Specifications

14 • Supply Temperature Control 026-1727 Rev 0 11-APR-2011
terminal load can range from -100% to +100%, where
all negative values indicate a demand for heating and
all positive values indicate a demand for cooling.
When the terminal load rises above 20%, cooling
mode will be activated. Conversely, when the termi-
nal load falls below -20%, heating mode will be acti-
vated. Once activated, both cooling and heating
modes will deactivate if the terminal loads goes back
to 0%.
6.4. Supply Temperature Con-
trol
The iPro DAC will determine the active supply air
temperature setpoint based on whether heating or
cooling is active as well as the amount of terminal
load.
When heating mode is active, the controller will
use the supply temperature heating setpoint as the ac-
tive supply temperature setpoint. Heat stages will be
turned on to maintain the supply air temperature at the
active setpoint. Conversely, when cooling mode is ac-
tive, the controller will use the supply temperature
cooling setpoint as the active supply temperature set-
point. Cool stages will be turned on to maintain the
supply air temperature at the active setpoint.
6.4.1. Supply Air Setpoint Reset
The active supply air setpoint may be automatical-
ly adjusted (reset) based on the heating or cooling ter-
minal load present. The active setpoint will be
increased or decreased up to the maximum amount
specified by the heating and cooling reset setpoints.
The maximum amount will be used when the terminal
load reaches +100% for cooling and -100% for heat-
ing.
6.4.2. Cooling Mode
The iPro DAC supports both staged and modulat-
ing mechanical cooling devices. Modulating devices
are treated as a cooling stage in the case of a unit hav-
ing a mixture of fixed and variable capacity compres-
sors.
6.4.2.1. Staged Cooling
Up to four stages of cooling can be used. Each
compressor stage can be configured to be fixed size,
digital scroll, VS, double size, or heat pump. The
fixed size and heat pump compressors assume a fixed
capacity while the digital scroll and VS compressors
assume a modulating capability. The double size
compressor indicates a fixed compressor which is
double in capacity compared to the other fixed com-
pressors.
When a compressor stage is defined as a heat
pump, it will turn on for both cooling and heating. A
reversing valve must also be used and can be defined
as active cooling or active heating.
6.4.2.1.1. Staging On
When cooling is required, the cool stages will
stage on if the current supply air temperature is above
the active supply air cooling setpoint. The lowest
stage that is off will be turned on first. Additional
stages will be brought on according to the Cool On-
Delay setpoint. A cooling stage will not be turned on
unless it has satisfied its minimum off time.
6.4.2.1.2. Staging Off
When the current supply air temperature drops be-
low the active supply air cooling setpoint minus the
Cool Stage Deadband, cooling stages will begin to
stage off. The highest stage that is currently on will be
turned off first. Additional stages will be turned off
according to the Cool Off-Delay parameter. A cooling
stage will not be turned off unless it has satisfied its
minimum run time.
6.4.2.2. Modulating Cooling
Up to two cooling stages may be defined as vari-
able capacity (VS or digital scroll). Variable capacity
stages should be assigned the lowest numbered cool
stages. As with fixed capacity staging, variable capac-
ity stages will be activated if the supply air tempera-
Figure 6-1 - Terminal Load Graph
NOTE: The application supports a maximum
of two digital/VS compressor stages.