Document wqMX6pOn4oNQoaam2QvLEjjo

Heating Ventilating Air Conditioning Guide 1939 requirements of different' sides of the building. The total cooling load fl for a building exposed to the sun on more than one side is of course less ; than the sum of the maximum cooling loads in the individual rooms since the maximum solar radiation load on the different sides occurs at different times. In determining the total cooling load for a building if the time when the maximum load occurs is not obvious, the load should be calcu. lated for various times of day to determine the times at which the sum J of the loads on the different sides of the building is a maximum. Heat Emission of Occupants ` The heat and moisture given off by human beings under various states I of activity are shown in Figs. 8 to 11 and Table 4 of Chapter 3. It will be ' iobserved that the rate of sensible and latent heat emission by human beings varies greatly depending upon state of activity. In many applica- tions this component becomes a large percentage of total load. Heat Introduced by Outside Air An allowance must be made for the heat and moisture in the outside "i air introduced for ventilation purposes or entering the building through i cracks, crevices, doors, and other places where infiltration might occur. * The volume of air entering due to infiltration may be estimated from f data given in Chapter 6. Information on the amount of outside air required for ventilation will be found in Chapter 3. \ In the event the volume of air entering an enclosure due to infiltration ^ exceeds that required for ventilation, the former should be used as a basis for determining the portion of the load contributed by outside air. Where s volume of air required for ventilation exceeds that due to infiltration it is * assumed that a slight positive pressure will exist within the enclosure with a-resulting exfiltration instead of infiltration. In this case the air required , for ventilation is used in determining outside air load. The sensible heat gain resulting from the outside air introduced may be 5 determined by the following formula: < H, = 0.24 X 60 do Q (to - t) |(4) where Ha = sensible heat to be removed from outside air entering the building, Btu per hour, i Q - volume of outside air entering building, cubic feet per minute. , do = density of air, pounds of.dry air per cubic foot at temperature to- | to = temperature of outside air, degrees Fahrenheit. t = temperature of inside air, degrees Fahrenheit. f The total heat gain resulting from outside air introduced may be deter S imined by the following formula: H = 60 do Q (ho -- h) (5) II; where H = total,heat to be removed from outside air entering the enclosure. Btu per hour. Q -- volume of outside air entering enclosure, cubic feet per minute. do = density of air, pounds of dry air per cubic foot of air (at temperature to). 156 Chapter 8. Cooling Load ho = hderyatacior n(atetntteomfpmeriaxturee toof).outside dry air and water vaPr- Bn,t" Per pound of h = hderyataciron(atetntet mofpmeriaxttuurreet)o.f inside dryy air aanndd water v_a__P_,,r. ^-tu per pound of deTtehremilnaetdenbtyhtehaet fgoalloinwirnegsufoltirnmguflrao: m outside o,v oduced, may be fi = H - h,a whHerie = latent heat to be removed, Btu per hour. H = total heat to be removed, Btu per hour. Ha = sensible heat to be removed, Btu per hour. (6) Heat Emission of Appliances Heat generating appliances which give off either sensible heat or both sensible and latent heat in an air conditioned enclosure may be divided into three general classes of equipment or devices: 1. Electrical appliances. 2. Gas appliances. 3. Steam heating appliances. In the first group may be found such devices as lights, motors, toasters, waffle irons, etc. The capacities of most electrical devices may be determined from the watt capacity indicated on their name plates. The Btu equivalent of heat generated per hour is determined by multi plying the watt capacity by 3.4 (one watthour is equivalent to 3.413 Btu). The capacities of electric motors are usually expressed in terms of horsepower instead of watts. If the motor efficiency is known, the watts input may be calculated from the formula: 746 (hp) (7) where P = motor input, watts. hp = motor load, horsepower, n = motor efficiency (expressed as a decimal). When the motor efficiency is not known the heat equivalent of electrical v.~ .nnrnvimomlv ih-tprminbv abblving data given in 1 able y. Table 9. Heat Generated by Motors Nameplate Hating Hobsepoweb Yt to Vi VS to 3 3 to 20 Heat Gaik ik Btu pen Hoira m Homipowea Connected Load in Same Room 4250 3700 2950 Connected Load Outside of Room 1700 1150 400 In the second group belong such appliances as coffee urns, gas ranges, steam tables, broilers, hot plates, etc. F,or heat generating capacities of'such appliances-refer,to Table 10, 157 ^