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Objectives Learn more about Psychrometrics

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Presentation on theme: "Objectives Learn more about Psychrometrics"— Presentation transcript:

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

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3 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

4 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

5 Adiabatic mixing Governing equation External heat

6 Fog formation above rivers
Solution is in Psychometric chart

7 Sensible heating

8 Dehumidification by Cooling

9 Real Dehumidification Process

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

11 Evaporative Cooling (air washing)

12 Condition Line for a Space

13 AHU

14 Single-Zone Systems Zone – any space with a thermostat

15 Air conditioning

16 Recirculation

17 Reheat

18 Evaporative Cooler

19 Air-to-air heat exchanger

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23 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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