ASHRAE Journal- September 2008

Case A Total Number of Active Chilled Beams Total Primary Air Capacity Total Secondary Air Capacity Total Sensible Cooling Capacity Total Airflow Total Water Flow Total Latent Cooling Available Total Cooling Effect Input Data/Beam Nominal Active Coil Length Nozzle Type Room Air Design Setpoint Room Relative Humidity Supply (Primary) Airflow Rate Supply (Primary) Air Temperature (DB) Inlet Water Temperature Water Flow Rate (Min. = 0.5 gpm/Circuit) Duct Connection Size Calculated Data Supply (Primary) Air Capacity Water Capacity (Two-Row Cooling Coil) Total Sensible Capacity Water Outlet Temperature Water Pressure Drop Plenum Static Pressure Sound Pressure Level Sound Values (Excluding Room Attenuation) Btu/h (W) Btu/h (W) Btu/h (W) °F (°C) ft w.c. (kPa) in. w.c. (Pa) dBA NC 272 (79.7) 2,120 (621.3) 2,392 (701.1) 60.2 (15.7) 4.0 (12.0) 0.40 (99.0) < 22 <18 MBh (kW) MBh (kW) MBh (kW) cfm (L/s) gpm (L/s) Btu/h (kW) Btu/h (kW) Module ft (m) A, B, C, D °F (°C) % cfm (L/s) °F (°C) °F (°C) gpm 156 42.4 (12.4) 33.1 (96.9) 37.3 (109.4) 3,990 (1882) 207.5 (13.1) 28.9 (8.48) 40.2 (117.8) 2 ft by 6 ft 6 ft (1.8) A 75.0 (23.9) 50.0 25.6 (12.1) 65.0 (18.3) 57.0 (13.8) 1.33 5 in. dia. Case B 99 42.5 (12.5) 32.5 (95.3) 36.7 (107.8) 4,001 (1887) 131.7 (8.3) 29.0 (8.50) 39.6 (116.3) 2 ft by 6 ft 6 ft (1.8) A 75.0 (23.9) 50.0 40.4 (19.0) 65.0 (18.3) 57.0 (13.8) 1.33 5 in. dia. 429 (126) 3,286 (963.1) 3,715 (1088) 61.9 (16.6) 4.0 (12.0) 1.00 (249) 29.5 25.5 Table 1: Comparing 0.4 in. w.c. and 1.0 in. w.c. working static pressures for active chilled beams. noise generated at any breach in the seal. The goal in the downstream duct design is to efficiently deliver the pressure to the beam plenums through the use of low velocity ducting. Beam Placement and Room Air Distribution A high induction ratio provides discharge air normalization as it relates to discharge temperatures. As a result, a lower approach exists between the beam’s discharge air temperature and the room air temperature. Consequently, the occupants can tolerate higher average room air velocities (30 fpm [0.15m/s]), and remain in compliance with ANSI/ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, for the design setpoints of 75°F (24°C) and higher, which is common criteria for ACB projects. Typical discharge temperatures from ACBs range between 64°F to 66°F (18°C to 19°C), and ultimately yield lower overall space temperature variations. Comfort levels are improved over conventional methods and occupant comfort complaints are reduced. Care should be exercised when placing beam discharges par54 ASHRAE Journal allel to the exterior glazing. During shoulder seasons in colder climates, cold surfaces of glazing with poor U-values could potentially accelerate the discharge air bathing these surfaces, and cause uncomfortable room air movement in the form of drafts. Consequently, ACBs that discharge perpendicular to the exterior glazing offer a more stable and comfortable thermal environment when coupled with superior glazing that allows such placement.3 Radiant perimeter panels or baseboard radiation also could be used at the curtain wall in the absence of high performance glazing, or for ACBs that are placed parallel to the exterior glazing. Due to the ease at which ACBs provide ventilation effectiveness to the space, beam placement becomes relatively easy. It is not uncommon to observe air turnover rates within the space of 10 to 20 times per hour. The room air mixing within the ACBs provides a more homogeneous temperature distribution, and a ventilation effectiveness of unity is common. Manufacturers typically publish guidelines for beam locations as they relate to minimum separation distances, minimum clearances from ashrae.org September 2008 http://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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