Operating instructions

40
STS
®
, LTS
®
and ULTRA-FOG
®
valve modulation
With a valve system, the modulation is very simple.
The demand signal simply determines how far the
valve is going to open. In other words, if the system
demand is 25%, the valve will be open 25%.
GTS
®
burner modulation
The burner modulation technique used on a GTS is
probably the most complicated. The burners can
operate anywhere from 25% to 100% of their
capacity. To accomplish this turndown, the blower
speed is varied by the VAPOR-LOGIC
®
3
controller.
(The blowers used on the GTS are variable speed
blowers with a tachometer feedback. The
VAPOR-LOGIC
3
controller monitors this feedback
and uses it, in conjunction with the demand signal, to
control the blower speed.) As the blower speed
varies, the gas valve automatically adjusts the amount
of gas being introduced into the burner. This variable
combination of gas and air results in clean
combustion in the range of 25-100% of burner
capacity.
When individual burner demand falls to below 25%
of capacity, the operation changes. Basically, a one-
burner GTS has full modulation in the range of
25-100%. Below 25%, the unit essentially time
proportions. A two-burner GTS has full modulation
in the range of 13-100%. Below 13%, the two-burner
unit will time proportion.
To explain this, lets first look at the operation of a
one-burner GTS. As the demand on the unit increases
from 0, the unit will remain off until the demand
reaches 14%. Once 14% demand is reached, the
controller will fire the burner and run it at 25% of its
rated capacity. (When a GTS burner fires, it fires at
72% of its rated capacity. If the tank is warm, then it
immediately modulates up or down to the desired
demand. This is done to provide the smoothest,
quietest, most reliable ignitions. If the tank is cold,
the unit will run at 100% capacity to preheat the tank.
Once the tank is hot, it will resume normal
operation.) The lit burner will stay at 25% of its rated
capacity unless the demand on the system exceeds
25%. At this point, the burner output will exactly track
with the demand. In other words, if the demand on the
system is 55%, the burner will be running at 55%
output. As the system demand drops down below
25%, the burner will continue to run at 25% until the
system demand drops to 11%. At this point, the
burner will be shut down. The controller will not fire
the burner again until the demand goes back to 14%
or higher. Then, the burner will again fire and run at
25% of its rated capacity. What this results in is a
modified time proportioning system for a system
demand below 25%, and exact demand tracking for
any system demand over 25%.
A two-burner GTS operates in much the same way
with a few slight differences. As demand increases
and reaches 8%, one of the burners will fire and run
at 25% of its rated capacity. This burner will run at
25% of its capacity until the system demand reaches
13%. At this point, the lit burner will be ramped up in
output, tracking with the total system demand. Once
the system demand reaches 30% (60% demand on
the one lit burner), the controller will fire the second
burner. Both burners will now be lit and running and
they will track the system demand together. In other
words, if the system demand is 48%, both burners
will be running at 48% of their rated capacities. Next,
as the system demand falls and reaches 25%, one of
the burners will shut off and the other burner will be
brought back up to 50% of its rated capacity. This
results in an overall system output of 25%. As the
demand continues to fall and reaches 13%, the one
operating burner will remain at 25% of its rated
capacity. When the total system demand falls
and reaches 5%, the one burner left running will be
shut off.
Operation:
Valve and burner modulation
Modulation types: valves and burners.
Operation