Document 1g270dVJMZ4RVjeeXweNny4N5

American Society 0/ Heating and Ventilating Engineers Guide, 1932 Ci = Combustion rate for coal, pounds of coal per square foot of grate per hour; E -- heater efficiency factor. F = fuel value ggr unit of the fuel,' Btu. Case A. (Fig. 2 or 11) All of the air circulated to be drawn from outside the building, in which case (<i -- t0). h M = 0.24 (ly - t) (1) Hi = 0.24 (/, - ti)M Hi C = FXE G= C_ _ Hi Ci FX.EX Ci (2) (3) (4) Example. The heat loss AT for a certain factory building is 700,000 Btu per hour. The mean inside temperature t to be maintained is 65 F. The assumed outside air tem perature to is 0 deg; I* = 0 and ty -- U and is assumed to be 140 F. Required, M and Hi. M= 700,000 0.24 (140 - 65) = 38,889 lb per hour. Hi = 0.24 (140 - 0) 38,889 = 1,305,000 Btu per hour If a fan furnace is to be employed with gaseous fuel having a calorific value of 530 Btu per cubic foot and if the manufacturers performance efficiency is 0.85: C= 1,305,000 530 X 0.85 = 2880 cu ft gas per hour or ifxoal at 12,000 Btu per pound is used in a furnace that has a performance efficiency of 0.60 at a combustion rate of 71b per square foot of grate per hour: G= 1,305,000 12,000 X 0.60 X 7 = 26 sq ft Case B. (Fig. 12) All of the air is to be recirculated, in which case A = Using the data from the preceding example, M = 38,889 and from Formula 2 Hi = 0.24 (140 - 65) X 38,889 = 700,000 Btu per hour ; This example illustrates the saving in fuel consumption by the recir culation ,of the air.:The heat to be supplied the apparatus is the same as that required for a direct system of heating and is equal to the heat loss of the building (Ht. = H), in the example (700,000 Btu per. hour) as compared with 1,305,000 for Case A. % 'Case C: : (Figi 3 or 13) A portion of the air circulated is recirculated air and the re mainder, as may be required for ventilating purposes, is drawn in from the outside. H M = Mo + Mr = 0.24(ty-t) (5) The temperature of the resulting mixture of outside and recirculated air entering the heater is:. M0(to + 460) + Mr(I + 460) ti = M0 + Mr 460 (6) Example. Assuming that a positive supply of outside air is required f<pr ventilation at the rate of 1800 cu ft per hour per employee, and assuming 50 employees in the 446 Chapter 31--Central Fan Systems preceding example, then M0 .= 0.075 X 50 X 1800 = 6750 lb per hour is required, measured at 65 F. Mr = M - M0 = 38,889 - 6750 = 32,139 lb. h, _----6--7-5--0---(-4--6-0--)--+--3332-,^13-9--(-6-5---+----4--6-0--)---- 460 = 54 F. Hi = 38,889 X 0.24 (140 - 54) = 802,669 Btu. The three preceding cases refer to installations in which conditioning the air to maintain certain relative humidity requirements does not enter Fig. 11. Heater and Fan Arranged for Outside Air Circulation (Case A) into the problem, as for example, certain types of industrial installations. In practically all modern public buildings, theaters, schools, and ir+many industrial installations the ventilating requirements include1 the provision for air washing and humidifyingthe air delivered to the various rooms of the structure. ** : In the following cases it is assumed, that in addition to maintaming a mean room temperature t, the heating and| ventilating apparatus is required to maintain a constant relative humidity in the rooms. Case D. (Fig. 4 or 14) The.maximum relative humidity that may be maintained with in the building without the precipitation of moisture on single glazed sash when the out side temperature is 30 F is approximately 35 per cent,. .If the inside temperature t is 70 F, 35 per cent relative humidity corresponds to a-dew-poirit temperature of|41 F. (See psychrometric.chart, Chapter 27): ;;rr: .c; ai'S The installation shown in Fig. 14 Contemplates the' use of ^ tempering coil, air washer provided with a water heater, and a hot-blast heater. The tempering coil, one section 447