1. Objectives Finish analysis of most common HVAC Systems
Learn about the psychrometric related to the cooling towers

2. Evaporative Cooler 2

3. Air Washer Sprays liquid water into air stream
Typically, air leaves system at lower temperature and higher humidity than it enters

4. Schematic

5. Air Washers/Evaporative Coolers
Heat and mass transfer is mutually compensating
Can evaluate based on temperature drop, humidification, or comparison to other energy exchangers

6. Single-Zone Systems with air washer – mister – or adiabatic humidifier
Winter operation 6

7. Air-to-air heat exchanger7

8. Multizone
Systems 8

9. 9

10. 10

11. Summary of HVAC Systems
Show HVAC processes on a psychrometric chart
Draw condition lines
Define sensible heat ratio
Draw HVAC processes for real buildings
Single zone
Multiple zone

12. Cooling towes Similarity and difference between
Evaporative coolers and
Cooing towers

13. Cooling Tower
Similar to an evaporative cooler, but the purpose is often to cool water
Widely used for heat rejection in HVAC systems
Also used to reject industrial process heat

15. Cooling Tower

17. Solution Can get from Stevens diagram (page 272)
Can also be used to determine
Minimum water temperature
Volume of tower required

18. Real World Concerns We need to know mass transfer coefficients
They are not typically known for a specific direct-contact device
Vary widely depending on packing material, tower design, mass flow rates of water and air, etc.
In reality, experiments are typically done for a particular application

19. Summary
Heat rejection is often accomplished with devices that have direct contact between air and water
Evaporative cooling
Can construct analysis of these devices
Requires parameters which need to be measured for a specific system

20. Reading assignments related to the HVAC systems Chapters 7 & 8 and Handout Section on the course website