Carrier 48/50AJ specifications Fan Status Monitoring

Therefore, the amount to add to the economizer’s ECONOMIN configuration is: (0.5/0.75) x (50-20) = 20%. In effect, for the positioning of the economizer, ECONOMIN would now be replaced by ECONOMIN + 10%.

Static Pressure PID Config (S.PID) — Static pressure PID configuration can be accessed under this heading in the Con- figuration→SP submenu. Under most operating conditions the control PID factors will not require any adjustment and the factory defaults should be used. If persistent static pressure fluctuations are detected, small changes to these factors may improve performance. Decreasing the factors generally reduce the responsiveness of the control loop, while increasing the factors increase its responsiveness. Note the existing settings before making changes, and seek technical assistance from Carrier before making significant changes to these factors.

Static Pressure PID Run Rate (S.PID→SP.TM) — This is the number of seconds between duct static pressure readings taken by the ComfortLink™ PID routine.

Static Pressure Proportional Gain (S.PID→SP.P) — This is the proportional gain for the static pressure control PID control loop.

Static Pressure Integral Gain (S.PID→SP.I) — This is the integral gain for the static pressure control PID control loop. Static Pressure Derivative Gain (S.PID→SP.D) — This is the derivative gain for the static pressure control PID control loop.

Static Pressure System Gain (S.PID→SP.SG) — This is the system gain for the static pressure control PID control loop.

STATIC PRESSURE RESET OPERATION — The Com- fortLink controls support the use of static pressure reset. The Linkage Master terminal monitors the primary air damper posi- tion of all the terminals in the system (done through LINKAGE with the new ComfortID™ air terminals).

The Linkage Master then calculates the amount of supply static pressure reduction necessary to cause the most open damper in the system to open more than the minimum value (60%) but not more than the maximum value (90% or negligi- ble static pressure drop). This is a dynamic calculation, which occurs every two minutes when ever the system is operating. The calculation ensures that the supply static pressure is always enough to supply the required airflow at the worst case termi- nal but never more than necessary, so that the primary air dampers do not have to operate with an excessive pressure drop (more than required to maintain the airflow set point of each individual terminal in the system).

As the system operates, if the most open damper opens more than 90%, the system recalculates the pressure reduction variable and the value is reduced. Because the reset value is subtracted from the controlling set point at the equipment, the pressure set point increases and the primary-air dampers close a little (to less than 90%). If the most open damper closes to less than 60%, the system recalculates the pressure reduction variable and the value is increased. This results in a decrease in the controlling set point at the equipment, which causes the primary-air dampers to open a little more (to greater than 60%).

The rooftop unit has the static pressure set point programmed into the CCN control. This is the maximum set point that could ever be achieved under any condition. To simplify the installation and commissioning process for the field, this system control is designed so that the installer only needs to enter a maximum duct design pressure or maximum equipment pressure, whichever is less. There is no longer a need to calculate the worst case pressure drop at design condi- tions and then hope that some intermediate condition does not require a higher supply static pressure to meet the load conditions. For example, a system design requirement may be

1.2in. wg, the equipment may be capable of providing

3.0in. wg and the supply duct is designed for 5.0 in. wg. In this

case, the installer could enter 3.0 in. wg as the supply static pressure set point and allow the air terminal system to dynami- cally adjust the supply duct static pressure set point as required.

The system will determine the actual set point required de- livering the required airflow at every terminal under the current load conditions. The set point will always be the lowest value under the given conditions. As the conditions and airflow set points at each terminal change throughout the operating period, the equipment static pressure set point will also change.

The CCN system must have access to a CCN variable (SPRESET which is part of the equipment controller). In the algorithm for static pressure control, the SPRESET value is always subtracted from the configured static pressure set point by the equipment controller. The SPRESET variable is always checked to be a positive value or zero only (negative values are limited to zero). The result of the subtraction of the SPRESET variable from the configured set point is limited so that it cannot be less than zero. The result is that the system will dynamically determine the required duct static pressure based on the actual load conditions currently in the space. This elimi- nates the need to calculate the design supply static pressure set point. This also saves the energy difference between the design static pressure set point and the required static pressure.

Third Party 4 to 20 mA Input — It is also possible to perform static pressure reset via an external 4 to 20 mA signal connect- ed to the CEM board where 4 mA corresponds to 0 in. wg of reset and 20 mA corresponds to 3 in. wg of reset. The static pressure 4 to 20 mA input shares the same input as the analog OAQ sensor. Therefore, both sensors cannot be used at the same time. To enable the static pressure reset 4 to 20 mA sen- sor, set (Configuration→SP→SP.RS) to Enabled.

RELATED POINTS — These points represent static pressure control and static pressure reset inputs and outputs. See Table 76.

Static Pressure mA (SP.M) — This variable reflects the value of the static pressure sensor signal received by the ComfortLink™ controls. The value may be helpful in trouble- shooting.

Static Pressure mA Trim (SP.M.T) — This input allows a modest amount of trim to the 4 to 20 mA static pressure trans- ducer signal, and can be used to calibrate a transducer.

Static Pressure Reset mA (SP.R.M) — This input reflects the value of a 4 to 20 mA static pressure reset signal applied to TB6 terminals 11 and 12 on the CEM board, from a third party control system.

Static Pressure Reset (SP.RS) — This variable reflects the value of a static pressure reset signal applied from a CCN sys- tem. The means of applying this reset is by forcing the value of the variable SPRESET through CCN.

Supply Fan VFD Speed (S.VFD) — This output can be used to check on the actual speed of the VFD. This may be helpful in some cases for troubleshooting.

Fan Status Monitoring

GENERAL — The A Series ComfortLink controls offer the capability to detect a failed supply fan through either a duct static pressure transducer or an accessory discrete switch. The fan status switch is an accessory that allows for the monitoring of a discrete switch, which trips above a differential pressure drop across the supply fan. For any unit with a factory-installed duct static pressure sensor, it is possible to measure duct pressure rise directly, which removes the need for a differential switch. All 48/50AK,AW,A3,A5 units with a factory-installed supply fan VFD will have the duct static pressure sensor as standard.

SETTING UP THE SYSTEM — The fan status monitoring configurations are located in Configuration→UNIT. See Table 77.

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