1. Air
  2. Displacement ventilation

Displacement ventilation

Features/Air/Feature 21

Displacement ventilation

Intent: 

To improve air quality in the breathing zone of the room and maintain thermal comfort by supplying low velocity outdoor air near the floor and expelling near the ceiling.

BACKGROUND

By strategically designing the height of air ventilation, displacement ventilation can enhance air change effectiveness. Displacement ventilation supplies air at very low velocity levels at or near the floor level, which then rises to the ceiling level. Since heat in a room is naturally stratified, displacement ventilation not only ensures that air is not delivered and pushed through the return air path (often the dirtiest portion of the air stream), but also tends to concentrate pollutants near the ceiling. Once there, the pollutants are out of the breathing zone and can be more easily removed.

Part 1
Displacement Ventilation Design and Application

Projects implement a displacement ventilation system for heating and/or cooling in which one of the following is met:
a.41
Low side wall air distribution with the air supply temperature slightly cooler or warmer than the desired space temperature. The system must use the System Performance Evaluation and ASHRAE Guidelines RP-949 as the basis for design.
b.37
Underfloor Air Distribution (UFAD) with the air supply temperature slightly cooler or warmer than the desired space temperature. This system must use ASHRAE's UFAD Guide (Design, Construction and Operations of Underfloor Air Distribution Systems) as the basis of design. Displacement ventilation applied as part of an underfloor air distribution system must be installed at a raised floor height whereby the underfloor area can be cleaned on an annual basis.

Part 2
System Performance

The following requirements are met:
a.
A Computational Fluid Dynamics (CFD) analysis is conducted for the displacement ventilation system.
b.92
The displacement ventilation system meets ASHRAE 55-2013 (Thermal Environmental Conditions for Human Occupancy) for comfort for at least 75% of all regularly occupied space.