontario, the Maritimes, and coastal BC summers, wet-bulb is too close to dry-bulb for effective cooling and adds unwanted humidity. Always check design wet-bulb temperature for your location before specifying this equipment.