Document 4a0ojn8R28axKdaj6b7RO6yGN

276 CHAPTER 19 . 1960 Guide from each dehumidifier can be taken, is required. Should the water level in the pas of the dehumidifiers be low in relation to that of the surge tank, return-water pumps will be required, and these pumps will have to be operated until the water supply tines are drained in order to prevent flood ing of the lower demunichfiers. Where-spray dehumidifiers are on the same level, equalizing lines between the pans may be required if a storage tftnir is not provided. It is exceed ingly important that watertight drained floors be provided under all overhead cooling systems, since water condensed out of. the air generally will be present and may damage the interior finish of the rooms below the apparatus. All of the various pieces of equipment from the outdoorair intake through the fan usually are connected together by sheet-metal casings. Frequently, the building structure or specially constructed. walls or partitions may be used to form a portion of the casing. In any case the casing or con nection must be sufficiently sturdy for the required duty. Sheet-metal work must be well braced not only to prevent vibration under pulsations in air flow, but also to withstand the abuse of normal usage. Casings should be braced wher ever access doors are installed, and all large panels should be adequately reinforced by structural, steel. Accessibility for Service Each apparatus layout should be made with accessibility in mind; Where cooling convectors are used, space for re moving and repairing or replacing them should be provided. Adequate space should be provided for the servicing and replacement of eliminators. Filters must be. so located that the proper cleaning, replacement, or routine servicing can be accomplished without difficulty. Free access to the bear ings of all moving machinery is a necessity. Provision should be made for the replacement of any parts that are subject to wear, deterioration, or damage, such as filters, fanwheels, motors, pump impellers, or beat transfer surface. I % '1 | i j i CHAPTER 20 AIR DISTRIBUTION Definitions, Standard* for Satisfactory Conditions, Principles of Air Distribution Ventilating Jets in Air Distribution, Outlet Per' formance, Outlet Types, Outlet Location and Selection, Directional and Volume Control, Return .and Exhaust Intakes, Specific Applications. ORRECT air distribution is essential in warm air heat 13. Plaque: A ceiling outlet in which the supply air impinges C ing, ventilating, and air-conditioning systems. Even against a plate or series of parallel plates, and is deflected air though a system delivers the required to a room, unsatisfactory conditions quantity result if tohfecoanirdiitsionedhdior1er4icz.toiDonnitfasfullasyneidrn:paAlalnlndeoisru.etclteiot ndsis. charging supply air in various .poorly distributed. 15. Primary Air: Tbe air delivered to the outlet by the sup This chapter deals with room air distributiononly; the ply duct. transmission of air through ducts is treated in Chapter 21, Air Duct Design. The objectives of this chapter are to: 16. Induction: The induction of room air drawn into an outlet by the primary air stream (commonly called aspiration). 1. Present the principles of room air distribution with a discussion of ventilating jets in air distribution. 2. Present general information on practical air distribution problems involving outlet performance, outlet types, location, selection, and outlet control. 17: Entrainment: The entrainment of room air by the air stream discharged from the outlet (commonly called'secondary air motion). - 18. Total Air: The mixture of discharged air and entrained air. 3. Illustrate the use of the basic concepts and of the practical experience gained in air distribution id making specific applica tions. Further pertinent information on air distribution will be found in Chapter 6, Physiological Principles; Chapter 12, Heating Load; Chapter 13, Cooling Load; Chapter 15, Unit Ventilators and Unit Heaters; Chapter 16, Unitary Air Con 19. Entrainment Ratio: Tbe total air divided by the dis charged air. 20. Throw (Blow): The horizontal or vertical axial distance an air stream travels on leaving the outlet (grille) before the maximum velocity is reduced to 50 fpm. 21.- Drop: The vertical distance, the lower edge of a hori zontally projected air stream drops between the outlet and the end of its throw. ditioning Equipment; Chapter 18, Warm Air Heating Sys-. 22. Rise: The converse of.drop. terns; Chapter 19, Central Systems for Air Conditioning; Chapter 25, Sound Control; Chapter 43, Automatic Control; Chapter 44, Instruments and Measurements; Chapter 48, Transportation Air Conditioning. DEFINITIONS 23. Envelope: The outer boundary of an air stream moving at a perceptible velocity. 24. Spread: The divergence of the air stream in a horizontal or vertical plane after itleaves the outlet- 25. Diffusion: Distribution of air within a space by an out let discharging supply air in various directions and planes. The following definitions referring to air distribution equip ment have gained general acceptance. 26. Radius of Diffusion: The horizontal distance from the diffuser outlet to the perimeter of the space, within which air motion in the occupied zone is reduced to 50 fpm minimum 1. Supply Opening or Outlet: Any opening through which air is delivered into a space which is being heated, cooled, humidi fied, dehumidified, or ventilated. 2. Exhaust Opening or Return: Any opening through which air is removed from a space which is being heated, cooled, humidified, dehumidified, or ventilated. 3. Outdoor Air Opening: Any opening used as an entry for air from outdoors. 4. Damper: A device used to vary the volume of air passing through a confined cross-section by varying the cross-sectional area. 27. Outlet Velocity: The average velocity of air emerging from the outlet, measured in the plane of the opening. 28. Terminal Velocity: The average air stream velocity at the end of the throw. 29. Temperature Differential: Temperature difference be tween primary and room air. 30. Temperature Variation: Temperature difference between points of the same space. STANDARDS FOR SATISFACTORY CONDITIONS fi. Grille: A covering for any opening and through which air passes. 6. Register: A grille equipped with a damper or control valve. 7. Free Area: The total minimum area of the openings in tbe air outlet or inlet through which air can pass. The object of air distribution in warm air heating, ventilat- y' ing, and air-conditioning systems is to create in the occupied zone of the conditioned room (floor to 6 ft above floor level), the proper combination of temperature, humidity, and air 8. Core Area.-.The total plane area of that portion of a grille, included within lines tangent to the outer edges of the outer openings through which air can pass. 9. Free Area Ratio: The ratio of the free area to the core area. 10. Coefficient of Discharge: Ratio of area at vena contracts to area of opening. 11. Aspect Ratio: The ratio of length to width of an opening or core of a grille. motion. To obtain comfort conditions within this zone, stand ard limits have been established as acceptable effective tem peratures. This term comprises air temperature, motion, humidity, and their physiological effect on the surface of the human body. Any variation from accepted standards of one of these elements may result in discomfort to tbe occupants. The same effect may be caused by lack of uniformity of con 12. Vane Ratio: The ratio of depth of vane to minimum width between two adjacent vanes. ditions within the space or by excessive fluctuation of-condi tions in the same part of the space. Such discomfort may 277