Q2 / A = 75 Btu/hr-ft2 The heat loss savings, Qs, and fuel energy savings, Es, from adding insulation would be: Qs = Q1 Q2 = 270 Btu/hr-ft2 75 Btu/hr-ft2 = 195 Btu/hr-ft2 – – Es = Qs / = 195 Btu/hr-ft2 / 50% = 390 Btu/hr-ft2  Thus, this measure reduce heat loss through the walls by 72% Reducing Radiation Loss through Openings Openings in furnace allow heat to radiate outward. Radiation heat loss can be reduced by covering openings. The figures below show openings in a heat treat furnace. The first opening shows for improvement”. The second opening is covered with “room flaps to reduce radiation loss to the surroundings. Heat is radiated from the hot interior temperature of a furnace through openings to the surroundings. Due their geometries, both the interior and the surroundings can be approximated as black bodies with emissivities equal to 1.0. Thus, heat loss, Q, through an opening of area, A, from the interior of a furnace at temperature, Tf, to the surroundings at temperature, Ta, is: Q = A Ffa (Tf4 Ta4) (4)  – where is the Stefan-Boltzman constant (0.1714 x 10-8 Btu/ft2-hr-R4) and Ffa is the view factor between the inside of the furnace and the surroundings. If the opening is approximated as a circle with radius r through a wall of thickness L, the view factor can be calculated from the following two equations (Cengal, 1998). S = 2 + (L /r)2 Ffa = 0.5 [ S (S2 4)0.5 ] (5) – – If the opening were blocked by a radiation shield with emissivity the heat shield, transfer would be reduced to (Cengal, 1998): Q = A Ffa (Tf4 Ta4) [sheild / 2 ] (6)  –
Q2 / A = 75 Btu/hr-ft2 The heat loss savings, Qs, and fuel energy savings, Es, from adding insulation would be: Qs = Q1 – Q2 = 270 Btu/hr-ft2 – 75 Btu/hr-ft2 = 195 Btu/hr-ft2 Es = Qs /  = 195 Btu/hr-ft2 / 50% = 390 Btu/hr-ft2 Thus, this measure reduce heat loss through the walls by 72% Reducing Radiation Loss through Openings Openings in furnace allow heat to radiate outward. Radiation heat loss can be reduced by covering openings. The figures below show openings in a heat treat furnace. The first opening shows “room for improvement”. The second opening is covered with flaps to reduce radiation loss to the surroundings. Heat is radiated from the hot interior temperature of a furnace through openings to the surroundings. Due their geometries, both the interior and the surroundings can be approximated as black bodies with emissivities equal to 1.0. Thus, heat loss, Q, through an opening of area, A, from the interior of a furnace at temperature, Tf, to the surroundings at temperature, Ta, is: Q =  A Ffa (Tf4 – Ta4) (4) where is the Stefan-Boltzman constant (0.1714 x 10-8 Btu/ft2-hr-R4) and Ffa is the view factor between the inside of the furnace and the surroundings. If the opening is approximated as a circle with radius r through a wall of thickness L, the view factor can be calculated from the following two equations (Cengal, 1998). S = 2 + (L /r)2 Ffa = 0.5 [ S – (S2 – 4)0.5 ] (5) If the opening were blocked by a radiation shield with emissivity shield, the heat transfer would be reduced to (Cengal, 1998): Q =  A Ffa (Tf4 – Ta4) [sheild / 2 ] (6)
EnergyEfficientProcessHeating.docx