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American Society of Heating and Ventilating Engineers Guide, 1934 Fig. 5. Section Through a Radiator-Heated Room Fig. 6. Section Through a Unit Venti lator-Equipped Room when Heating Corridor Chapter 20--Air Distribution volume of air to be introduced with the upward system is about 25 cfm of air per person at a low velocity, say at 150 fpm (linear), and at a tem perature not more than 6 deg below the room temperature. For partial occupancy, higher entering air temperatures can be used, with corre spondingly less danger from drafts. Downward System Theaters usually are equipped with downward air distribution with horizontal diffusion of the entering cool air so as to combine it, both as to temperature and dilution, with the heated air which inevitably must rise from the bodies of the patrons. The waste or the recirculated air is with drawn from the room at the floor. If the theater is large, and if the Fig. 7. Section Through a Unit Con ditioner-Equipped Room when Cooling School Ventilated by a Central Fan In Fig. 8 the cloakroom ceiling is furred down so as to conceal the metal air supply duct, which is close to the ceiling. The air for ventilation usually is controlled by a duct thermostat near the fan, at a temperature slightly higher than the temperature required in the room, to allow foq heat losses in the duct system. THEATERS Theaters are usually ventilated or cooled by introducing pre-con ditioned air. No ventilating system for a theater should be given con sideration without definite provision for cooling. Theater cooling generally is far more important than theater heating. There are two widely different methods of theater air distribution, the upward and the downward. Upward System If no inlet openings are possible in the ceiling, the upward system may be the least objectionable alternative. Fig. 9 shows a section through a theater with the upward system of air distribution. The occupants often suffer from drafts due to the cool air which comes from the unoccupied zones. When the entire seating area is occupied, the upward system gives little trouble when cooling, and since very little heating is required under such conditions, practically no difficulty is encountered. The maximum 276 Fig. 9. Theater with Upward System Fig. 10. Section Through a Theater of Ventilation with Downward Ventilation exhaust openings are placed in the side walls at the floor, drafts may be felt by the people who sit near the openings. There is no objection, how ever, except that of cost, to the use of small exhaust openings under each seat. These may be cleanable floor grilles or may have mushroom covers. In a downward system, if the entering cool air is not deflected hori zontally, it will fall through the surrounding much hotter air, and will reach high velocities by the time it strikes the heads of the occupants. Air at a temperature 10 deg below that of the surrounding air is decidedly objectionable when forced over one's head at a velocity of nearly 400 fpm. Fig. 10 shows a section through a theater with downward ventilation. The deflectors cause the entering cool air to be spread horizontally so that it will mix with the hotter air. The final escape is through well-distributed openings in the floor. There have been cases in which the downward system of air distribution such as that illustrated in Fig. 10 gave trouble due to overheating at the rear, both above and below the balcony, especially when not provided with refrigeration for cooling, and when not adequately controlled. It is especially necessary that adequate removal of the heatoi air be provided at these low-ceiling points and it is probable that auxiliary exhaust at or through the ceiling after the manner of the arrangements shown in Fig. 5 would be helpful. VANES In order to cause the supply air to a room to take a fixed or desired direction when leaving the inlet opening of a flue, stationary vanes may 277