1. Lecture Objectives: Finish cooling / heat pump example
Review Psychrometrics
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. Ice Rinks
Energy flow

4. Challenges for this problem
Circulating fluid
Adjustment of evaporation and condensation temperatures
Adjustment of capacity for design condition
Control of capacity for non design conditions
Need to study load profiles
Design sophisticated control
Provide backup system

5. Psychrometrics (Swimming pool example)

6. High humidity
High humidity and
low temperature

7. 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:

9. 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

10. 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

11. Adiabatic mixing
Governing equation
External heat

12. Sensible heating

13. Dehumidification by Cooling

14. Real Dehumidification Process

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

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

17. 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

18. Swimming pool energy and mass balance

19. 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

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

21. Swimming pool heating

22. Dehumidification using outside air in Winter and Summer

23. More advance control
MENERGA
ThermoCond 29

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

25. Recirculation of air with dehumidification
catalog