Because there are many days when outside temperatures are less than design conditions, the temperature of the air supplied to the coil will fluctuate, and the temperature of the air leaving the coil may drop a few degrees. This will result in sweating ducts. It is good practice, therefore, to design the discharge-air temperature about 3
F higher than the room dew point. FIGURE 13.32 Evaporative condenser for an air-conditioning system. FIGURE 13.31 Water tower connection to a condenser of an airconditioning system. Thus, for 80
F DB, 50% RH, and dew point at 59
F, the minimum discharge air temperature would be 62
F as insurance against sweating. The amount of air to be handled may be obtained from Eq. (13.30), with a temperature difference of 18
F. If a water-cooled condenser is employed to remove heat from the refrigerant, a water tower (Fig. 13.31) may be used to cool the condenser discharge water, which can then be recirculated back to the condenser. Where practical, the water condenser and tower can be replaced by an evaporative condenser as in Fig. 13.32. The capacity of heat rejection equipment, such as towers or evaporative condensers, depends on the wet-bulb temperature. The capacity of these units decreases as the wet-bulb temperature increases. Such equipment should be sized for a wet-bulb temperature a few degrees above that used for sizing air-conditioning equipment. As an example, consider an area where the design wet-bulb temperature is 75
F. If we size the air-conditioning equipment for this condition, we shall be able to maintain design inside conditions when the outside conditions happen to be 75
F WB. There will be a few days a year, however, when the outside air may register 79 or 80
F WB. During the higher wet-bulb days, with the air-conditioning equipment in operation, we shall balance out at a relative humidity above design. For example, if the design relative humidity is 50%, we may balance out at 55% or

modification coefficient, R System overstrength factor, o Deflection amplification factor, Cd System limitations and building height limitations (ft) by seismic design category A and B C D E F Ordinary reinforced concrete shear walls 7 21/2 6 NL NL NP NP NP Composite eccentrically braced frames 8 21/2 4 NL NL NL NL NL Composite concentrically braced frames 6 21/2 5 NL NL NL NL NL Composite steel plate shear walls 8 3 61/2 NL NL NL NL NL Special composite reinforced concrete shear walls with steel elements Ordinary composite reinforced concrete shjear walls with steel elements Special reinforced masonry shear walls 7 3 61/2 NL NL NL NL NL Intermediate reinforced masonry shear walls 61/2 3 51/2 NL NL NL NP NP Dual systems with intermediate moment frames Special steel concentrically braced frames 6 21/2 5 NL NL 160 100 NP Ordinary steel concentrically braced frames 5 21/2 41/2 NL NL 160 100 NP Special reinforced concrete shear walls 6 21/2 5 NL NL 160 100 100 Ordinary reinforced concrete shear walls 51/2 21/2 41/2 NL NL NP NP NP Ordinary reinforced masonry shear walls 3 3 21/2 NL 160 NP NP NP Intermediate reinforced masonry shear walls 5 3 41/2 NL NL 160 NP NP Composite concentrically braced frames 5 21/2 41/2 NL NL 160 100 NP Ordinary composite braced frames 4 21/2 3 NL NL NP NP NP Ordinary composite reinforced concrete shear walls with steel elements TABLE 5.9 Design Coefficients and Factors for Basic Seismic-Force-Resisting Systems (Continued) Basic seismic-force-resisting system

4. The loads act in a plane containing the centroidal axis of the beam and are perpendicular to that axis. Furthermore, the neutral surface is perpendicular to the plane of the loads. Thus, the plane of the loads must contain an axis of symmetry of each cross section of the beam. (The flexure formula does not apply to a beam loaded unsymmetrically. See Arts. 5.5.18 and 5.5.19.) 5. The beam is proportioned to preclude prior failure or serious deformation by torsion, local buckling, shear, or any cause other than bending. Equating the bending moment to the resisting moment due to the internal stresses at any section of a beam yields I C FIGURE 5.25 Unit stresses on a beam cross section caused by bending of the beam. M is the bending moment at the section, is the normal unit stress in a plane at a distance c from the neutral axis (Fig. 5.25), and I is the moment of inertia of the cross section with respect to the neutral axis. If is given in pounds per square inch (psi), I in in4, and c in inches, then M will be in inch-pounds. For maximum unit stress, c is the distance to the outermost fiber. See also Arts. 5.5.11 and 5.5.12. 5.5.11 Moment of Inertia The neutral axis in a symmetrical beam is coincidental with the centroidal axis; i.e., at any section the neutral axis is so located that