Lo / hi or lo / lo, Lo / hi, Lo / lo – tekmar 268 Boiler Control User Manual

Page 7: Staging, Fire delay, Fire delay 1, Fire delay 2, Stage delay

7 of 32

D 268 - 11/10

LO / HI OR LO / LO

When using multi-stage boilers, a selection must be made regarding the staging order of the boiler(s). This adjustment is made in
the ADJUST menu of the control.

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 in order 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.

FIRE DELAY

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 second and the fourth stages is fixed at 10 seconds.

Boiler T

mperature

Time

Interstage Delay

Stage 1
Contact Closes

Stage 1
Fires

Seconds

Fire

Delay 1

Fire

Delay 2

Stage 2
Contact Closes

Stage 2
Fires

Stage 3
Contact Closes

Stage 3
Fires

MODE 1

MODE 2

MODE 3

MODE 4

MODE 5

MODE 6

MODE 7

MODE 8

RELAY 1

RELAY 2

RELAY 3

RELAY 4

RELAY 5

RELAY 6

RELAY 7

RELAY 8

RELAY 9

Boiler 1

Boiler 1
Stage 1

Boiler 2

Boiler 1
Pump

Boiler 1
Stage 2

Boiler 3

Boiler 2

Boiler 2
Stage 1

Boiler 1
Pump

Boiler 1
Stage 3

Boiler 4

Boiler 2
Pump

Boiler 2
Stage 2

Boiler 2
Stage 1

Boiler 1
Pump

Boiler 1
Stage 4

Boiler 5

Boiler 3

Boiler 3
Stage 1

Boiler 2
Stage 2

Boiler 2
Stage 1

Boiler 1
Pump

Boiler 6

Boiler 3
Pump

Boiler 3
Stage 2

Boiler 2
Pump

Boiler 2
Stage 3

Boiler 2
Stage 2

– – –

Boiler 7

Boiler 4

Boiler 4
Stage 1

Boiler 3
Stage 1

Boiler 2
Stage 3

– – –

Boiler 8

Boiler 4
Pump

Boiler 4
Stage 2

Boiler 3
Stage 2

Boiler 2
Pump

Boiler 2
Stage 4

– – –

Boiler 9

– – –

Boiler 3
Pump

Boiler 3
Stage 3

– – –

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.

STAGE DELAY

The stage delay is the minimum time delay between the firing of stages. After this delay has expired the control can fire the next
stage if it is required. This setting can be adjusted manually or set to an automatic setting. When the automatic setting is used, the
control determines the best stage delay based on the operation of the system.