Document mBp9OxXdLLZ9Yr7kX9bGrDYpJ

858 CHAPTER 78 1962 Guide And Data Book moisture levels is extremely important to permit adequate . observation and data analysis. The testing of paper and textiles of necessity must be carried out under rigidly maintAinf-H temperature and humidity conditions as variations, particularly in their mois ture content, will have a considerable effect on physical char acteristics, etc. in the same category should be considered rubber compounds which are extremely susceptible to mtmI1 variations in the surrounding air temperature and relative humidity. A few degrees difference in air temperature significantly affects stress values, tensile strength and ultimate elongation. A 2 percent variation in the moisture content of the *twpl possible with a few percent increase or decrease in the room's relative humidity, will change tensile strength 200 to 400 psi. Since test results would thus vary widely throughout the country, the U. S. Government originally established opti mum values for each test, for various compounds, and these values have been generally accepted by the rubber industry. These values were obtained by testing samples at 77 F and at constant relative humidity. Bacteriological and plant growth rooms, as well as dry boxes and environmental chambers must also be rigidly nra.intn.inAH at determined moisture levels in order to permit toating of processes or products under a wide range of possible usage con ditions. Environmental rooms and chambers nan be main tained by use of sorption dehumidifiers under the range of humidity from zero to essentially 100 percent, depending on the accuracy available from the control instrumentation. Testing of window-type air conditioners has been greatly accelerated and simplified by the use of sorbent HahnmiHifipra to regulate humidity levels. Frequently, the sorption unit is used in conjunction with heating and cooling coils to provide the required dry-bulb temperatures. Humidity conditioning has tymmo an indinpAngahlA tool in establishing standard environments for testing, rechecking, and repairing electronic navigation and fire control instru ments before installation with several aircraft manufacturers. While humidity control is a vital element in instrument pro duction and calibration, it also anahW highly bIHUaH person nel to work more comfortably and thus more efficiently on instruments being ch^rk-arf APPLICATIONS FOR DRYING AT ELEVATED PRESSURE Preservation of Materials Generally, materials in storage are preserved at wnt5aI1y atmospheric pressure but there are a limited number, of ap plications for the preservation of stored materials at elevated pressures, particularly where the dried media is an inert gas surrounding the material to be stored. These applications would include materials which would deteriorate when sub jected to either high relative humidity or oxygen content in the surrounding media. The drying of high pressure air which is subsequently reduced to a range of 5 to 10 pgig has been used most effectively in pressurising coaxial cables to elim inate electrical shortage causing interference in telephone lines due to moisture infiltration. This same principle, but at somewhat lower pressures, is also used in wave guides and redomes to prevent moisture film on the envelope, etc. Process Drying of Air and Other Gases The drying of air and other gases in refineries, chemical plants, power stations, etc., has long been an essential factor toward efficient plant operation, quality control, etc. Drying of instrument air, particularly in areas where the air lines are run outdoors and exposed to temperatures below the dew-point of the air leaving the aftercooler, to a level of --40 F, will prevent condensation or freeze-up in the in. strument control lines. Not only is continuous trouble-free operation assured, but considerable savings in instrument repair and down time is also realized. Most industrial proc esses cannot tolerate inaccurate instrument control. The drying of plant air used for pneumatically operated valves, tools and other equipment is oecessary in arg where the piping is exposed to low ambient temperatures in order to prevent condensation and freezing. In addition, the use of dry air prevents rusting of the air lines which produce abrasive impurities which cause excessive wear on tools, etc Use of dry air for these purposes will considerably reduce maintenance and replacement costs. Drying of industrial gases or fuels such as'natural gas has been accepted as a necessary step in the industry. For ex ample, fuels including natural gas are cleaned and dried before storage underground to assure that valves and trans mission lines will not freeze from condensed moisture during extraordinarily cold weather when the gas is most needed. Propane likewise must be clean and dry to prevent ice ac cumulation. Other gases, such as bottled oxygen, nitrogen, hydrogen, and acetylene must have a high degree of dryness. In the manufacture of liquid oxygen and ozone, the weather air supplied in the particular process must be clean and dry. ' Drying of air or inert gas for conveying of hygroscopic ma terials in either liquid or solid state is mandatory to insure continuous, trouble-free plant operation. Normally, for this purpose are dried to a --40 F dew point. Purging and blanketing operations in the petro-chemical industry depend on the use of dry inert gas for reduction of explosive hazards, reaction of chemicals with moisture or oxygen, etc. Testing of Equipment Dry, high pressure air is used extensively for testing of re frigeration condensing units to insure tightness of components and prevent moisture infiltration. Similarly, dry inert gas is used in testing of copper tubing, and coils to prevent corro sion or oxidation. The manufacture and assembly of transis tors and other electronic components require exclusion of all moisture, and final testing in dry boxes must be carried out in moisture free atmospheres. The simulation of dry high altitude atmospheres for testing of aircraft and missile com ponents in wind tunnels require extremely low dew-point conditions. Liquid Phase Drying Use of solid adsorbents offers an economic method for re moving water from liquid hydrocarbons where high purity is desired and water content is relatively low. This is of par ticular value for many organic liquids in the petrol-chemical industry. Among liquids which can be dried with good re sults are: Benzene, toluene, zyiene, butane, propane, trichlorethylene, Refrigerants 11 and 12, and methyl chloride. BIBLIOGRAPHY W. L. Ross and E. R. McLaughlin: An analysis method for pre dicting behavior of solid adsorbents in solid sorption dehumidifiers (ASHAE Transactions, Vol. 61, 1955, p. 321). Symposium Bulletin on Dthumidification (five papers pre sented at Symposium held at 63rd Annual Meeting, ASHAE, February 26, 1957). G. C. F. Asker and T. H. Urdahl: Ship DehttnridifiaUion Sys tems (International Institute of Refrigeration, Nantes, France, June 20,1957). Several references included. CHAPTER 79 OWNING AND OPERATING COSTS Fixed Charges, Amortization, Merest, Taxes, Insurance, Rent, Maintenance Costs, tabor for Operation, Energy Costs, Constant Loads, Electric Refrigeration, Heat-Operated Refrigeration, Water Costs, Heating THE total cost for the use of heating, ventilating, and 6. Water conservation devices including towers, evaporative condensers, etc. air-conditioning systems may be divided into two classi 7. Ttiwilatiwn of pipes, ducts, and equipment. fications. The first of these is the relatively fixed and unvary 8. Building alterations, fumng-in ducts and pipes, structural ing expense of ownership, and the second is the variable and work, electrical work, plumbing, fees, permits etc. somewhat controllable expenditure for actual operation of the equipment. Owners and prospective purchasers of this equipment are particularly concerned with both once the actual expenditure is generally predicated upon the possible return on the investment resulting from increased patronage, greater efficiency on the part of the employees, meeting of competition, or the improvement and maintenance of quality in a manufactured product. These costs may be grouped under four headings: (1) Fixed Charges, (2) Maintenance Costs, (3) Labor for Operation, (4) Energy Costs, and (5) Wa&r Costs. To estimate the first cost of any system prior to installa tion, the best procedure is to determine the heating and cool ing load, and then after thorough engineering study, select the type of system. The installed cost of systems will vary widely, depending upon the type of equipment selected, and the design of the distribution system, equipment and labor costs in the locality, demands for the particular installation, etc. A reasonably approximate cost may be determined for a selected design in a given locality from the sum of the es timated unit costs of the component parts of the system. A reasonably precise estimate of the cost of the components FIXED CHARGES may be obtained from cost records of recent installations of a comparable design, or from quotations submitted by Fixed charges are the animal expenses arising from the manufacturers and contractors. ownership of the installation, including use of the owner's Approximate costs are given in Table 1 for mechanical money, and protection of the equipment in the form of in air-handling systems including heating and cooling coils for surance. Such costs are usually unchanged from year to year distributing Wt cfm per square'foot of floor area and re regardless of whether the equipment is in or out of service. frigeration equipment based upon a requirement of one ton Fixed charges may be grouped under five headings: (1) for every 333 sq ft of floor area. Different types of service Amortization, (2) Interest, (3) Taxes, (4) Insurance, and demand may change the floor area per ton of refrigeration (5) -Rent. and air volume per square foot between wide limits and, con Amortization sequently, the table should be used with caution. Other first costs may be incurred because of the installa As air-conditioning equipment becomes older, its ability or capacity to perform present and future service is reduced. Provision must be made for the owner to recover each year a portion of the initial value of the equipment as an expense to be charged against revenue, or to amortize the cost. This decrease in the value of property is usually determined by an accountant or engineer using some theoretical method and will depend upon (1) the total first cost, and (2) the' amortization period. The total first cost of an installation is the actual capital expenditure required to buy and install the air-conditioning, heating, or ventilating system ready for operation. It repre sents the first cost of the equipment combined with addi tion of the air-conditioning or heating and ventilating sys tem. These will include such items as electrical work, {jumbl ing, miscellaneous piping, building alterations, cutting, patching, furring-in of ducts or pipes, foundations, structural supports, remodeling or redecorating after installation, con sulting engineer's fees, licenses, and permits. As these costs vary widely no approximations are practicable. Therefore, each case must be considered individually. If a quotation can be secured from a manufacturer or contractor covering the complete job, it will usually include the items that have been mentioned. The length of the amortization period to be used depends upon (1) the type and remaining life of the building or tional costs incurred because of the installation of the system. space for which the system is to be used; (2) the type of eduipment to be employed as a part of the system; (3) the The first cost of air-conditioning, heating, or ventilating character of the business; (4) lease or ownership conditions; systems includes the following: anq (5) the taxing authorities. Depreciation, due to deterioration or obsolescence, must' I- Heat producing equipment including boilers, burners, controls, etc. 2. Heat distributing equipment including direct radiation, PlPing. etc. 3. Air h*nHimg equipment including fans, air heaters, air conditioners, filters, controls, etc. be considered in arriving at the amortization period. Main tenance and deterioration usually have the effect of offset ting one or the other. If a long depreciation period is to be used, then the item for maintenance, repair, and the re placement of wearing parts must be greater than for a short 4. Air distribution system including ducts, outlets, grilles, etc. 5. Refrigerating equipment including piping, pumps, etc depreciation period. In determining the length of the amortization period, the 859