Document E1MKvMBn8dMV2v3e5bYo66Vn

314 CHAPTER 13 1956 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. 25.Table Rates of Heat Gain fbom Occupants op Conditioned Spaces1 Degbee op Activity Typical Application Total Heat Adults, . Male Btu/Hb Total Heat Bto/Hb Sensible Heat. Bto/Hb Latent Heat Bto/Hb . Seated at Rest................................ Seated, Very light Work............ Moderately Active Office Work.. Standing, Light Work: or' Walking Slowly............................... Walking; Seated.................. Standing; Walking Slowly. Sedentary Work.................. Light Bench Work.. ----Moderate Dancing............... Walking 3 mph; Moderately Heavy Work.. Bowling"............................... Heavy Work.......................... Theater-Matinee.... Theater-Evening-- Offices, Hotels, Apartments............... Offices, Hotels, Apartments............... Department Store, Retail Store Dime Store.............. Drug Store Factory..................... . Factory.................... 390 390 475 550 550 490 800 1000 1500 330 350 400 450 500 550 750 850 1000 1450 180 195 195 200.. 150 155 205 250 200 300 220 330 220 530 245 605 300 700 465 985 tota*l Nhoetaet:reTmabauinlasttehde vsaalmuees, baruet bthaesesdenosnib8l0eFheroaot mva,ldureys-bshuolbultdembepeinrcarteuarsee. d Fboyrapp*rorxoimomateulryy1-u0 upieuro, e.nmts, and the latent heat values decreased accordingly. b Adjusted total heat sain 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 75 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 (30 Btu sensible and 30'Btu latent). d For bowling figure one person per alley actually bowling, and all others as sitting (400 Btu per hour) or standing (550 Btu per hour). Example 12: 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: 9. = 1000 X 1.08 (95 - 80) = 16,200 Btu per hr. From psychrometric data JF0 <= 0.01413, W, = 0.01122. Substituting in Equations 8 and 9: 9. = 1000 X 4840 (0.01413 - 0.01122) = 14,100 Btu per hr. 9, = 9. + 9. = 30,300 Btu. HEAT SOURCES WITHIN THE CONDITIONED SPACE People. The rates at which heat and moisture are given off by human beings under different states of activity are given in Table 25. In many applications these sensible and latent heat gains become a large fraction of Cooling Load 315 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 lighting32 may be calculated from the following relation: 9.1 total light wattage X ( use (factor X special allow ance factor X 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 factor 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: = /\HoMrsoetpoor wEeffricRieanctiyng)\ X (/FLaocatdor\) X 2544' ,,BtU per hr' U6) 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 hp rating, increasing to 80 percent at 1 hp, and to 88 percent at 10 hp 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 26 presents recommended data.34 Note that the maintaining rale 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 is being made, no toast is being made, no food is being cooked in the fry kettle, etc. 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 Table 26. Consideration must be given to the heat contributed by appli ances which are in use at the time of peak load. The quantity of heat will depend upon whether products of combustion are vented to a flue, whether they escape into the space to be conditioned, or whether appliances are hooded allowing part of the heat to escape through a stack. There are bo generally accepted data available on the effects of venting and shielding