tekmar 274 Boiler Control - Manual (Page 19)

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If the building is not up to temperature at the correct time,
the BOOST setting should be lengthened and the setback
timer should be adjusted accordingly. If the building is
up to temperature before the required time, the BOOST
setting should be shortened and the setback timer should be adjusted accordingly. If the system is operating near
its design conditions or if the supply water temperature
is being limited by settings made in the control, the time
required to bring the building up to temperature may be
longer than expected.
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 Boiler
Control 274 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.
Bus 1
Network
tekmarNet ® 4
Thermostats
274
Boiler Control 274
The Boiler Control 274 is the system control for a hydronic
heating system. The 274 operates up to 4 on/off boilers,
a domestic hot water tank, and responds to other heating
requirements such as pool heating and snow melting. The
274 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 devices can connect to a single tN4 bus.
Zone Load Shedding (tN4)
Zone load shedding helps protect non-condensing boilers
from sustained flue gas condensation damage. Zone load
shedding starts when the boiler supply temperature is below
the boiler minimum setting and all boilers are operating
at 100% output. Zones are shut off in order of their tN4
address.
Second stage heat zones are the first to shut off starting
with thermostat address b:24, continuing downward until
the last to shut off is b:01.
Once all second stage heat zones are shut off, first stage
zones shut off starting with highest thermostat address
b:24 and ending at the lowest b:01.
When the boiler supply temperature reaches the boiler
minimum, the first stage heating zones turn back on in
order from b:01 to b:24, and then the second stage in order
from b:01 to b:24.
Cycle Length Setting in Adjust Menu (tN4)
The control includes an adjustment for the cycle length.
The cycle length adjustment allows for synchronization of
tN4 zones. An Auto setting allows for the cycle length to
be automatically calculated to balance equipment cycling
and comfort.
In the tekmarNet ® 4 system, all of the tekmarNet ® 4
Thermostats determine the best cycle length for their
zone. The thermostats look at trying to maintain the longest
possible cycle length while keeping temperature swings to
a minimum. The Thermostats do this every cycle and send
their ideal cycle length time to the 274.
In order to operate the system as efficiently as possible,
all of the zones must operate based on the same cycle.
In order to do this, the 274 listens to all of the cycle length
requests from all of the tekmarNet
® 4 Thermostats. The 274
then determines the average cycle length and sends this
information to all of the tekmarNet
® 4 Thermostats, allowing
them to operate on the same cycle.
Indoor Temperature Feedback (tN4)
Indoor feedback applies when the 274 is connected to a
tN4 Thermostat network operating on a boiler bus. Indoor
temperature feedback fine tunes the water temperature of
the system based on the requirements of the thermostats.
Each thermostat tells the tN4 System Control the water
temperature that it requires to heat its zone.
If the zone is becoming too cool, the thermostat asks for
a higher water temperature.
If the zone is becoming too warm, the thermostat asks
for a cooler water temperature.
The 274 provides the highest water temperature required
by all of the thermostats.
The thermostat with the highest water temperature
requirement stays on 100% of its cycle.
The remaining thermostats stay on for a percentage of
their cycles.
Reset Water
Temperature
100%
On Time
85%
On Time
90%
On Time
Device Count (tN4)
The control includes a device count of all the tN4 devices
connected to the boiler bus. This item is always found in
the Miscellaneous Menu called NUM DEV. Use this to
confirm that the correct number of devices are connected
to the boiler bus.
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tekmarNet ® 4 Communication Section M