Lochinvar 399, 999 - 750 Staging Logic, Graphic Symbols, Programming For Mode 1, Boiler Operation

Installation and Service Manual

System Sensor: This is used for boiler applications. This sensor will control the water temperature within the building loop.

Staging Logic

There are two different types of staging logic used in the temperature control; Proportional (step) Staging Logic and PID Staging Logic. The staging logic used depends upon what mode the control is running under.

Proportional (Step) Staging Logic

The proportional method of staging is based on manually adjusted settings which determine when the next stage is required to fire. This method is used on Mode 1 for set point operation (with no outdoor sensor) and Mode 2 for water heating. The adjustable settings are:

Set Point TARGET 1, 2, 3, or 4: Staging set point target for each stage. Typically, users set the four different stages a few degrees apart to allow segments of the heater to come on as the temperature drops.

DIFF 1, 2, 3, or 4: Staging differential for each stage.

STG DLY: Interstage delay to turn on between stage 1 and 2 and between stage 3 and 4.

How It Works

A stage will turn on once the temperature drops to its Set point TARGET minus DIFF. The stage will turn off once the temperature rises to its Set point TARGET.

EXAMPLE:

Using stage one of the control as an example, the corresponding load would be energized and de-energized at the following temperatures based on the programmed settings.

Settings

Set Point: 160°F (71°C)

Differential: 8°F (5°C)

Output Energized

Stage One: Energized at 152°F (67°C)

Output De-energized

Stage One: De-energized at 160°F (71°C)

There is a time delay (STG DLY) that applies in the staging on sequence between stage 1 and 2 and between stage 3 and 4. For example, in order for stage 2 to turn on, the temperature must drop to Set point TARGET 2 minus DIFF 2, and the STG DLY must elapse. The STG DLY begins once stage 1 turns on. This operation applies between stage 3 and 4 as well.

Stage 1 and 2 are independent of stage 3 and 4. Stage 2 cannot fire before stage 1 and stage 4 cannot fire before stage 3.

PID Staging Logic

(Outdoor Air Mode 1 Only)

This method is used on Mode 1 for outdoor reset with reset override operation (using the outside air temperature sensor). The PID method of staging allows the control to decide the most effective way to operate the stages to maintain an accurate temperature and minimize short cycling.

The control continuously monitors the actual supply temperature and compares it to the target temperature. The amount of error (proportional), the time the error has been present (integral), and the rate of change (derivative), determine if an additional stage is required to turn on or off.

The control automatically calculates the inter-stage differential as well as the delays between stages turning on or off.

OUTDR START, OUTDR DSGN, BOIL START and BOIL DSGN need to be field set based on installation design criteria to establish the reset curve. Verify that the WWSD is set to the desired value. Adjust BOIL MAX and BOIL MIN to appropriate values for the application.

Note: BOIL MIN should not be less than a setting which will ensure the return water temperature to the unit being 140°F minimum.

BOIL MASS should only need adjustment if changes in the interstage delay are necessary.

Graphic Symbols

The screen will display two graphic symbols. One is a circle with a triangle inside and the other is a graphic representation of a blower (see FIG. 50). The circle with a triangle inside represents the pump. When this symbol is present, the pump is operating. When the blower symbol is present, the controller is calling for heat.

FIG. 50 Graphic Symbols

Programming For Mode 1, Boiler Operation

Mode 1 is for boiler operation. Under Mode 1, there are two sublevels of operation.

1.Operate off of set point.

2.Operate off of outdoor air reset curve.

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