Chilled Beam Design Guide - TROX

Active Beam Selection Examples
The primary air supply is to be delivered at 55˚F with a
dew point temperature of 52˚F (W = 0.0082 LBM H 2 O
per pound dry air). The beams are to be located directly
above the work benches in order to capture the most
sensible heat. Figure 34 illustrates the bench layout for
the lab.
SOLUTION:
As the space dew point temperature is 55.2˚F, a 56˚F
chilled water supply temperature will be used. As the
beams are to be located directly above the benches
where most of the space heat sources reside, the induced
air entering the beams will be assumed to be 2°F
warmer than the room air resulting in a 21˚F temperature
differential between the room air and the entering
chilled water.
The minimum primary air delivery to the space for ventilation
purposes is 8 ACH-1, or 800 CFM. The amount of
primary air required to satisfy the space latent load may
be calculated as:
Figure 35 illustrates the proposed beam placement.
Referring to figure 19, the total air supply from each
beam will be 666 CFM or 40 CFM per linear foot of slot.
As A/2 is 8 feet and X is 7 feet, the value of VH 1 and
VL 6 at the six foot (H - H1 = 4 feet) level will be 56 and
86 FPM, respectively.
The water side pressure drop for DID602-US and
DID602-HC can be found in figures 37 and 39, respectively.
Lab
Benches
8 feet
(typical)
CFM LATENT = q LATENT / 4840 x (W ROOM – W PRIMARY )
= 2,000 / 4840 x (0.0092 – 0.0082)
= 413 CFM
As this is less than the ventilation requirement, the minimum
primary airflow delivery will be 800 CFM.
The total space sensible load is 42,000 BTUH. Ideally,
the beam selected should provide 52.5 (42,000 / 800)
BTUH of sensible cooling per CFM of primary air. Table
4 indicates that DID602 beams with “C” nozzles can
provide such a ratio.
The layout of the laboratory would favor the placement
of one or two beams over each bench, so we will consider
the use of four (8) eight foot beams. Applying the
correction factors from figure 46 we see that an eight
foot beam can provide 25 CFM/LF of primary air while
keeping the air side pressure drop of inches H 2 O. The
NC level (39) would also be acceptable. In order to supply
the required air changes (800 CFM), we would need
32 feet of these beams or four (4) eight foot lengths.
As figure 46 is based on an 18°F temperature difference
between the air and chilled water entering the beam, we
must correct the water side sensible cooling according
to the correction factor (1.16) shown in table 6 (page
38) while the primary air contribution (567 BTUH/LF or
17,400 BTUH total) remains the same. The sensible
cooling provided the chilled water coil must thus be
24,600 BTUH or 769 BTUH/LF. Applying the correction
factor (1.16) from table 6, we enter figure 46 to determine
the chilled water flow rate that will provide 663
(769/1.16) BTUH/LF of water side sensible cooling or
1,230 (663 + 567) BTUH/LF of total sensible cooling.
This relates to a chilled water flow rate of 1.0 GPM.
Figure 34: Lab Bench Arrangement
for Example 5
16 feet
(typical)
DID602-US Active
Chilled Beam
(8 ft. Long, "C" Nozzles)
(typical of 4)
Figure 35: Chilled Beam Arrangement
for Example 5
37