tekmar 422 Universal Reset Module - Manual (Page 22)

© 2007 D 422 - 08/07 22 of 32
Mix 1 Mode
A mixing device allows the control to reduce the boiler
water temperature down to a lower water temperature. A
mixing device when used with a boiler sensor also allows
the control to protect the boiler from sustained flue gas
condensation and thermal shock.
The Mix 1 outputs are built-in to the 422. The type of mixing
device for Mix 1 is selected using the Mix 1 Mode setting.
The mixing devices that can be selected are variable speed
injection (VAr) and floating action (FLt).
•
• Locate the Mix 1 Mode setting in the Adjust menu.
Mixing Operation Section G
Zone Load Shedding Section F
Boiler Enable Section E
If the 422 is one of many controls that can call for heat to
a single boiler or there is a boiler sequencer other than a
tekmar Stager (Boiler Control 264, 265, 268), operating
multiple boilers or multiple stages, then the boiler sensor
must be located on the return pipe of the boiler(s).
When the sensor is located on the return, the 422 provides
a boiler enable. The 422 no longer tries to control the
boiler supply water temperature directly, but allows another
operating control such as an aquastat to regulate the boiler
supply temperature.
When there is a requirement for heat from the 422 mixing
device(s), or a DHW Demand, or a Setpoint Demand is
present, the 422 boiler contact closes to enable the boiler.
The boiler contact remains closed until heat is no longer
required.
When the boiler sensor is located on the boiler return, the
control is able to provide boiler return protection through the
use of a mixing device. This protects the boiler sustained
flue gas condensation and thermal shock.
*Important note: The tN4 DIP switch cannot be set to Boiler
while the Boiler Sensor DIP switch is set to Return.
To operate the control without a boiler sensor and prevent
the control from displaying an error message, set the boiler
sensor DIP switch to Return and power up the control
without the boiler sensor connected.
The control operation will be similar to that as having the
boiler sensor on the return except that boiler return protection
is no longer provided.
The 422 has two tN4 communication buses. The first bus
is dedicated for a mix water temperature and is known as
Mix 1. The second bus can be selected to be either boiler
or mixing depending on the tN4 DIP switch position. When
the tN4 DIP switch is set to Mixing, the second bus is known
as Mix 2. Mix 2 requires that a Mixing Expansion Module
be connected to the Mix 2 tN4 bus.
A Mixing Expansion Module is required in order to use the
second mixing temperature. The Mixing Expansion Module
operates at the percent output that the 422 determines is
required.
Each of the following settings must be set for the Mix 1
bus and for the Mix 2 bus when the tN4 DIP switch is set
to Mix 2.
If the boiler temperature approaches the boiler minimum
setting, the control can turn off certain high temperature
zones in order to reduce the load on the boiler. This is
known as Zone Load Shedding. Zones are shed in the
following order:
1. The second stage of any 2-stage thermostats which
have “BOIL” selected as their heat source in order of
decreasing priority. Priority is determined by the address
number of the thermostat (b:01 is the highest priority,
3:24 is the lowest priority).
2. The first stage of any thermostats on the boiler bus,
again, in order of decreasing priority. The first stage
of the highest priority thermostat (lowest address
number) will not be shed unless there is also a setpoint
or DHW call.
When the boiler supply temperature goes above the
minimum setting, the control begins restoring the load by
turning first stages back on in the reverse order that they
were shed, followed by second stages in the reverse order
that they were shed.