Task 3 - Comparing VAV Duct Designs

ASHRAE has sponsored several research projects for the purpose of updating friction loss coefficients for duct fittings in rectangular, round and flat oval ducts and for improving design methodologies for HVAC air distribution systems in buildings. This has helped to significantly improve the design of HVAC air distribution systems up to the point where branch ducts supply air to variable volume terminal units and room air terminal devices (grills, registers, and diffusers). Design information on duct design from variable volume terminal units to room air terminal devices is primarily anecdotal in nature, and it is predicated on ideal system installations, which seldom if ever occur in field installations. There are very little measured data concerning the effects on building air distribution, energy and sound due to poor duct installations between air terminal units and room diffusers, leaky diffuser plenums, improperly placed volume dampers and improper diffuser connections.

This task compares the performance of conventional air distribution (CAD) systems built according to current design specifications and workmanship standards with CAD systems that have been built with common variations in construction and workmanship that are made in typical field installations. Variations examined in this task are those found in the ducted air distribution system from the variable air volume (VAV) unit to the diffuser. Information is being developed to identify the sensitivity of CAD systems to the typical variations. A protocol has been developed to test performance of CAD VAV systems with respect to comfort, energy use and acoustics. The tests are being performed in the UNLV Center for Mechanical & Environmental Systems Technology (CMEST) laboratory test room, known as the Throw Room.

The objectives of this project are:

To identify common construction variations that are made with typical field installations of ducted CAD VAV systems.

To upgrade and modify the laboratory at UNLV/CMEST (Throw Room) to conduct airflow, energy and sound tests on ducted conventional air distribution (CAD) variable air volume (VAV) systems.

To simulate typical CAD VAV system configurations in the Throw Room and conduct tests with the systems properly installed and then installed with common construction variations.

To conduct comparison tests between selected CAD and under floor air distribution (UFAD) systems.

The experimental design of this task requires knowledge of the common construction variations that are made with typical field installations of ducted CAD VAV systems and knowledge of previous research on HVAC system duct design and installation that provide information on the system effects of those variations. A panel of industry experts was formed to assess the state of the art on common construction variations. A literature research was conducted to review the state of HVAC duct design knowledge.

This task is closely linked to National Center for Energy Management and Building Technologies’ Task 2.  The airflow, energy, sound and other related tests that will be conducted on selected VAV mock-ups under this Task will also be used for the UFAD tests under Task 2.

The University of Nevada Las Vegas (UNLV) is conducting this task. The principal investigator is Brian J. Landsberger, Ph.D. This project is scheduled to be completed by July of 2005.