Re-thinking Air Distribution with HVAC


Different air flow techniques can make happier tenants and greener buildings

The most common form of air distribution HVAC system is by overhead air mixing. Look in almost any commercial building – offices, schools, hospitals – and you will see air distribution devices (called diffusers) blowing tempered air.

These devices use high pressure to throw the tempered air into the space, mix with the room air and heat or cool. This technology is not without its problems, however. The mixing approach allows airborne contaminations to stay in the space, which can lead to lower indoor air quality. In addition, the diffusers are typically located between 8-12 feet above the floor. That height means we are spending energy to heat and cool unoccupied space (not so “green”).

But as energy and HVAC design engineers are learning, there are more effective, efficient, and clean ways to temper a space.

An increasingly popular alternative, called displacement ventilation, releases low velocity air through larger diffusers located near floor level to “sweep” across the room. The conditioned air then migrates naturally to the heat sources, or occupants, throughout the room. This is due to the fact that heat drives air movement, and since our bodies naturally give off a “thermal plume” of consistent heat, the conditioned air finds its way to us and cools us off.

As the conditioned air enters the space, it displaces the room air through natural buoyancy and exhausts through a high point in the room. The air is not mixed so contaminant particles can be removed.

What does this approach mean?

  • Using less energy because we only condition the occupied space and not unnecessary overhead.
  • Using less energy from reduced fan power by blowing the air at a much slower pace.
  • Occupants feel more comfortable because we feel less air movement in the space.
  • Air isn’t mixed, which means potential contaminants in the space aren’t mixed either.

These types of technology shifts are occurring more frequently in the HVAC industry as we push to go “green”. The question always is: what’s next?


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