Objectives

• Finish with ducts and fans

• Define project topics

Two types of Duct design procedure

• Equal friction - Covered in classes and book

- keeps same pressure per unit of length P/L

• Static regain - keeps the same static pressure at each branch

Two types of duct design problems

• You design a duct and then select the fan

• You have the AHU with the fan and you need to design a duct that will fit in

Fan Performance

Centrifugal fans

Axial Fans

Fan Laws

• “Approximate relationships”

• Given two aerodynamically similar fans, can extrapolate performance data

• Be very careful

Question

• How does fan power consumption vary with volumetric air flow rate?

Controlling Air Flow

Dampers

Effect on Fan Curve

VAV Operation

Summary of Air Distribution Systems

• Select diffuser based on ADPI

• Given a layout of duct system• Calculate total pressure drop• Identify fittings contributing most to pressure drop• Deal with non-circular ducts

• Use fitting loss coefficient or equal length method

• Select the fan based on fan and duct curve

VAV Systems

DOAS configurations

Project topics(groups of 3)

1) VAV system design

•Fresh air requirements and recirculation rate calculation

•Selection of zonal and central HVAC components based on cooling and heating load components • For zones: VAV boxes, reheaters, reheater plumbing

• For whole system: AHU and components, chiller & cooling tower, boiler, and electric power requirement

•Control description – sequence of operation

•Heat recovery system and or economizers

 2) DOAS system design

•Fresh air requirement and split between air and hydronic loads (sensible and latent cooling loads)

•Selection of zonal and central HVAC components based on cooling and heating load components • For zones: fan coils and plumbing

• For whole system: AHU and components, chiller & cooling tower, boiler, and electric power requirement

•Control description – sequence of operation

•Heat recovery system and or economizers

Project topics3) Duct Design (in Revit and Manually)

•- Diffuser selection, design of local and central duct system components

•- Spacing issues and difference between round and square ducts

•- Difference between manual calculation and calculation by Revit (for a section of the duct system)

•- Balancing and fan selection

•- Life cycle analysis and optimization (fan power consumption vs. system cost)

Some graduate student project topics (group of 2)

1) Cooling systems and distribution •Air cooled condenser vs. water cooled condenser (energy performance analysis) •Design of plumbing systems for campus and pumping stations •Control of centralized system •…

2) Design of air-conditioned storage space •Specific load•Dehumidification is the major task •….

3) Heat recovery systems •…..

4) Your topic

Cooling and Heating Loads (For Project)

»Fresh air requirement based on number of occupants:

Cooling Load Calculation

• Mostly computer based

• Handouts for manual calculation• http://www.ce.utexas.edu/prof/Novoselac/classes/ARE346N/Handouts/heatloss_table_2008.doc

• http://www.ce.utexas.edu/prof/Novoselac/classes/ARE346N/Handouts/ASHRAE_%20Gains_Calculation_Tables.doc