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136 CHAPTER 8 1962 Guide And Data Book tures by room thermometers, and the determination of the temperature drop of water flowing through a heating unit or zone by means of surface contact thermometers or ther mometers installed in the piping. When adjustment is mad* 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 ail units equaL (ProWoon ihmAd fa* noda for expontion in eod> doted drcmT) ' 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 gjn are minimum; ie., nighttime or an overcast day. Outdoor tempera tures should be such as to require at least 50 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 control 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 zones. 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 syatem 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 <wtjhliah 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 merfc the position of each of the adjusting fit- or valves, *11118 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 maintninH properly. Maintenance instructions for individual dements of the system such as burners, motors, pumps, and accessory, may be obtained from the manufacturers who supply this equipment. Two factors contribute in a most important wav to the satisfactory operation and life of the hot water heat ing system: (1) the proper cleaning of the system when i. stalled; and (2) a minimum change of water in the system except as required hv periodic maintenance of the boiler or draining of the expansion tank. INITIAL CLEANING OF SYSTEM Rules that should be followed for the initial cleaning gf 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 minimize 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. Drips 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 * J. H. Keenan and F. G. Keyes: Thermodynamic Properties of Steam (John Wiley A Sons, New York, 1936, 1st ed.). * F. E. Giesecke and J. S. Hopper: Friction heads in standard six-inch pipe (ASHVE Transactions, Yol. 47, 1941, p. 71). *F. E. Giesecke and J. 8. Hopper: Comparative study cf friction heads in screwed and welded elbows (ASHVE Trans actions, Vol. 48, 1912, p. 201). *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 ol water in iron pipes and elbows (ASHVE Transactions, Vol. 23,1917, p. 499). TF. 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, 1932, p. 529). aF. E. Giesecke and W. H. Badgett: Supplementary friction heads in one-inch cast-iron tees (ASHVE Transactions. Vol 38, 1932, p. 111). m- . u. ujeanae. i wo metnous oi ngurrng tne motion loss id pipe lines (ASHVE Transactions, Vol. 59, 1953, p. 49). "L. N. Montgomery and W. S. Harris: Sources of vent gw m a hot water heating system (ASHAE Transactions. VoL 61, 1955, p. 483). " Low-pressure heating boilers (ASME Boiler and Pressure Vessel Code, with 1954 and 1955 addenda. Section IV). **R. C. Chewning and R. W. Peterson: Consider pump heads when sizing hot water expansion tanks (Heating, Piping and Aw Conditioning, July 1955, p. 106). " H. A. Lockhart and G. F. Carlson: Compression runfa selec tion for hot water heating systems (ASHVE Transactions. Vol 59, 1953, p. 55). Gscar Faber and J. R. Kell: Heating and Air Conditioning of Buddings (Architectural Press, London). CHAPTER 9 HIGH-TEMPERATURE WATER SYSTEMS Fixture*' Bosic System; Design Considerations: D/red-Rred High-Temperature Wafer Generator?,. Pressurization, Direct-Contact Heaters, System Circulating Pumps; Distribution Piping Design; Heat Exchangers, Air Heating Coils; Space Heating Equipment; Temperature Control; Water Treatment; Storage; Safety Considerations IGH-TEMPERATURE water systems have been 10. More engineering effort is required to design a high- H figggjfiari as those operating with supply water tem temperature water system that is successful, safe, and easy to operate, a comparative steam or low-temperature water peratures above 350 F, and medium-temperature water syssystem. Hie design should be undertaken only by responsible tems as those with operating temperatures above 250 F and engineers with previous experience. Systems should be inherently below 350 F. The usual practicable, limit of temperature is approximately 450 F, due to pressure limitations on pipe simple, but mould incorporate all essential components for safety and ease of operation. fittings, equipment, and accessories. The general design principles are basically the same for both medium-tempera THE BASIC SYSTEM ture and' high-temperature systems. Both require water ' High-temperature water systems are basically similar to the undffr considerable pressure, and therefore require special conventional forced hot water heating systems. They require pumps, boilers, and equipment. The basic differences are in a beat source for heating the water, which may be direct- the pressure, temperature drops and average temperatures, fired high-temperature water generators, steam boilers, or with resulting differences In cost. In this chapter, the abbrevi heat exchangers of the open or closed type. The expansion of ation HTW will be used to refer to both medium-tempera the water upon heating is usually taken up in an expansion ture and high-temperature systems. vessel which at the same time is used for pressurizing the sys This chapter is intended to give a broad general idea of tem. Heat transport is dependent upon circulating pumps. principles and practices that apply to high-temperature sys The distribution system is closed, comprising supply and tems and distinguish these systems from the systems operat return pipes under the same basic pressure, and heat emission ing below 250 F. at the terminal unit is indirect by heat transfer through heat transfer surfaces. The basic system is shown in Fig. 1. FEATURES OF SYSTEMS The principal differences from low-temperature water sys tems are the higher pressure used, the consequently heavier The following are among the outstanding features of HTW equipment, the generally smaller pipe sizes, and the manner systems as compared to steam distribution systems or low- in which pressure is maintained on the water. temperature water systems: Most systems may be divided into either of two types: (1) 1. The system ia generally a completely closed circuit with amply and return mains maintained under pressure. There are no uses due to flashing, and the heat not utilized in the terminal heat transfer equipment is returned to the high-tempcrature water generator. Corrosion within the system is minimized. 2. In general, all mechanical equipment other than that which controls the performance of individual terminal units is confined to the central station. 3. Piping may slope up or down or run at a variety of eleva tions to suit the terrain and the architectural and structural re quirements without provision for drainage at each low point, except for emptying sections of piping for shut down.This may reduce the amount of excavation required, and the number of drip points and return pump locations, as compared to steam. 4. It is common practice to use greater temperature drops than in low-temperature water systems. . 5- The pressure in any part of tho system must always be above the pressure corresponding to the temperature at saturation in the system, in order to prevent flashing of the water into steam. 6. Terminal units requiring different temperatures of water niay be served at their required temperatures by regulating the Bow of water, by rnnHnbtimg the water supply temperature, by placing some units in series, by the use of neat exchangers, or other methods. 7. The high heat content of the water contained in the hightimperature water circuit acts as a thermal flywheel evening out fluctuations in the load. The heat storage capacity may be further `"creased by build-up of temperature m the return mains, or by other methods, during periods of light, load. 8. The high heat content of the heat carrier makes high- temperature water unsuitable for systems that are operated inter mittently if rapid start-up and shutdown is desired, unless the is designed for a minimum water volume and is operated the steam cushion system in which the high-temperature water ruses its own pressure, and (2) the gas-pressurized system in which the pressure is imposed externally. The high-temperature water generators, as well as. all ftiiriliftripH such as water makeup and feed equipment, pressure tanks and circulating pumps, are usually located in a central station. DESIGN CONSIDERATIONS Selection of the system pressure, supply temperature,-tern-' perature drop, type of high-temperature water generator, as well as the method of pressurization,.are the most important initial design considerations. Some determining factors are: 1. Type of load (apace heating, process, or both). Load fluctuation during a 24 hr period, ana fluctuation during a one year period should be considered. Process loads may require water ci response type controls. 9. Its physical properties make high-temperature water, less o&ogerous in case of a line or equipment break, than steam under toe game pressure. Fig. I..,. Elements of a High-Temperature Water System 137