Page 44
FIGURE 45
ENTHALPY CHART
CHART
CURVE
CONTROL
POINT 50% RH
°F °C
A
B
C
D
73
70
67
63
23
21
19
17
Two types of adjustment may be made at the con
trol.The first is the control setpoint.The setpoint de
termines the temperature and humidity conditions at
which the outdoor air dampers will open and
close.The recommended setpoint is A."If the econo
mizer is allowing air which is too warm or too humid
into the system, the control may be changed to a low
er setpoint (B,C or D).Refer to enthalpy chart figure
45.
Example:
If the enthalpy control is set at setpoint A" as shown in
figure 45, the following situation could occur.A cooling
demand when the outside air is at 75° and 20 percent
humidity would drive the economizer outdoor air
dampers open to utilize outdoor air for cooling.The
compressor cooling circuit would be disabled.Howev
er, if the outdoor 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 damper motor to the preset minimum posi
tion.If cooling demand 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.
b-Minimum Positioner
The second type of adjustment which may be made
at the control is the minimum position of the outdoor
damper blades.Each economizer has a minimum po
sitioner switch (potentiometer) which allows the out
door dampers to be adjusted to a preset minimum
position.This allows a preset amount of air exchange
at all times during blower operation.When unit opera
tion stops, the dampers drive closed.The potentiom
eter is located on the enthalpy control face.
c-Enthalpy Sensor
The enthalpy sensor is located on the outside portion
of the outdoor damper blades (as shown in figure
46).The sensor monitors the total heat content of the
outdoor air (temperature plus humidity) and sends the
information to the enthalpy control.The enthalpy con
trol uses the information to determine if outdoor air can
be used for cooling.
FIGURE 46
MERCURY
SWITCH
(optional PED16 only)
ENTHALPY
SENSOR
WIRE
TIE
BRACKET
DAMPER BLADE
MERCURY SWITCH
SWITCH STRAP
REMD16M-185,-300
ENTHALPY SENSOR AND MERCURY SWITCH
d-Mixed Air Sensor
The mixed air sensor measures the resultant tempera
ture of the mixed air downstream from the evaporator
coil.Temperature is measured in the heating compart
ment (figure 47).The mixed air temperature is used by
the enthalpy control when outdoor dampers are open to
help determine outdoor air damper position.The econ
omizer is factory equipped with a single mixed air sen
sor which fits through a factory supplied hole in the pan
el dividing unit return and supply air (see figure 47).
To Next Page
Loading...
Need help?
General
