MSP = Sasp +

OCCUPIED/UNOCCUPIED Ð The unit control system will initiate normal occupied mode functions (including Morn- ing Warm-up, Economizer Minimum Position, and Cooling Cycle) whenever a contact closure is made that emulates the normal timeclock contacts. See Fig. 23. (``Occupied/Unoccupied Switch''). The contact closure from the BMS must be an iso- lated contact set, normally open, and suitable for 24-volts AC pilot duty.

NIGHT SETBACK CONTROL Ð Night setback control is used to control the space to a set point level that is typically lower than during normal occupied periods (Heating Only mode). Some applications also require a limitation on the maximum space temperature during unoccupied periods (Cool- ing mode). Both modes are possible by closing the same con- tacts used in the Occupied/Unoccupied control, or by installing a dedicated contact set in parallel with the Occupied/ Unoccupied control contacts, and using the BMS space tem- perature sensing system and its logic to determine when to initiate unit operation.

Once the unit operation has been initiated by the BMS contact closure, the unit operates in its normal occupied mode manner, initiating morning warm-up if needed (as sensed by return air temperature to the unit) or cooling (controlling to current SASP value). The Night Setback Control contacts will interrupt normal unit operation when the BMS senses that space temperatures have returned to unoccupied set point levels, and the unit will shutdown normally.

The contact closure from the BMS must be an isolated contact set, normally open, suitable for 24-volts AC pilot duty.

NOTE: If the rooftop unit is equipped with a VFD and night setback cooling operation is intended, the fan system must be controlled to permit FULL SUPPLY FAN AIR DELIV- ERY during unoccupied cooling operation. This is most con- veniently attained by replicating the HIR relay function of the rooftop unit. An HIR control sequence will force all room terminals to their minimum heating CFM position, thus as- suring adequate air¯ow through the rooftop unit during night setback cooling operation. During night setback cooling op- eration, the return-air temperature (RAT) will be well above normal levels. The higher RAT means that the air tempera- ture leaving the evaporator coil will also be well above nor- mal levels. This situation is interpreted by the unit control system as a demand for additional cooling stages. The unit control responds to this demand by bringing on more stages, until typically all stages are active. If the VFD is not work- ing in-step with the refrigeration system demand, it is pos- sible to produce low suction pressures and local frosting on the evaporator coil during the night setback cooling operation.

UNIT SUPPLY AIR SET POINT ADJUSTMENT Ð The minimum Supply Air Set Point (SASP) temperature is es- tablished by the setting at Potentiometer P1 on the unit dis- play board (see Fig. 6). The control point can also be adjusted upward by emulating the function of the accessory Space Temperature Reset package. The BMS can be used to cause this reset by adjusting the resistance value in a variable re- sistance transducer with a 4 to 20 mA or 2 to 10 vdc signal generated by the BMS.

This emulation requires the following ®eld-supplied parts:

·Variable resistance transducer (Kele RES-1 or equivalent, range 0 to 1000 ohms)

·Series resistance with potentiometer, suitable for manual adjustment to 12.5 to 13.0 k-ohms total resistance

Field Connections (see Fig. 30) Ð Connect ®xed resistance with manual potentiometer and variable resistance trans- ducer in series.

Connect wiring to rooftop unit at: Size 034-044: TB3-12 and TB3-15 Size 054-104: TB4-12 and TB4-15

Con®guration Ð Con®gure as follows:

1.Set DIP switch no. 2 to ON.

2.Adjust manual potentiometer to 12.6 to 12.8 k-ohm.

3.Con®gure transducer for job site input signal from BMS.

4.Adjust Potentiometer (P3) on the rooftop to MAXIMUM SASP value (typically 65 to 70 F). The maximum P3 SASP control limit is 70 F.

Operation ÐUnit will initiate SASP Reset (adjust con®g- ured SASP upward) when the sum of the resistance (®xed resistance + potentiometer + transducer) exceeds 13.1 k-ohm. Once reset is initiated, full range of reset (P3 setting minus con®gured SASP) will be reached with 500-ohm increase in transducer resistance (TR).

During Reset mode operation, Code 21 will appear on unit display board.

Formula:

[	(P3 − SASP)	x		(0.6 F)	x (TR − R@13.1) ]
	(3)		(100 ohm)

MSP: Modi®ed SASP (SASP plus Reset)

TR: Resistance at transducer

R@13.1: TR required to reach 13.1 k-ohm start level

DEMAND LIMIT (1-STAGE OR 2-STAGE) Ð Both of the Demand Limit functions on the units rely on external switches to initiate the reset functions. Contact closures by the BMS can be used in place of these switches. Contacts must be isolated and suitable for 115-vac pilot duty operation.

For Single-Step Demand Limit, emulate function of switch SW with contact closure controlled by the BMS. Set poten- tiometer P4 manually at the unit control box. Alternatively, potentiometer P4 might also be emulated by a variable re- sistance transducer, with the BMS now able to adjust the amount of demand limit.

For 2-Step Demand Limit, install the accessory Demand Limit Control Module (DLCM) according the instructions on page 18. Replace switch functions Switch 1 and Switch 2 with contact closures controlled by the BMS (see Fig. 29).

Follow unit control con®guration instructions in the De- mand Limit section on page 18.

SUPPLY DUCT PRESSURE SET POINT ADJUSTMENT

ÐSupply duct pressure set point adjustment from a remote BMS is possible when the unit has been equipped with a factory-option VFD (variable frequency drive). There are two methods available:

·Direct 4 to 20 mA signal

·DDC direct to the VFD

Direct 4 to 20 mA Signal Ð During normal unit operation, the factory-installed VFD receives a 4 to 20 mA signal from the Duct Pressure (DP) transducer which indicates current supply duct pressure. The VFD then determines the appro- priate fan speed (using its internal PID logic feature) and adjusts its output to the supply fan motor to suit. It is pos- sible to emulate this 4 to 20 mA control signal by the BMS, which will transfer control of the VFD to the BMS.

NOTE: When providing a direct 4 to 20 mA signal to the VFD from a BMS with DP logic, disable the PID (propor- tion integrated derivative calculation process) feature of the VFD.

DDC Direct to the VFD Ð Several accessory interface boards are available for the VFDs that permit direct communication between the VFD and several BMS communication sys- tems. Contact your Carrier representative for information on selecting an appropriate accessory interface board and the name of the local service office (for sale and installation of the accessory boards).