ASHRAE Journal - July 2009 - 36

Participants Design Architect Interior Design Mechanical Engineer Design outdoor air quantities to meet occupant needs (ASHRAE 62.1). Diffuser airflow range should span normal to peak loads. Do not oversize. Avoid complete mixing. Design diffuser location to minimize conflicts with furniture (coordinate with interior design) and components in the underfloor space (coordinate with mechanical engineer), while maintaining the recommended minimum distance to occupants. Select an easily adjustable diffuser type (i.e., “salad spinner”). Avoid overcooling by using VAV or thermostatically controlled diffusers in potentially unoccupied spaces. Design diffuser airflow to allow temperature stratification and avoid draft. In open plenum, use design guidelines by Bauman, et al.3 To account for air leakage, heat transfer through floor and ceiling and thermal decay. Design air-side economizer control (if applicable). Design water-side economizer (if applicable). Improved Indoor Air Quality Leave room for diffusers in the furnishing design. Improved Thermal Comfort Potential Benefits of UFAD Welcome the maximum amount of diffusers. This increases temperature stratification and reduces thermal decay in open plenum systems (coordinate with mechanical engineer). Extended Economizer Use Reduced Energy Use Higher COP Reduce cooling loads to allow use of UFAD (prerequisite): good envelope thermal characteristics (walls, windows, shading) and low lighting power density and plug loads (coordinate with electrical engineer and interior design). Reduce interior heat gains in the occupied zone: select light colors and efficient light fixtures to allow low lighting power density, reduce use of task lamps, and use occupancy sensors. Reduced Cooling Loads Design airflow to limit conditioning to occupied zone through temperature stratification. Reduced Fan Power Leave room in the underfloor plenum to allow for changes in equipment (coordinate with mechanical engineer). Consider likely future space distributions when laying out wall partitions. Provide easy access to underfloor equipment that will require maintenance access (coordinate with mechanical engineer). Reduce static pressure: minimize duct work in the plenum and use multiple vertical shafts (coordinate with architect).10 Design equipment in the underfloor to allow easy reconfiguration: open plenums, flexible ducts (ducted systems), mobile terminals. Easy Reconfiguration Table 1: Role of participants in the achievement of UFAD benefits. Table 1 continued on facing page. Either could drastically reduce comfort levels and energy performance, which UFAD is supposed to improve. A poorly implemented UFAD system will cause more problems than it will provide benefits. A greater risk exists with technology that is new to many participants. Commissioning UFAD Most of the requirements shown in Table 1 would be missed in a conventional commissioning process. Commissioning must evolve to address the coordination of the raised floor system, carpet and furnishings, as well as nuances in control such as temperature stratification, comfort and ventilation. This is a larger scope than for conventional systems, which 36 ASHRAE Journal will increase commissioning costs, but is required to realize the benefits of UFAD. Since avoiding errors is usually cheaper than fixing them over the first few years of operation, there could be a net saving. For example, early review of the floor design and construction could reduce later corrections and associated costs.16 Finally, one should consider commissioning cost relative to the overall building cost to put things in perspective. In an office building that costs tens of millions of dollars, a commissioning process costing tens of thousands of dollars is three orders of magnitude smaller. Investing a small percentage of the total building cost could greatly improve performance. ashrae.org July 2009

ASHRAE Journal - July 2009

Table of Contents for the Digital Edition of ASHRAE Journal - July 2009