LO / HI OR LO / LO |
FIG. 9
FIRE DELAY
When using
Lo / Hi
If the Lo/Hi staging option is selected the control stages in sequence all of the stages in a single boiler. Once all of the stages are turned on, the control then stages in sequence all of the stages in the next boiler in the rotation sequence.
Lo / Lo
If the Lo/Lo staging option is selected, the control stages all of the Lo stage outputs in all of the boilers first. Once all of the boilers are operating on their Lo stages, the control then operates the second stage in each boiler in the same order.
STAGING
The control operates up to nine stages to supply the required temperature. After a stage is turned on in the firing sequence, the control waits for the minimum time delay. After the minimum time delay between stages has expired, the control examines the control error to determine when the next stage is to fire. The control error is determined using Proportional, Integral and Derivative (PID) logic.
Proportional compares the actual supply temperature to the boiler target temperature. The colder the supply water temperature, the sooner the next stage is turned on.
Integral compares the actual supply temperature to the boiler target temperature over a period of time.
Derivative compares how fast or slow the supply water temperature is changing. If the supply temperature is increasing slowly, the next stage is turned on sooner. If the supply temperature is increasing quickly, the next stage is turned on later, if at all.
7
The Fire Delay is the time delay that occurs between the time that the control closes a stage contact to fire a stage and the burner fires for that stage. The fire delays for the first and third stages in a boiler are adjustable using the F DLY 1 and F DLY 2 settings. The fire delay for the sec- ond and the fourth stages is fixed at 10 seconds, see Figure 10 below.
Fire Delay 1
Fire Delay 1 is available in all modes of operation. Fire Delay 1 is the fire delay of the first stage of the boiler.
Fire Delay 2
Fire Delay 2 is only available in the modes of operation for Three and Four Stage Boilers. Fire Delay 2 is the fire delay of the third stage of the boiler.
FIG. 10
