How to engineer manufacturing, industrial buildings: HVAC
Manufacturing and industrial facilities can be particularly complex projects, involving large facilities containing behemoth machinery, hazardous chemicals, and a range of other concerns. HVAC systems and ventilation are complex issues engineers must manage.
- C. Erik Larson, PE, LEED AP BD+C, Principal, Industrial Systems, Wood Harbinger, Bellevue, Wash.
- Ronald R. Regan, PE, Principal, Triad Consulting Engineers, Morris Plains, N.J.
- John Schlagetter, NCARB, PMP, CSI, CCS, CCCA, LEED Green Associate, Senior Architect, Process Plus, Cincinnati
- Wallace Sims, SET, NICET Fire Alarm Level IV, Lead Life Safety Engineer, CH2M Hill, Portland, Ore.
CSE: What unique HVAC requirements do manufacturing/industrial structures have that you wouldn’t encounter on other structures?
Regan: Manufacturing plants are designed based on the requirements for the products being manufactured, which in many cases are very specific. Typical requirements may be:
- High and low temperature depending on the product
- High and low humidity requirements depending on the product
- High volume of air (air changes per hour) depending on the operation
- Large quantities of outdoor air requirements.
All of these requirements are unique to specific products for the pharmaceutical industry, food industry, petrochemical plants, etc. Such stringent requirements are not needed for normal commercial structures. Unlike HVAC systems for commercial structures, which are designed based on occupant comfort and code compliance, HVAC systems for manufacturing structures are designed based on the product requirements.
Larson: There are several factors that impact the HVAC design for what I normally consider to be large, wide-open spaces. These factors include pressurization, humidity control, and dust control. With lots of different point-of-use exhaust systems, dust control can be provided, but this can have an undesired impact on pressurization. If there are processes that rely on tight humidity control, pressurization is even more important to consider. Of course, encapsulation of any area with humidity control is key—and don’t forget to manage airflow through the entrance/exit points.
Schlagetter: Higher-quality filtered air, increased control of humidity, greater requirement for once-through air versus recycled, and pressurization differences between spaces to control for airborne contaminants.
CSE: What changes in fans, variable frequency drives (VFDs), and other related equipment have you experienced?
Regan: Modern fan systems are more efficient, and by introducing the VFD to such systems we can improve the overall energy efficiency of the systems and provide much better comfort levels to occupants. VFDs in the HVAC industry are used for varying the air and water flow to the building load pumping systems. Most commercial HVAC systems incorporate variable air volume (VAV) systems. These systems are served by variable volume air handlers, supplying conditioned air through a metal duct distribution system with variable air terminals serving the spaces. The majority of these air handlers include inlet guide vanes that control the quantity of air supplied depending on the building load dictated by the individual thermostats controlling the variable air terminals serving the spaces. As these air terminals demand more or less air, the system pressure increases or decreases changing the position of the inlet guide vanes, increasing or reducing the pressure in the system. While using this method saves some energy by riding the fan curves, the more efficient and controlled way of achieving energy savings and system operation is by using a VFD. We also use VFDs in commercial buildings with water systems requiring constant pressure regardless of flow rate.
Larson: More and more flexibility and efficiency are available as mainstream vendors expand their offerings. Sustainable design has pushed fan-wall technology, and fan arrays have allowed us to design air handling systems with a much larger range of operation. This provides the flexibility we need to truly take maximum advantage of turn-down, and it allows small portions of an area served by a large air-handling unit (AHU) to be controlled in an occupied mode without wasting energy, keeping the whole space conditioned.