Document 2Rqy64mB6BQ2z70dobOm4Nx5p

512 CHAPTER 19 ..jssiev'' -n.JprlMM Guide ditioning. Systems: (National IVarm Air Heating .and, Air Conditioning, Association. Manual 7, 1953.) . .V,V; _ Warm Air Perimeter Heating (National Warm Air Heating arid Air Conditioning Association, Manual 4, ]CJ50.) ;. : Calculating Heat Losses (National Warm Air Heating and Air Conditioning Asso ciation, Manual 3, 1956:) i. ` . ` -'I-1'' ' Four-Inch Pipe-Warm Air Perimeter Heating (National Warm Air Heating and Air Conditioning Association, Manual 10, 1956.) , . ; J ,; h : Proposed'Design Procedures for Large Mechanical-Warm: Air .Heating Systems by S. Konzo, R. J. Martin, D. S. Levinson, and R-. W. Roose,(ASHVE Transactions, Vol. 53, 1947, pi 177.) ' 9 Code and Manual for the Design and Installation of Warm Air Winter Air Con ditioning Systems and Year 'Round Air Conditioning Systems (National. Warm Air Heating and Air.Conditioning. Association, Manual 9, 1956.) .19 Automatic Controls, for Forced-Air Heating Systems, by S. Konzo and A. F. Hubbard. (ASHVE Transactions, Vol. 40, 1934, p. 37.) 11 Code and Manual for the Design and Installation of Warm Air Ceiling Panel Systems (National Warni Air Heating and Air Conditioning Association, Manual 7-A, Third Edition, 1950.) 19 Gravity Code and Manual for the Design and Installation of Gravity Warm Air Heating Systems (National Warm Air Heating and Air Conditioning Association, Manual 5, 1954.) c >. Simplified Procedure for Selecting Capacities of Duct Systems for Gravity Warm Air Heating Plants; by A. P. Kratz and S. Konzo (University of Illinois, En gineering Experiment Station Circular 45, Dec., 1942). CHAPTER 20 STEAM HEATING SYSTEMS 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;.Connec tions to Heating Units; Control Valves STEAM heating systems may be classified according to any one of, or combination of, the following features: (1) piping'arrangement, (2) pressure or vacuum conditions obtained in operation, (3) 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 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 systemwhen 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. These latter classifications are proprietary designations. 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 boiler, so that thte 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 Urshaped ontainer, with the boiler steam pressure on the top of the water at one end, and the team main pressure on the top ofthe water at the other end. The difference between toTk fl PressurRS is the pressure drop in the system, i.e., the friction and resistance the flow of steam in passing from the boiler to the far end of the main, and the p essure reduction in consequence of the condensation occurring in the system. balftW W ^ar end will rise sufficiently to.overcome.this difference in order to _ nce pressures, and it will rise far enough to produce a flow through the.return t P and overcome the resistance of check valves, if installed. ; : is a hhe-pipe steam system is designed, for example, for a total pressure drop of utilizes a. Hartford return connection instead of a check valve on the return, se In the water level at the far end of the return, due to the difference in steam 513