York R-407C Controls, Control Sequences For All Units, General, Unoccupied / Occupied Switching

Controls

CONTROL SEQUENCES FOR ALL UNITS

GENERAL

The control system for the YORK eco2 Packaged Roof- top Unit is fully self-contained and based around an OptiLogic™ rooftop unit controller. To aid in unit setup, maintenance, and operation, the OptiLogic™ rooftop unit controller is equipped with a user interface that is based around a 4 line x 20 character backlit LCD dis- play. The LCD displays plain language text in a menu- driven format to facilitate use. In addition to the display, the OptiLogic™ user interface is also equipped with an LED indicator light, which will warn of any abnormal operation of the equipment or communication failures.

For the maximum in system flexibility, the YORK ECO2 Packaged Rooftop Unit can be operated by either a typical 7-wire thermostat (2 cool / 2 heat), a space tem- perature sensor, or stand-alone (VAV only). Note, a field wiring terminal block is provided to facilitate unit setup and installation.

In lieu of the hard-wired control options, the OptiLogic™ rooftop unit controller can be connected to and oper- ated by a Building Automation System (BAS). If re- quired, the OptiLogic™ rooftop unit controller can be equipped with an optional BACNet IP communication card, which allows communication, via Ethernet, to a BACNet IP based BAS.

UNOCCUPIED / OCCUPIED SWITCHING

Depending on application, the unit can be indexed be- tween unoccupied and occupied modes of operation by one of three methods, hard-wired input, internal time clock, or BAS. A contact-closure input is provided for hard-wiring to an external indexing device such as a central time clock, thermostat with built in scheduling, or a manual switch. The unit controller is also equipped with a built in 7-day time clock which can be used, in lieu of the contact closure input, to switch the unit be- tween Unoccupied and Occupied modes of operation. The internal time clock is fully configurable via the user interface and includes Holiday scheduling. In addition to the hard-wired input or the internal time clock, the unit can also be indexed between unoccupied and oc- cupied modes of operation via a BAS command.

Note a unit operated from a space sensor can be equipped to temporarily override an unoccupied mode of operation. This Unoccupied Override feature is fully configurable via the OptiLogic™ user interface.

ECONOMIZER OPERATION

The unit can be equipped with one of three types of optional economizers, dry bulb, single enthalpy, or com- parative enthalpy. When the unit controller determines that Outside Air is suitable for economizing, the unit controller will control the outside air damper(s) open to provide economizer cooling. If economizer cooling alone is insufficient for the cooling load, the unit controller shall stage up compressors, one at a time, to meet demand.

The control logic for the three types of economizers is as follows:

Dry Bulb Economizer

The dry bulb economizer is the default economizer con- trol scheme. With the dry bulb economizer, the unit con- troller monitors the Outside Air temperature only and compares it to a reference temperature setting. Outside Air is deemed suitable for economizing when the Out- side Air temperature is determined to be less than the reference temperature setting. This method of econo- mizing is effective, but is prone to some changeover in- efficiencies due to the fact that this method is based on sensible temperatures only and does not take Outside Air moisture content into consideration.

Single Enthalpy Economizer

With the optional single enthalpy economizer, the unit controller monitors the Outside Air enthalpy in addition to the Outside Air temperature and compares it to a reference enthalpy setting and a reference tempera- ture setting. Outside Air is deemed suitable for econo- mizing when the Outside Air enthalpy is determined to be less than the reference enthalpy setting and the Out- side Air temperature is less than the reference tem- perature setting. This method of economizing allows the reference temperature setting to be set higher than the DB Economizer and is consequently a more effi- cient packaged rooftop economizer.

Comparative Enthalpy Economizer

With the optional comparative enthalpy economizer, the unit controller monitors and compares the Outside Air and Return Air enthalpies in addition to comparing the Outside Air temperature to the reference temperature setting. Outside Air is deemed suitable for economiz- ing when the Outside Air enthalpy is determined to be

26 YORK INTERNATIONAL