Document OvjGM0rDx44pYwqLEZY8ZK61

Heating Ventilating Air Conditioning Guide 1939 heated by the sun or near exhaust air openings; indoor air temperatures, measured at various heights to secure a good average. 8 How much air must be supplied for dissipating the heat generated ia a dairy bam housing 100 cows if the outside temperature is 20 F and the inside temperature is to be maintained at 45 F? The total heat generated is 100 X 3000 = 300,000 Btu per hour. Then from Formula 3, Q =,___VH___ v cm (t-to) 13.5 X 300,000 0.24 X 60 (45 - 20) = 11,250 cfm. This amount of air should also keep down humidity and odors. 9 a. What precaution is necessary in the ventilation of garages using natural ventilation? b. How, much window area is required for a garage with 50 z 100 sq ft floor area if natural ventilation is used? a. The carbon monoxide content of the air should be kept below 1 part in 10.000 and windows should be kept open at all times. b. The window area should aggregate 5 per cent of the floor area. 0.05 X 50 X 100 = 250 sq ft of window area. This area should be evenly distributed along two sides of the building. 698 M- Chapter 37 AUTOMATIC CONTROL Purpose of Automatic Control, Definitions of Control Units and Terms, Types of Control, Central Fan Systems, Unit Systems, Control of Automatic Fuel Appliances, Residential Control Systems, Control of Refrigeration Equipment, Indus trial Processes THIS- chapter is prepared with the purpose of acquainting the engi neer with the principles underlying the use of automatic rontrol, the general types and varieties of control equipment available and their application. Automatic control, properly applied to heating, ventilating and air conditioning systems, makes possible the maintenance of desired con ditions with maximum operating economy. A properly designed and complete control system has the ability to interlock and coordinate the various functions of heating, ventilating and air conditioning in a manner impossible to accomplish with manual regulation. Automatic control is an integral and essential part of a heating, venti lating or air conditioning installation and cannot be regarded as an acces sory. In order to insure satisfactory results, the control should be designed with and incorporated in the heating, ventilating ,or air conditioning system. The control equipment should be given careful consideration in the planning of any installation in order that the entire system may operate together with satisfactory results. In order that proper selection and application of controlling devices may be made it is important that a broad understanding exist as to the types of control available and their principles of operation. Improper selection and application of control equipment will result in unsatis factory and inefficient' operation. Specific control devices and systems are described in the Catalog Data Section, PURPOSE OF AUTOMATIC CONTROL Automatic control is normally applied to heating, ventilating or air conditioning systems: 1. To insure the maintenance of certain desired or required conditions of temperature, pressure, humidity, air motion or air distribution. 2. To serve a safety function, limiting pressures or temperatures within predetermined points, or preventing the operation of mechanical equipment unless it may function without hazard. 3. To produce economical results and thereby insure operation of the system at a minimum of expense. 699