FORM 145.05-EG2 (618)
JOHNSON CONTROLS
81
The plenum wall shall be insulated with 3-inch, 3.0 pcf density fiberglass acoustical in-
sulation. For acoustical purposes, the interior walls of the plenum shall be lined with
20-gauge, galvanized steel, perforated liner.
Closed cell gasket and clear silicon caulking shall be placed between the unit and the
discharge plenum to prevent air leakage. Brackets anchored with bolts shall attach the
plenum to the unit. When the plenum is to be shipped loose, mounting hardware including
bolts, brackets, gasket and caulking shall be provided from the factory. It shall be shipped
inside the plenum.
Airside Economizer Inlet Plenum
For air economizer applications, an inlet plenum with integral low leak dampers shall be
provided. This section shall be shipped separate from the unit for field installation. The
inlet plenum panels shall be made from 18-gauge painted galvanized steel. The frame cas-
ing shall be constructed of 16-gauge galvanized steel. The section shall include dampers
for the return and outdoor air. Dampers shall be airfoil shaped, and sealed by vinyl gasket
along the edges for low leakage. The dampers shall be fabricated from 16-gauge galva-
nized steel and rotate on nylon bearings.
The return and outdoor air opening locations will be back and top respectively. Control
actuator with linkages for the return air dampers and another for the outdoor air dampers
shall be factory installed. The dampers actuator shall modulate in response to the cooling
load during the economizer mode. The outdoor air damper and return air damper shall be
controlled in a reverse-acting fashion by the unit controller.
Economizer operation shall be controlled to maximize free cooling operation based on
outdoor air conditions. If outdoor air is suitable for cooling, the outdoor air dampers shall
modulate to maintain temperature set point. If the outdoor air cannot satisfy the cooling
load, mechanical cooling shall assist the pre-cooling to achieve temperature set point. To
maximize energy savings, the economizer shall pre-cool until disabled by the enthalpy or
temperature. When the economizer is disabled, the outdoor air dampers shall be set to the
minimum position of 15% (keypad adjustable).
This option is available only when waterside economizer is not chosen.
Sound Attenuating Inlet Plenum
For additional sound attenuation, a field installed inlet plenum shall be provided. Inlet
plenum will have return air access from both sides and shall be made out of 4-inch 3-lbs/
lb density fiberglass with black facing that contains flame retardant and biocide, and
20-gauge galvanized steel perforated metal liner. The plenum shall be available on the
units without low service clearance units.
This option is available only when airside economizer is not chosen.
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