CH-12-C037 -- An Innovative Dedicated Outdoor Air Application for a Government Office Tower PDF

The BRAC 133 Building in Alexandria, Virginia is a 1.7 million square foot office tower owned by the Department of Defense. The building utilizes an innovative Fan Powered Induction Terminal Unit (FPIU) system
with Outside Air (OSA) provided by a Dedicated Outdoor Air System (DOAS). The building is programmed to achieve LEED NCv2.2 Gold status with an energy savings of 24.7% over the ASHRAE 90.1-2004 baseline system. The Fan Powered Induction Unit is a modified series fan powered variable air volume terminal unit equipped with a filter, primary (outside) air valve, supply air fan and Electrically Commutated Motor (ECM), heating coil and sensible only cooling coil. Dehumidified OSA is supplied to the zone for humidity and CO2 concentration control. Induced air is filtered and then cooled or heated through the use of a sensible only cooling coil, or heating hot water heating coil. Induced air is supplied to the space along with outdoor air to maintain the zonetemperature, humidity and CO2 level set-points.

The building is supplied with two chilled water cooling loops. A 42°F [5.6°C] latent chilled water loop utilized for dehumidification of outdoor air and cooling in zones where a high latent load is present. A 55°F [12.8°C] sensible chilled water loop is utilized to provide sensible only cooling to the fan powered induction units and Information Technology (IT) loads. The use of the warmer, sensible chilled water loop yields significant increase in water side economizer usage along with increased chiller efficiency. The net result is a high efficiency cooling system that provides optimal occupant thermal comfort.