Dependencies — Water Economizer option is enabled, and Fan is On, and Inlet Water Temperature is below set point; or from “Remote Scheduler,” or from “Remote Linkage.”
Economizer mode is switched to Off or no start if: there is no condenser waterflow, Fire Input is On, Fan is not On, or Un- occupied mode is On.
Variable Waterflow Systems — Whenever water economizer is off, the economizer flow control valve is fully closed, and the reverse flow valve directly to the condenser is fully open. Upon engagement of the water economizer, the economizer flow con- trol valve shall be controlled to maintain the MA_RA located between the economizer coil and the DX cooling coil, at a tem- perature near the supply air set point. The the reverse flow valve will be controlled in reverse of the economizer flow control valve’s position. The following formula is an example: Reverse/ Head Press Ctrl output = 100 – two-position/Econo output.
When the unit is off, both valves are closed.
Constant Waterflow Systems — Control of the economizer flow control valve is same as for variable waterflow systems. Control of the reverse flow control valve position will inversely track the economizer flow control valve, such that the total sum of the two valves open positions always equals 100%. The only difference between the variable waterflow system and the constant waterflow system is that for the constant flow system when the unit is off, the economizer valve will be closed and the reverse flow control valve will be open.
WATER ECONOMIZER COIL (50BV) — For the 50BV unit, this factory-installed option contains a water-to-air coil, a two-position diverting valve, and related piping. The water econ- omizer is controlled by an Aquastat and a return-air thermostat.
HEATING COILS AND VALVE (50XJ PCB2) — Water or steam heating options are factory installed. Each includes a motorized, variable control water or steam flow control valve, which can be factory supplied for field installation outside the unit. Installed in the water or steam inlet pipe, this valve is wired to the unit main controller and operates on a 4 to 20 mA signal. A Heating mode PID control is needed to control the valve position (i.e., coil heating capacity) variably between 10 and 100%. The PID will control a set point to + 1° F; for VAV Units this set point is at the Supply Air Temperature Sensor, or as communicated from a remote thermostat.
HEAD PRESSURE CONTROL (50XJ PCB2) — Head Pres- sure Control is required for unit installations that will experience entering condenser water temperatures of 55 F or lower.
NOTE: Head Pressure Control is not needed or used in conjunction with a Water Economizer. A refrigerant pres- sure transducer will monitor head pressure on compressor circuit 1, allowing the unit main controller to regulate water flow rate in the main water line entering the unit; i.e., flow to all condensers. (Water header design to the condensers will be optimized such as to provide relative flow rates to each condenser based on its compressor capacity, enabling successful waterflow control at the main entering pipe.) There are two possible water valving configurations, as outlined below.
Pressure transducer input is factory installed in the discharge line of compressor circuit 1. It is provided 5 vdc by the unit main controller and returns a signal 1 to 5 vdc linearly. The sensor’s range is 0 to 550 psig.
Water Valve(s) Control
Variable Building Waterflow Systems — Variable waterflow configurations use only one water valve in the main water supply pipe. The factory installed valve is a normally open motorized variable control type. The valve is controlled by a 4 to 20 mA signal from the main unit controller using the Reverse/Head Press Ctrl output, which modulates to maintain the head pressure set point (Setpoint 04).
Constant Building Waterflow Systems — Constant waterflow configurations use two (2) water valves, only one of which is in the main water supply pipe. The second valve is located in a bypass pipe to the main outlet water pipe branched off of the supply pipe immediately ahead of the first valve. This valve is same type, but normally closed and is controlled in unison with the first valve, but opposite position, such that the total opening of the 2 valves always equals 100%.
VFD BYPASS (50XJ PCB2) — The VFD Bypass option provides backup for the VFD Drive in VAV units. It uses a manually operated rotary switch, which includes a series of high voltage contacts. The bypass is a direct input to the unit controller, and will be activated via a switch on the unit front panel. When manually activated, the rotary switch takes the VFD out of the fan power circuit and provides the 3-phase power directly to the fan motor, running it at constant speed. A low voltage control circuit ensures that the unit controller pro- vides a signal to allow all VAV dampers to open fully before the fan is turned on (at constant/full speed). A blue indicator light located on the front of the unit indicates that the VFD By- pass is active. A High Duct Static Switch (HDS) shuts the fan down if duct static exceeds a maximum setting.
VENTILATION OUTPUT (50XJ PCB2) — The ventilation output is controller output signal (available for field connection) to a field-supplied ventilation damper(s). This signal is activated whenever the unit is in the occupied mode.
SPACE TEMPERATURE SENSOR (50XJ PCB2) — A field- supplied Carrier space temperature sensor is required to maintain space temperature in sensor mode.
SUPPLY AIR RESET (50XJ PCB2) — Supply air temperature set point may be reset using either the SPT or MA_RA.
SUPPLY AIR RESET (50BV) — Reset is provided by a field-installed temperature sensor.
EXHAUST FAN CONTROL OUTPUT (50XJ PCB2) — This output is activated whenever the unit is in the Occupied mode. This is a modulating output that controls based on the Building Pressure Input set point.
CONDENSER WATER PUMP/WATER TOWER (50XJ PCB2) — This output (provided for field connection) is used to control condenser water flow. Either an On/Off signal or a variable output may be required for this feature.
PHASE LOSS/REVERSAL PROTECTION SWITCH (50XJ PCB2) — This switch monitors VFD/Fan Motor sup- ply leads to detect phase loss or reversal. If the switch detects improper phasing, an input is sent to the unit controller, which shuts the unit down. After a time delay, the controller attempts to restart the unit.
A phase loss/reversal switch may be installed in the unit to detect over/under voltage conditions and phase loss or reversal. When the switch opens, the controller outputs are forced to off with Safety forces, the alarm output will close and the red alarm light will be lit. A system alarm will be generated and displayed on the unit keypad. Unit reset is automatic when the voltage and power phases have been restored.
FREEZE THERMOSTAT (FREEZSTAT) (50XJ PCB2) — The Economizer Freezestat, used in conjunction with an optional water economizer coil or heating coil, is a factory installed averaging (capillary tube) air temperature sensor positioned in the unit inlet airstream.
If the freeze protection switch contacts open the ventilation request output will be closed for 15 minutes and the warning light will light. If the freeze protection switch contacts are still open after 15 minutes the supply fan will be stopped, all compressor cooling will stop, the economizer valve will open to 100%, the pump request output will remain on, and the alarm light will light. This will maintain condenser water flow through the coil to prevent freezing the coil while stopping all other operations that could have contributed or will be affected
