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            Urecon | Celebrating 40 Years | 1969-2009

            Heat Loss Calculations and System Design

            Note: Urecon offers a complete computer assisted engineering service providing such information as: heat loss, time to freeze, fluid outlet temperature, minimum flow rates, tracing wattage required, heat gain, etc., all based on the specific requirements of each project. Basic information needed for typical heat trace design includes: project name/location; minimum ambient temperature; above and/or below ground; depth of bury if applicable; core pipe material and diameter; pipe length per circuit; insulation thickness; required maintain temperature; flow direction for sensor positioning; power point location (one or both ends, middle etc.); voltage available.

            Contact Urecon for more info and help with custom design/calculations.

            It is recommended that a safety factor of 10 to 25% be added to allow for such field conditions as voltage drop, under voltage condition, etc.

            Heat Flow Chart Watts/ft/hr/100°F  T(2)

            Dia.(1) Urethane Insulation Thickness
            25 mm (1 in) 40 m (1½ in) 50 mm (2 in) 63 mm (2½ in) 75 mm (3 in)
            1 1.8 1.4 1.2 1.1 1.0
            2 2.9 2.2 1.8 1.6 1.4
            4 4.9 3.6 2.9 2.5 2.2
            6 6.9 4.9 3.9 3.3 2.9
            8 8.9 6.3 4.9 4.1 3.6
            10 n/a 7.6 5.9 4.9 4.2
            12 n/a 9.0 6.9 5.8 4.9
            14 n/a 10.4 7.9 6.5 5.6
            16 n/a n/a 8.9 7.4 6.2
            18 n/a n/a 9.9 8.3 6.9
            20 n/a n/a 10.8 9.0 7.6
            22 n/a n/a 11.8 9.9 8.3
            24 n/a n/a 12.7 10.8 9.0

            Heat flow in watts per lineal foot

            The table is based upon the application of the following formula:
            Heat flow in watts per lineal foot

            Where:
            W = Watts/ft/hr (W x 3.414 = Btu/hr)
            K = Btu/ft²/hr/1°F/ft = 0.0108 for Urethane
            T = temperature differential°F
            D = outside diameter of insulation
            d = outside diameter of pipe

            1. Diameters for (D/d) taken as 3/1 for 1" pipe +1" insulation and is typical for all other combinations.

            2. For other than 100°F  T, divide by 100 and multiply by required  T.

            Formula

            The heat loss for an externally traced pipe may be calculated by the following formula:
            Heat loss for an externally traced pipe

            Where:
            W = Watts per foot of pipe
            Tm = maintained temperature°F
            Ta = ambient temperature°F
            Ln = natural log
            Di = outside diameter of insulation (in)
            Dp = outside diameter of pipe (in)
            Ki = K value of insulation (BTU • in / hr • ft² •°F)
            Dj = outside diameter of jacket (in)
            Kj = K value of jacket (BTU • in / hr • ft² •°F)
            Sf = Safety Factor

            For more information on time to freeze and raw data requirements: