What are the advantages and disadvantages of the two primary approaches to delivering air through underfloor plenums: (1) pressurized plenum, and (2) zero-pressure plenum?
In pressurized plenums, a central air handler delivers air through the plenum and into the space through passive grills/diffusers. Typical static pressures (relative to the occupied space) are quite low, falling in the range of 12.5 – 50 Pa (0.05 – 0.2 in. H2O). In zero-pressure plenums, air is delivered into the conditioned space through local fan-powered (active) supply outlets in combination with the central air handler. In practice, plenum design solutions often represent a hybrid approach in which both passive and active diffusers are used. Underfloor plenums have usually, although not always, been designed to be pressurized. Pressurized plenum systems have been more prevalent in office buildings because of their simplicity, lower installation costs, and ease of operation and control. Many system designers and operators prefer to avoid the large number of small fan-driven outlets that are required for zero-pressure plenum systems. Although this approach has been very successful, t
