1. Objectives Plot processes in AHU and buildings on Psychrometric chart
Discuss equations for calculation of moist air properties

2. Thermodynamics properties of most air are also in Tabel A4 E (textbook)

3. Condition Line for a Space

4. AHU

5. Sensible heating

6. Dehumidification by Cooling

7. Real Dehumidification Process

8. Adiabatic mixing
Governing equation
External heat

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

10. Evaporative Cooling (air washing)

11. Alternate calculation for W
PV = mRT
What do we know about R ratio?
P = Pw + Pa
Then you can connect RH and W:
R = gas constant
P = pressure
V = volume
T = absolute temperature
W = humidity ratio
Subscripts: w is water vapor, a is dry air, and
s indicates saturated

12. 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
More details are in Chapter 7 of the textbook

13. Transport of saturated air
tsurface < tdp
Condensation
Mold in a duct

14. Summary Describe psychrometric quantities
Given any two psychrometric quantities, calculate any other quantity
Use Tables A4 or psychrometric charts to look up psychrometric quantities
Calculate psychrometric quantities at non-standard conditions
Reading assignment: Chapters 7 & 8

15. Example: Single-Zone Air Systems
Zone – any space with a thermostat