Filter
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Site Preparation and Installation
10
2.4.2 Evaporator Air Distribution
Filter Box
The optional filter box mounts directly to the return air opening of the evaporator. The filter box is
supplied with two (2) 20% (Liebert part no. A-0320) or 30% (Liebert part no. A-0400) 25" x 20" x 4" fil-
ters.
Connections for Ducted Systems
Use flexible duct work or non-flammable cloth collars to attach duct work to the unit and to help con-
trol the transmission of vibrations to building structures. Insulation of duct work is vital to prevent
condensation during the cooling cycle. The use of a vapor barrier is required to prevent absorption of
moisture from the surrounding air into the insulation.
If the return air duct is short, or if noise is likely to be a problem, sound-absorbing insulation should
be used on the duct. Duct work should be fabricated and installed in accordance with local and
national codes.
NOTE
Do not operate the unit without filters installed in return air system.
Table 5 Evaporator external static pressure (60) at 3750 CFM (6371 CMH)
Turns
Open
2 hp Motor (std) 3 hp Motor (opt)
RPM
External
Static, in. RPM
External
Static, in.
0n/a n/a 1146 1.9
0.5 n/a n/a 1125 1.8
1n/a n/a 1104 1.7
1.5 946 0.9 1083 1.6
2 922 0.8 1063 1.5
2.5 972 0.7 1042 1.4
3 899 0.6 1021 1.3
3.5 851 0.5 1000 1.2
4 828 0.4 979 1.1
4.5 804 0.3 958 1.0
5 780 0.2 938 0.9
5.5 757 0.1 917 0.8
6 733 0 896 0.7
If free-cooling or hot water coil is ordered, reduce available external static
pressure by 0.3" (8 mm). Contact Liebert Representative for other Air Volumes.
Factory setting is 0.5" (13 mm) with 2 hp motor. Field adjust to suit application.
NOTE
Maximum return air static pressure should not exceed 0.3" (8 mm) to provide proper drainage
of the unit.