Emerson E2 operation manual Analog and Digital Combiners, Lead/Lag

adjustment.

As the value of the reset sensor varies within the mini- mum and maximum range, an equivalent portion of the maximum setpoint adjustment will be added or subtracted from the heating or cooling setpoint. When the reset sen- sor value is directly in between the minimum and maxi- mum range values, nothing will be added or subtracted from the setpoint. Between the halfway point and the min- imum value, part of the setpoint adjustment will be sub- tracted from the setpoint. Between the halfway point and the maximum value, part of the setpoint adjustment will be added to the setpoint. An example of this is shown in Fig- ure 11-28.

RESET	SET
SENSOR	POINT
RANGE	CHANGE
MAX	MAX
RANGE	CHANGE
	ADD
MIDPOINT	+0
	SUBTRACT
MIN	MAX
RANGE	CHANGE

Figure 11-28- Setpoint Reset Diagram

11.17.5 Lead/Lag

A Heat/Cool application may be linked with another Heat/Cool application in what is called a “Lead/Lag” arrangement. In this arrangement, one Heat/Cool is desig- nated as the Lead loop and used as the primary space tem- perature control device. The other Heat/Cool, the Lag loop, becomes active only to support the Lead loop when it is unable to keep the space temperature within a certain proximity of the setpoint (called the setpoint delta).

Figure 11-29shows how a pair of Heat/Cool applica- tions using a Lead/Lag arrangement would operate in Cooling mode. When the temperature is in between the

setpoint and the setpoint delta, the Lead loop alone will control cooling. However, when the temperature is above the setpoint delta, the Lag loop will come on-line, and both Lead and Lag loops will work to bring the tempera- ture down.

The Lead/Lag arrangement works similarly in Heating mode, except that the setpoint delta is below the Heating setpoint, and Lead and Lag are both on when the tempera- ture is below the setpoint delta.

TEMPERATURE
SETPT
DELTA
SET POINT
LEAD AND	LEAD ON ONLY	LEAD AND	LEAD ON ONLY
LAG ON
		LAG ON
TIME			26512037
Figure 11-29- Lead/Lag Arrangement

Heat/Cools in a Lead/Lag arrangement take turns act- ing as the Lead loop. The user designates the maximum amount of time a Heat/Cool will act as a Lead loop; after this duration, the current Lead loop will switch places with its Lag loop.

Lead/Lag arrangements only work when both Heat/ Cools are in Occupied mode.

Dehumidification control uses the AHU’s existing cool stages (and a separate dehumidification device such as a desiccant wheel, if available) to remove moisture from the air.

The dehumidification setpoint is placed at the 0% end of the dehumidification PID throttling range. In other words, the dehumidification output will start at 0% when the humidity is equal to the setpoint and increase to 100% when the humidity is equal to or above the setpoint plus the throttling range.

The dehumidification output percentage is used much like a heating or cooling output percentage is used in Tem- perature Control. The percentage represents the percent- age of total dehumidification capacity available to the AHU (including cool stages and other dehumidification devices).

11.18Analog and Digital Combiners

Instead of using a single output source as an applica- tion input, you may use a combination of up to sixteen input sources. To use multiple inputs, a Multiple Input cell

11-48 • E2 RX/BX/CX I&O Manual 026-1614 Rev 4 5-JAN-2013