Air Conditioning

CHAPTER-20 AIR-CONDITIONING

1.When 100 kg/min of outside air at 32°C dry bulb and 200 kg/min re-circulated air at 22°C dry bulb are mixed with an air conditioning system, the resulting dry bulb temperature A. 25.33°C B. 35.44°C C. 46.33°C D. 26.88°C

2.The amount water carried by air in a cooling tower is 15 lb/min. The change in humidity ratio in outlet and inlet is 0.025 lb/lb. Determine the volume flow of air needed if specific volume is 13ft3/lb. A. 6000 ft3/min B. 7800 ft3/min C. 7500 ft3/min D. 5000 ft3/min

3.The change of enthalpy of air in a cooling tower is 35 Btu/lb and the mass flow of air is 453.17 lb/min. Water enters the tower at the rate of 50 gpm and 115°F. Determine the exit temperature. A. B. C. D.

45°F 55°F 65°F 77°F

4.The change of enthalpy in an air conditioning unit is 10 Btu/lb. The mass supply air is 150,000 lb/hr. What is the conditioner capacity? A. B. C. D.

125 100 150 200

TR TR TR TR

5.re-circulated air of 8 kg/sec with 53 KJ/kg enthalpy and outside air of 2kg/sec with 90 KJ/kg enthalpy enters the conditioning unit. Determine the air conditioning capacity if supply enthalpy to conditioned space is 42 KJ/kg. A. B. C. D.

154 164 174 184

KW KW KW KW

6.Outside air of an air conditioning system is 25% of re-circulated air. Determine the mass of outside air if supply air is 15 kg/sec. A. B. C. D.

1 kg/sec 2 kg/sec 3kg/sec 4 kg/sec

7.The sensible heat load and latent heat load in air conditioning system is 120 KW and 47 KW, respectively. What is the sensible heat factor? A. B. C. D.

65.34% 29.45% 76.54 71.86%

8.The total heat load and latent heat load of theater is 150 KW and 60 KW, respectively. Supply air is at 15°C and has a mass of 9 kg/sec. Determine the temperature to be maintained in the theater. A. B. C. D.

20°C 25°C 30°C 35°C

9.A cooling tower has an efficiency of 65%. Water enters the tower at 55°C. The wet bulb temperature of surrounding air is 27°C. What is the temperature of water leaving the tower? A. B. C. D.

36.8°C 44.5°C 46.9°C 30.4°C

10.The change to temperature entering the cooling tower and wet bulb temperature of surrounding air is 25°C and efficiency is 65%. If mass of water leaving the tower is 10 kg/sec, determine the heat carried by air. A. B. C. D.

720 540 680 700

KW KW KW KW

11.The approach and efficiency of cooling water is 10°C and 60%, respectively. If temperature of water leaving the tower is 37°C, what is the temperature of water entering? A. B. C. D.

46°C 52°C 68°C 48°C

12.A cooling tower is used to control a jacket water loss from the engine. The heat generated by fuel is 2500 KW and cooling loss is 30%. If temperature range of the tower is 15°C. Determine the mass flow of water entering the tower A. B. C. D.

12 14 16 18

kg/sec kg/sec kg/sec kg/sec

13.A dryer is to deliver 1000 kg/hr of cassava with 2% moisture and 20% moisture in the feed. Determine the mass of air required if the change in humidity ratio is 0.0165. A. B. C. D.

3.57 4.67 3.79 5.36

kg/sec kg/sec kg/sec kg/sec

14.The moisture remove from a material is 250 lb/hr and a change of humidity ratio dyer is 0.0175. Determine the fan capacity if specific volume of air entering is 35 ft3/lb. A. B. C. D.

400,000 450,000 500,000 550,000

ft3/hr ft3/hr ft3/hr ft3/hr

15.The change of enthalpy in a heating chamber of dryer is 25 Btu and the mass of air supplied is 30,000 lb/hr. What is the heat supplied by heater? A. B. C. D.

560 450 350 220

KW KW KW KW

16.Water at 55oC is cooled in a cooling tower which has an efficiency of 65%. The temperature of the surrounding air is 32oC dry bulb and 70% relative humidity. The heat dissipated from the condenser is 2,300,00 KJ/hr. Find the capacity in liters per second of the pump used in the cooling tower. A. B. C. D.

8.55 7.34 6.34 9.23

17.Fifty gallons per minute of water enters a cooling tower at 115oF. Atmospheric air at 60oF and 55% relative humidity enters the tower volume at 6,000 cfm and leaves at 90oF saturated. Determine the volume of water that leaves the volume in gpm. A. B. C. D.

32.34 48.62 34.23 65.33

18. Fifty gallons per minute of water enters a cooling tower at 115oF. Atmospheric air at 60oF and 55% relative humidity enters the tower volume at 6,000 cfm and leaves at 90oF saturated. Determine the exit temperature of water, oF A. B. C. D.

56.23 65.33 76.61 45.34

19.An atmospheric cooling tower is to provide cooling for the jacket water of a 4 stroke, 800 KW diesel generator with useful output of 34% and cooling loss of 30%. The cooling tower efficiency is 60% at a temperature of approach of 10oC. If ambient air has a relative humidity of 70% and dry bulb temperature of 32oC, determine the cooling water supplied to the diesel engine in li/hr. Generator efficiency is 97%. A. B. C. D.

41,713 45,232 43,345 47,234

20. 250,000 kg/hr of water at 35oC enters a cooling tower where it is to be cooled to 1.75oC. The energy is to be exchanged with the atmospheric air entering the unit at 15oC and leaving the unit at 30oC. The air enters at 30% RH and leaves at 85%RH. If all process are assumed to occur at atmospheric pressure, determine the percentage of total water flow that is make up water. A. 3.44% B. 8.34% C. 3.94% D. 2.22%

21.An auditorium is to be maintained at a temperature of 26oC dry bulb and 50% RH. Air is to be supplied at a temperature not lower than 15oC dry bulb. The sensible heat gain is 110 KW and the latent heat gain is 37.5 KW. Take ventilating air as 25% RH. Determine the refrigeration capacity in tons. A. B. C. D.

43.45 54.23 63.28 76.34

22.An assembly hall was to have an air conditioning unit installed which would be maintained at 26oC dry bulb and at 50% RH. The unit delivers air at 15oC dry bulb temperature and the calculated sensible heat load is 150 kw and latent heat is 51.3 KW. 20% by weight of extracted air is made up of outside air at 34oC dry bulb and 60% RH while 80% is extracted by air conditioner from the assembly hall. Determine the air conditioner’s refrigeration capacity in tons refrigeration and its ventilation load in KW. A. B. C. D. NO

83.22, 132 75.34, 412 56.23, 45.32 54.23, 83.23 ANSWER

23.An air conditioned theater is to be maintained at 80oF dry bulb temperature and 50% RH. The calculated total sensible heat loaded in the theater is 620,000 Btu/hr, and the latent heat load is 210,000 Btu/hr. The air mixture at 84oF dry bulb and 73oF wet bulb temperature is cooled to 63oF dry bulb and 59oF wet bulb temperature by chilled water cooling coils and delivered as supply air to the theater. Calculate the tons of refrigeration required. A. B. C. D.

123 125 124 128

24.A room being air conditioned is being held at 25oC dry bulb and 50% relative humidity. A flow rate of 5m3/s of supply air at 15oC dry bulb and 80% RH is being delivered to the room to maintain that steady condition at 100 Kpa. What is the sensible heat absorbed from the room air in KW? A. B. C. D.

50.8 60.8 40.5 70.9

25.Copra enters a dryer containing 60% water and 40% of solids and leaves with 5% water and 95% solids. Find the weight of water removed based on each pound of original product. A. B. C. D.

0.34 0.63 0.86 0.58

lb lb lb lb

26. Copra enters a dryer containing 60% water and 40% of solids and leaves with 5% water and 95% solids. Find the weight of water removed based on each pound of final product A. B. C. D.

1.375 lb 1.19 lb 1.872 lb 2.345 lb

maintained constant by the use of steam coils within the dryer. The product enters the dryer at the rate of 1 metric ton per hour. The initial moisture content is 3 kilograms moisture per kilograms dry solid and will be dried to a moisture content of 0.10 kg moisture per kg solid. Air enters the dryer with a humidity ratio of 0.016 kg moisture per kg dry air leaves with a relative humidity of 100% while the temperature remains constant at 60°C. if the total pressure of air is 101.325 Kpa, determine capacity of forced draft fan to handle this air in m3/min.

A. B. C. D.

80 84 82 86

28. Wet material, containing 215% moisture(dry basis) is to be dried at the rate of 1.5 Kg/sec in a continuous dryer to give a product containing 5% moisture(wet basis). The drying medium consist of air heated to 373°K and containing water vapor equivalent to a partial pressure of 1.40 Kpa. The air leaves the dryer at 310°K and 70% saturated. Calculate how much air will be required to removed the moisture. A. B. C. D.

213,233 177,142 177,242 198,242

kg/hr kg/hr kg/hr kg/hr

29. A Dryer is to deliver 1000 kg/hr of palay with a final moisture content of 10%. The initial moisture content in the feed is 15% at atmospheric condition with 32°C dry bulb and 21 degrees centigrade wet bulb. The dryer is maintained 45°C while the relative humidity of the hot humid air from the dryer is 80%. If the steam pressure supplied to the heater is 2 Mpa, determine the heat supplied by heater in kw. A. 3.23 B. 5.46 C. 4.23 D. 6.23

final moisture content of 10%. The initial moisture content in the feed is 15% at atmospheric condition with 32°C dry bulb and 21 degrees centigrade wet bulb. The dryer is maintained 45°C while the relative humidity of the hot humid air from the dryer is 80%. If the steam pressure supplied to the heater is 2 Mpa, 3 determine the air supplied to dryer in m /hr. A. 1332.25

B. 1532.34 C. 1234.23 D. 1982.34

31. At 30°C, air vapor mixture has a relative humidity of 70%. Find the humidity ratio if barometric pressure is 100°C. at 30°C , Psat=4.246 kpa. A. B. C. D.

0.123 0.986 0.054 0.019

32. The humidity ratio of air is 0.045. if barometric pressure is 101 kpa, find the partial pressure of water vapor. A. B. C. D.

4.23 7.34 6.81 5.23

kpa kpa kpa kpa

33. Air at 36°C and pressure of 101.2 kpa has a density of 1.08 kg/m3. find the humidity ratio of air. A. 0.0352 B. 0.6350 C. 0.0653 D. 0.0173

34. What is the enthalpy of the airvapor mixture at 60% RH and 35°C when the barometric pressure is 102 kpa? C: Psat= 5.628, hg= 2565.3 A. B. C. D.

89.63 74.23 67.34 53.34

KJ/kg KJ/kg KJ/kg KJ/kg

35. Air-vapor mixture has an enthalpy of 75 KJ/kg at 30°C . Find the partial pressure of water vapor, at 30°C: hg= 2556.3 KJ/kg A. B. C. D.

6.34 kpa 1.34 kpa 4.231 kpa 2.791 kpa

36. Air in an air-conditioner enters at 60% RH with w= 0.021 and leaves at 25°C dry bulb and 16°C wet bulb. If mass of air is 10 kg/s, find the refrigeration capacity in tons of refrigeration. At 60% RH, w= 0.021: h=87kj/kg, v= 0.903 m3/kg at 25°C db, 16°C wb: h= 45KJ/kg; A. B. C. D.

134.34 TR 119.45 TR 102.45 TR 98.34 TR

37. A 160 kw air conditioner has an initial condition of 40°C db and 60% RH and leaves at 20°C db and 20% RH. Find the volume of air entering the conditioner. At 40°C db and 60% RH: h= 112 KJ/kg, w=0.93m3/kg; at 20°C db and 20% RH: h=26 KJ/kg A. B. C. D.

3.22 2.62 2.12 1.73

m3/s m3/s m3/s m3/s

38. Outside air in an air conditioning unit has a mass of 50 kg at 45°C is mixed with re-circulated air at 30 kg at 26°C, find the temperature after mixing. A. 35.23°C B. 32.23°C C. 37.87°C D. 40.40°C

39. Twenty kilograms air enters the dryer at 25°C db and 30% RH. Fifteen kg of re – circulated air from the dryer has a partial pressure of water vapor of 10kpa. Find the humidity ratio after mixing. At 25°C db, 30% RH: w=0.0059 A. 0.0325 B. 0.1930 C. 0.0653 D. 0.0842

40. Sixty kilogram of air with enthalpy of 80 KJ/kg enthalpy. Find the enthalpy of x air before mixing. A. B. C. D.

23.23 17.45 43.75 55.01

KJ/kg KJ/kg KJ/kg KJ/kg

41. An 80% efficient cooling tower has water entering at 48°C and wet bulb temperature of air entering at 25°C . Find the water exit temperature of water. A. B. C. D.

16.23°C 29.60°C 32.34°C 23.44°C

42. Water enters the cooling tower at 50°C and leaves at 28°C while the heat rejected to air is 100 KW. Find the capacity of the pump needed to pump the water. A. B. C. D.

1.08 3.22 2.34 4.23

li/s li/s li/s li/s

43. Air enter the tower at the rate of 50 kg/s. the air entrance enthalpy is 53 KJ/kg and exit enthalpy is 86 KJ/kg. find the temperature range of the tower if mass flow rate of water is 32 kg/s. A. B. C. D.

14.34°C 16.34°C 10.23°C 12.31°C

44. A 100 BHP diesel engine has a break thermal efficiency of 35% and jacket water loss of 30%. The engine is to be cooled by means of a cooling tower having a range of 30°C. find the mass of water leaving the tower. A. 5,238.45 kg/hr B. 4,284.56 kg/hr C. 1,832.24 kg/hr D. 6,108.62 kg/hr

45. A 130 tons refrigeration system with COP of 4 has a condenser which is to be cooled by means of a cooling tower. Air enters the tower at 25°C db and 50% RH and leaves at 35°C db and 80% RH. Find the volume of air needed m3/hr. At 25°C db and 50% RH: h=50KJ/kg, v= 0.86m3/kg. At 35°C and 80% RH: h=108 A. B. C. D.

8.47m3/s 7.34m3/s 4.98m3/s 3.16m3/s

46. The evaporative condenser of an ammonia refrigeration plant has a water flowrate of 130 kg/s and enters a natural draft cooling tower at 43°C. the water cooled to 30°C by air entering at 27°C db 24°C wet bulb. The air leaves the tower as 90% RH and 32°C db. Calculate the percent of make-up water needed the tower. At 27°C db and 24°C wb: h=72.5 KJ/kg, w=0.0178 At 90°C db and 32°C db: h=102 KJ/kg, w=0.0275

A. B. C. D.

2.34% 1.79% 3.12% 2.84%

47. A cooling tower cools water from 39°C to 27 °C at the rate of 20 kg/s. air enters the tower at 22 °C at the rate of 35 kg/s. find the temperature of air A. leaving the tower. A. 50.71 °C B. 28.86 °C C. 45.23 °C D. 34.45 °C

48. The sensible heat rate is 0.8, which of the following is correct?

A. 20 latent and 80 sensible heat B. 80 latent heat and 20 sensible heat C. 80 sensible heat and 20 sensible heat and latent heat D. 20 latent heat and 80 sensible and latent heat NO ANSWER

49. The amount of sensible heating, the sensible heat ratio of 0.80 and a total cooling load of 100.: A. B. C. D. NO

80 20 100 60 ANSWER

50. A coil has an inlet temperature of 60 °F and outlet of 90 °F. if the mean temperature of coil is 110 °F, find the bypass factor of the coil. A. B. C. D.

0.4 2 1 3

51. A 4m x 4m x 4m room has a relative humidity of 80%. The pressure in the room is 120 kpa and temperature is 35 °C(Psat=5.628). What is the mass of vapor in the room(Rv=0.4615 Kpa-m3/kg=°K). A. B. C. D.

2.03 1.50 0.80 4.80

52. The evaporative condenser of an ammonia refrigeration plant has a water flowrate of 126 kg per second and enters a natural draft cooling tower at 40 °C. the water is cooled to 29 °C by air entering at 38 °C db and 24 °C wb. The air leaves the tower as saturated at 40 °C db. Calculate the make-up water required in kg per hour. Water properties: At 40 °C, hf= 167.48 KJ/kg At 29°C, hg= 121.43 KJ/kg Air properties: At 38 °C db and 24 °C wb: h=72.5 KJ/kg w=0.013kg/kg At 40 °C db saturated: h=166KJ/kg w=0.0488kg/kg

A. 8977 B. 8699 C. 8055 D. 8388 NO ANSWER