HVAC FORMULA

Useful Formulas

 
-        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   T_m = (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.