Document rBv1DjXakgqp0Zw7dNR8Nj9rG

442 CHAPTER 19 1950 Guide ..REFERENCES ,. > Specifications for the furnace unit and the installed duct system are shown in The Yardstick, Manual' 8, and Manual 7 published by National Warm Air Heating and Air Conditioning Association. * Performance of a Forced.Warm-Air Heating System as Affected by Changes in Volume and Temperature of' Air Recirculated, by A. P. Kratz and S. Konzo (A.S.H.V.E. Transactions, Vol. 48,1942, p. 393). . * Automatic Controls for Forced-Air Heating Systems, by S. Konzo and A. F. Hubbard (A.S.H.V.E. Transactions, Vol. 40, 1934, p. 37). * Proposed Design Procedure for Large Mechanical Warm Air Heating Systems, by 8. Konzo, R. J. Martin, D. S. Levinson, and R. W. Roose (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, May, 1947, p. 108). > Summer Cooling in the Research Residence, by A. P. Kratz, S. Konzo, M. K. Fahnestock and E. L. Broderick (University of Illinois Engineering-Experiment Sta tion Bulletins Nos. 290j 305 and 321). A.SH.V.E. Research Report No. 1177-- Summer Cooling in the Research Residence with a Gas-Fired Dehydration Cooling Unit, by A. P. Kratz, S. Konzo and E. L. Broderick (A.S.H.V.E. Transactions, Vol. 47,1941, p. 203); CHAPTER 20 STEAM HEATING SYSTEMS AND PIPING Classification of Steam Heating Systems by Types; One-pipe; Two-pipe, . Sub-atmospheric and Orifice Systems; Sizing Piping for Steam Heating Systems; Pressure Reducing Valves; Boiler Connections; Condensate Return Pumps; Vacuum Heating Pumps; Traps; Drips; Con nections to Heating Units; Control. Valves STEAM heating systems may be classified according to any one of, or combination of, the following features: (1) by the piping arrange ment, (2) by the pressure or vacuum conditions obtained in operation, (3) by the method of returning condensate to the boiler. X. By Piping Arrangement. A steam heating system is known as a one-pipe system 6 when a single main serves the dual purpose of supplying steam to the heating unit |; and conveying condensate from it. Ordinarily, to each heating unit there is but one connection which must serve as both the supply and the return, although separate n supply and return connections may be used. . - , , ..4 A steam heating system is known as a two-pipe system when each heating unit is provided with two piping connections and when steam and condensate flow in sepa rate mains and branches. Heating systems may also be described as up-flow or down-flow depending on the direction of steam flow in the risers; and as a dry-return or a wet-return depending on .whether the condensate mains are above or below the water line of the boiler^or con densate receiver. 2. By Pressure or Vacuum Conditions. Steam heating systems may also be classi fied as high pressure, low pressure, vapor, and vacuum systems, depending on the pressure conditions under which the system is designed to operate. A system is known as a high pressure system when the operating pressures employed ' are above 15 psig; as a low pressure system when pressures vary from 0 to 15 psig; as a vapor system when the system operates under both vacuum and low pressure condi tions without the use of a vacuum pump; and as a vacuum system when the system operates under vacuum and low pressure conditions with the use of vacuum pump. When automatic controls are employed to vary the pressure conditions in the sys tem in accordance with outside weather conditions, tne system may be known as a sub-atmospheric, differential, or synchronized system. These latter classifications are proprietary designations. A ' When orifices are employed on the inlets to the heating units the system may be known as an orifice system. 3. By Method of Returning Condensate. When condensate is.returned to:the boiler by gravity, the system is known as a gravity return system. In this system all heat ing units must be elevated sufficiently above the water line' of the bdiler, so that the condensate can flow freely to the boiler. Elevation of theheating units above the water line'must therefore be sufficient to overcome pressure drops due to flow as well as pressure differences due to operation. 3 Referring to Fig. 1 it will be noted that the boiler and wet-retum form a U-shaped container, with the boiler steam pressure on the top of the water at one end and the steam main pressure on the top of the water at the other end. The difference between these two pressures is the pressure drop in the system, i.e., the friction and resistance to the flow of steam in passing from the boiler to the far end of the main and the pressure reduction in consequence of the condensation, occurring in the system. I The water in the far end will rise sufficiently to overcome this difference in order to balance the pressures, and it will rise far enough to produce a flow through the return pipe and overcome the resistance of check valves, if installed.. If a one-pipe steam system is designed, for example, for a total pressure drop of ' 't- t psi, and utilizes a Hartford return connection instead of a check valve on the return,