Document KRzn7BzOzN5LOyO9VGgk4z3zw

408 CHAPTER 28 1959 Guide tures by room thermometers, and the determination of the temperature drop of water flowing through a heating unit or zone by mp-ana of surface contact thermometers or ther mometers installed in the piping. When adjustment is made by means of water temperature drop, the capacity of the units after adjustment must equal the heat delivery actually required. Control is then accomplished by making the tem perature drop through all units equal. {Prortxiao dtoM bu made far expansion in eadi dosed dmdt) Fig. 20.... Vertical Zoning of Hot Water Heating System in a 12-Story Building The procedure for making a permanent adjustment of heat distribution in a larger system should be as follows: 1. Select a time or day when conditions of heat gain are minimum; ie., nighttime or an overcast day. Outdoor tempera tures should be such as to require at least SO percent of the sys tem capacity to maintain the design indoor temperature. 2. Place the system in operation and make certain that all valves, adjusting fittings, and dampers are in the open position. Automatic oontrol which might reduce the flow or capacity of any unit should be rendered inoperative. Doors and openings between rooms should be closed. 3. Prepare a form for recording data on temperatures in spaces or at the supply and return of heating elements or of sones. 4. After the. system has reached equilibrium a complete rec ord should be made of temperatures throughout the system. 5. An initial adjustment of flow regulating devices in the sys tem should be made on the basis of the record of the original readings. A new set of temperature readings should be recorded after sufficient time has been allowed to establish a new equilib rium throughout the building. 6. Continue adjustments of flow control devices until a satis factory condition is obtained. 7. When a satisfactory adjustment has been accomplished, it is advisable to mark the position of each of the adjusting fit tings or valves. This facilitates return to proper control settings if the flow controls are disturbed by accidental or emergency changes at any time. CARE AND MAINTENANCE OF SYSTEMS A hot water heating system should last during the life of the building if it is designed, installed, and maintained properly. Maintenance instructions for individual elements of the system sucu as burners, motors, pumps, and accessories . may be obtained from the manufacturers who supply this equipment. Two factors contribute in a most important way to the satisfactory operation and life of the hot water heat ing system: (1) the proper cleaning of the system when in stalled; and (2) a minimum change of water in the system, except as required by periodic maintenance of the boiler or draining of the expansion tank. INITIAL CLEANING OF SYSTEM Rules that should be followed for the initial cleaning of the system are: 1. All equipment and piping should be thoroughly cleaned of iron cuttings and other refuse during assembly and installation. 2. When installation is complete, the system should be filled with a solution of 1 lb of trisodium phosphate per 50 gal of water and should be operated for 24 hr at maximum tempera ture with all pumps operating. The system should then be drained and thoroughly flushed with water before refilling. In order to minimise the addition of water to the heating- system, the operation of air-vent valves, relief valves, and the tightness of the system generally should be subject to continuous inspection. Drip6 from automatic air-vent valves should discharge in places where leakage is readily detected. Continual operation of the pressure relief valve should be a signal for the inspection, repair, or replacement of the relief valve, or a check on the operation of the expansion tank or the automatic water feeder, if one is provided. REFERENCES 1J. H. Keenan and F. G. Keyes: Thermodynamic Properties of Steam (John Wiley it Sons, New York, 1936, 1st ed.). * F. E. Giesecke and J. S. Hopper: Friction heads in standard aix-inch pipe (ASHVE Transactions, Vol. 47, 1941, p. 71). *F. E. Giesecke and J. 8. Hopper: Comparative study of friction heads in screwed and welded elbows (ASHVE Trans actions, Vol. 48, 1942, p. 201). 4 F. E. Giesecke: Friction heads due to water flow in copper, brass, and other smooth pipes (ASHVE Transactions, Vol. 49, 1943, p. 175). *F. E. Giesecke: Determination of pipe sizes for hot water heating systems (ASHVE Transactions, Vol. 21, 1915, p. 473). * F. E. Giesecke: Friction of water in iron pipes and elbows (ASHVE Transactions, Vol. 23,1917, p. 499). T F. E. Giesecke: Effect of temperature upon the friction of water in pipes (ASHVE Transactions, Vol 31, 1925, p. 9). F. E. Giesecke: Friction of water in elbows (ASHVE Transactions, Vol. 32, 1926, p. 303). '*F.. E. Giesecke and W. H. Badgett: Friction heads in oneinch standard cast-iron tees (ASHVE Transactions, Vol. 37, 1931, p. 395). "F. E. Giesecke and W. H. Badgett: Loss of head in copper pipe and fittings (ASHVE Transactions, Vol. 38,`1832, p. 529). UF. E. Giesecke and W. H. Badgett: Supplementary friction heads in one-inch cast-iron tees (ASHVE Transactions, Vol. 38, 1932, p. 111). u F. E. Giesecke: Two methods of figuring the friction loss in pipe lines (ASHVE Transactions, Vol. 59, 1953, p. 49). "L. N. Montgomery and W. 8. Harris: Sources of vent gas in a hot water beating system (ASHAE Transactions, Vol. 61, 1955, p. 483). 14 Low-pressure heating boilers' {ASMS Boiler and Pressure Vessel Code, with 1954 and 1955 addenda, Section IV). " R. C. Chewning and R. W. Peterson: Consider pump heads when rising hot water expansion tanka (Heating, Piping and Air Conditioning, July 1955, p. 106). ** H. A. Lockhart and G. F. Carlson: Compression tank selec tion for hot water heating systems (ASHVE Transactions, Vol. 59, 1953, p. 55). "Oscar Faber and J. R. Kell: Healing and Air Conditioning of Buildings (Architectural Press, London). CHAPTER 29 HIGH-TEMPERATURE WATER SYSTEMS Features; Basic System; Design Considerations: Boilers, Boiler Piping and Controls, Direct-Contact Heaters and Auxiliary Heat Exchangers, Boiler Feed Pumps, Circulating Pumps; Distribution Piping Design: 'District Distribution, Pipe, Valves and FifKngs, Thermometers and Pressure Gages; Space Heating Equipment; Temperature Control; Water Treat ment; Storage HIGH-TEMPERATURE water systems discussed in The size of insta.11a.tion, the extent of the load, and the this chapter are those operating with supply water at operating temperature will govern central boiler-plant de temperatures exceeding 250 F. Operating temperatures rangseign and construction. Some determining considerations are: from 250 to 430 F, with pressures from 55 to 350 psig. Hightemperature water systems used in the United States are predominantly closed-type systems. 1. Type of load: heating, procem, or both. 2. Distance from heating plant to space or process requiring heat. This chapter is intended to give a broad general idea of 3. Terrain of land on which buildings are located. principles and practices that apply to high-teraperature systems and distinguish these systems from the systems op 4. Zoning requirements based on occupancy and load dis tribution. erating below 250 F. 5. Quantity of steam used for power equipment, if required. FEATURES OF SYSTEMS The following ore among the outstanding features of high temperature as compared to low temperature systems: 1. It is common practice to use greater temperature drops. 2. Supply and return piping may be given the same pitch or grade, or may be run level. Grading is desirable but a definite minimum pitch is not required. 3. Piping may slope up or down or run at a variety of ele vations to suit the terrain and the architectural and structural requirements without provision for drainage at each low point except for emptying sections of piping for shutdown. This fea ture may reduce the excavations required. 4. The pressure in any part of the system must alwayB be ' above the pressure corresponding to the temperature at satura tion in the system in order to prevent flashing of the water into steam. 5. Processes requiring different temperatures of water may be served at their required temperatures by use of heat ex changers, by regulating tbe flow to certain processes, by plac ing some processes in series with others, etc. 6. Heat may be stored in the mains and boiler by build-up of temperature in the return main during periods of light load. THE BASIC SYSTEM High-temperature water systems are basically similar to the conventional forced hot water heating systems since they require boilers or direct contact heaters for heating the wa ter, expansion or pressurizing tanks or both, circulating pumps, distribution piping, and heat transfer or emission equipment, as shown in Fig. 1. The principal differences from the low temperature system are the higher pressure used, the consequently heavier equipment, and the manner in which pressure is maintained on the water. When cush ioned by steam in the boiler, the system in effect is a hot water system using a boiler, producing stedm to beat the water. The supply piping draws water from the boiler below its water level so that water'flow may occur even though steam is kept above the surface of the water. For an equiva lent heat load the rate of water flow through the boiler is 6 to 10 times that for steam systems. Water is circulated in a closed circuit from the central sta tion to areas where heat is required and back to the boiler. Variations in elevation may make it desirable to locate tbe boiler house on the highest ground in order to obtain maxi mum static presure bead on the system. Boiler auxiliaries such as boiler feed pumps, pressure tanks, economizers, and system circulating pumps are usually located in the boiler house, as indicated in Fig. 2. DESIGN CONSIDERATIONS Factors to be considered in selecting the type of boiler are (l) the maximum operating pressure of tbe system, (2) the water temperature requirements during a 24-hr operat ing period, and (3) the size of the load. Process loads may require water at a given minimum supply temperature con tinuously, while space heating and other loads may permit a lower water temperature at night or an off period during each 24-hr operating period. Water temperature requirements also influence the man ner of pressurizing the system. Simplicity of operation is an important consideration in selecting a method of pressuriz ing when boilers are not operated during the night. Varia tions in supply water temperature and temperature drop also should be taken into account in selecting a pressurizing method. Theoretically, water temperatures up to about 350 F may be provided using boilers and piping suitable for 125 psig, but practically,-maximum water temperatures will be limited