Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTS 



as a higher or lower temperature in conjunction 

 with compensating relative humidity and air 

 motion. 



The term used to identify the net effect of 

 these three factors is effective temperature. 

 The effective temperature cannot be measured 

 with any instrument, but can be found on a 

 special psychrometric chart when the dry-bulb 

 temperature, the wet-bulb temperature, and 

 the air velocity are known. 



Although all of the combinations of tem- 

 perature, relative humidity, and air motion of 

 a particular effective temperature may produce 

 the same feeling of warmth or coolness, they 

 are not all equally comfortable or healthful. 

 For best health and comfort, a relative humidity 

 of 40 to 50 percent in cold weather and 50 to 

 60 percent in warm weather is desirable. An 

 overall range of 30 to 70 percent is acceptable. 



168.23 

 Figure 19-14.— Exposed view of hand electric 

 psychrometer. 



water vapor given off by the body and increases 

 in relative humidity . The body is thus surrounded 

 by an envelope of air which is at a higher tem- 

 perature and higher relative humidity than the 

 ambient air, and the amount of heat that the body 

 can lose to this envelope of motionless air is 

 considerably less than that which it can lose to 

 the ambient air. If the air is set in motion, the 

 motionless envelope of air is broken up and 

 replaced by ambient air, thereby increasing the 

 heat loss from the body. When the increased heat 

 loss improves the heat balance of the body, we 

 are likely to speak cheerfully of feeling a 

 "breeze," but when the increase is excessive, 

 we speak less cheerfully of feeling a "draft." 



SENSATION OF COMFORT .-From the pre- 

 vious discussion, it is evident that the three 

 factors of temperature, relative humidity, and 

 air motion are closely interrelated and that all 

 three factors have a definite effect upon comfort 

 and efficiency. In fact, a given combination of 

 temperature, relative humidity, and air motion 

 produces the same feelingof warmth or coolness 



MECHANICAL COOLING 



Mechanical cooling equipment is provided on 

 ships to cool and dehumidify practically all 

 parts of the ship except the machinery spaces. 

 In general, three types of mechanical cooling 

 equipment are used aboard naval ships: refrig- 

 erant circulating systems, chilled water circu- 

 lating systems, and self-contained air condi- 

 tioners. 



Refrigerant Circulating Systems 



A refrigerant circulating system is shown 

 in figure 19-15. As may be seen, this system 

 is essentially a refrigeration system consisting 

 of a compressor, a condenser, cooling coils, 

 a fan, an air filter, and the necessary controls. 



Hot moist air from the space to be cooled 

 is drawn through a duct, where it mixes with 

 fresh air drawn from outside. The fan blows the 

 air over the cooling coil and the refrigerant 

 inside the coil cools the surface of the coil. 

 Heat flows from the air to the coil and excess 

 moisture in the air is condensed on the coil. 

 The moisture drips off into a pan below the 

 coil and is carried off by drain piping. The cool 

 dry air leaving the coil is blown into the com- 

 partment to be cooled, where it absorbs the 

 excess heat and moisture from the air already 

 in the space The air is then returned to the 

 cooling coil and the cycle is repeated. Air is 

 exhausted from the space being cooled in order 

 to allow fresh air to be drawn into the space. 

 The cooling coils are installed in the ventilation 



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