Best Practice Guide

Food and Beverage Growers and Processors

Central HVAC System

Air Handling Subsystem

Fans, ducts, and dampers that move air through a building are collectively known as the air handling subsystem of the HVAC system.

As with chillers, older central HVAC systems tend to have oversized fans. In fact, nearly 60 percent of all buildings have oversized fans that waste as much as 60 percent of the energy consumed . This money is literally blown out the door. Rightsizing fans removes excess capacity and lowers energy consumption of the air handling subsystem by an average of 50 percent.

Air handling subsystems are fixed at either a constant air volume or variable air volume (VAV). As the name implies, VAV systems enable fans to adjust according to actual heating and cooling loads, rather than running full-on or full-off. Installing variable speed drives (VSDs) on VAV fans and motors makes sense for motors that run long hours or have fluctuating loads - the larger the motor, the bigger the savings possible. Adjust the air handling subsystem to the lowest point possible without compromising occupant comfort or product safety and while continuing to meet local codes and requirements for air quality. This reduced flow can result in energy savings of up to 50 percent. Preset two or more pressure settings, e.g., daytime/nighttime or summer/winter, to maximize savings throughout the day and year.

Unfortunately, it can be quite expensive to replace a constant volume unit with a VAV. If replacing the unit is not cost-effective, consider improving efficiency by rightsizing fans and replacing fan V-belts with synchronous belts that help reduce slippage and wear.

Some air handling subsystems include an economizer that provides free cooling by automatically intakes outside air when it is cooler than return air. When outside temperatures rise, a damper closes vents so that only the minimum amount of outdoor air needed to maintain air quality is allowed to enter. Air economizers can also be used to pre-cool a building in the evening and early morning hours, further reducing the need to run cooling equipment.

Business Examples

Mission Foods uses evaporative pre-coolers on air handling units at the company's new plant in Rancho Cucamonga. With high average temperatures and low humidity, Rancho Cucamonga is ideally suited for evaporative cooling, which works by drawing air through moist pads; air is cooled as the moisture evaporates. As such, evaporative coolers work best in hot, dry climates where humidity won't dampen effectiveness. Because no mechanical cooling is used, evaporative coolers, also referred to as "swamp" coolers, are more energy efficient than condensers or chillers.


At Mission, manufacturing areas need at least 50 percent outside air for health and safety. With precoolers, the chilled water plant does not need to work as hard to satisfy indoor air requirements. Evaporative coolers are also used to condition air in manufacturing support areas, further reducing mechanical cooling loads.


Resources

Roos, C. Overview: Heating, Ventilation, and Air Conditioning. Northwest Food Processors Association webpage, Building and Facility Efficiency.

Energy Star. Building Upgrade Manual. Chapter 4, Fan System Upgrades, and Chapter 5, Heating and Cooling System Upgrades.

North Carolina Division of Pollution Prevention and Environmental Assistance.
Energy Efficiency in Industrial HVAC Systems
. September 2003.