^{Compound System}

_{1. The condenser of system 2 is shown at point}

^{The compound system uses two or more com}pressers connected in series in the same refrigeration system. In this type of system the first stage also indicated in the figure. Notice the use of oil _{separators to minimize the circulation of oil. D in the figure. Two TEV refrigerant controls are} ^{compressor is the largest and for each succeeding} stage the compressor gets smaller. This is because

Figure 14-9.-Multistage refrigerating system.

Figure 14-10.-Air-cooled condenser mounted on a compressor unit.

as the refrigerant passes through each compressor, it becomes a more dense vapor. A two-stage compound system can attain a temperature of approximately -80F. A three-stage system, like the one depicted in figure 14-9, can attain a temperature of -135F efficiently. Compressor 1 pumps vapor into the intercooler and then into the intake of compressor

2. This operation is repeated between the second and third stages. In the third stage, the refrigerant vapor is further cooled and travels to the evaporator for specific cooling use.

MECHANICAL COMPONENT SELECTION

There are several mechanical components required in a refrigeration system. In this section, we discuss the four major components of a system and some equipment associated with the major components. These components include condensers, evaporators, compressors, refrigerant lines and piping, refrigerant capacity controls, receivers, and accumulators,

CONDENSERS

There are several condensers to be considered when making a selection for installation. They are air-cooled, water-cooled, shell and tube, shell and coil, tube within a tube, and evaporative condensers. Each type of condenser has its own unique application. Some determining factors include the size and the weight of the unit, weather conditions, location (city or rural), availability of electricity, and availability of water. For example, is electricity available in single phase or three phase? Is electricity economical or prohibitive? Water in some locations may be scarce, expensive, or contain chemicals that make it unsuitable for use. Local zoning laws should also be checked to ensure there are no restrictions as to use of electricity, water, or location of the unit. If you installed a unit on a roof, the roof load strength is very important. In some locations, the noise factor of an operating unit is an important consideration. With the rapid advances in technology, you should contact a manufacturer whenever possible to get the latest condenser design features available for a special-purpose installation. Figure 14-10 shows a typical installation of an air-cooled condenser mounted on a compressor unit. Figure 14-11 shows a cutaway view of a water-cooled condenser.

Figure 14-11.-Water-cooled condenser. 14-9

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