Demand Determination - Carrier 48LC Series Controls, Start-Up, Operation And Troubleshooting

cool and heat setpoints (EFF COOL SETPOINT and EFF HEAT
SETPOINT). However, to minimize unnecessary cool to heat and
heat to cool changes, there is a 10 minute delay after the last stage
turns off before the control will switch modes. Linkage operation
overrides the mode changeover delay to 15 seconds. The cooling
and heating Mode Select Time guards (COOL MODE T.GUARD
and HEAT MODE T.GUARD) show the remaining time before
allowing the respective mode to be entered.

Demand Determination

Based on the unit control type (UNIT CONTROL TYPE), alarm
conditions, and user interaction, the control will determine an
MODE OFF
STARTING UP
IDLE - NO DEMAND
SUB-
MODE TIMEGUARD
MODE
UNIT DISABLED
URGENT SHUTDOWN
SAFETY CONTROL
DEMAND
EMERGENCY
SAFETY FAULT
SERVICE TEST
SHUTDOWN
NO DEMAND
FAN ONLY
DEHUM
LOW COOL
MED COOL
HIGH COOL
LOW COOL & DEHUM
MED COOL & DEHUM
HIGH COOL & DEHUM
UFC LOW COOL
UFC MED COOL
UFC HIGH COOL
LOW HEAT
HIGH HEAT
SUPPLY AIR TEMPERING
Thermostat Inputs
Y1 Y2 Y3
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
* Y3 is ignored
** Set the LOW COOL COMP as needed, and Y3 is ignored
VENT
MODE TIMEGUARD
SUPPLY FAN ON
Fig. 10 - - Modes and Sub- -Modes
Table 8 – Demand List and Priority
Priority
1 An emergency condition occurs which requires a unit shutdown
2 A safety diagnostic requires the unit to run in safety mode.
3 User request test mode
4 A minor or user condition requires the unit to shutdown
There is no comfort demand from the building
Only circulation or ventilation is requested form the building
A dehumidification load is present in the building
A low cooling load is present in the building
A medium cooling load is present in the building
A high cooling load is present in the building
A low cooling and dehumidification load is present in the building
A medium cooling and dehumidification load is present in the building
5
A high cooling and dehumidification load is present in the building
A low cooling load is present in the building due to the unoccupied free cooling algorithm
A medium cooling load is present in the building due to the unoccupied free cooling algorithm
A high cooling load is present in the building due to the unoccupied free cooling algorithm
A low heating load is present in the building
A high heating load is present in the building
Due to outside air, supply air is uncomfortably cool during ventilation
Table 9 – Thermostat Cooling System Demands
CONV 2C2H**
No Cool
No Cool
Alert & Low Cool
Alert & Low Cool
Low Cool
Low Cool
High Cool
High Cool
overall demand of the unit. Table 8 shows the possible system
demands with their priority level and summary description.
Thermostat Demand
When the unit control type is configured for thermostat (UNIT
CONTROL TYPE = TSTAT) the level 5 demand in Table 8 will be
determined by thermostat inputs and the Thermostat Type
configuration (THERMOSTAT TYPE) as shown in the tables
below. Table 9 shows the cooling thermostat inputs and how they
map to the system demand. Table 10 shows the heating thermostat
inputs and how they map to the system demand.
COOL
ECON FREE COOLING HEATING
UNOCC. FREE COOL OUTSIDE AIR TEMPERING
MECH. COOLING HEATING PREVENTED
ECON/MECH COOLING SHUTTING HEAT OFF
DEHUMIDIFICATION
DEHUM/MECH COOL
DEHUM PREVENTED
COOLING PREVENTED
SHUTTING COOL OFF
Description
THERMOSTAT TYPE
CONV 3C2H
No Cool
Alert & Low Cool
Alert & Low Cool
Alert & Med Cool
Low Cool
Alert & Med Cool
Medium Cool
High Cool
14
HEAT
MANUAL TEST
AUTO TEST
SHUTTING TEST OFF
DIGI 2C2H* DIGI 3C2H
No Cool No Cool
No Cool High Cool
Medium Cool Medium Cool
Medium Cool High Cool
Low Cool Low Cool
Low Cool High Cool
High Cool Medium Cool
High Cool High Cool
TEST
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