An air-handling unit (AHU), as indicated in Figure 1 serves the space cooling loads for an...

  

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An air-handling unit (AHU), as indicated in Figure 1 serves the space cooling loads for an office building. Outdoor air (OA), return air (RA), and discharge air (DA), as well as the cooling coil (CC) are indicated on the figure. The ODA and RA mix well to form the mixed air (MA) that enters the cooling coil. The supply fan gives off negligible heat to the air. ODA Abbreviations Air Handling Unit (AHU) Equations @=0.622- Properties used in psychrometric calculations: • Dry air cp = 0.24 Btu/lb°F • Water vapor cp = 0.444 Btu/lb°F • Liquid water cp = 1.0 Btu/lb°F • Water hfg=1061 Btu/lb Supply Fan • CFM = Cubic feet per minute RA Figure 1: AHU Schematic CC Pv P-Pv h = 0.240T + w (1061 +0.444T) Discharge During a hot summer day (103°F/77°F DB/WB) when the building is fully occupied, CO₂ sensors on the AHU actuate the outdoor air dampers and cause 1,000 CFM of outdoor air to be brought into the AHU where it is mixed with return air. The sensors on the AHU immediately upstream of the cooling coil record drybulb and wetbulb temperatures of 87°F/68.5°F for the mixed air and a flow rate of 2,000 CFM. Determine the following information. Place all answers in the appropriate box. Draw and label the process on the psychrometric chart. Mass flow rate of the ODA: Mass flow rate of the mixed air (MA): Mass flow rate of RA. Enthalpy of RA: Wetbulb Temp of RA: Drybulb Temp of RA: Units: lb/hr Units lb/hr Units. lb/hr Units: BTU/lb Units: °F Units: °F An air-handling unit (AHU), as indicated in Figure 1 serves the space cooling loads for an office building. Outdoor air (OA), return air (RA), and discharge air (DA), as well as the cooling coil (CC) are indicated on the figure. The ODA and RA mix well to form the mixed air (MA) that enters the cooling coil. The supply fan gives off negligible heat to the air. ODA Abbreviations Air Handling Unit (AHU) Equations @=0.622- Properties used in psychrometric calculations: • Dry air cp = 0.24 Btu/lb°F • Water vapor cp = 0.444 Btu/lb°F • Liquid water cp = 1.0 Btu/lb°F • Water hfg=1061 Btu/lb Supply Fan • CFM = Cubic feet per minute RA Figure 1: AHU Schematic CC Pv P-Pv h = 0.240T + w (1061 +0.444T) Discharge During a hot summer day (103°F/77°F DB/WB) when the building is fully occupied, CO₂ sensors on the AHU actuate the outdoor air dampers and cause 1,000 CFM of outdoor air to be brought into the AHU where it is mixed with return air. The sensors on the AHU immediately upstream of the cooling coil record drybulb and wetbulb temperatures of 87°F/68.5°F for the mixed air and a flow rate of 2,000 CFM. Determine the following information. Place all answers in the appropriate box. Draw and label the process on the psychrometric chart. Mass flow rate of the ODA: Mass flow rate of the mixed air (MA): Mass flow rate of RA. Enthalpy of RA: Wetbulb Temp of RA: Drybulb Temp of RA: Units: lb/hr Units lb/hr Units. lb/hr Units: BTU/lb Units: °F Units: °F

Answer rating: 100% (QA)

SOLUTION Given Flow rate of ODA out door air Q1 1000 CFM Flow rate of MA mixed air Q2 2000 CFM Dry b... View the full answer