Document bOLa1084ZD39qqGmJgZ62NEZ3

82 CHAPTER 5 1962 Guide And Data Book passing warm air over the cooler basement walls floor.. In areas of high prevailing dew points, however, this prac tice may cause objectionable dampn*"* to develop in the basement. Complete summer air conditioning can be readily com bined with forced warm air systems either by using factory- built units incorporating both refrigeration and heating equipment, or in tome coset by adapting separate refrigera tion equipment or well-water coils to existing warm air systems. A more complete treatment of residential summer air con ditioning is given in Chapter 13. GRAVITY WARM AIR SYSTEMS In gravity warm air heating systems the motive head pro ducing flow depends upon the difference in weight between the heated air leaving the top of the furnace casing and the cooled air entering the bonnet of the casing. Hence, the mo tive head is very small and the system must allow free flow. A gravity warm air furnace hearing plant consists of a fuel-burning furnace or heater, enclosed in a casing of sheet metal, which is placed in the basement of the building. The heated air, taken from the bonnet on the top of the furnace casing, is distributed to the various rooms of the building through sheet-metal warm air pipes. The warm air pipes in the basement are known as leaders, and the vertical warm air pipes which are installed in the inside partitions of the building are called stacks. The heated air is discharged into the rooms through registers which are set in register boxes placed either in the floor or in the side wall, usually at or near the baseboard. .The air supply to the furnace is usually taken entirely from inside the building through one or more recirculating ducts, although in some cases an outside air supply duct is provided. Gravity warm air heating systems may be designed- by following the procedures given in Manual 5 of the National Warm Air Heating and Air Conditioning Association. This publication also gives information on terminology, outlet and return locations, and standard sizes of pipe and fittings. The data underlying this information and the design procedure are given in a circular11 issued by the University of Illinois, and are based on research conducted there. REFERENCES 1 Application Guide for Residential Central Air Conditioning System*--Winter and Year-Round (National Warm Air Heat ing and Air Conditioning Association, Manual 8, Fifth FHi tion, 1958). . * A. P. Krats and S. Konso: Performance of a forced warm, air heating system as affected by volume and temperature of air recirculated (ASHVE Transactions, Vol. <8, 1942, p. 383). * Manual for Adjusting Winter Air Conditioning Systems for Maximum Comfort (National Warm Air Heating and Air Conditioning Association, Manual 6, 3rd ed., 1957). * Warm Air Perimeter Heating (National Warm Air Heating and Air Conditioning Association, Manual 4, 6th ed., 1959y * Four-Inch Pipe Warm Air Perimeter Heating (National Warm Air Heating and Air Conditioning Association 10, 1956). * Code and Manual for the Design and Installation of Warm Arr Winter Air Condttiompg Systems (National Warm Air Heating and Air Conditioning Association, Manual 7, 1953). 1 Standards tor the Installation of Residence Type Warm Air Heating and Air Conditioning Systems (National Board of Fire Underwriters No. 90B and National Fire Protecflbn As sociation No. 90B, I960.) ' * Standard for the Installation of Air Conditioning and Ventilating Systems of Other than Residence Type (National Board of Fire Underwriters No. 90A and National Fire Pro tection Association No. 90A, I960.) * Criteria and Test Procedures for Combustible Materials Used for Warm Air Ducts Encased in Concrete Slab Floors (Federal Housing Administration, 1956.) '* Load Calculationfor Residential Winter and Summer Air Con ditioning, (National Warm Air Heating and Air Conditioning Association, Manual J First ed., 1961). .. "S. Konso, R. J. Martin, D. 8. Levinson, and R. W. Roose.: Proposed design procedures for' large mechanical warm air heating systems (ASHVE Transactions, Vol. 53, 1947, p. 177). - "Code and Manual for the Design and Installation of Warm Air Winter Air Conditioning Systems and Year 'Round Air Conditioning Systems (National Warm Air Heating and Air Conditioning Association, Manus] 9, 6th ed., 1958). ' a Perimeter Warm Air Heating and Ventilating of Industrial, Commercial, and Public Buildings (National Warm Air Heat- ing'&nd Air Conditioning' Amociation, Supplement to Manual "S. Konso and.A. F. Hubbard: Automatic controls for forced-air heating systems (ASHVE Transactions. Vol. 40 1934, p. 37). "Code and Manual for the Design and Installation.of Warm Air Ceiling Panel System* (National Warm Air Hating and Air Conditioning Association, Manual 7-A, 1950, 3rd ed.). " 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). "A. P, Krats and S. Konso: Simplified Procedure for Se lecting Capacities of Duct Systems for Gravity Warm Air Heating Plants (University of Illinois, Engineering Experiment Station Circular 45. December 1942). CHAPTER 6 STEAM HEATING SYSTEMS Classification of Steam Heating Systems by Types; One-pipe, Two-pipe, Suixstmosphnric and Orifice System* Sizing Piping for Steam Heafing Systems} Pressure-Redwing Valves; Boiler Connection* Condensate Return Pumps; Vocuum Heating Pumps; Traps; Drips; Connections to Heating Units; Control Valves TEAM hearing systems may be classified according to to the boiler. Elevation of the heating units above the water S any one of, or combination of, the following features: line must therefore be sufficient to overcome pressure drops (1) piping arrangement, (2) pressure or vacuum conditions due to flow, as well as pressure differences due to operation. obtained in operation, (3) method of returning condensate Referring to Fig. 2 it will be noted that the boiler and wet- to the boiler. return form a U-shaped container, with the boiler steam pressure on the top of the water at one end, and the steam Classification by Piping Arrangement main pressure on the top of the water at the other end. The A steam Eating system is known as a one-pipe system when a angle main serves the dual purpose of supplying rtpam to the heating unit and conveying condensate from it. Ordinarily, to each heating unit there is but one connec tion 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 connec tions, and when steam and condensate flow in separate mains and branches. Heating systems may also be described as up-flow or dovm-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 condensate receiver. difference between these two pressures is the pressure drop in the system, in., 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 condensa tion occurring in the system. The water in the far end will rise sufficiently to overcome this difference in order to bal ance 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 14 psi, and utilizes a Hartford re turn connection instead of a check valve on the return, the rise in the water level at the far end of the return, due to the difference in steam pressure, would be Vs of 28 in. (28-in. head being equal to one pound per square inch), or 314 in. Adding 3 in. to overcome the resistance of the return main, and 6 in. as a factor of safety for heating ups gives Gossification by Pressure or Vacuum Conditions 1214 in. as the distance the bottom of the lowest part of the Steam hearing systems may also be classified as highpressure, low-pressure, vapor, and vacuum systems, depend ing on the pressure conditions under which the system is designed to operate'. A system is known as a high-pressure system when the pending pressures employed are above 15 psig; as a lowpressure system when pressures vary from 0 to 15 psig; as a vapor system when the system operates under both vac uum and low-pressure conditions without the use of a vac uum pump; and as a vacuum system when the system oper ates under vacuum and low-pressure conditions with the use of vacuum pump When automatic controls are employed to vary the pres steam main and all heating units must be above the boiler water line. The same system, however, installed and sized for a total pressure drop of Vs psi, and with a check valve in the return, would require V4 of 28 in., or 14 in. for the differ ence in steam pressure, 3 in. for the flow through the re turn, 4 in. to operate the check valve, and 6 in. for a factor, of safety, making a total of 27 in. as the required distance. Higher pressure drops would increase the distance accord ingly. When conditions are such that condensate cannot be re turned to the boiler by the acticto of gravity, and either traps or pumps must be employed, the system is known as a mechanical return system. There are three general types of sure conditions in the system in accordance with outride 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. Classification 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 11 heating units must be elevated sufficiently above the wa ter line of the boiler, so that the condensate can flow freely Fig. I.... Difference in Steam Pressure on Water m Boflef and at End of Steam Main