Why the “Simple Underfloor Air Distribution System” Isn’t Quite as Simple as It Seems

Larry Luskay and David Sellers, Portland Energy Conservation, Inc.

Keywords

Abstract

The rapid evolution of modern office technology coupled with high churn or occupant turnover rates has resulted in an increasing use of underfloor supply plenums to support displacement ventilation and underfloor air distribution technologies. In concept, this provides a flexible, sustainable approach to handling the requirements of the modern office environment. However, successful implementation of the underfloor plenum as an air supply and distribution system requires a very persistent and rigorous effort on the part of the design and construction team, as well as the commissioning provider to assure success. Improper application or poor installation of an underfloor plenum can result in significant comfort complaints and energy usage. When commissioning an underfloor air distribution system, the commissioning provider should address the following design, construction, and operational issues:

Design

Design addresses perimeter vs. internal loads and humidity issues
Design includes sufficient detail to ensure the plenum will be properly sealed
Designing systems and equipment to facilitate maintenance
Designing equipment and systems to deal with catastrophic occurrences such as flooding

Construction

Maintaining cleanliness during construction and operation
Constructing an air tight assembly
Coordinating with various contractors to assure air flow is not impeded
Maintenance access is not impaired due to installation constraints

Operations

Maintaining an air tight assembly as systems age and after remodels
Changes to system layout do not impede maintenance access

This paper looks at design and construction issues from a commissioning and operational perspective and discusses recent field experiences with underfloor plenum systems. The discussion includes the theoretical importance of the issues listed above as well as case study information for projects where these issues came into play in the real world operating environment. The case studies include a new construction project applying for LEED Gold certification and the renovation of an existing facility.