Lochinvar 000 - 2 - Manual (Page 46)

Electronic Temperature Controller
(Operator)
A 2-stage electronic temperature controller is provided on the
unit and it serves to maintain a user selectable temperature set
point. Ultimately, the temperature controller delivers 24VAC to
the ignition module and pressure switch when it senses heat
mode is desired. It also activates the pump relay. If more heat is
needed, it activates the high fire stage.
Ignition Module
(Controlled by Electronic Temperature Controller)
One ignition module is provided on the unit. Upon sensing the
24VAC delivered to it by the electronic temperature controller,
the ignition module checks for a shorted pressure switch and
then, provided the air switch isn't shorted, supplies 120VAC to
its blower output relay and waits for a pressure switch signal.
Two Speed Blower (Controlled by Ignition
Module and Relay Board)
A single 2-speed blower on the 985,000 - 2,065,000 Btu/hr
models (single 1-speed blower on the 495,000 - 745,000 Btu/hr
models) provide combustion air to the unit. The blower is
provided with a high and low speed tap. The blower operates
in tandem with the ignition module when a call for heat signal
is received. Depending upon the number of stages in operation,
the blower's speed may increase or decrease accordingly.
Pressure Switch (Activated by Blower Turning
On)
One pressure switch is provided to monitor the blower On/Off
operation. Upon a call for heat, 24VAC is delivered to the
pressure switch. If the blower generates adequate air pressure,
the pressure switch closes to deliver 24VAC to the ignition
module pressure switch monitoring input terminal.
Prepurge (Ignition Module Function)
Once the ignition module sees a 24VAC input from the
pressure switch, it runs the blower for approximately 15
seconds in order to purge the combustion chamber of any
unburned fuel/air mixture.
Trial for Ignition (Ignition Module Function)
Once the ignition module has completed its prepurge period, it
turns on the hot surface igniter. Once the hot surface igniter's
current draw reaches a proper level, the ignition module begins
a trial for ignition period of approximately 25 seconds to allow
time for the igniter to reach the ignition temperature necessary
to ignite the fuel/air mixture.
Igniter (Controlled by Ignition Module)
One igniter is provided in order to ignite the fuel/air mixture
and its on/off operation is controlled by the ignition module.
Relay Board (Controlled by Electronic
Temperature Controller and Ignition Module)
A small relay board is provided on the 985,000 - 2,065,000
Btu/hr models to switch the blower from low to high speed and
to deliver power from the low fire stage (Stage 1) to the high
fire stage (Stage 2) depending upon the electronic thermostat's
settings.
Ignition (Ignition Module Function)
Once the trial for ignition period has been completed, the
ignition module sends 24VAC to the gas valves on the low fire
stage (Stage 1). Gas valves should open and allow gas to flow
to the burners in Stage 1 being energized. The fuel/air mixture
should ignite from the hot surface igniter. Once this voltage has
been sent to the valves, the hot surface igniter is turned off. The
ignition module then monitors the status of the flame and will
either allow ignition to continue or shut down the gas valves
should flame not be proven and proceed to a Flame Failure
condition. If flame was proven briefly during the ignition
period, the module may not proceed to Flame Failure, but
rather post-purge and then go into another trial for ignition.
Heat Transfer Process (Gas Valves, Burner,
and Heat Exchanger)
Once flame has been proven, the ignition module will hold the
gas valves open as long as there is proof of flame and a call for
heat is present. If the low fire stage cannot provide enough heat
to raise the system temperature, the electronic temperature
controller turns on the high fire stage. The high fire stage will
operate until the system water temperature shows a gain that
can be handled by low fire operation. The high fire stage shuts
off at this point. When the low-fire stage alone produces more
heat than is required, the electronic temperature controller
turns off the call for heat.
Post-Purge (Ignition Module Function)
When 24VAC is removed from the ignition module's
thermostat input, the module turns off the gas valves and
maintains the blower for approximately 25 seconds in order to
allow the combustion chamber to be purged of all combustion
by-products.
Pump Delay (Electronic Thermostat Function)
When the electronic thermostat removes 24VAC from the
ignition module, it continues to hold the pump relay on for 30
seconds in order to get the remaining heat out of the
combustion chamber. The pump then turns off to prevent the
heat in the water from going back into the combustion chamber
and up the flue.
Idle (Electronic Thermostat Function)
After completion of the post-purge cycle, the unit will go into
an idle state whereby the electronic thermostat continuously
monitors the water temperature until the water temperature
drops to levels that require additional heat.
Hydronic Heating Boilers and
Domestic Water Heaters
46