tekmar 422 Universal Reset Module - Manual (Page 19)

19 of 32 © 2007 D 422 - 08/07
The 422 is able to operate a single, hot water, on-off or
modulating boiler as a heat source. For proper operation of
the boiler, the 422 must be the only control that determines
when the boiler is to fire. In this case, the boiler sensor
should be located on the boiler supply pipe and the Boiler
Sensor DIP switch is set to Supply.
*Important note:
The boiler operator, also known as
an aquastat, remains in the burner circuit and acts as a
secondary upper limit on the boiler temperature. The boiler
operator temperature setting must be adjusted above the
422’s Boiler Maximum setting in order to prevent short
cycling of the boiler burner.
Boiler Target Temperature
The boiler target temperature is determined by connected
tN4 devices or by a DHW or Setpoint demand received by
the control. The tN4 devices determine the highest water
temperature required and then, requests this temperature
on the tN4 boiler bus. The temperature request creates a
Boiler Demand and this is indicated on the display. A DHW
demand and a Setpoint demand have temperature settings
to which the boilers are operated to meet and are able to
override the tN4 bus temperature if required.
The control displays the temperature that it is currently trying
to maintain as the boiler supply temperature in the View
menu. If the control does not presently have a requirement
for heat, it does not show a boiler target temperature.
Instead, “– – –” is displayed in the LCD.
Operation of the tN4 Boiler / Mix 2 Bus
The 422 has two available tN4 communication buses. One
bus is dedicated for a mix water temperature and is known
as Mix 1. The second bus can operate at either boiler
water temperatures or at mixing water temperatures. The
tN4 Boiler / Mix 2 DIP switch affects the operation of the
boiler target temperature. The mix 1 bus is connected to a
Zone manager via the plug on the underside of the board.
The boiler / Mix 2 bus is connected to a Zone manager via
terminals 59 and 60.
Boiler Temperature Zones
When the control is to operate boiler temperature zones,
the Boiler / Mix 2 tN4 DIP switch must be set to Boiler. The
Boiler Bus then operates the boiler directly in order to heat
the zones operated by tN4 thermostats connected to this
bus. The boiler water temperature target will be determined
based upon boiler outdoor reset and indoor feedback from
the tN4 thermostats.
Mix Temperature Zones
When the control is to operate mix temperature zones, the
Boiler / Mix 2 tN4 DIP switch must be set to Mix 2. The
Mix 2 Bus uses a second mixing device to maintain a mix 2
water temperature target. The boiler target temperature is
determined using Boiler Load Reset, in which the boiler
water temperature is maintained at the lowest possible
temperature that satisfies the heating load of the two mixing
devices. See Mixing Operation for more information.
Boiler Minimum
The boiler minimum is the lowest temperature that the
control is allowed to use as a boiler target temperature.
During mild conditions, if the control calculates a boiler
target temperature that is below the Boiler Minimum setting,
the boiler target temperature is adjusted to at least the
Boiler Minimum setting. During this condition, if the boiler is
operating, the minimum segment is turned on in the display
when viewing either the boiler supply temperature or the
boiler target temperature. Set the Boiler Minimum setting
to the boiler manufacturer’s recommended temperature.
•
• Locate the Boiler Minimum setting in the Adjust menu.
Boil MIN + ½ Boiler Differential
Boil MIN
Boil MIN– ½ Boiler Differential
MIN segment on
Boil Water Te
mp
era
tu
re
Boil Water Te
mp
era
tu
re
Boiler Maximum
The boiler maximum is the highest temperature that the
control is allowed to use as a boiler target temperature. If
the control does target the Boiler Maximum setting, and the
boiler temperature is near the boiler maximum temperature,
the maximum segment will be displayed in the LCD while
either the boiler target temperature or the boiler temperature
is being viewed. At no time does the control operate the
boiler above 248°F (120.0°C).
•
• Locate the Boiler Maximum setting in the Adjust menu.
B
oil Wa
te
r T
em
peratur
e
B
oil Wa
te
r T
em
peratur
e
Boil MIN + ½ Boiler Differential
Boil MAX
Boil MIN – ½ Boiler Differential
MAX
segment
on
MAX
segment
on
Fire Delay
The Fire Delay is the time delay that occurs between the
time that the control closes the boiler contact to fire the
boiler and when the burner fires.
•
• Locate the Fire Delay setting in the Adjust menu.
Boiler Contact Closed
Time
Fire Delay
Burner On
Boiler Temperature Control Section C