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Handbook of air conditioning and refrigeration / Shan K

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13.32 CHAPTER THIRTEEN<br />

<strong>refrigeration</strong> capacity, as determined from the temperature <strong>of</strong> the chilled water returned to the evaporator,<br />

the DDC unit controller closes the vapor <strong>and</strong> liquid shut<strong>of</strong>f valves <strong>and</strong> starts the compressor.<br />

The vaporized refrigerant from the evaporator is extracted by the compressor, discharged to the<br />

condenser, <strong>and</strong> condensed to liquid refrigerant as in normal operation.<br />

Free Refrigeration Capacity<br />

FIGURE 13.14 Free <strong>refrigeration</strong> operation for a single-stage, water-cooled centrifugal chiller.<br />

Free <strong>refrigeration</strong> capacity depends on the following parameters:<br />

● The temperature difference between the chilled water leaving the evaporator <strong>and</strong> the condenser<br />

water entering the condenser.<br />

● The size <strong>of</strong> the evaporator.<br />

● Condenser water flow.<br />

● Fouling factors at the evaporator <strong>and</strong> the condenser. An allowable fouling factor is usually<br />

0.00025 h�ft 2 �°F/Btu (0.000044 m�C/W). A higher fouling factor means a lower free <strong>refrigeration</strong><br />

capacity.<br />

Free <strong>refrigeration</strong> capacity is always expressed as a percentage <strong>of</strong> the base capacity <strong>of</strong> the centrifugal<br />

chiller. For a st<strong>and</strong>ard-size evaporator in a typical centrifugal chiller that is running in a free<br />

<strong>refrigeration</strong> cycle, if the chilled water leaves the evaporator at 48°F (8.9°C) <strong>and</strong> the condenser

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