New Findings Contradict Common Perception of Parallel Fan Efficiency

A new study finds that despite common perception, parallel fan-powered air-terminal units, which are used to distribute cooled or heated air in commercial building cooling systems, may not be more efficient than series fans.

10/02/2007


A new study from ASHRAE,t than series fans.

When designing a cooling system, building designers can choose between either a series or parallel configuration for a building’s fan-powered, air-terminal unit. Since parallel fans run intermittently while a building is occupied, this configuration has been thought to be more efficient than series fans, which run continuously during the work day.

In the study, tests conducted by investigators at Texas A&M University’s Energy Systems Laboratory, found considerable air leakage from parallel fans’ back-draft dampers and terminal box seams, greatly reducing their efficiency. Leak rates for tested parallel fan terminals were found to be, on average, between 10% to 20%, and in some cases higher than 30%. These leaks reduced the airflow from the central air handler and caused the air to bypass the room to be conditioned, resulting in more energy needed to move more air to maintain comfort in the conditioned space.

When no leakage occurs, the parallel fan terminals are more efficient, consuming 17% less energy than series fan terminals; however, tests showed that when leaks are present, series fans appear to outperform parallel fans. When a 20% leakage rate was introduced, the series terminal unit outperformed the parallel unit and used 5.5% less energy.

“For manufacturers and building design engineers, this research provides new insights into the magnitude of air leakage in parallel fan powered terminals and its impact on system operation and overall energy consumption,” said Karim Amrane, ARI’s vice president of policy and technology. “It also serves as a useful reference in prompting changes in design practices to provide more energy efficient building.”

To read the final report, “ASHRAE 1292-RP: Comparison of the Total Energy Consumption of Series vs. Parallel Fan Powered VAV Terminal Units Phase I, Development of Models for Series and Parallel Fan Variable Air Volume Terminal Units,” click here .





No comments
Consulting-Specifying Engineer's Product of the Year (POY) contest is the premier award for new products in the HVAC, fire, electrical, and...
Consulting-Specifying Engineer magazine is dedicated to encouraging and recognizing the most talented young individuals...
The MEP Giants program lists the top mechanical, electrical, plumbing, and fire protection engineering firms in the United States.
Integrating electrical and HVAC for energy efficiency; Mixed-use buildings; ASHRAE 90.4; Wireless fire alarms assessment and challenges
integrated building networks, NFPA 99, recover waste heat, chilled water systems, Internet of Things, BAS controls
40 Under 40; Performance-based design; Clean agent fire suppression; NFPA 92; Future of commissioning; Successful project management principles
Transformers; Electrical system design; Selecting and sizing transformers; Grounded and ungrounded system design, Paralleling generator systems
Commissioning electrical systems; Designing emergency and standby generator systems; VFDs in high-performance buildings
Tying a microgrid to the smart grid; Paralleling generator systems; Previewing NEC 2017 changes
As brand protection manager for Eaton’s Electrical Sector, Tom Grace oversees counterfeit awareness...
Amara Rozgus is chief editor and content manager of Consulting-Specifier Engineer magazine.
IEEE power industry experts bring their combined experience in the electrical power industry...
Michael Heinsdorf, P.E., LEED AP, CDT is an Engineering Specification Writer at ARCOM MasterSpec.
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me