Document kazDgpdxNO5B8bVvQdqoXmYKV

648 CHAPTER 24- . i ; > ; > .1958 Guide Table 1. Constants for Determining the Capacity op IInit^Heatersfob Various Steam Pressures and Temperatures op Entering Air (Based onSiedm Pressure of t psig and Entering Air Temperature of 60 F) Steam PbebSUBB PSIQ -10 0 Temperatube op Entering Air 10 20 30 40 50 60 `70 '80 90 100" a CL, >.'.>* 1-. ' . O' Q' . 05 W O - 0 1.54 Tl45 1.37 f 1.27 1.19 1.11 i:03 0.96 0.88 0.81 0^74 0.67 2 1.59 1.50 1.41 1.32 1.24 1.16 1.08 1.00 0.93 0.85 0.78 0.71 5 1.64 1.55 1.46 1.37 1.29 1.21 1.13 1.05 0.97 0.90 0.83 0.76. 10. 1.73 1.64 1.55 1.46 1.38 1.29 1.21 .1.13 1.06 0.98 0.91 0.84 15 ' 1.80 1.71 1.61 1.53 1.44 1.34 1.28 1.19 1.12 1.04 0.97 0.90 20 1.86 1.77 1.68 1.58 1.50 1.42 .1.33 1.25 1.17 1:10 1.02 0:95 30 .1.97 1.87 1.78 1.68 1.60 1.51 1.43 ,1.35 1.27 1.19 1.12, .1.04: . 40 2.06 1.96 1.86- 1.77. 1.68 :1.60 1.51 1.43 1.35 1.27 1.19 1.12 50 2.13 2.04 1.94 1.85 1.76 .1.67 1.58 1.50 1.42 1.34 1.26. 1.19 60 2.20 2.09' 2.00 1.90 1.81 1.73 1.64 '1.56 1.47 1.39 1.31 1.24 . 70 75 80 90 . 100 2.26 2.16- 2.06 1.96- 1.87 1.78, 1.70 1.61 1.53 1.45 1.37 ,1.29; 2.28 2.18. 2.09. 1.99 1.90 1.81 1.72 1.64. '1.65 1.47 1.40 1.32, 2.31 2.21 2.11 2.02 1.93 1.84 1.75 1.66 1.58 1.50 1.42 1.34 2.36 2.26 2.16 2.06 1.97 1.88 1.79 1.71 1.62 1.54 1.46 i.38' 2.41 2.31. 2.20 2.11. 2.02 1.93 1.84. 1.75 1.66 1.58 1.50 1.42 125 2.51 2.41 2.31 2.21 2.11. 2.02 1.93 1.84 1.76 1.68 1.59. 1.51 150 2.60 2.50 2:40 2.30 2.20 2.11 2.02 1.93 1.84 1.76 1.67 1.59, a CL) .W o. o 05 H es! 05 Q 0 1.48 1.41 1.33 1.25 1.18 1.11 1.03 0.96 0.89 0.82 0.75 0:69! 2 1.52 1.44 1.36 1.29 1.22 1.14 1.07 1.00 0.93 0.86 0.79 0.73 i 5 1.57 1.49 1.41 1.33 1.26 1.19 1.11 1.05 0.98 0.91 0.84 0.77 .10 1.64 1.56 1.48 1.40 1.33 1.25- 1.18 1.11 1.04 0.97 0.90 0.84 15 1.69 1.61 1.53 1.46 1.38 1.31 .1.24 1.17 ,1.10 4.03 0.96 0.90 x 20' K73 1.65 1.57 1.50 1.42 L35 "1:28 1.21 1.14 1.07 1.00 0.94 30' 1.80 1.73 1.65 1.57 1.50 1.42 1.35 1.28 i.21 1.15 1.08 1:01* 40 1.86 1.79 1.71 1.64 1.56 1.49 '1.42' 1.35 1.28 1.22 1.15 1.08' 50 1.93 1.85 1.77 1.70 1.63 1.55 1.48 1.42 1.35 1.28 1.21 1.15 60 i:97 1.90 1.82 1.75 1.67 1.60 1.53 1.46 1.40 1.33 1.26 l.M; 70 2.02 1.94 1.87' 1.80 1.72 1.65 1.5S 1.51 1.44 1.38 1.31 4.24 75 2.04 1.97 1.90 1.82 1.75 1.68 1.61 1.54 1.47 1.40 1.33 1.27. 80 2.06 1.99 1.91 1.84 1.77 1.70 1.63 1.56 1.49 1.42 1.35 1.29 90 2.10 2.03 1.95 1.88 1.80 1.73 1.66 1.59 1.52 1.46 1.39 >; 100 2.15 2.07 1.99 1.92 1.85 1.77 1.70 1.63 1.56 1.49 1.43 1.36 125 2.21 2.14: 2.06 1.99 1.91 1.84 1.77 1.70 1.63 1.56 1.49 1.43; 150 2.28 2.20 2.13 2.05 1.98 1.91 1.84 1.77 1.70 1.63 1.56 1.50v Note: To determine capacity at any steam pressure and entering temperature, multiply rated capo?1*? at 60 F entering air and 2 psig by constant from table. ' . When increasing steam pressure it is important to determine whether the heater is suitable for;the increased pressure application, and whether the resulting increased outlet temperature is factory. _ lii, of 60 F. This applies to all types of unit heaters, the steam or hot water type, the electric type and the direct fired type. There are, however, other factors which must be taken into account, especially when an attempt is made to compare one type of heater with another. These are the tgfflj- perature of the heating element and the velocity of air through it. Con-t sideration is given to these factors in the discussion of ratings for each type of unit heater in the following paragraphs. !js.t , Steam.. Rating of steam unit heaters has been standardized by a code\ip which the following items are the basis of rating: dry saturated steam^k Unit Heaters and Unit Ventilators 649 2 psig pressure at the heater coil; air at 60 F (29.92 in. Hg barometric pressure) entering the heater; and heater operating free of external resist ance to air flow. The capacity of a heater increases as the steam pressure increases, and decreases as the entering air temperature increases. The heating capacity for any condition of steam pressure and entering air temperature other than standard may be calculated approximately from any given rating by the use of factors in Table 1 for the blow-through or draw-through types. Hot Water. A standard for the rating of hot water type unit heaters has also been established by code8 in which the following items are the basis of rating: entering water at 200 F; entering air at 60 F (29.92 in. Hg baro metric pressure); and heater operating free of external resistance to air flow. This code also prescribes a method of translating the output in Btu and the temperature rise as obtained under test conditions to stand ard conditions of air and water'temperature. Electric. Electric type unit heaters are available in sizes up to at least 60 kw capacity. They consist of resistance type heating elements combined with fan and motor, together with a suitable casing. Electric unit heaters are rated on the energy input to the heater, expressed in terms of kilowatts, Btuh or EDR (Equivalent Direct Radiation). Gas-Fired. Gas-fired unit heaters are built in both suspended and floor models, with either propeller or centrifugal type fans. They are rated in terms of both input and output in accordance with the approval require ments of the American Gas Association. Oil-Fired. The oil-fired unit heater is usually equipped with a centrif ugal fan or fans and is available in either the floor-mounted or in smaller sizes in the suspended type. Ratings are based on heat delivered at heater outlet in Btu per hour. Stoker-Fired. The stoker-fired unit heater can be obtained in a wide range of capacities. Ratings are based on heat delivered at the heater outlet in Btu per hour. Effect of Resistance Upon Capacity Unit heaters are customarily rated as free delivery type units. If outs'ue air intakes, air filters, or ducts on the inlet or discharge are used, a reduction in air and heating capacity will result because of this added resistance to air flow. The percentage of this reduction in capacity will depend upon the characteristics of the heater, and on the type, design, and fPee n 2* ^ans> so that no specific percentage reduction can be assigned tor all heaters at a given added resistance. The heat output to be expected under other than free delivery conditions should be secured from the manulacturer. Location of Unit Heaters ci S'10u^ he taken in the location of unit heaters to insure free air lev 1 to the intake and proper heat distribution over the working e Manufacturers' catalogs usually give suggestions for best arrange- nts the various heaters. Types and makes of available heaters are m the Catalog Data Section of this volume, the h* TM working zones should have their discharge outlets above air hne> and suspended heaters should be so adjusted that the heated j ream will not be objectionable. connection with the use of vertical type unit heaters, care must be