Document 9vr12Qwr524G1zJxX2x30KaD

326 CHAPTER 13 1957 Guide conditions and quantity of air supplied to the space. All the various sen sible and latent heat loads within the space must be included. Infiltration must be included in the space load since this air enters the doors and win dows, and its heat and moisture load must be offset by the introduction of cooler, dryer air to the space. However, since-outdoor air is taken through the conditioning, equipment and cooled, this portion- does not be come a part of the space load, except a small portion which passes through the coil untreated. To determine the total load on the refrigeration ma chine, the remaining outdoor air load must be included in the grand total load. Table 25. Kates of Heat Gain from Occupants of Conditioned Spaces* Degree of Activity Typical Application Total Heat Adults, Male Btu/Hb Total Heat Adjusted5 Btu/Hb Sensible Heat Btu/Hb Latent Heat Btu/Hb Theater-Matinee___ 390 330 180 150 Theater-Evening-- 390 350 460 195 Moderately Active Office Work-- Offices, Hotels, 475 450 200 250 Standing, Light Work; or Department Store, Retail Store 550 450 Drug Store 660 500 300 490 800 900 550 850 220 220 530 245 605 Walking 3 mph; Heavy Work......................................... Bowling Alley......... Factory.................... 1000 1500 1000 1450 300 700 466 985 * Note: Tabulated values are based on 80 F room dry-bulb temperature. For 78 F room dry-bulb, the total heat remains the same, but the sensible heat values should be increased by approximately 10 percent, and the latent heat values decreased accordingly. b Adjutted total heat gain is based on normal percentage of men, women, and children for the application listed, with the postulate that the gain from an adult female is 85 percent of that for an adult male, and that the gain from a child is 76 percent of that for an adult male. c Adjusted total heat value for sedentary work, restaurant, includes 60 Btu per hour for food per individual (SO Btu sensible and 30 Btu latent). d For bowling figure one person -per alley actually bowling, and all others as sitting (400 Btu per horn) o standing (550 Btu per hour). Example IS: For outdoor design conditions of 95 F dry-bulb and 75 F wet-bulb, and indoor design conditions of 80 F dry-bulb and 67 F wet-bulb, and for the supply of outdoor air at the rate of 1000 cfm and the exhaust of room air at the corresponding rate, calculate the total, sensible and latent heat gains. Solution: Substituting in Equation 7: q. = 1000 X 1.08 (95 - 80) = 16,200 Btu per hr. From psychrometric data W<, = 0.01413, W, = 0.01122. Substituting in Equations 8 and 9: q, = 1000 X 4840 (0.01413 - 0.01122) = 14,100 Btu per hr. qt = ?.+ ?. = 30,300 Btu. HEAT SOURCES WITHIN THE CONDITIONED SPACE People. The rates at which heat and moisture are given off by humMl beings under different states of activity are given in Table 25. In maw applications these sensible and latent heat gains become a large fraction.of Cooling Load 327 the total load. Appreciable variations in heat-emission rates must be recognized according to the age and sex of the individual, state of activity, environmental influences, and duration of occupancy (since for short occupancy the extra heat and moisture brought in by people may be a significant factor). While Chapter 6 should be referred to for detailed information, Table 25 in this chapter summarizes practical data representing conditions com monly encountered. Lighting. In general, the instantaneous rate of heat gain from electric lighting35 may be calculated from the following relation: = (total light <?"1 = (wattage {use (special allow- factor A \ance factor 3.41, Btu per hr. (15) The total light wattage is obtained from the ratings of all fixtures installed, both for general illumination and for display use. The use/actor is the ratio of the wattage in use, for the conditions under which the load estimate is being made, to the total installed wattage. For commercial appli cations such as stores, the use factor would be unity. The special allowance factor is introduced to care for fluorescent fixtures, and for fixtures which are either ventilated or installed so that only part of their heat goes to the conditioned space. For fluorescent fixtures, the special allowance factor is recommended to be taken as 1.20 in order to allow for power consumed in the ballast. For ventilated fixtures, recessed fixtures, and the like, manufacturers' or other data** must be sought to establish the fraction of the total wattage which may be expected to enter the conditioned space. Power. When equipment of any sort is operated within the conditioned space by electric motors, the heat equivalent of this operation must be considered in the cooling load. The general equation for calculating this load is: q.m -- ^Horsepower Rating) Motor Efficiency / x (wLoad ) \Factor/ X 2544, Btu per hr. (16) It is assumed that both the motor and the driven equipment are within, the conditioned space. If the motor is without the space, then do not divide by the motor efficiency in Equation 16. The load factor is merely the fraction of the rated load which is being delivered under the conditions of the cooling-load estimate. Motor efficiencies may be approximated as follows: about 50 to 60 percent at j hp rating, increasing to 80 percent at 1 hp, and to 88 percent at 10 bp and above. Appliances. Care must be taken in a cooling-load estimate to take into account the heat gain from all appliances, electrical, gas, or steam. Table fp presents recommended data.34 Note that the maintaining rate in table 26 is the heat input required to maintain the appliance at the normal operating temperature even though it is not being used, i.e., no coffee being made, no toast is being made, no food is being cooked in the fry tb' vf' e^c' The maintaining rate is useful in setting up a lower limit to the heat gain to a room from the appliance when in operation. Experienced judgment must be used in the application of data given in able 26. Consideration must be given to the heat contributed by applinces which are in use at the time of peak load. The quantity of heat will spend upon whether products of combustion are vented to a flue, whether i fcaPe into the space to be conditioned, or whether appliances are ^ooded allowing part of the heat to escape through a stack. There are generally accepted data available on the effects of venting and shielding