Dunkirk Helix VLT Vertical Laser Tube, Wall Hung Modulating Condensing Boiler - Manual (Page 7)

7
5 - Cascade – Start/Stop Sequence
Following sequence of operation occurs if there is call for
heat (CH or DHW) boilers will start as following:
Starting Boilers
1. Do not open manual gas shut off valve before purging
all air from system.
2.
Do not start boiler if water is leaking. Fix all leaks
immediately.
3.
When demand for CH is present and system
temperature is below Cascade CH Setpoint - (minus)
Start Boiler Differential setting, fi rst boiler will start.
4. Managing boiler sends calculated setpoint to dependent
boilers. Power of boilers is PID controlled on basis of
Calculated Setpoint and Supply Temperature.
5. Managing boiler waits for 3 minutes (Default) before
next boiler can start.
6. When fi ring rate of all boilers is 80% (Default, can be
adjusted by changing Next Boiler Start Rate setting)
or greater and system temperature is below Cascade
CH Setpoint, next boiler starts. Start Delay Time starts
over.
7. Managing boiler checks power of all operating boilers.
If power of all boilers is above 80% rate and wait time
has elapsed, Managing boiler starts next boiler.
8.
Cycle will continue until conditions below are met.
Stopping Boilers
• When one boiler is below 30% (Default, can be adjusted
by changing Next Boiler Stop Rate setting) last boiler is
stopped. See Stop Delay Time period below.
• When power of one boiler is below 30% next boiler is
stopped.
• Boilers are allowed to stop when system temperature is
above Cascade Setpoint + Stop Boiler Differential (can
be adjusted). If system termperature is below this point
no boilers are stopped.
• All boilers are stopped when system temperature is
above Cascade Setpoint + (plus) Stop Boiler Differential.
6 - Cascade – Boiler Rotation
Rotation Interval setting allows user to select frequency
lead boiler will be rotated.
Rotation Interval=5 start sequence is as follows (x is last
boiler):
Days Start/Stop sequence
Day 0-1 1-2-3-4-5..x
Day 1-2 2-3-4-5..x-1
Day 2-3 3-4-5..x-1-2
Day 3-4 4-5..x-1-2-3
Day 4-5 5..x-1-2-3-5
When Rotation Interval = 0 boiler rotation is not active.
If one boiler is assigned DHW demand, this boiler will
always be last boiler in start/stop queue.
MULTIPLE BOILER GUIDE