Latent Heat Evaporative Cooling

Cooling effect from evaporation rate and h_fg.

Run the calculator

Example

You enter

Evaporation rate (lb/hr) 10

You get

Cooling effect 10540 BTU/hr
Cooling effect (tons) 0.878

Checked against published worked examples from: PDHonline.com (A. Bhatia).

Details, formula, and sources

Formula or tableCooling (Btu/hr) = water evaporated (lb/hr) x latent heat of vaporization h_fg (Btu/lb), default 1054 Btu/lb (water near 70-80 F; 970.3 is the 212 F value); tons = Btu/hr / 12,000.

Source and editionASHRAE Fundamentals psychrometrics by name; classical thermodynamics.

Free accessPsychrometric formulas free in published engineering texts.

What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.

API field namesevaporation_rate_lb_hr, cooling_btu_hr, cooling_tons

Latent heat h_fg 1054 Btu/lb at typical evaporating temperatures unless the user supplies another; the supply-temperature effectiveness relations are in the evaporative-cooler tiles, not heresteam tables