1. Objectives Air mixing and humidifying
Discuss equations for calculation of moist air properties

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

3. Real Dehumidification Process

4. Adiabatic mixing
Governing equation
External heat

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

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

7. Evaporative Cooling (air washing)

8. 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

9. 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

10. 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

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

12. Air conditioning 12

13. Recirculation 13

14. Reheat 14

15. Evaporative Cooler 15