FIGURE 21
RMF16
MOUNTING FRAME
Page 46
XI-ACCESSORIES
This section describes the application of most of the optional
accessories which can be connected to the CHA/
CHP16/20.
1-RMF16 Mounting Frame
When installing a CHA/
CHP16/20 unit on a combusĆ
tible surface for downflow disĆ
charge applications, RMF16
roof mounting (figure 21) frame
is required. Otherwise, the
RMF16 is recommended but
not required. The CHA/
CHP16/20, if not mounted on a
flat (roof) surface,
MUST
be supported under all edges and
under the middle of the unit to prevent sagging. The CHA/
CHP16 /20
MUST
be mounted level within 1/16" per linear
foot in any direction.
The assembled RMF16 mounting frame is shown in figure
21. Refer to the RMF16 installation instructions for details of
proper assembly and mounting. The roof mounting frame
MUST be squared to the roof before mounting. Plenum sysĆ
tem MUST be installed before the unit is set on the mounting
frame. Refer to the RMF16 installation instructions for propĆ
er plenum construction.
Many types of roof framing or supports can be used to mount
the CHA/CHP16/20 unit, depending upon different roof
structures.
2-Economizers
a-REMD16 Downflow Economizer
REMD16M Downflow Economizer
The REMD16 and REMD16M economizers (figure 22)
are designed for use with standard (downflow) CHA/
CHP16/20s. The economizer opens a set of dampers to
allow 0 to 100 percent outdoor air to be used for cooling
when outdoor humidity and temperature are acceptĆ
able. Additional (2nd stage) cooling demand is directed
to the compressor while the dampers remain open. If
outdoor air becomes unacceptable, the outdoor air
dampers close to a predetermined minimum position
while the compressor cooling circuit cycles as needed.
Refer to the REMD16-41/65 Installation Instruction
Manual for specific details regarding installation. Refer to
the sequence of operation flowcharts (in back of this
manual) for detailed operation of the economizer. The
sequence of operation flowcharts also describe how the
economizer interacts with the CHA/CHP16/20's and the
control system being used.
3-EMDH16 Horizontal Economizer
EMDH16M Horizontal Economizer
The EMDH16 and EMDH16M economizers (figure 23)
operate like the REMD16 and REMD16M except they
are designed for CHA/CHP16/20 units requiring horiĆ
zontal discharge and return air. Internal components
and operation of the horizontal economizer are identiĆ
cal to the downflow economizer.
Refer to the EMDH16-41/65 Installation Instruction
Manual for specific details regarding installation.
The physical location of controls in REMD16M and
REMD16 economizers is shown in figure 22. The
physical location of controls in EMDH16M and
EMDH16 economizers is shown in figure 23.
4-Economizer Operation
a-Enthalpy Control: Setpoint Control
The key to economizer operation is the enthalpy conĆ
trol. The enthalpy control senses total heat content in
outside air (temperature plus humidity) and uses that
information to control the amount of outside air brought
into the system. When the outside air enthalpy is below
the control setpoint, the control actuates a motor which
in turn adjusts outdoor dampers to meet cooling deĆ
mands of the building. When the heat content rises
above control setpoint, the control de-activates and
dampers close to preset minimum (not closed) posiĆ
tion.
Two types of adjustment may be made at the control.
The first is the control setpoint. The setpoint deterĆ
mines the temperature and humidity conditions at
which the outdoor air dampers will open and close.
The recommended setpoint is A." If the economizer
is allowing air which is too warm or too humid into the
system, the control may be changed to a lower setĆ
point (B,C or D). Refer to enthalpy chart figure 24.
