Document mpey11nq1mjJpDRB2Y5bnJoLO

284 CHAPTER 15 : 1948 Guide' of these require rather detailed calculations. Refer to Chapter 3, Page 59, under section on Cooling Load and Chapter 43 in section on Apparatus Dew Point. The following equations are considered--to be sufficiently accurate for use at usual design conditions as their accuracy is within 1 per cent. " Sensible Load gs = Q X 60 X 0.244 X 0.075 (l - (to - ti) (lfi) = Q X 1.08 (to -- ti), Btu per hour Latent Load qe = Q X 60 X 0.075 X 1076 (WQ - Wi) = Q X 4840 (W0 -- W{), Btu per hour (16) Total Load 2t = 2s + 2e (17) where Q = Rate of entry of outside air, cubic feet per minute. to = Outdoor dry-bulb temperature, Fahrenheit degrees. ti = Indoor dry-bulb temperature, Fahrenheit degrees. . W0 = Outdoor humidity ratio, pounds moisture per pound of dry air. Wi = Indoor humidity ratio, pounds moisture per pound of dry air.: 0,075 = Standard air density, pounds per cubic foot. 0.244 = A constant approximating the specific heat of dry air corrected for moisture Btu per (pound) (Fahrenheit degree). ,1076 = A factor approximating the average Btu released in condensing one pound of water vapor from air. Standard air weight (0.075 lb per cu ft) is recommended for use in all calculations as this is the basis for'rating fans and its consistent use keeps all parts of the calculations in conformity. Actually the outdoor air used for ventilation would pass through the conditioning equipment and be cooled and dehumidified to a lower.tem perature and humidity ratio than room conditions before entering the room; but for heat-balance purposes the cooling load chargeable to the outdoor air is that corresponding to the difference between the outdoor and indoor air conditions. Example 10. 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, calcu late the total, sensible and latent heat gains substituting in Equation 15: . 2s = 1000 X 1.08 (95 - 80) = 16,200 Btu per hr.. ; From psychrometric data W0 -- 0.01413, Wi = 0.01122. . Substituting in Equations 15 and 16: 2e = 1000 X 4840 (0.01413 - 0.01122) = 14,100 Btu per hr. 2t = 2s + 2e = 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 Chapter 12. In many applications these sensible and latent heat gains become a large fraction of 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). Pooling Load 285 Table 22. Rates of Heat Gain from Occupants of Conditioned Spaces* Degree of activity Typical Application ^Seated at Rest...... ...... ............ ... Theater-Matinee.... Theater-Evening..-- Seated, Stery Light Work.-------- Offices, Hotels, Apartments....... ..... Moderately Active Office Work Offices, Hotels, Apartments____ -- Standing, Light Work; or Walking Slowly... ...................... Department Store, Retail Store Dime Store.............. Walking; Seated;TM Standing; Walking Slowly.. Sedentary Work--------------Light Bench Work.............. Moderate Dancing.----------- Drug Store Bank__ ------ ........... Restaurant............ Factory....... ........... Dance Hall--.......... Walking 3 mph; Moderately Heavy Work.... Bowling4............ .................. Heavy Work--................... Factory...... ..... Bowling AlleyFactory_--..... Total Heat Adults, Male Btu/Hr 390 390 450 475 Total Heat Adjusted* Btu/Hr Sensible Heat- Btu/Hr 330 350 ` 400 450 180 195 195 200 550 ` 550 490 800 900 1000 1500 450 500 550! 750 850 1000 1450 200 200 220 .220 245 300 465 Latent . Heat Btu/Hr 150 155 205 250 250 300 330 530 605 700 985 Note; Tabulated values are based on 80 F room dry-bulb temperature. For 78 F room dry-bulb, the total beat remains the same, but the sensible beat values should be increased by approximately 10 per cent and the latent heat values decreased accordingly. *Adjusted 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 per cent of that for an adult male and that the gain from a child is 75 per cent of that for an adult male. Adjusted total heat value for sedentary work, restaurant, includes 60 Btu per hour for food per individual <30 Btu sensible and 30 Btu latent). *For bowling figure one person per alley actually(bowling and all others as sitting (400 Btu per hour) or standing (550 Btu per hour). The usefactor 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 applications such as stores, the use factor would be unity. While Chapter 12 should be referred to for detailed information, Table 22 in this chapter summarizes the most useful data representing conditions commonly encountered. Lighting. In general, the instantaneous rate of heat gain from electric lighting 15 may be calculated from the following relation: _ f total light 9el "" 1 wattage x {factor X j^torW- X3.41, Btu per hour. (18). The total light wattage is obtained from the ratings of all fixtures in stalled, both for general illumination and for display use. The special allowancefactor 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 ito allow for power consumed in the ballast. For ventilated fixtures, recessed fixtures, and the like, manufacturer's or other data 16 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 con ditioned space by electric motors, the heat equivalent of this operation must be considered in the cooling load. The general equation for calcu lating this load is: _ /Horsepower RatingX / Load \ x 2544> Btu per hour. ~ ( M,,tnr F.ffiriencv 1 \ Factor / (19)