Document qay79m4wgYYM4aa68N7Z3Yx8n

460 CHAPTER 22- 1949Guide . REFERENCES -. :-.V. 1 Specificatiohs;fdr the furnace unit and'the installed duct`system are shown in The Yardstick, Manual'No; 8,: and Manual No; 7 published by National Warm Air Heating cmd Air Conditioning Association* . v ; . Performance ofa 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. 3S)3). 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 S. Konzo, R. J. Martin, D. S.; Levinson, and .R. W.. Roose, A.S.H.V.E. Journal Section,. Heating, .Piping, and Atr Conditioning, May; 1$47, 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'JRiiZ/eltni:Nbs."<290`, 305/.and 321). "A.S.HiV.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 23 STEAM HEATING SYSTEMS AND PIPING Classification of team 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 follo\ving features: (I) 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. 1. By Piping Arrangement. A steam heating system is known as a one pipe system 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 supply and return connections may be used. / 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 condehsate 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, the system may be known as a sub-atmospheric, differential, or synchronized system. Theselatter-classifications are proprietary designations. When orifices are employed on the inlets to the heating units the system may be known as an orifice system. . l: '.W; ' - . 3. By Method of Returning Condensate. .When condensate isreturned 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 boiler, so that the condensate can flow freely to the boiler. Elevation of the heating units above:the water line must therefore be sufficient to overcome pressure drops due .to flow as well as pressure differences due to operation. Referring to Fig. 1 it will be noted that the boiler and wet return form a U-shaped container, with the boiler steam pressure oh 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. 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.. 4 If a one-pipe steam system is designed, for example, for a total .pressure drop of .| psi, and utilizes a Hartford'return conhectipn instead of a check valve on the return, 461