Air Distribution

By: Robert J. Tsal, Ph.D. and Geoffrey C. Bell, PE

Energy Efficiency and Air Distribution

Air distribution through a laboratory is critical to the facility's safety and energy efficiency; nonetheless, air distribution systems are typically treated as an afterthought in the design process. Small ductwork is often routed circuitously, resulting in significant energy waste. In addition, the system air velocity is usually selected by rule-of-thumb and its noise impact is addressed afterward. However, the design of an energy-efficient air distribution system should be an iterative process, facilitated with the "T-Method," which incorporates life-cycle cost. A key to saving energy is to reduce the friction loss of the air distribution system by using large-diameter, round ductwork, efficient fittings, lower coil and filter face velocities, and energy-efficient noise attenuators. [Houghton, et al, 1992]

Air distribution components typically used in the research laboratory include:

·Air handler with fan,

·Cooling/heating coils,

·Air filters,

·Sound attenuators,

·Ductwork or plenums,

·Variable air volume (VAV) terminals or air balancing devices,

·Duct fittings,

·Fire and smoke protection devices (supply side only), and

·Fume hoods, biological safety cabinets, or other exhaust devices. [Naughton, "HVAC Systems… Part 1," 1990]

Laboratory cleanrooms require special consideration because of the need to move large, laminar volumes of air for contaminant removal. For cleanrooms, energy efficiency is increased with efficient ductwork design and lower face velocities for coils, dampers, and filters. Naughton, in "HVAC Systems for Semiconductor Cleanrooms - Part 1" (1990) notes that,

When hundreds of thousands of cfm are involved, the reduction in fan static pressure of just 0.1 in. WC (24.9 Pa) can result in $7,200 per year of savings for a 10,000 ft2 (929m2) clean room. In addition to fan horsepower savings, each 0.1 in WC (24.9 Pa) will also produce 3.9 tons (13.7 kW) of air-conditioning savings due to the reduced fan heat load.


Ductwork Design Fundamentals

Low-velocity Duct Design

Ductwork System Effect

Ductwork Pressure Balancing

Ductwork Air Leakage

Duct Construction and Leakage

Duct Leakage and Laboratory Isolation

Ductwork Material and Construction

Ductwork Layout Recommendations

Duct Shape Considerations

Duct Fittings

Duct Fittings and Economics

Duct Insulation Guidance

Ductwork Sizing

Computerized Ductwork Simulation

Ductwork Optimization

Economic Duct Optimization for California Laboratories

Displacement Air Flow

Cleanroom Air Distribution

Cleanrooms—Pressurized Plenum vs. Ducted Designs

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