Ashrae Journal - December 2008 - (Page 30) coils, each beam is 6 ft to 10 ft (2 m to 3 m) in length, 2 ft (0.61 m) in width, and about 7 in. (178 mm) in depth. Two 6 ft (2 m) chilled beams are adequate for a typical 100 ft2 (9 m2) block of interior laboratory space, (all of the labs at the NJEDA Tech IV Building are interior spaces), with 8.5 W/ ft2 (91.5 W/m2) of equipment load and 2 W/ft2 (21.5 W/m2) of lighting load, (a total of 10.5 W/ft2 [113 W/m2] cooling load, for interior laboratory spaces without shell or solar heat gains). The beams occupy about 24% of the ceiling area. Figures 2 and 3 illustrate the basic airflow pattern and air balance within the 100 ft2 (9 m2) block of typical laboratory space, (using active chilled beams each receiving 30 cfm (14 L/s) of primary neutral air from a central air-handling unit with dual energy recovery), under two different scenarios. In Figure 2 a fume hood exhausting 500 cfm (236 L/s) is present in the space, whereas in Figure 3 there is no hood present, and the total ventilation air is based on 6 ACH. Under both scenarios, supplemental neutral air is supplied to the space as required, through separate air devices. Care should be taken in the layout of the chilled beams, supplemental air supply devices, and fume hood exhausts to maximize ventilation effectiveness in the space. The beams and other supply air devices should be arranged to avoid having adverse effects on fume hood containment. Although the supplemental neutral air is not used for temperature control in the space, this air is also located and aimed in a manner that does not interfere with the cooling effect of the chilled beams. Figure 4 represents, in plan and section, the air velocity profile for a typical 100 ft2 (9 m2) block of laboratory space. The model was generated with the beam manufacturer’s software. Air velocity at the perimeter of the block is close to 50 fpm (0.25 m/s) at the ceiling elevation, and is expected to drop even lower at a height closer to the work bench or fume hood entrance. Although velocities in this range are well suited to laboratory design, (in accordance with ANSI/AIHA Standard Z9.5, Laboratory Ventilation, jet velocity at the hood should be less than half of the face/capture velocity, which is typically 80 Supply Air 110 cfm Primary 30 cfm Supply Air 220 cfm Primary 30 cfm Supply Air 110 cfm 68°F Inlet “Neutral” Air From Air-Handling System Primary Air Duct Induction Nozzle 59°F Chilled Water Cooling Coil Ceiling Supply to Room Air Induced Into Beam From Room 6 ft to 10 ft Long x 2 ft Wide x 7 in. Deep Supply to Room Figure 1: Chilled beam schematic (active beam). to 100 fpm [0.41 to 0.51 m/s]), it is prudent that the beams be oriented perpendicular to the fume hoods to prevent directed airflow toward the face of the fume hood.4 In this example, the flow graphic does not account for the effects that the supplemental neutral air supplied to the room through the separate air devices might have on air velocity. However, the manufacturer’s software used does have the capability to incorporate supplemental air devices. Ideally, these separate air devices have low velocity and throw to result in less than 50 fpm (0.25 m/s) velocity in the occupied zone, preventing drafts or adverse effects on containment at fume hoods where present. Dual Energy Recovery System for Neutral Air Supply Figure 5 shows the airflow arrangement planned for the NJEDA Tech IV Building. The temperatures are based on a summer design day. For simplicity, only a single chilled beam Primary 30 cfm Exhaust 45 cfm (Far) Supply 30 cfm (Near) Exhaust Primary 45 cfm 30 cfm (Far) 90 cfm 90 cfm 250 cfm 170 cfm to Hood 340 cfm 90 cfm 90 cfm 170 cfm 250 cfm to Hood 340 cfm 340 cfm 60 cfm 150 cfm 60 cfm 135 cfm 135 cfm Figure 2 (left): Active chilled beams (100 ft 2 of laboratory space with 500 cfm hood). Figure 3 (right): Active chilled beams (100 ft 2 of laboratory space without hood). 30 ASHRAE Journal ashrae.org December 2008 http://www.ashrae.org
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