If you?re referencing louvers in the envelope for exhaust, AHU ventilation, relief, or combustion air intake (and similar), I think you can normally account for their impact between increased skin (conductive) loads and increased/scheduled infiltration (as occurring, with or without dampers deployed). I may exclude these effects depending on my perception of relative importance/purpose for the simulation at-hand, but such loads and their impact on system operations can be a big deal, particularly when things aren?t running right.

How exactly you apply those adjustments to envelope and space infiltration depends on the application, and an understanding of when/how any associated dampers are controlled (or not controlled? or badly controlled? or if they?re simply broken?).

For new construction, I think you can assume properly installed spec-grade louvers with motor-actuated dampers to be relatively airtight. These would typically feature flexible blades/strips to seal gaps and by design will allow very little air passage in the closed position. Brand new gravity (or ?barometric?) dampers, if they are properly balanced/weighted, will also largely restrict air passage however the moving parts are necessarily free-acting and so you should expect a slightly larger amount of free ?leakage? area.

Louvers will also occur in new design entirely without dampers in which case they?re effectively keeping the rain/birds out of a space that should by design be outside of the ?conditioned envelope.?

Any and all damper types are susceptible to weathering, mechanical failures, and random acts of nature that can prevent normal operation and/or substantially increase infiltration rates. In a field audit ? seek out opportunities to observe louvers in action (or not in action when they should be). Also try to observe how much daylight can be seen from behind closed louvers (where safe to do so!). Listen in mechanical & plenum spaces for ?clattering? where a gravity damper isn?t properly weighted (it?s probably not a ghost? probably!). BAS screenshots can sometimes provide clues regarding odd louver behavior as well (if not open during economizer operation, for example).

Consider for louvers associated / attached directly to air handling units: the associated increases in skin/infiltration loads are being handled in a literal sense directly by those systems as occurring. I would in such cases try to assign any adjustments to SPACE infiltration or envelope constructions to one or more of the spaces served by that system (which may not include the actual mechanical room the louver is associated with).

Food for thought!

~Nick

Nick Caton, P.E.

Senior Energy Engineer
Energy and Sustainability Services
North America Operations
Schneider Electric

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