ORANGE EMPIRE FEBRUARY MEETING

 A new air system design concept using chilled boxes

By Dan Int-Hout, FASHRAE and Distinguished Lecturer on Air Control and Distribution Systems.

The chilled box is a new application of existing technologies.  Using a sensible cooling coil at the induction intake port of a fan induction terminal opens an interesting mix of control options.  

The primary air valve would be supplied by a dedicated outdoor air system (DOAS) producing constant dewpoint pre-conditioned supply air at variable volume.  A cooling coil at the induction intake of the box designed for low air pressure drop adds sensible cooling to the induction air mixed with the primary air before discharging it to the space.  To make this coil do sensible cooling only, the chilled water must be maintained a few degrees above space dewpoint temperature similar to the original Carrier high-pressure perimeter induction systems of yesteryear.

The fan induction terminal would include a small standard pressure-independent VAV control damper insert to control the primary air into the terminal, having a low-speed fan with speed controllable ECM fan motor providing blended discharge air to the space.  These two ingredients with proper controls allow the chilled box to regulate the ventilation air quantity and the induced airflow rate independently.  This feature can be used to avoid subcooling an interior space (without needing a reheat coil) while providing additional space sensible cooling and air volume when required.

For perimeter zones, adding a sensible heating coil to the mix (or using the sensible cooling coil for dual purpose) provides enough downstream pressure to permit the use of ducted slots at the windows to ensure compliance with Standard 62.1-2010 heating requirements.  It also allows ducting to be used to reach remote areas, such as lobbies without producing condensation issues leading to dripping diffusers.

By maintaining the lowest possible mix of primary and induced air means that optimal amounts of DOAS and fan-induced air can be managed at each zone, yielding the lowest possible energy consumption commensurate with good system design practice.

Come to the February 28^th Orange Empire Chapter meeting.  You won’t want to miss this presentation.

Dan has been the Chief Engineer for Krueger Manufacturing, an air terminal and distribution device manufacturer for more than 30 years, and he knows of what he speaks.

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