Controls - Carrier GEMINI SELECT 38APS025-065 Product Data

Controls

Microprocessor
The ComfortLink™ microprocessor controls overall unit
operation. Its central executive routine controls a number
of processes simultaneously. These include internal timers,
reading inputs, analog to digital conversions, fan control,
display control, diagnostic control, output relay control, de-
mand limit, capacity control, head pressure control, and
temperature reset. Some processes are updated almost
continuously, others every 2 to 3 seconds, and some every
30 seconds. The microprocessor also has the capability of
communicating with the Carrier Comfort Network
es using the CCN protocol and other popular protocols in-
cluding BACnet, MODBUS*, LonWorks, etc.
The microprocessor routine is started by switching the
Emergency ON-OFF switch to ON position.
Cooling control options
When mechanical cooling is required ComfortLink™ con-
trols have the capability to control the staging of the com-
pressors in several different ways. The control checks on
various other operation parameters in the units to make
sure that safety limits are not exceeded and the compres-
sors are reliably operated.
The 38AP unit ComfortLink controls offer two basic
control approaches to mechanical cooling: constant
volume (CV) with 2 stages of cooling and variable air vol-
ume (VAV) with multiple stages of cooling. In addition to
these traditional methods of control, the 38AP Series
ComfortLink controls offer the ability to run multiple stag-
es of cooling in constant volume applications and accept
an external input for desired percent of capacity.
COOLING
CONTROL
CONTROL
TYPE
METHOD
CV Thermostat
Thermostat
2-Stage
CV Thermostat
Thermostat
Multiple Stage
CV SPT Space Temperature,
Multiple Stage T-55/T-56
Supply Air
VAV
Temperature
% Capacity 4-20 mA Input
LEGEND
CV — Constant Volume
SPT — Space Temperature Sensor
VAV — Variable Air Volume
Control type — The control type determines the selec-
tion of the type of cooling control as well as the technique
for selecting a cooling mode. The control types are:
VAV — This configuration refers to standard VAV opera-
tion. If the control is occupied and fan status input closed,
the controls vary capacity based on supply-air temperature
CV TSTAT-2 Stage — This configuration will force the
control to monitor the thermostat inputs (Y1,Y2) to make
a determination of mode and capacity.
CV TSTAT-Multiple Stage — This configuration will force
the control to monitor the thermostat inputs (Y1,Y2) to
make a determination of mode. Unlike traditional 2-stage
thermostat control, the unit is allowed to use multiple
stages of cooling control and perform VAV-style capacity
control.
*Registered trademark of Schneider Electric.
92
®
devic-
STAGING
UNIT SIZE
CONTROLLED BY
025 to 030 2-Stage Thermostat
025 to 130 Supply Air Temperature
025 to 130 Supply Air Temperature
025 to 130 Supply Air Temperature
025 to 130 Supply Air Temperature
CV SPT-Multiple Stage — This configuration will force the
control to monitor a space temperature sensor to make a
determination of mode. The unit is allowed to use multiple
stages of cooling control and perform VAV-style capacity
control.
% Capacity Control — This configuration will force the
control to monitor a 4 to 20 mA external input and vary
compressor capacity from 0 to 100% depending on the 4
to 20 mA input.
Cooling control method
Three different cooling control methods are used to step
through the available stages of capacity depending on the
unit size, circuiting, compressor type and cooling control
method. Refer to Loading Sequences tables in the Applica-
tion Data section on page 99 for specific capacity control.
Multiple-Stage Supply Air Temperature (SAT) — The
capacity of the compressors are controlled based on the
supply-air temperature and supply air temperature set
point. This control method uses an adaptive PID (propor-
tional, integral, derivative) algorithm to calculate the esti-
mated change in supply-air temperature before engaging
or disengaging the next stage of cooling. The algorithm
compensates for varying conditions, including changing
flow rates across the evaporator coil, to provide better
overall control of compressor staging.
Multiple Adaptive Demand — This control method will
base the capacity compressors on the supply air discharge
temperature and one of two supply air temperature set
points. The control will be able to call out a LOW COOL or
a HIGH COOL mode and maintain a low or high cool sup-
ply air set point. The unit will use either the input from a
conventional thermostat to turn the Y1, Y2 signals into a
high and low demand signal, or with a space temperature
sensor use a differential from set point to determine the
mode. Once the mode has been established the control
uses the same algorithm as with VAV control.
Two-Stage Demand — The unit will operate 2 stages of
compressor capacity control.
Demand limiting — The control supports demand limit-
ing using one or two fixed capacity limits initiated by dis-
crete input switches or a variable capacity limit function
based on an analog input signal. On CCN systems this can
be done through the network, or for non-CCN network
jobs this can be done by adding the energy management
module.
Diagnostics
The ComfortLink controls have fully integrated all controls
and sensors into a common control system. The control
monitors these inputs as well as many of the routines to
provide advanced diagnostics. These include adaptive logic
to allow the unit to continue to operate in a reduced output
mode and automatic resets where applicable. The last 10
alarms and alerts are stored in memory and can be ac-
cessed through the display. The alarms can also be moni-
tored through the Carrier Comfort Network connection.
The unit also supports the use of the hand held Navigator™
display which can be plugged in at the main control box.