work on rac

2.  INTRODUCTION
 DEFANATION
 WORKING
 PRINCIPLE
 SPICIAL FEACTURE
 APPLICATION
 ADVANTAGE
 DISADVANAGE
 CONCLUSION
 REFERENCE

3.  Standard Test
 Test Method for Determining Air Change in a Single
Zone by Means of a
Tracer Gas Dilution
 Inject predetermined volume of gas into room
 Mix room air to get uniform concentration
 Monitor gas concentration decay
 Aim for 10 samples over measured time
 Use reactor model to predict concentrations

4. The definition is based on a comparison of
the age of air in the occupied portions of
the building to the age of air that would
exist under conditions of perfect mixing of
the ventilation air.

5. Poor Mixing
 Occupant complaints
 ASHRAE Standard, Ventilation for Acceptable
Indoor Air Quality
 ASHRAE Standard is based on amounts of
outside air getting to breathing zone not to
supply air louvers
Short – circuiting airflow patterns
 Where a significant portion of supply air flows
directly to the exhaust, bypassing the
occupied portion (breathing zone) of the
ventilated space.

6.  The age of the air at a give location is the average amount of
time that has elapsed since the air molecules at that location
entered the
 building.
 Amount of time outside air has been in an area
 Two Methods of determination
• Step-up constant tracer gas injection
• Tracer gas concentration decay
Injection and mixing
• Air in the room is marked with tracer gas (injection and mixing)
• Ventilation turned on
Age of Air Measurements
• Locations of interest
• In the exhaust (C)

7.  In 1970s, smoke evacuation fans used to
find air leakage
1. Install blower door
2. Use fan to create artificial pressure
difference between inside and outside
3. Use smoke stick (or cigarette, etc.) to
visualize flow patterns.
4. Seal leaks

8. How well is outside supply air distributed to
breathing zones in occupied areas?
Air exchange efficiency
ASHRAE Standard 129 – Measuring Air
Change Effectiveness
Uses Tracer Gas Techniques
Age-of-Air Measurements

9. • Don’t need to release precise amount
• Don’t need to measure volume (if Cout = 0)
A Good Tracer Gas?
Non-toxic
Environmental friendly
Colorless and odorless
Easily detectable
Inert
No other sources

10. • Need to keep building well-mixed
• Recontamination from buffer spaces
• House needs to stay in one condition for entire
test
Common Tracer Gases
Used
Carbon Dioxide
Nitrous Oxide
Freon
Helium
Sulfur Hexafluoride

11.  The age of the air at a give location is the
average amount of time that has elapsed since
the air molecules at that location entered the
 building.
 Amount of time outside air has been in an area
 Two Methods of determination
• Step-up constant tracer gas injection
• Tracer gas concentration decay

12.  1. Energy Management Hand Book / W.C. Turner (Ed)
 2. Energy Management Principles / CB Smith/
Pergamon Press
 3. Energy Management / W.R.Murthy and G.Mc.Kay /
BS Publication
 4. Management / H.Koontz and Cyrill Donnel / McGraw
Hill
 5. Financial Management / S.C.Kuchhal / Chaitanya
Publishing House