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Objectives

Objectives. Learn more about Psychrometrics Describe equations for psychometric processes Plot processes on psychrometric chart Use protractor to calculate SHR. Alternate calculation for W. PV = mRT (IGL) What do we know about R ratio? P = P w + P a. R = gas constant

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Objectives

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  1. Objectives • Learn more about Psychrometrics • Describe equations for psychometric processes • Plot processes on psychrometric chart • Use protractor to calculate SHR

  2. Alternate calculation for W • PV = mRT (IGL) • What do we know about R ratio? • P = Pw + Pa R = gas constant P = pressure V = volume T = absolute temperature W = humidity ratio Subscripts: w is water vapor, a is dry air

  3. Calculation of psychometric quantities • For an ideal gas, • hda = ∫cpadT, hw = ∫cpwdT • So, hda = cp,dat which assumes a reference state of 0 °F or 0 °C – Tables A4 • Note different reference • hw = cpwt + hg0 • h = cp,dat + W(cpwt + hg0) Or you can use: • h = cpt + W∙hg0, cp = cp,da + Wcpw cp = specific heat h = enthalpy T = absolute temperature t = temperature W = humidity ratio Subscripts: w is water vapor, a is dry air, g is saturated water vapor

  4. Adiabatic mixing • Governing equation External heat

  5. Fog formation above rivers Solution is in Psychometric chart

  6. Sensible heating

  7. Dehumidification by Cooling

  8. Real Dehumidification Process

  9. Humidification hw Specific enthalpy of water added to system hg Specific enthalpy of saturated water vapor

  10. Evaporative Cooling (air washing)

  11. Condition Line for a Space

  12. AHU

  13. Single-Zone Systems • Zone – any space with a thermostat

  14. Air conditioning

  15. Recirculation

  16. Reheat

  17. Evaporative Cooler

  18. Air-to-air heat exchanger

  19. Summary • Show HVAC processes on a psychrometric chart • Draw condition lines • Define sensible heat ratio • Draw HVAC processes for real buildings • Single zone • Multiple zone • Skipping Chapter 9

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