Document rpbMKXZ8QakEg05g2RwegBjKG

254 CHAPTER 11 1958 Guide tendency of temperature difference. Openings on the. leeward side of the monitor result in cooperation of wind and temperature difference. 9. In an industrial building where furnaces that give off heat and fumes are to be installed, it is better to locate them in the end of the building exposed to the prevail ing wind. The strong suction effect of the wind at the roof near the windward end will then cooperate with temperature difference, to provide for the most active and satisfactory removal of the heat and gas-laden air. 10. In case it is impossible to locate furnaces in the windward end, that part of the building in which they are to be located should be built higher than the rest, so that the wind, in splashing therefrom, will create a suction. The additional height also increases the effect of temperature difference to cooperate with the wind. 11. The intensity of suction, or the vacuum produced by the jump of the wind, is greatest just back.of the building face. The area of suction does not vary with the wind velocity, but the flow due to suction is directly proportional to wind velocity. . .12. Openings much larger than the calculated areas are sometimes desirable, espe cially when an increase in occupancy may occur, or when extremely hot days may be anticipated. In the former case, free openings should be located at the level of occu pancy for psychological reasons. 13. In single story industrial buildings, particularly those covering large areas, natural ventilation must be accomplished by taking air in and out of the . roof open ings. Openings in the pressure zones can be used for inflow, and openings in the suc tion zone, or openings in zones of less pressure, can be used for outflow. The ventila tion is accomplished by the manipulation of openings to get air flow through the zones to be ventilated. VENTILATION OF ANIMAL SHELTERS10 Animal shelters require ventilation to remove moisture, odors and, in the case of dairy stables, excess heat. Outlets. Outlet flues for natural draft systems should be round or approximately square. A thermal resistance (1/U) of not less than two is required in their side walls. They should extend at least two feet above the highest part of the roof. Only one outlet is recommended for each room or pen. The use of several outlet flues may result in excessive up-drafts in some flues, and down-drafts in others. If flues have roofs or covers, these should be high enough to provide unobstructed openings on all sides, equal in height to one-half the least dimension of the flue, Fig. 5. A level, heavily insulated ceiling under the flue roof, and over the entire area of the flue, is important. Inlets. Inlets should direct the incoming air vertically upward so as to avoid drafts on the animals, and to insure immediate mixing of incoming air with the room air. A reasonably uniform distribution around the stable or pen is desirable. Inlet flues, that deliver air close to the side walls, stimulate convection currents, which is desirable. When so placed, they also tend to bathe the side walls with cool air, thus reducing temperature differ ence between the inside and outside of the wall. From the standpoint of air movement, insulation of inlet flues is not important. Condensation is, however, likely to occur on them, unless the thermal resistance of their walls is at least two. Controls or throttling devices in inlet flues are seldom required. If used, they are best applied to the inlets and limited to the side of the building facing prevailing winter winds. They should be so made that an opening, at least one inch wide by the width of the flue, will always remain open. Amounts of heat and water produced by livestock vary not only with the different kinds of animals, but also with age, weight, feed consumption and production. These facts, and the vagaries of the weather, make exact Infiltration and Ventilation 255 calculations impossible. The following practical recommendations are based on numerous, carefully checked observations. It is desirable to keep the relative humidity of livestock shelters below 85 percent. Temperatures may be as indicated in the discussion for each kind of animal. Dairy Stables The most usually accepted temperatures for dairy stables, where cows are confined in stanchions or tie stalls, are from 45 to 55 F. These tempera tures are readily maintained in winter weather by the body heat of the herd in well constructed, well stocked and well ventilated stables. Stable volume in excess of 600 cu ft, and exposed wall area in excess of 130 sq ft per 1000 lb animal weight are, in general, undesirable. Side walls should have an . overall thermal resistance of from 2 to 5, depending on the temperature'zone and wind exposure. Thermal re- Fio. 5. Recommended Type op Coveb for Wooden Outlet Flue The opening H should equal one-hall the least dimension ol the flue. Heavy insulation ol the level deck is essential. sietance of the ceiling should be 50 percent greater than that of the side walls. In stables of this size and so insulated, a ventilation rate of 3200 to 3800 cu ft per (hr) (1000 lb of animal) usually insures good conditions. The following recommendations do not apply to so-called pen stables or loafing bams in which there is a thick manure and bedding pack on the floor, and in which doors are normally kept open. Outlets. One flue will serve a stable 200 ft long. In stables over 120 ft long, the flue should be about midway between the ends or, if the stable is L-shaped, near the angle. In shorter stables, it may be at any con venient location. The exhaust point in the stable should be not more than 18 in. above the floor. This permits removal of only the coolest air, and prevents rapid fluctuations in stable temperature. A basic rule for finding the cross-section of the outlet flue is where 176 N A Vh (6) area of the outlet flue, square inches.