Finned copper tube gas boilers & water heaters – Boiler Manual
32
Relay Board
The relay board is located in the control tray. It provides sequencing
of the gas valves and blower(s) based on the staging controller's
input. It also provides the following time delays for proper unit
operation:
• A 40 second prepurge when stage 1 is energized.
• A 10 second pressure switch sequencing delay when the blowers
switch from low fire to high fire. The delay enables the blower to
come up to speed before the high pressure side of the pressure
switch confirms proper air flow.
These time delays are set within the separate time delay board
connected to the relay board.
Gas Pressure Switch
An optional low and/or high gas pressure switch will shut
down the 24V circuit if excessively high or low gas pressure exists
in the gas train or supply piping.
BTC Staging Control
The staging control is located at the front of the control tray. It
utilizes various temperature sensors to calculate boiler/water heater
demand and adjust the stages as required. Various features of the
control can be adjusted from the 3-button panel on the controller.
To change settings of the staging controller, press and hold all three
buttons approximately 2 seconds until the “adjust” screen appears,
then release them. The staging controller provides 6 modes of
operation based on the requirements of the system. The desired
mode can be set manually from the controller. Each mode is defined
below. Refer to the control manufacturer’s documentation for more
information on the controller and its adjustment features.
At the rear of the controller, two DIP switches are provided to allow
an installer to modify staging control operation. These switches are
factory set to provide a "lockout" with minimum adjustment
capabilities in the field. However, for experienced installers and
operators, changing these switch settings can offer many fine-tuning
features. Consult the control manufacturer's documentation for
more information on the controller and its adjustment features.
DO NOT change DIP switch or controller settings
unless you have completely read and understood this
document and the control manufacturer's instructions.
Doing otherwise will lead to improper stage control
operation.
Mode 1: Setpoint control
. Dominator piped in parallel with
the system. The firing stages are operated to provide a setpoint
temperature at the boiler/water heater outlet.
SETPOINT OPERATION - The control operates the boiler stages
to maintain the programmed temperature at the boiler/water heater
outlet sensor whenever a heat demand is present.
Mode 2: Setpoint control
. Dominator piped in primary/
secondary configuration. An additional system sensor is required
to properly control the system supply (primary loop) temperature.
The firing stages are operated to provide a setpoint temperature in
the primary loop.
SETPOINT OPERATION - The control operates the boiler/water
heater stages to maintain the programmed temperature at the supply
sensor (primary loop sensor) whenever a heat demand is present.
Mode 3: Domestic Hot Water (DHW) generation.
Dominator
piped in parallel with the storage tank. DHW demand from sensor
located in tank or pool supply pipe. The firing stages are operated
to provide a setpoint temperature and maintain DHW tank
temperature.
DHW OPERATION - The control operates to maintain the
programmed tank target temperature at the outlet sensor whenever
a DHW demand is present. A DHW demand is generated whenever
the temperature sensed by the DHW sensor drops below the
programmed tank target temperature by 1/2 the programmed
differential, adjustable from
2 to 10°F
,
-17 to -12°C
. The demand
remains until the temperature sensed by the DHW sensor rises
above the programmed tank target temperature plus 1/2 the
programmed differential.
Mode 4: Outdoor reset control.
Dominator piped in parallel
with the system. The firing stages are operated to provide outdoor
reset temperature control at the boiler/water heater outlet.
OUTDOOR RESET OPERATION - The control operates the
water heater/boiler stages to maintain the calculated target supply
temperature at the boiler outlet sensor. The temperature is calculated
by the outdoor reset feature, which increases the target boiler outlet
temperature as outdoor temperature drops. Whenever the outdoor
temperature is greater than the WWSD (Warm Weather Shut Down)
setting, the control ignores the call for heat.
OUTDOOR RESET WITH DHW OPERATION - A DHW tank
controlled by a pump provides reset override whenever DHW
generation is required. In Mode 4, reset override will occur if
the staging controller receives a signal across the "STPT DEM"
and "DEM SIG" terminals of the terminal strip. (i.e., closing a tank
aquastat switch wired to these terminals). In this case, the control
will temporarily override outdoor reset and increase the target
temperature to
180°F
,
82°C
to provide sufficient heat to satisfy
the DHW requirement.
Mode 5: Outdoor reset control.
Dominator piped in primary/
secondary configuration. An additional system sensor is required
to properly control the system supply (primary loop) temperature.
The firing stages are operated to provide outdoor reset temperature
control in the primary loop.
OUTDOOR RESET OPERATION - The control operates the
water heater/boiler stages to maintain the calculated target supply
temperature at the supply sensor. The temperature is calculated by
the outdoor reset feature, which increases the target supply tem-
perature as outdoor temperature drops. Whenever the outdoor
temperature is greater than the WWSD (Warm Weather Shut Down)
setting, the control ignores the call for heat.
