ASHRAE Journal- September 2008

Design Considerations For Active Chilled Beams By Darren Alexander, P .Eng.; and Mike O’Rourke A ctive chilled beams (ACBs) are becoming popular with design consultants as a means of managing large sensible cooling loads with excellent en- ergy performance and low acoustic signatures. This type of active chilled beam is generally installed within a T-bar ceiling grid and is often supplied in 1 ft or 2 ft (300 mm or 600 mm) widths, and lengths ranging from 2 ft to 10 ft (0.6 m to 3.0 m). Active chilled beams provide the advantage of a substantial sensible cooling effect, often by using as little as only the required ventilation air. Also known as high induction diffusers, ACBs recirculate room air through a unit-mounted coil, driven by ventilation air (primary air) with mixing ratios as high as 6:1 (discharge air to primary air). The coil is provided chilled water, which is maintained above the dew point of the primary air to prevent condensation from forming on the coil. The driving force in dehumidifying a space is the mixing of moist room air with drier primary air. By decoupling the ventilation load from the space load, perpetual fan energy savings 50 ASHRAE Journal are created when compared to VAV and other types of all-air systems. Although the low air volume advantage may be reduced when addressing higher latent loads, ACBs offer the beneﬁt of warmer chilled water temperatures for cooling, and cooler hot water temperatures for heating (low exergy systems) to provide high levels of controlled comfort within the occupied zone. This allows for consideration of additional system options in the design process, and offers a new world of possible solutions to the ashrae.org total HVAC system design process. A system advantage in terms of improving the chilled water temperature range is open to sites that use a dedicated outdoor air system (DOAS)* evaporator return water to service part of the secondary chilled water loop, minimizing the total pumping requirements. Fin-enhanced, closed-circuit ﬂuid coolers allow for ACB water-side economization, and mixed mode ventilation can be used to great effect to further reduce the carbon footprints of new and existing buildings. In addition to their relatively shallow depth (generally less than 12 in. [300 mm] clearance requirements), ACBs offer About the Authors Darren Alexander, P .Eng., is a partner and technical director for Twa Panel Systems in Nisku, AB Canada, a member of Technical Commitee 5.3’s subcommittee for chilled beams, and a corresponding member of TC 6.5, Radiant and Convective Space heating and Cooling, as well as a contributing member to the AHRI committee for establishing chilled beam testing standards. Mike O’Rourke is a past chairman of TC 6.5, and president of Radiant Advantage in Highlands Ranch, Colo. September 2008 http://www.ashrae.org

Table of Contents Feed for the Digital Edition of ASHRAE Journal- September 2008

ASHRAE Journal- September 2008 Section: Contents Contents Section: Commentary Options for Sustainability Section: Industry News The Silk Route for Energy Solar Thermal Is Unrealized Opportunity Industry Groups Sue City of Albuquerque Section: Letters Letters Section: Meetings and Shows Meetings and Shows Section: Feature Articles Article-Radiant Floor Cooling Systems Article-HVAC Design for Sustainable Lab Article-Mixed Mode Ventilation Article-Single- Design Considerations For Active Chilled Beams Article-Acoustic Design In Green Buildings Article-Teams, Contracts & BIM Section: Building Sciences Some Old Lessons Distilled Section: Washington Report Energy in Federal Buildings Section: Products HVAC&R Product Showplace Section: Emerging Technologies Toplighting & Lighting Controls For Commercial Buildings Section: Special Products Fans & Blowers Section: Classified Ads Classified Ads Section: Advertising Index Advertising Index

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