Document 551Zad81dZd0Y8nXLnpzVJ9N

<660 CHAPTER. 30 1953 Guide '' 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 outdoor air 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 connection 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 wherever 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 removing and repairing or replacing them should be provided. Adequate space should be provided for the servicing and replacement of eliminators. Whether these accom pany sprays or wetted coils, filters must be so located that the proper cleaning, replacement or routine servicing can be accomplished without difficulty. Free access to the bearings of all moving machinery is a neces sity. Provision should be made for the complete removal and replace ment of any parts of the apparatus that are subject to wear, deterioration or damage, whether they be filtered, fanwheel, motor, pump impeller, or . heat transfer surface. DESIGN PROCEDURE The customary design procedure is outlined herewith. For simplifica tion the procedure is set up on the basis of a year-round system. For systems designed only for winter or for summer, the unrelated parts may be omitted. 1. Selection of design conditions (inside and outside): (a) summer, (b) winter. 2. Determination of outside air requirements. 3. Determination of cooling load: (a) room sensible heat gain, (b) room latent heat gain, (c) room total heat gain (d) grand total heat gain. 4. Determination of heating load: (a) room sensible heat loss, (b) room moisture loss, (c) humidification requirement, (d) total heating requirement. .. 5. Determination of apparatus dewpoint and dehumidified or humidified air quant ity: (a) summer (full load and part load), (b) winter. 6. Supply air temperature difference and quantity: (a) summer, (b) winter. 7. Equipment selection. 8. Equipment layout. The foregoing steps are merely typical. Many - applications will require at least a preliminary, investigation of some of the latter steps before pro ceeding with the earlier steps. A permanent record of all design assump tions and computations should be made and preserved for comparison with the performance of the installation. CHAPTER 31 AIR DISTRIBUTION Standards for Satisfactory Conditions, Definitions, Mechanics of Air Distribution, Outlet Performance, Types of Air Outlets, Outlet Location and Selection, Directional and Volume Control, Return and Exhaust Intakes, Specific Applications CORRECT air distribution contributes as much or more to the success of a forced air heating, ventilating, cooling or air conditioning system as does any other single factor. An air conditioning system may deliver the required quantity of conditioned air and still fail to give satisfactory room conditions because of poor air distribution. The scope of the chapter is limited to the air distribution within the conditioned space. Reference is made to the distributing duct system only insofar as it affects the per formance of the air distribution outlet. (See Chapter 32 for information on air duct design). STANDARDS FOR SATISFACTORY CONDITIONS The object of air distribution is to create within the space the proper combination of room temperature, air motion and humidity, whether by. cooling, heating or ventilating. The purpose to be accomplished deter mines the factors to be controlled. For instance, in many industrial ap plications it is necessary to maintain proper standards throughout a large portion of the space; sometimes almost throughout the entire enclosure. In these cases design room temperature, room air motion and humidity will depend entirely upon the requirements of the product and its manu facturing processes. If, however, comfort of the occupants is the principal objective, con sideration of the occupied zone (floor to 6 ft above floor level) is primarily required. In order to obtain comfort conditions within this zone, standard limits have been set up as acceptable effective temperatures. 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 the occupants.. The same effect may be caused by lack of uniformity of conditions within the space or by excessive fluctuation of conditions in the same part of the space. Such discomfort may arise due to excessive room air temperature variations (horizontally, vertically, or both), excessive air motion (draft), failure- to deliver or distribute the air according to the load requirements at the dif ferent locations, or too rapid fluctuation of room temperature or air motion (gusts). In addition the noise level created by the introduction of supply air should be kept within acceptable limits, and streaking or smudging of walls or ceilings should be prevented. With reference to permissible room air motion it is not possible to estab lish a specific standard covering the entire complex problem of air distribu tion. Velocities less than 15 fpm generally cause a feeling of air stagna tion, whereas velocities higher than 65 fpm will disturb loose paper sheets 661