Useful Formulas
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- Total Heat (BTU/hr) = 4.5 x cfm x ∆h (std. air)
- Sensible Heat (BTU/hr) = 1.1 x cfm x ∆t (std. air) - Latent Heat (BTU/hr) = 0.69 x cfm x ∆gr. (std. air)
NOTE: For conditions other than standard air please see this page.
- Total Heat (BTU/hr) = 500 x gpm x ∆t (water)
- TONS = 24 x gpm x ∆t (water)
- GPM cooler = (24 x TONS) / ∆t (water)
- Fluid Mixture Tm = (Xt1 + Yt2) / X + Y (this works for air or water)
- BTU/hr = 3.413 x watts = HP x 2546 = Kg Cal x 3.97
- Lb. = 453.6 grams = 7000 grains
- psi = ft. water/2.31 = in. hg/2.03 = in. water/27.7 = 0.145 x kPa
- Ton = 12,000 BTU/hr = 0.2843 x KW
- HP (air) = cfm x ∆p (in.H2O)/6350 x Eff.
- HP (water) = gpm x ∆p (ft.)/3960 x Eff.
- Gal. = FT3/7.48 = 3.785 Liters = 8.33 lb. (water) = 231 in. 3
- gpm = 15.85 x L/S
- cfm = 2.119 x L/S
- Liter = 3.785 x gal = 0.946 x quart = 28.32 x ft3
- Therm = 100,000 BTU = MJ/105.5
- Watt/sq. ft. = 0.0926 x W/M2
- yd. = 1.094 x M
- ft. = 3.281 x M
- ft2 = 10.76 x M2
- ft3 = 35.31 x M3
- ft/min = 196.9 x M/S
- PPM (by mass) = mg/kg
NOTE: Liter/sec is the proper SI term for liquid flow. M3/sec is the proper SI term for airflow. Due to the awkward nature of using M3/S at low air flow rates (lots of decimal points), L/S is commonly used to express air flow for HVAC applications.
