Tuesday, June 27, 2017: 11:00 AM-12:30 PM
Fundamentals and Applications
Chair:
David John, P.E., Stan Weaver & Co.
Technical Committee: 5.3 Room Air Distribution
This session covers the history of ADPI and the recently completed RP 1546 Expansion and Updating of the Air Diffusion Performance Index Method conduct at the University of Texas. The session consists of four presentations: Background of using ADPI in diffuser selection process, Updated ADPI tables for cooling operation, Additional development of the effective draft temperature for heating, Findings from the research to ensure ventilation effectiveness in overhead heating applications and Effect of return air placement in heating applications. A preview of the updates which will be included in the ASHRAE Application Handbook Room Air Distribution Chapter is included.
1 Updates in Air Diffusion Performance Index (ADPI) Diffuser for Cooling Operation
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Atila Novoselac, Ph.D., University of Texas at Austin |
The current diffuser selection guide described in ASHRAE handbook-fundamentals provides the correlation between diffuser characteristics, such as throw length and types, and its performance to distribute supply air and thereby to optimize space air diffusion. However, the current guideline considers only five diffuser types and the range of sensible cooling loads that is up to four times larger than those we find in today’s energy efferent buildings. This presentation shows the updated ADPI-based guideline that includes 15 diffuser types at lower cooling loads, typical for today’s buildings. The new guideline shows the minimum airflow set-point for a VAV systems.
2 A New Air Diffusion Performance Index (ADPI) for Heating Operation
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Atila Novoselac, Ph.D., University of Texas at Austin |
The performance of air distribution using overhead mixing diffusers is evaluated using ADPI. The ADPI methods is often used for selection of diffusers used for both cooling and heating. However, the current diffuser selection guide confines the application to only cooling mode. This presentation introduces a new ADPI for heating mode and specify the criteria of diffuser selection from the perspectives fluid dynamics and occupant thermal comfort based on ASHRAE Standard-55. The presentation covers the development of the effective draft temperature for heating applications and the resulting ADPIs curves with various diffuser types.
3 Connection between Air Diffusion Performance Index (ADPI) and Ventilation Effectiveness (EV): Effects of Diffuser Adjustment and Return Air Placement
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Hideyuki Amai, University of Texas at Austin |
This presentation provides fundamental design data that supports optimal diffuser selection in mixing ventilation with heating and cooling operation. It shows how diffuser adjustment, room-supply air temperature differences and return air grille location impact ADPI and EV. The study points out connections between ADPI and EV and shows similarities and differences for heating and cooling operation. It presents the operation characteristic that provide good EV while maintaining acceptable ADPI. Also, it shows how diffuser adjustment may improve EV. Furthermore, the presentation shows the cases where return air location may have a significant effect on ADPI and EV.
4 The History of Air Diffusion Performance Index (ADPI) and the Results of Research Project RP 1546 Expansion and Updating of the Adpi Method
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David John, P.E., Stan Weaver & Co. |
The effective draft temperature was experimentally developed in 1949 in Sweden. This is the current equation used to calculate ADPI for cooling. In 1972 Nevins and Miller presented an ASHRAE paper which determined that boundaries for ADPI to obtain a 70% occupant comfort level. After 33 years, this method needed many updates as buildings and air distribution systems changed. The ASHRAE RP 1546 updated and confirmed the ADPI predicted comfort levels using Standard 55. It produced the effective draft temperature equation for heating. Furthermore, it developed ADPI values that can predict thermal mixing in heating.