Chapter 13B: PSYCHROMETRIC MOIST AIR PROCESSES Agami Reddy (rev- May 2017) Overall conservation equations Adiabatic mixing of air streams Sensible heating and cooling Adiabatic cooling Cooling and dehumidification - Cooling coil process line - Bypass factor -Apparatus dew point Heating and humidification Various conditioning processes HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Conservation Equations Fig. 13.8 (13.26) (13.27) (13.28) HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Adiabatic Mixing of Air Streams Resulting in: (13.33) (13.34) Fig. 13.9 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes 12.65 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Contd. HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Sensible Heating or Sensible Cooling (13.36) (13.37) HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Example 13.9: Sensible Heating Fig. 13.11 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Contd. HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes HVAC calculations usually involve volume flow rates: Volumetric flow rates change during A/C Sensible heating example : An air handling unit conditions (i.e., in this case heats) 1000 CFM outdoor air from 40 F and 40 % RH to 70 F. Determine the outlet CFM considering the change in specific volume with temperature Solution: From the Psychrometric chart: v at 40 F = 12.6 ft3/lbm, and v at 70 F = 13.4 ft3/lbm Hence: outlet cfm = 1000 cfm x 13.4/12.6= 1063 cfm (a 6.3% increase in volumetric flow rate) HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Example 13.12: Residential Evaporative Cooler Fig. 13.13 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Contd. HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Cooling and Dehumidification (13.41) (13.42) Fig. 13.14 (13.43) (13.44) HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Example 13.14: Cooling of Moist Air Fig. 13.16 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Contd. HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Determining Sensible and Latent Loads Separately (contd...) HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Simplified Approach: Let us solve the previous Example 13.14 using these equations: HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Simplified Equations used by Industry Professionals: Amount of water condensed: lb/h 4.5 =(0.075 lb/ft3) x (1 ft3/min) x 60 min/h Sensible heat equation: Btu/h =1.08 Where T is in 0F 1.08=(0.075 lb/ft3) x (1 ft3/min) x 60 min/h x 0.24 Btu/lb-oF Latent heat equation: Btu/h Where W is in grains/lb 0.68= (1075 Btu/lb)/7000 gr/lb x 4.5 HCB 3-Chap 13B: Psych Processes

Cooling Coil Process Line (13.47) HCB 3-Chap 13B: Psych Processes

Also called “coil dew point temp.” (13.48) Fig. 13.16 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes For previous example 13.14 Contd. Manufacturers do not design coils with zero by-pass factors because higher contact factor increase fan pressure drop across the coil and hence require higher fan electric power.  Typical ranges for the BP factors: -0.3-0.5 for coils in residences - 0.1-0.2 for those in commercial buildings. HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Heating and Humidification (13.51) (13.52) Fig. 13.17 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Example 13.15: Warming and Humidification and specific volume =12.65 ft3/lba HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Contd. 2 1 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Lookup values:  Saturated steam enthalpy at 212°F, hvap = 1150.5 Btu/lbw (which is equal to hliq,2). From psychrometric chart, h1 = 13 Btu/lba, v1 = 12.67 ft3/lba, W1 = 0.003 lbw/lba, h3=30 Btu/lba Fig. 13.18 HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Contd. HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Fig. 13.19 Different psychrometric processes HCB 3-Chap 13B: Psych Processes

HCB 3-Chap 13B: Psych Processes Outcomes Understanding of the laws of conservation applicable to conditioning moist air streams Knowledge of the important air conditioning processes common in HVAC Be able to solve problems involving various air conditioning processes Be able to plot the various air conditioning processes on a psychrometric chart and solve related problems Understanding the concepts of coil sensible heat factor, coil dew point temperature, and by-pass factor Understanding the directional process changes of various air conditioning processes as plotted on a psychrometric chart HCB 3-Chap 13B: Psych Processes