8.17 An evaporative cooler (air washer) is used to cool a bus located in Phoenix. The...

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8.17 An evaporative cooler (air washer) is used to cool a bus located in Phoenix. The system, similar to that shown in Fig. 8.18, takes outside air, first passes it through an evaporative cooler, then passes it through the bus, and finally exhausts it back to the outside. The system operates with a mass flow rate of 11,400 lbm/hr. On a very hot day the air exits the evaporative cooler saturated at 65 F. Atmospheric pressure is 14.7 psia. (a) If the outdoor dry-bulb temperature is 95 F, what is the outdoor relative humidity. (b) If the sensible and latent heat gains of the bus are 55,200 Btu/hr and 16,800 Btu/hr, respec- tively, what are the dry-bulb and dew-point temperatures in the bus? Problem 8.17 Fan (1) Space + , Air washer ***000000000000 (2) -Exhaust Dry bulb temperature [F] t = 65 13=95 Filter O.A. (3) Space-condition line SHR 0 Ah/AW I 1 Lastly I can read the outdoor humidity ratio which is: 3 = 18 % 0 Parallel dew point temperature [F] t = 65 13 = 65 1,4 (a) Figure 8.18 Schematic elementary evaporative-cooling system. 2 I 1 Dry-bulb temperature (b) 3 (a) To solve question (a) using the psychrometric chart, I will do following: - I will start locating the (saturated temperature on the chart) for the air that exits the eparotive cooler saturated at 65F, which is number 1 correspoonding to figure 8.18. - Now I will find point 3 corresponding to figure 8.18. When I know that the outdoor dry-bulb temperature is 95F, by looking on figure 8.18 we know following: 13* = 14* Humidity ratio 8.17 An evaporative cooler (air washer) is used to cool a bus located in Phoenix. The system, similar to that shown in Fig. 8.18, takes outside air, first passes it through an evaporative cooler, then passes it through the bus, and finally exhausts it back to the outside. The system operates with a mass flow rate of 11,400 lbm/hr. On a very hot day the air exits the evaporative cooler saturated at 65 F. Atmospheric pressure is 14.7 psia. (a) If the outdoor dry-bulb temperature is 95 F, what is the outdoor relative humidity. (b) If the sensible and latent heat gains of the bus are 55,200 Btu/hr and 16,800 Btu/hr, respec- tively, what are the dry-bulb and dew-point temperatures in the bus? Problem 8.17 Fan (1) Space + , Air washer ***000000000000 (2) -Exhaust Dry bulb temperature [F] t = 65 13=95 Filter O.A. (3) Space-condition line SHR 0 Ah/AW I 1 Lastly I can read the outdoor humidity ratio which is: 3 = 18 % 0 Parallel dew point temperature [F] t = 65 13 = 65 1,4 (a) Figure 8.18 Schematic elementary evaporative-cooling system. 2 I 1 Dry-bulb temperature (b) 3 (a) To solve question (a) using the psychrometric chart, I will do following: - I will start locating the (saturated temperature on the chart) for the air that exits the eparotive cooler saturated at 65F, which is number 1 correspoonding to figure 8.18. - Now I will find point 3 corresponding to figure 8.18. When I know that the outdoor dry-bulb temperature is 95F, by looking on figure 8.18 we know following: 13* = 14* Humidity ratio