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Underfloor Air HVAC systems (sometimes referred to as “displacement air”) can provide a healthier building and office environment, often with lower energy consumption. This is due a breathable “zone” from floor to about 6’ above the floor is created and “conditioned” (heated or cooled as needed/and ventilated all the time) as the underfloor air system provides the supply air down low, and that the air returns up high through natural buoyancy.
The healthy environment factor is due to two aspects:
- The delivery of the supply air generally nearer to the occupants assures consistently healthy indoor air quality (coupled with these systems often also employ better filtration) and the ease of flexibility in moving supply diffusers in the floor when occupants move when the need for a new arrangement of personnel is necessary. This flexibility extends to the power and data cabling easily accessible in the floor as well.
- Since the supply air is delivered at the floor it is not as cold as a normal HVAC system (say 62F vs 57F), thus can be provided in airside economizer mode – meaning more fresh air and less cooling more often.
The energy savings are realized as this “zone” is a smaller volume of air that needs to be conditioned than a conventional VAV air system (which must address from floor to the 9’ ceiling and offset skin load at the above ceiling plenum even). The energy efficiency can positively result in reduced capital costs also.
There are some limits to the amount of solar load that a system like this can handle, which means the architects and engineers need to review and study the glazing quality and amount.
TLC has designed multiple corporate office buildings with underfloor air, usually build to suit headquarter types as opposed to spec buildings. Though your consideration of underfloor air may not be related to COVID, “in a world where EVERY conversation finds its way to COVID”, we refer you to this excerpt from the ASHRAE Position Document on Infectious Aerosols:
“Personalized ventilation systems that provide local exhaust source control and/or supply 100% outdoor, highly filtered, or UV-disinfected air directly to the occupant’s breathing zone (Cermak et al. 2006; Bolashikov et al., 2009; Pantelic et al. 2009, 2015; Licina et al. 2015a, 2015b) may offer protection against exposure to contaminated air. Personalized ventilation may be effective against aerosols that travel both long distances as well as short ranges (Li 2011).”
Additional resources on this topic can be found below:
Underfloor Air Distribution Systems by David Stenftenagel
Performance of Underfloor Air Distribution: Results of a Field Study
Energy Savings Potential of Flexible and Adaptive HVAC Distribution Systems for Office Buildings