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

Evaporative Cooler 2

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

Schematic

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

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

Air-to-air heat exchanger 7

Multizone Systems 8

9

10

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

Cooling towes Similarity and difference between Evaporative coolers and Cooing towers

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

Cooling Tower

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

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

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

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