tekmar 421 Mixing Reset Module - Manual (Page 11)

11 of 20 © 2007 D 421 - 08/07
tekmarNet ® 4 Communication Section A
tekmarNet ® 4 (tN4) communicates between tN4 devices
(thermostats, Reset Module and Expansion Modules). Each
tN4 device is connected to a tN4 communication bus using
two wires. Each tN4 bus adjusts a single water temperature
in the system using indoor temperature feedback. The Mixing
Reset Module 421 allows for one tN4 bus. This allows you
to control a system with one water temperature.
A system that has more than one tN4 bus is referred to as
a tN4 network.
Outdoor Reset Module
The Mixing Reset Module 421 is the system control for a
hydronic heating system. The 421 operates a single heat
source such as a boiler and one mixing device. The 421
also coordinates and optimizes the operation of all the tN4
thermostats.
tN4 Thermostat
The tN4 thermostat operates heating, cooling, and or
ventilation equipment for a zone. Several tN4 thermostats
may work in a group when operating a cooling system. Up
to 24 tN4 thermostats can connect to a single tN4 bus.
Outdoor Reset Section B
In a heating system, the rate of heat supplied to the building
must equal the rate of which heat is lost. If the two rates are
not equal, the building will either cool off or over heat.
The rate of building heat loss depends mostly on the outdoor
temperature. Outdoor Reset allows a hot water heating
system to increase the water temperature, adding heat to
the building, as the outdoor temperature drops. The rate
at which the water temperature is changed is defined by
the characterized heating curve.
Characterized Heating Curves
A characterized heating curve determines the amount the
supply water temperature is raised for every 1° drop in
outdoor air temperature. There is a characterized heating
curve for each tN4 communication bus.
The characterized heating curve takes into account the
type of terminal unit that the system is using. Since different
types of heating terminal units transfer heat to a space using
different proportions of radiation, convection and conduction,
the supply water temperature must be controlled differently.
Each tN4 bus is assigned a terminal unit setting that the
control uses to vary the supply water temperature to suit
to the terminal unit used. This improves the control of the
air temperature in the building.
Indoor Temperature Feedback
Most buildings have internal heat gains due to people,
passive solar heating and mechanical or electrical equipment.
Likewise, wind loads cause a building to lose heat faster than
during design conditions. If only the outdoor temperature is
measured, the control cannot compensate for these internal
heat gains or loses and the building may over or under heat.
In order to maintain the most comfortable temperature,
the control uses indoor temperature feedback from tN4
thermostats in order to adjust the water temperature on
each tN4 bus on a continual basis.
Sequence of Operation
tN4
Test
Item
Menu /
Do not apply power
Zone A1 Zone A2 Power Zone Group Pump A Zone A3 Zone B1 Zone B2 Zone B3
tN4
tektra 996-02 Zone Group Pump B
Bus 1 Bus 2
Network
tekmarNet ® 4
Thermostats
tekmarNet ® 4
Thermostats
Test
Wait
3
seconds
Test
Hold
for 6
seconds