Consulting-Specifying Engineer - October 2007 - (Page 35)

Codes & Standards Understanding NFPA’s Standard 90A for air conditioning and ventilation systems BY LARRY WILSON, PE, Senior Vice President, Environmental Systems Design, Chicago astering the National Fire Protection Assn. (NFPA) 90A, “Standard for the Installation of Air Conditioning and Ventilating Systems,” can be daunting. Here are some tips: Divide the work. Architects and structural engineers on the project team will define the massing, compartmentalization, interior construction details, means of egress, function of the ceiling and raised floor plenums, and fire and smoke separations for inclusion in the project’s code-compliance drawings. Critical to successful building systems integration, all project changes must be documented in the code-compliance drawings so team members can continually reassess impacts on their systems. Even a subtle change in design can compromise the HVAC system and its life safety features, not to mention initiating a change order that affects contract values and schedules. Define the HVAC system. Defining ingredients that make up the HVAC system is crucial to 90A M A key to complying with NFPA 90A for air conditioning and ventilating systems is documentation of all changes in the code-compliance drawings. compliance. Screen requirements for outdoor air intakes, flame-spread and smoke-developed product index ratings; access panel requirements in ductwork; flexible duct connector length restrictions; and protection for exposed fan inlets are all details that need to be documented in project specifications. Taking it a step further, 90A requires drawing of fan arrangements for proper inspection and maintenance, identifying specific locations of air outlets, inlets and light fixtures used as return air paths, and indicating fan rooms used as an extension of ceiling plenums or used as a return air path. Seemingly insignificant details can affect the HVAC system design. For example, the need to provide access panels in return and exhaust system ductwork affects the integrity of the duct- work itself, i.e., one needs to estimate how much more duct leakage will occur and provide fan capacity accordingly. Integrate all the systems. Superimposing HVAC infrastructure on architectural and structural systems is where the fun begins. Protection of duct, pipe and conduit penetrations in firerated walls and partitions, floors, roof-ceiling assemblies, shafts and smoke barriers is a focus of 90A. The standard includes a handy diagram outlining a couple dozen of the most common penetrations in these building components. Next, make sure that fan rooms comply with all requirements. This is particularly important for rooms that house fan systems serving multiple floors with ducts routed into vertical shafts. Standard 90A dictates which ducts can share shaft space with each other. For example, kitchen exhaust duct risers cannot be installed in the same shaft as supply and return air duct risers. Note: When this situation is met in an existing building, there are techniques that can be implemented to achieve separation without having to reconstruct shafts and duct risers, including special duct wraps for kitchen exhaust duct risers. Requirements for fire and smoke dampers and combination fire/smoke dampers in smoke barriers are also outlined in 90A as well. Fire dampers need to be installed in the plane of the wall, partition or floor and must be rated for dynamic conditions. Smoke dampers can be installed up to 2 ft. away from the smoke barrier (the concept is that the duct itself provides some protection from the passage of smoke). Access panels must be provided in the ductwork of all fire and smoke dampers and combination fire/smoke dampers, and they must be installed immediately adjacent to the device. Additionally, there may be cases where project architects and structural engineers choose to extend a fire-rated shaft below the elevation of a floor slab in order to protect a duct riser. When the shaft is extended down into the ceiling plenum of the floor below, a fire damper can be installed in its vertical plane, instead of having to Consulting-Specifying Engineer • OCTOBER, 2007 35

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Consulting-Specifying Engineer - October 2007 Contents On the Web In the News M/E Roundtable How To Beat the Energy Codes Professional Practices Codes & Standards A Capital Job on Engineered Buiding Systems Going Green in Data Centers Overcurrent Protection: Fuses or Breakers? Third-Party Liability Management Report New Products Product Spotlight Jobs/Classifieds Specifier's Notebook

Consulting-Specifying Engineer - October 2007

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