Honeywell R7426A, R7426B, R7426C Start Point Ystart P.15, Compensation Changeover Point Wcomp P.03

R7426A,B,C TEMPERATURE CONTROLLER WITH AND WITHOUT REAL TIME CLOCK

Setting Guidelines for Reset Time of P+I Control

The reset time tr should be adjusted to 2...3 times of the response time Tu , which is the time interval between the beginning of a sustained disturbance (e.g. rapid step change of valve position) and the instant when the resulting change in the output signal reaches a specified fraction of its final steady-state value, either before overshoot or in the absence of overshoot.

The response time Tu in discharge air control is normally in the range of 0.1 to 0.6 min, which allows adjustments of the reset time tr in a range of 0.2 to 2 min.

In room control the response time Tu is in the range of 0.5 to 5 min, which results in a setting of 1 to 15 min.

Start Point Ystart (P.15)

This control parameter is available only on the single output controller R7426A and on the R7426B controller if the three 3- position floating outputs are configured for 6-stage ON/OFF sequence control and on the R7426B,C controllers if YMode = 1 is selected.

The start point determines the midrange shift of the output Y1 from the calculated control point.

The start point is calibrated in degrees K and is the offset (plus or minus) from the set values or calculated control points at which the output Y1 is at 50%. Normally and especially in P+l control, the start point should be set at zero. A change is required only in specific applications where a asymmetrical arrangement results in improved control per- formance, e.g. if for heat-up of a large space in the morning a high heat capacity is needed and for normal control the valve must be opened by only a small amount.

Compensation Changeover Point Wcomp (P.03)

The control parameter Wcomp defines the start point of summer or winter compensation. Above the compensation changeover point (Wcomp) summer compensation and below Wcomp winter compensation is performed.

Summer / Winter Compensation Authority Su / Wi (P.04 / P.05)

These authority settings determine the reset effect (OATComp) the compensation sensor (T3) has on the main setpoint W1 in percentages. Outside temperature reset in summer and winter time are commonly used applications.

To calculate winter and summer authority, the throttling range must be considered in proportional-only control according to Table 12.

Table 12. Calculation of summer/winter compensation

control		room temp.			outdoor air				throttling
						temp.
schedule		(T1)							range (XP)
						(T3/Tcomp)
		20°C			20°C				2°C
		22°C			-15°C				2°C
		Aut Wi =		∆T1+ Xp			⋅ 100%	=
Winter				∆t Outside Air
			(22 - 20) + 2
						⋅ 100% =≈ 12%
			35
		20°C			20°C				2°C
		26°C			35°C				2°C
		Aut Su =		∆T1− Xp			⋅ 100%	=
Summer				∆t Outside Air
	(26 - 20) - 2
						⋅100% =≈ 27%
			15

Compensation change-over at +20 °C outdoor air temperature

NOTE: With P+I control Xp = 0

Occupied/Unoccupied Function SOFFS (P.16)

A potential-free contact can be used between terminals 1 and 4 to switch the controller between occupied (contact closed) or unoccupied (contact open) mode.

In occupied mode, the temperature set point W1 is used for the control point calculation. In unoccupied mode, the SOFFS parameter value is added (cooling) to or subtracted (heating) from the calculated control point.

In the case of the R7426A controller, the parameter Y1CTRF must be set to 0 or 1 (≠ Cho) to match the required heating or cooling application.

If the configuration parameter Y1CTRF is set to 2 (summer / winter changeover), the parameter SOFFS is not considered.

In sequence applications of heating and cooling, the SOFFS parameter value is added to the control point for cooling (CTRPC) and subtracted from the control point for heating

(CTRPH) (see Fig. 5).

Night Mode Offset NOFFS (P.26: Controller with RTC only)

This control parameter is used to set the night mode offset.

During night mode, freeze protection is active and the occupied / unoccupied function is inactive.

Night Cycle NightLow and NightHigh (P.24 and P.25: with RTC, only)

The control parameters NightLow and NightHigh are used by the night cycle program (controller mode = OFF) to assign unoccupied night low or high limits for the protection of a space and its contents against temperature extremes.

EN1B-0203GE51 R0507C 10