Emerson E2 operation manual Losing Contact With Zone Applications, Stand-Alone MultiFlex RTUs

pied to occupied mode occurs, the temperature will already be at or near the occupied heating setpoint. During the pre-stop, which occurs before the Zone application goes from occupied to unoccupied mode, heating is sus- pended and the temperature is allowed to “coast” down to the unoccupied setpoint.

OCCUPIED	UNOCCUPIED	PRE-START	OCCUPIED	PRE-STOP(COAST)	UNOCCUPIED
SET POINT
UNOCCUPIED
SET POINT
					26512036

Figure 11-17- Diagram of Pre-Start and Pre-Stop Operation

Intelligent Pre-Starts and Pre-Stops

OSS is designed to handle pre-starts and pre-stops in the most energy-efficient manner possible. Every time a pre-start or pre-stop occurs, OSS measures the amount of time it takes to bring the temperature from the previous setpoint to within the “comfort zone” of the new setpoint (a user-defined range of values above and below the set- point within which the temperature is considered accept- able). This duration is used to determine the average rate of temperature change, called the K-factor.

The K-factor is stored in the memory along with the average value of the outdoor air temperature during the pre-start or pre-stop. Over time, collected K-factor data will be sorted and combined into a table. As a result, by constantly observing and recording the results of previous pre-starts and pre-stops, OSS will be able to intelligently guess how much time a pre-start or pre-stop mode should last based on the outside temperature.

AHU Control keeps track of three different kinds of K- factors:

•Heat K-factor - used to guess pre-start dura- tions for AHUs operating in heating mode.

•Cool K-factor - used to guess pre-start dura- tions for AHUs operating in cooling mode.

•Coast K-factor - a measurement of the change in temperature when no heating or cooling is active. This is used to determine pre-stop durations for both heating and cool- ing AHUs.

11.7.13Losing Contact With Zone Applications

When a MultiFlex RTU or AHU loses contact with the Zone application to which it was assigned, it is forced to operate in Stand-Alone Mode. Each of the different appli- cations have different stand-alone capabilities.

11.7.14 Stand-Alone MultiFlex RTUs

The MultiFlex RTU uses its own occupied and unoccu- pied heating and cooling setpoints when it operates in Stand-Alone Mode. These values are programmed through the MultiFlex RTU application and stored in the memory on the MultiFlex RTU board itself. During Stand-Alone Mode, the MultiFlex RTU uses its space temperature sen- sor value as the control input.

The MultiFlex RTU also has a seven-day fallback occupancy schedule that it may use to determine occupied or unoccupied building status. Different times may be pro- grammed in the MultiFlex RTU application for Sunday through Saturday. Holiday scheduling is not supported.

Economization control is available if the sensor pro- viding the economization checking is connected to an input on the MultiFlex RTU. Otherwise, economization is disabled.

As it does in Temperature Control, the MultiFlex RTU stores its own occupied and unoccupied dehumidification setpoints. If the MultiFlex RTU has its own humidity sen- sor, it will continue dehumidification using the stored fall- back setpoints.

11.7.15MultiFlex RTU/ARTC and AHU Zone Association

MultiFlex RTUs and AHUs are assigned to Zone appli- cations using the Zone Association screen. To access this screen:

1.Press for the Main Menu.

2.Press for System Configuration.

3.Press  the Network Setup menu.

4.Press  for Associations.

Zone Control Software Overview • 11-29