Latent and sensible load in designing chilled beam system!
April 5, 2016

Latent and sensible load in designing chilled beam system!

Latent Load

Understanding the latent load is where most engineers get wrapped around the axle. All chilled beams only provide sensible cooling — meaning they are not supposed to create any condensation. Most beams do not have drain pans. The good news is that there is no need for condensate piping (space and capital savings) and no filters to service (dry coils don’t need filters). The space humidity load is met by providing primary air at a lower dewpoint than the design space condition (typically 75 °F and 50-55% RH). The concern about condensation at the beam can lead the engineer to oversize the primary airflow, but this is a serious error. Oversized airflow rates will negate all the energy savings chilled beam systems can offer, and worse, lead to over cooling and occupant comfort complaints. For an office space with 5 to 8 gr/lb difference between the primary air and the space condition, the latent airflow requirement will be around 0.4 to 0.6 cfm/ft².

Sensible Load

The third requirement is based on meeting the zone sensible cooling load. The primary air itself will pick up about one third of the zone cooling load in an office application. There needs to be enough primary air to induce room air through the beam coil to deliver the other two thirds of cooling. An induction ratio (primary to induced air ratio) between 2 and 4 is common.

Excerpt from the article “Chilled Beam Systems” by Hugh Crowther published in the Canadian Consulting Engineer Magazine, December 2015. Read the article here (link here).


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