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5-Economizers
a-Application
REMD16(M) and EMDH16(M) economizers can only
be applied to CHA/CHP16/20 commercial units.
b-REMD16 Downflow Economizer
REMD16M Downflow Economizer
The REMD16 and REMD16M economizers (figure 22)
are designed for use with standard (downflow) CHP16s.
The economizer opens a set of dampers to allow 0 to
100 percent outdoor air to be used for cooling when outĆ
door humidity and temperature are acceptable. AddiĆ
tional (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.
6-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 units requiring horizonĆ
tal discharge and return air. Internal components and
operation of the horizontal economizer are identical 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.
7-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.
FIGURE 24
ENTHALPY CHART
°°
CHART
CURVE
A
B
C
D
°F °C
CONTROL
POINT 50% RH
73
70
67
63
23
21
19
17
Example:
If the enthalpy control is set at setpoint A" as shown in
figure 24, the following situation could occur. A cooling
demand when the outside air is at 75° and 20 percent huĆ
midity would drive the economizer outdoor air dampers
open to utilize outdoor air for cooling. The compressor
cooling circuit would be disabled. However, if the outĆ
door air should change to 70°F (a drop in temperature)
and 70 percent humidity (a dramatic rise in humidity), the
total heat content" of the outdoor air would rise above
the enthalpy control setpoint and de-activate the dampĆ
er motor to the preset minimum position. If cooling deĆ
mand is still present when the total heat of the outside air
rises above the control setpoint, cooling demand is
routed from the economizer to the compressor cooling
circuit.
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