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APPLICATION DATA (cont)
b. CONTROL FEATURES — The EconoMi$er IV controller
provides superior functionality for rooftop unit operation.
EconoMi$er IV control features are included as follows:
Remote Minimum Position
— The EconoMi$er IV con-
troller can be used with a field-supplied and field-
installed remote minimum position control switch that will
enable and disable the EconoMi$er IV to open or close
the damper beyond the minimum position for modified
ventilation, providing 2 to 10 vdc output.
NOTE: Minimum position signal takes priority over the
DCV (demand control ventilation) maximum position
signal.
Demand Control Ventilation (DCV)
— The EconoMi$er
IV has DCV capability when using an IAQ sensor. This
sensor is typically installed in the return duct or occupied
space. When implementing a DCV control scheme with
the EconoMi$er IV, the control algorithm will modulate
the position of the damper between two user-configured
damper positions, Maximum DCV Position and Minimum
Occupied position. Design airflow rates for these two
damper positions should be such that when the damper
is at the Maximum DCV position, enough fresh ventila-
tion air will be brought in to remove contaminants and
CO
2
generated by sources other than people (i.e., since
in unoccupied mode). The Maximum DCV position is
intended to satisfy the IAQ “Base Ventilation Rate.” The
Minimum Occupied position design airflow rate should
be sufficient to satisfy ventilation requirements for
removing CO
2
from all sources including people at the
maximum occupancy.
IAQ Sensors
— EconoMi$er IV can be utilized with any
IAQ (CO
2
) sensor that provides a 2 to 10 vdc output. The
controller will modulate the outdoor air damper to pro-
vide ventilation based on the sensor output and the IAQ
setting of the controller. When used, an IAQ sensor will
modulate the damper from the minimum position (base
ventilation rate based on CO
2
levels) to maximum posi-
tion (full occupancy ventilation rate).
Damper Operation — The EconoMi$er IV allows the
damper to be configured for two adjustable damper posi-
tions including maximum position and occupied mini-
mum positions. The two (2) position damper capability is
a unique feature of EconoMi$er IV and includes opera-
tion flexibility as follows:
1. Minimum Occupied Position: This adjustable position
allows a minimum ventilation (base ventilation rate)
airflow rate through the unit during occupied periods.
2. Demand Control Ventilation (DCV) Maximum Posi-
tion: A DCV maximum occupied position is provided
when using an IAQ sensor for DCV. See DCV and
Control sections for sequence. The DCV Maximum
Position limits outdoor airflow into the rooftop when
the DCV routine overrides the mixed air sensor. Set-
ting the DCV Maximum Position of the outdoor air
damper prevents large amounts of hot or cold air into
the space.
IMPORTANT: When the DCV Maximum Position is set
below the minimum position, the minimum position
overrides the maximum position, negating most DCV
functions.
Power Exhaust
— The EconoMi$er IV has the capability
to control one stage of power exhaust for maintaining air
balance and pressurization. Control is activated based
on outdoor air damper position (adjustable); factory-set
at the “middle” position (dampers halfway open).
Compressor Staging
— The EconoMi$er IV is an inte-
grated economizer and has the ability to utilize simulta-
neous outdoor air and compressors. The EconoMi$er IV
can be configured to support economizer and compres-
sor operation. Only one or two compressor operation is
available with 3 to 12
1
/
2
ton units.
c. CHANGEOVER STRATEGIES — The EconoMi$er IV
controller can be configured to accommodate all avail-
able economizer control strategies that place the rooftop
unit in economizer mode including:
Remote Minimum Position
— Used when a remote sig-
nal from a remote minimum position control will enable
and disable the EconoMi$er IV (remote enable control).
Outdoor Dry Bulb
— EconoMi$er IV will be enabled
based on the outdoor-air temperature. This is provided
standard with the EconoMi$er IV.
Differential Dry Bulb
— EconoMi$er IV will be enabled
whenever the outdoor-air temperature is lower than the
return-air temperature.
Outside Air Enthalpy
— EconoMi$er IV will be enabled
based on the outside air enthalpy curves as shown in the
EconoMi$er IV Changeover diagram below. The A, B,
C, and D curves shown have been in use for many years
and have been included as part of the latest
ASHRAE 90.1 energy efficiency code. The curves are
designed to take into consideration both outdoor temper-
ature and humidity. These curves are used to set up the
EconoMi$er IV controller to use the EconoMi$er IV for
free cooling when the conditions to the left of the curve
exist. When the conditions are to the right of the curve,
then outdoor air cooling will not be used and the outdoor
air damper position will be set at the minimum position.
Deciding which curve is used is a function of the outdoor
climate and the type of economizer utilized. Since
EconoMi$er IV is a fully integrated economizer, the
range where outdoor air can be utilized for free cooling is
expanded and the A and B curves may be used. The
control point table in the EconoMi$er IV Changeover dia-
gram below provides assistance for whether the A and B
curves will be suitable. In general terms, a hot and humid
climate may be a reason not to use the A curve, while a
cooler climate might be more applicable for using the A
or B curve.
The EconoMi$er IV has expanded outdoor air capability.
For a changeover economizer which cannot utilize
simultaneous economizer and compression, both A and
B curves would potentially be undesirable since the tem-
perature and humidity levels are too high without com-
pression assistance to provide effective cooling.
Therefore, most changeover economizers utilize the D
curve.
Differential Enthalpy
— The EconoMi$er IV will be
enabled based on the comparison of the enthalpy of the
return air and outside air. When the outside air enthalpy
is lower than he return side, the unit will be in econo-
mizer mode.
Using the EconoMi$er IV controller for implementing
different control changeover strategies requires the use
of different combinations of dry bulb and humidity
sensors as outlined in the EconoMi$er IV Sensor Usage
table.