1. Lecture Objectives: Learn about air-conditioning (psychrometric)
by looking into swimming pool example

2. Heat pump example A recreation center Heat Pump Ice Rink Swimming pool
Condenser
Evaporator
85-89oF
30oF
Consumes heat energy
Rejects heat energy
Electric power
for a compressor

3. Psychrometric Chart Need two quantities for a state point
Can get all other quantities from a state point
Can do all calculations without a chart
Often require iteration
Many “digital” psychrometric charts available
Can make your own
Best source is ASHRAE fundamentals (Chapter 6)
Or electronic version at:

5. Connection between W and Pw (W humidity ratio – Pw water partial pressure)
PV = mRT (Ideal Gas Law )
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

6. 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

7. Adiabatic mixing
Governing equation
External heat

8. Sensible heating

9. Dehumidification by Cooling

10. Real Dehumidification Process

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

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

13. 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

14. HW Assignment
Textbook (Thermal Environmental Engineering) problems: 8.1, 8.8, 8.13, 8.20 Posted at: (both textbook section and problems)

15. Swimming pool energy and mass balance

16. Evaporation Heat loss by evaporation: hm
Tpool
Tair
pool
W s W ≈ hm Ws
Tpool
Wair
pool
Depends on the air speed and even
more on the condition of the water surface
(people splashing in the water)
Further analysis can be conducted in the psychrometric chart

17. Process in AHUs
Example AHUs for swimming pools
MENERGA ThermoCond 19

18. Swimming pool heating

19. Dehumidification using outside air in Winter and Summer

20. More advance control
MENERGA
ThermoCond 29

21. Dehumidification using outside air in winter
Condenser in the air stream
Evaporator
Compressor of
the heat pump
Condenser in the swimming pool

22. Recirculation of air with dehumidification
catalog