Document RO7om62dZQpndekMxBGKB9eB

282 CHAPTER 24 1962 Guide And Data Book 75 and 80 P with 1 F deg tolerance. The relative humidity conditions generally maintained are between 45 and 50 per cent. Cleaning of the air is generally obtained by both im pingement and electrostatic type air filters. Not only must the parts be accurate and dean, but the workers' hands must not impart moisture or dirt to the accurate and delicate parts and surfaces such as jewel bearings and stems which ride in these hearings. Air conditioning has made important contribu tions towards the increase in accuracy of modern instruments. Drafting Rooms Drafting rooms are air conditioned for both precision manu facture and work efficiency. In the first place, designs which are pictured on drawings have to be drawn to scale. In many plants the drawings or reproductions of the drawings are used as templates for the manufacture of working tools or parts, especially in the aircraft industry. Here temperature and humidity control prevent variations in size and distortion in shape. Concerning work efficiency, it has been proven that draftsmen turn out more and better work where uniform air conditions are maintained, and where perspiration and dirt are not allowed to affect the drawing. Conditions in drafting rooms are generally kept at normal comfort levels, usually at 75 F and 50 percent rh with normal variations. Since drafting rooms are often large, open spaces, special attention has to be given to air distribution. Uniform condi tions should be obtained over the room whether near the out side walls or far from them. As draftsmen usually lean over their work, special attention has to be given to keeping the space free from drafts on the backs of their necks. Aspirating types of air outlet grilles are recommended. Air movements at the working height should not exceed 10 to 30 ft per min. If the room is large or has two or three exposures, it should be zoned. Blackout Plants Wartime blackout and other modern windowless plants have generally been one-story buildings extending over large areas. As a result, different methods for air conditioning have been developed. Two general methods have resulted: (1) the conventional method using a central machinery room, or building where a chilled medium and a beating medium have been produced and pumped to many air-handling units, each of which would handle an individual area or zone; (2) the zone-unit system. Cooling machinery, suitably sized for each zone, is located at that zone. The beating equipment may be located at the zone or at a central location. The zone unit system saves one heat exchange as the cooling mu generally be done by the direct method. Other advantages are the sav ing in first and operating cost of such auxiliary equipment as pumps and insulated piping. Both of these methods have been used extensively in these large-area, single-floor plants. The air-handling units for each zone are generally located in roof trusses or in penthouses on the roof. These air-conditioned factories proved themselves during the war and also since the war for different purposes. The ex perience confirmed the basis on which they were originally designed and especially the sir conditioning. They definitely showed (1) better and more uniform quality of product, (2) increase in production due to conservation of workers' health and energy, (3) reduction of accidents due to fatigue and (4) less absenteeism. Mining The heat and humidity encountered in mines may cause higher body temperatures and acceleration of pulse, injurious to productiveness. Dust from mining processes endangers health of workmen; gases, sometimes poisonous or explosive must be removed. It has been found economical and desirable to air condition gold mines by machinery located at the out door level or at lower levels. This permits working of lower levels of mining. The Rand Mine, in South Africa, uses an air circulation of 400,000 cfm and 7500 gal of water per min circulated to a spray pond. Fans lead to a duct system which enters the ver tical shaft 100 ft below the surface. The refrigeration system in this mine has three 750 ton centrifugal machines and a dehumidifier 50 ft X 16 ft wide. The average depth of a gold mine in the vicinity is 4000 ft. It is believed that mining can be carried on as far below the surface as 12,000 ft, if air conditioning can be provided eco nomically. This means an increase in revenue in the South African mines of $100,000,000 in the value of gold available for every increase of 200 ft in depth. If the depth goes 6000 ft more, three billion dollars worth of gold may become avail able. Wet-bulb temperature is the guide to mine conditions; a wet-bulb of 92 F with a velocity of 50 ft per min is the mini, mum requirement. In the case of a mine producing 150,000 tons monthly at 6000 ft, the heat load appears to be 70,000,000 Btu per hr. Three methods of cooling are possible: (1) surface refrigera tion consisting of a plant to cool air and force it down from the top; (2) underground refrigeration plant (for example, one installation, 6400, ft below the surface, cools 8000 tons of sir per day to a maximum temperature of 83 F); (3) com pressed air operation of machinery in the mine. ' Air conditioning to temperatures below normal by means of well water and refrigeration is practiced in certain coal mines in tins country, where trouble is experienced in warm weather with falling roofs. There are various theories as to why roofs are more likely to fall in warm weather, such as (1) the effect of temperature variation on expansion of rocks, (2) weakening of roof material due to wetting, and (3) unknown chemical action. A single set of fans with an air-washer type of cooler was used in the first of the coal mines devoting at tention to this problem in 1931. Later a mine in Indiana set up a dehumidifier arrangement by ingfadling sprays in a bricklined chamber at the foot of the main vertical shaft. Air was blown by motor-driven fans through a course in the horizontal shafts. Water for coding purposes was available from a flooded, unused portion of the mine, and, after use, was pumped from the spray to another abandoned portion. Tem peratures of 50 F were reported in both cases. MoHon Picture Studios Modem movie stages are large, insulated buildings; the soundproofing makes other treatment necessary for satisfac tory occupancy. Ughting, the greatest contributor of heat within, is variable as to amount and duration, and must be correctly controlled. Size and number of sets are variable and create individual problems, and both the number and types of persons on a sound stage play their parts in relation to air conditioning. High-salaried personnel, often in costume, demand comfort while working. Less time is lost in make-up retouching and less delay brought about by perspiration-dampened costumes, when sets are properly cooled. An air-conditioning system should have the ability to heat, cool, ventilate, and clean. Stages are generally maintained at 75 F and 50 percent rh, with temperature settings above and below, at the option of the occupants. Floor distribution of air has the advantage of more economical removal of rising heat Precision Manufacturing, Laboratories and Testing 283 jjut the disadvantage of placing set construction and per^nnel too Dear the source of cooling. Overhead distribution baa the advantage of better temperature distribution but b economical in the removal of rising heat from lights. Film raking demands precision manufacture, and air con ditioning is necessary. This application b treated more fully in.Chapter 30. Optical Goods Modern optical instruments such as bomb tights, range finders, telescopes, binoculars, cameras, etc., require extreme care in manufacture in order to obtain optical accuracy. The fundamental part of such devices b the lens. The lens must be ground and polished. In this process, the accuracy required b such as to make air conditioning necessary. The air must be dust-free and temperature constant. The wax in which the are imbedded must be firm. The polishing rooms must be free from air-borne dust and impurities. When the com ponent are assembled into groups, they must be free of dirt find perspiration marks, and the cement must be main tained under constant conditions. The conditions generally maintained are similar to those in othpr manufacturing processes, such as 80 F dry-bulb tem perature and 50 percent rh. To get the desired cleanliness of air combinations of impingement and electrostatic air cleaners are often used. Abrasives In the precision manufacture of abrasive materials such as wnH paper and abrasive wheels, controlled conditions of temperature and humidity contribute much to manufacturing efficiency and quality. Precision depends in many cases on grinding operations, and accurate grinding calls for a highgrade grinding wheel. The quality of the grinding wheel de pends in part upon the air conditions under which it b manu factured and used. Abrasive wheels are normally bonded with materials such as bakelite, clay, hard rubber or sodium silicate; in some cases hygroscopic. Abrasive grains are added when bakelite b in liquid form; the room temperature b controlled to insure constant consistency. When the bonding material b of ceramic day, relative humidity control prevents lumping of the clay. Unless used (and stored) in an atmosphere free of excessive humidity, deterioration of the wheel will take place. The usual air conditions for the manufacture of abrasives are 78 F dry-bulb temperature and 50 percent rh. Clay Modeling Rooms In the automotive industry (and in other industries, as well) clay models of future designs are used extensively.'Such models are costly and must be preserved until they have served their purpose. Dry-bulb temperatures of approximately 75 F and relative-humidities in the 40 to 60 percent range are used in these rooms. PART U: LABORATORIES AND TESTING FACILITIES Laboratory and testing facilities are spaces arranged, equipped and environmentally controlled for experimental and study work. These may be enclosures within a room, one or more rooms in a building or an entire building devoted to particular research, development or testing activity. Such facilities are employed by industrial, educational and govern mental agencies for scientific and medical study and for in dustrial product development. Environmental requirements for these facilities relating to the regulation of temperature, humidity, pressure, air motion, air cleanliness, sound and vibration are attained and affected by the application of air conditioning, ventilation and re frigeration processes. In order to develop the design of these processes to fulfill required conditions, it is important that requirements are explicitly stated and fully understood. Requirements necessary for design determinations are: (1) design conditions, (2) thermal loads, (3) time during which conditions are to be maintained, (4) air flow rates, (5) air flow patterns, (6) contaminant control, and (7) sound and vibration limits. The definition of these requirements requires close communication between the designer and researcher and a responsibility on the part of the designer to obtain all necessary information and convey to the researcher's full understanding the performance capabilities and, limitations of the intended design. DESIGN CONDITIONS Exhaust requirements for laboratory and testing facilities for the conveyance of contaminants to the atmosphere require the treatment of large quantities of outdoor air. Selection of . outdoor design conditions, therefore, materially affects the size and cost of refrigeration and steam facilities. One degree Fahrenheit difference in outdoor design wet-bulb tempera ture involves approximately 0.375 tons of cooling capacity per 1000 cfm of outdoor air. Outdoor design data for each locality if not available in standard design references, there fore, should be obtained from local weather bureau or airport weather records. For comfort air conditioning, outdoor con ditions commonly employed in the locality or those equalled or exceeded in weather records 5 percent of the time are satis factory for cooling load computations. For spaces with specified maximum or maintained indoor states, maximum values of outdoor conditions should be applied. Indoor conditions should be defined in terms of dry-bulb temperature, wet-bulb temperature, or relative humidity with specified tolerances for each value. Indication should be ob tained on whether a stated set of conditions represent limiting values or levels to be maintained. For variable temperature rooms corresponding humidity requirements for the specified dry-bulb range should be obtained or an indication whether humidity levels are to be selectively available for any value within the specified dry-bulb range. HOURS OF OPERATION The periods during which specific indoor states are to be maintained in particular laboratory spaces bear directly on whether such spaces will be served by individual ventilation, air conditioning and refrigeration systems operable at any time of the day or year or by central plants operating on common daily and seasonal schedules. A system designed to continuously maintain and limit the dry-bulb temperature of an interior laboratory space when operating at a dew point of 55 F or less requires mechanical refrigeration which auto matically operates whenever the outside dry bulb exceeds 55 F. It is erroneous to assume that, because a system serving such space operates on 100 percent outdoor air, it will be capable of fulfilling conditions during the winter season with out mechanical refrigeration. A dry-bulb temperature of 55 F is frequently exceeded during the winter months. Require ments relating to the hours and seasonal periods during which specified conditions are to be maintained should be specifically expressed. THERMAL LOADS Transmission, solar, lighting, and occupant room sensible and latent load components are supplemented in laboratories f