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736 CHAPTER 69 1962 Guide And.Data Book resulting from the different speeds of the two compressors. This type can also be reduced by installing mufflers. When.the noise is a result of turbulence and insulating the line is not effective enough, either the use cf a supplementary line or the installation of a larger line to reduce the velocity will be helpful. .Code Restrictions Restrictions imposed by codes, laws and regulations apply ing at the rite of an installation must be known to the de signer and obeyed. The Safety Code for Mechanical Refrigera tion (ASA-B9.1) and the Code for Pressure Piping (ASA331.1) are primarily drawn up as guides for safe practice, and should be followed whether they have been given the force of law- in a particular community or not. Their principal re quirements as-they apply to refrigeration piping are prac tically identical. They are the basis of most municipal and state codes/' and will become more so as time goes on. How ever, some ordinances go beyond them in requiring heavier piping and other special features, and it is necessary for the designer to become familiar with the specific requirements applying at the rite where tire piping is to be installed. REFERENCES 1 Refrigerant Piping Data (Air-Conditioning and Refrigeration Institute, 1961). 1 Piping Application Data (Carrier Air Conditioning rv Sections 25B-2, 11-1541, and 25X-2, 10-15-46). ' * Piping Application Data (Carrier Air' Conditioning Cq Section 25B-1, p. 8, 5-1-46. Initially compiled from data of Mueller Brass Co. and Tube-Turns, Inc.). 4 Flow of Fluids though Vaises, Fittings and Pipe (Crane Company Technical Paper No. 409, May 1942, p. 21). 4 S. C. Dietrick: Refrigerant piping for air conditioning gys- terns (Heating and Ventilating, March 1953, p. 95). ` * Equipment Manual, Section B-10 (York Corp., subsidiary of Berg-Warner Corp., May 1, 1955). * Design and Installation Instructions, Refrigerant Piping (Westinghouse Electric Corp., Information Bulletin 105-620-1 September 1951). ' CHAPTER 70 REFRIGERANT PIPING SYSTEMS FOR REFRIGERANTS 12, 22 AND 500 Basic Principles; Liquid Lines; Sucfion Lines; Discharge (Hof Gas) Lines: Oil Entrainment, Minimum Gas Velocities; Piping from Condenser to Receiver; Piping at Multiple Compressors; Piping at Various System Components; Refrigerafion Accessories; Bead Pressure Control for Refrigeranf Condensers; Control of Compressor; Manual Compressor Operation; Hot Gas Bypass Arrangements THE success of a refrigeration system is largely dependent Lubricating oil is continually leaving the compressor, in upon proper design of the refrigerant piping and under small amounts, with the discharge gas. The complete refrig standing of the system accessories required to perform the eration system must be designed to return this oil to the necessary operating functions. compressor at the same rate that it leaves. Wide variations This chapter discusses the fundamentals of refrigerant in system loading require careful system design to return piping and the application of the various accessories that are oil at lowest leading and yet not impose excessive pressure involved in tire satisfactory operation of a complete refrig drops in the piping and equipment at full load. erant piping system. It deals with systems using Refrigerants liquid feed devices are designed to operate efficiently 12, 22 and 500. Ammonia piping application is covered in down to about 50 percent of full capacity. Below this their Chapter 71. performance is not entirely satisfactory. A valve operating at Reference should be made to Chapter 69 covering the fol 25 percent capacity is badly oversize and attempts to operate lowing general information on refrigerant piping: refrigerant in a nearly closed position. Modulation is practically im flow data, refrigerant line siring data, general piping practice possible at this condition and the valve will tend to cycle and other general references. Piping for multi-stage systems badly. liquid distribution to multi-circuit evaporators will is discussed in Chapter 72. depreciate at very low capacity conditions causing, uneven air temperatures across the face of a coil. Cycling of the BASIC PRINCIPLES liquid feed device plus poor distribution causes periodic or Refrigerant piping systems should be designed and operated to generally accomplish tire following: 1. Insure proper refrigerant feed to evaporators. 2. Provide practical refrigerant line sues without excessive pressure drop. . 3. Prevent excessive amounts of lubricating oil from being trapped in any part of the system. 4. Protect the compressor from loss of lubricating oil at all. tames. 5. Prevent liquid refrigerant from entering the compressor, either during operating or idle time. 6. Maintain a clean and dry system. continual flooding of liquid refrigerant back to the com pressor. These and other problems should be analyzed and allowed for in the initial system design stage. LIQUID LINES Liquid lines present the fewest problems in design. Re frigeration oil is sufficiently miscible with Refrigerants 12, 22 and-500 in the liquid form to insure adequate mixing and positive oil return. Low liquid velocities and traps in the line do not pose oil return problems. In dowigning a liquid line, however,-it is desirable to have SYSTEM CAPACITY REDUCTION PROBLEMS The universal use of automatic capacity control on modern compressors necessitates careful analysis and design of re frigeration systems. The compressor is capable of loading and unloading, as* it'floats with the system load requirements, through a considerable range of capacity variation. A single machine <*>.n unload down to 25 percent of full load capacity, slightly subcooled liquid reach the liquid feed device, at a sufficiently high pressure for proper operation. This doeS present two factors which must be considered: 1. The liquid line, and all the valves and accessories in it, must be sized for a practical pressure drop due to friction. (See Chapter 69.) 2. Precautions should be taken to prevent flash gas in tne liquid line, or to handle it if prevention is impractical. while multiple machines connected in parallel can unload down to a system capacity of 12J-3 percent and even lower m some cases. This ability of refrigeration compressors to match widely fluctuating load requirements poses certain problems that must be recognised and properly handled. Flash Gas in fhe Liquid Line Refrigerant remains in liquid form only as long as its tem perature is at; or below the saturation temperature corre sponding to the liquid pressure. If the liquid is only slightly subcooled, either an increase in its temperature or a decrease 737 ; fj ;1 ;; 11 ;f i I vii