Table 30 – Available Cooling Stages
NUMBER OF | 0 | 1 | 2 | 3 | |
STAGES | (ECONOMIZER*) | ||||
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Compressor 1 | Off | Off | On | On | |
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Compressor 2 | Off | Off | Off | On |
* If conditions are suitable for economizer operation.
Any time the compressors are running, the PremierLink controller will lockout the compressors if the SAT becomes too low. These user configurable settings are found in the SERVICE configuration table:
Compressor 1 Lockout at SAT < SATLO1 (50 to 65_F) (default is 55_F)
Compressor 2 Lockout at SAT < SATLO2 (45 to 55_F) (default is 50_F)
After a compressor is locked out, it may be started again after a normal
Dehumidification — The PremierLink controller will provide occupied and unoccupied dehumidification control when AUXOUT = 5 in the CONFIG table and is installed on HVAC units that are equipped with additional controls and accessories to accomplish this function. This function also requires a space relative humidity sensor be installed on the OAQ/IRH input.
When in the occupied mode and the indoor relative humidity is greater then the Occupied High Humidity setpoint, then the H3_EX_RV output point will be energized. When in the unoccupied mode and indoor relative humidity is greater then the Unoccupied High Humidity setpoint, then the H3_EX_RV output point and supply fan output will be energized. There is a fixed 5% hysteresis that the indoor relative humidity must drop below the active setpoint to end the dehumidification mode and deenergize the H3_EX_RV output. If the PremierLink controller is in the unoccupied mode, then the fan relay will deenergize if there is no other mode requiring to the fan to be on. This function will not energize mechanical cooling as a result of the indoor relative humidity exceeding either setpoint.
A high humidity alarm will be generated if the indoor relative humidity exceeds the high humidity setpoint by the amount configured in the Control Humidity Hysteresis in the ALARMS table for 20 minutes. The alarm will return to normal when the indoor relative humidity drops 3% below the active humidity setpoint.
Economizer — The economizer dampers are used to provide free cooling and indoor air quality if optional CO2 sensor is installed and when the outside conditions are suitable. Temperature control is accomplished by controlling the SAT to a certain level determined by the Economizer PID Loop by calculating a submaster reference (ECONSR) value. This algorithm will calculate the submaster reference temperature (ECONSR) based on OAT and enthalpy conditions and cooling requirements. The ECONSR value is then passed to the Economizer Submaster Loop, which will modulate dampers to maintain SAT at ECONSR level.
The following conditions are required to determine if economizer cooling is possible:
S Indoor fan has been on for at least 30 seconds S Enthalpy is low
S SAT reading is available S OAT reading is available S SPT reading is available
S OAT ≤ SPT
SOAT < OATMAX (OATMAX default is 75_F) S Economizer position is NOT forced
If any of the above conditions are not met, the ECONSR will be set to its MAX limit of 120_F and the damper will go to its configured minimum position. The minimum damper position can be overridden by the IAQ routine described later in this section.
The calculation for ECONSR is as follows:
ECONSR = PID function on (setpoint - SPT), where:
setpoint = ((OCSP+STO) + (OHSP+STO))/2 when NTLO (Unoccupied Free Cool OAT Lockout) < OAT < 68_F
setpoint = (OCSP+STO) - 1 when OAT ≤ NTLO setpoint = (OHSP+STO) + 1 when OAT ≥ 68_F
The actual damper position (ECONPOS) is the result of the following calculation. Values represented in the right side of the equation can be found in the SERVICE configuration table descriptions in this manual. Note that that the OAT is taken into consideration to avoid large changes in damper position when the OAT is cold:
ECONPOS = SubGain x
If the OAT < DXLOCK (DX Cool Lockout setpoint) then the damper will be modulated to maintain the SAT at the ECONSR value.
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