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HVAC 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 click here.

 

         -        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.