Face Velocity Considerations In Air Handler Selection | P2S

Kent Peterson

Vice President

PE, ASHRAE Presidential Fellow, LEED AP BD+C, BEAP, MCIBSE

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Fan energy can account for 30% to 40% of building HVAC system energy. In addition, fan energy use is directly proportional to the pressure drop. Therefore, the more restrictive the supply system, the higher the pressure drop, and the higher the fan energy use. Most air-handling units are still selected at the typical 500 fpm (2.5 m/s) rule-of-thumb, regardless of application. However, energy efficiency proponents say that lower velocity is better for high-performance operation. This month’s column evaluates methods to reduce fan energy from internal pressure drop along with the increased initial costs and reduction in annual operating costs.

Air-Handling Unit Applications

Applications for using air-handling units in HVAC systems can range from providing ventilation and controlling temperature and humidity in a typical office building to providing precise temperature and humidity control in 24/7 facilities. To determine the system’s air-handling unit requirement, the designer must consider the function and physical characteristics of the space to be conditioned. Specific design parameters must be evaluated to balance initial cost, operating expense, maintenance, and noise.

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