The Boiler Control 274 operates up to four on/off boilers to provide outdoor reset operation, domestic hot water and setpoint
operation with priority. When operating as a tN4 System Control, the 274 can connect with up to 24 tN4 devices on a single
boiler bus. The 274 has primary pump sequencing capabilities along with a flow proof or combustion air damper proof
demand.
Additional functions include:
tN4 Compatible
•
24 Hour, 5-1-1, 7 Day Schedule
•
Flow or Combustion Air Proof
•
Four On/Off Boilers
•
Equal Run Time Rotation
•
Primary Pump Sequencing
•
DHW Operation
•
Optional DHW Sensor
•
Setpoint Operation
•
tN4
Boiler
Bus
VIEW
1
Primary
DHW
13
24
MenuItem
Boiler Control 274
One tN4, Four Stage Boiler & DHW / Setpoint
Do not apply power
2513
46
BRet/
ComtN4
OutCom
Boil
+
–
DHW
Sup
Boiler Demand
DHW / Setpoint Demand
Proof Demand
Zone Load Shedding
Priority Override
EMS Input Signal
Relay1Relay2Relay3Relay4C.A. /
Setback
Rotate
Off
EMS
Demands
Exercise
Off
Test
Modes
1 Up to 4 On/Off Boilers
2 Up to 2 On/Off Boilers & 2 Pumps
3 Up to 2 Lo/Hi Boilers
4 1 Lo/Hi Boiler & 1 Pump
5 1 Three Stage Boiler & Pump
6 1 Four Stage Boiler
Made in Canada by
tekmar Control Systems Ltd
tektra 1020-02
Power 115 V ±10% 60 Hz 7 VA, 1150 VA max.
Relays 230 V (ac) 5 A 1/3 hp
Demands 20 to 260 V (ac) 2 VA
Signal wiring must be rated at least 300 V.
20
Alert
1719109121114131615
DHW
/ P2
18
Prim
Power
P1 L N
Boiler
Demand
222187
Pump Sequencer
Fixed Last
Fixed Lead
First On / Last Off
First On / First Off
off
red
red
For maximum heat,
press and hold Tes t
button for 3 seconds.
The Control Settings section of this brochure describes
the various items that are adjusted and displayed by the
control. The control functions of each adjustable item are
described in the Sequence of Operation.
The control uses a Liquid Crystal Display (LCD) as the
method of supplying information. You use the LCD in
order to setup and monitor the operation of your system.
The control has four push buttons (Menu, Item, ▲, ▼) for
selecting and adjusting settings. As you program your
control, record your settings in the ADJUST menu table,
which is found in the second half of this brochure.
Menu
All of the items displayed by the control are organized
into five menus (View, Adjust, Time, Schedule, and Misc).
These menus are listed on the top left hand side of the
display (Menu Field). To select a menu, use the Menu
button. By pressing and releasing the Menu button, the
display sequences between the five menus. Once a menu
is selected, there will be a group of items that can be viewed
within the menu.
Item
The abbreviated name of the selected item will be displayed
in the item field of the display. To view the next available
item, press and release the Item button. Once you have
reached the last available item in a menu, pressing and
releasing the Item button will return the display to the first
item in the selected menu.
The items can be quickly scrolled through by holding the
Item button and then pressing the ▼ button. To rapidly
scroll through the items in the reverse order, hold the
Item button and press the ▲ button.
Adjust
To make an adjustment to a setting in the control, begin by
selecting the ADJUST, TIME, SCHEDULE or MISC menu
using the Menu button. Then select the desired item using
the Item button. Finally, use the ▲, and / or ▼ button to make
the adjustment.
Additional information can be gained by observing the
Status field of the LCD. The status field will indicate
which of the control’s outputs are currently active. Most
symbols in the status field are only visible when the
VIEW menu is selected.
Display
Menu Field
Displays the
current menu
Status Field
Displays the current
status of the
inputs, outputs and
control’s
operation
Buttons
Selects Menus, Items
and adjusts settings
Number Field
Displays the current value
of the selected item
MenuItem
Item Field
Displays the current
item selected
Symbol Description
PRIMARY PUMP
Displays when primary pump 1 or
primary pump 2 is in operation
BOILER
Displays which boiler stage is
operating
LOCK
Displays when adjusting Access level if
Switch is set to lock.
WARNING
Displays when an error exists.
COMMUNICATION BUS
Displays when tN4 thermostats are
connected.
DHW PUMP
Displays when the DHW Pump is
operating
Schd Wake
UnOcc Sleep
Away
BOILER PUMP
Displays when the boiler pump 1, 2, 3,
or 4 are operating
COMBUSTION AIR DAMPER
Displays when the combustion air
damper relay is closed
SCHEDULE MASTER
Displays when the 274 is a schedule
master
WARM WEATHER SHUT DOWN
Displays when the control is in warm
weather shut down
MINIMUM & MAXIMUM
Displays when the boil target or the boil
supply is at a minimum or maximum
Displays the control operation as
indicated by the text
Access Level
The access level restricts the number of Menus, Items,
and Adjustments that can be accessed by the user. The
Access Level setting is found in the Miscellaneous (MISC)
Menu. Select the appropriate access level for the people
who work with the control on a regular basis. There are
three Access Level Settings:
•
User (USER): Select this access level to limit the highest
number of settings available to the end user.
Installer (INST): Select this access level to limit some of
•
the settings available to the installer. This is the factory
default access level.
Advanced (ADV): Select this access level to have complete
•
access to all of the control settings. In the following menu
tables, the appropriate access level needed to view each
item is shown in the Access column.
Note: the Lock / Unlock switch on the front of the control
must be set to unlock to change the access level.
Sequence of Operation
In order for the control to have a target water temperature there must be a demand. There are three different demands the
control can have: boiler demand, DHW demand, and setpoint demand.
Boiler Demand Section A
Once the control receives a boiler demand it calculates a
target water temperature based on the characterized heating
curve to provide outdoor reset for space heating. The control
can receive a boiler demand three different ways:
1. By applying 20-260 V (ac) to the boiler demand
terminals (21 & 22) when the DIP switch is set to
Demands.
2. From an Energy Management System (EMS) by
applying a 0-10 or 2-10 V (dc) signal to terminals 2 &
3 when the DIP switch is set to EMS.
3. From a tN4 device. This requires a tN4 thermostat to
be wired to terminals 1 & 2 so that the call for heat
can go over the communication bus.
20-260 V (ac)
2221
Boiler
Demand
Demand
23
OutCom
+
–
OROR
0-10 or
2-10 V (dc)
from EMS
21
tN4 Com
–
tN4
Demand
Outdoor Reset Section B
In a heating system, the rate of heat supplied to the building
must equal the rate at 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 as a function
of outdoor temperature is defined by the characterized
heating curve.
Characterized Heating Curve
A characterized heating curve determines the amount the
target water temperature is raised for every 1° drop in outdoor
air temperature.
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.
The control uses the terminal unit setting to vary the supply
water temperature to suit the terminal unit being used. This
improves the control of the air temperature in the building.
Boiler Characterized Heating Curve
Boiler
Design
Terminal
Unit
Outdoor
Design
Boiler
Indoor
Decreasing Outdoor Temperatures
Increasing Water Temperatures
Terminal Unit Setting in Adjust Menu
Select the appropriate terminal unit in the adjust menu.
This will change the shape of the characterized heating
curve to better match the heat transfer properties of that
specific terminal unit.
Hydronic Radiant Floor (HRF1)
A heavy or high mass, hydronic radiant floor system. This
type of a hydronic radiant floor is embedded in either a thick
concrete or gypsum pour. This heating system has a large
thermal mass and is slow acting.
Hydronic Radiant Floor (HRF2)
A light or low mass, hydronic radiant floor system. Most
commonly, this type of radiant heating system is attached to
the bottom of a wood sub floor, suspended in the joist space,
or sandwiched between the subfloor and the surface. This
type of radiant system has a relatively low thermal mass
and responds faster than a high mass system.
Radiator (RAD)
A radiator terminal unit has a large heated surface that is
exposed to the room. A radiator provides heat to the room
through radiant heat transfer and natural convection.
Baseboard (BASE)
A baseboard terminal unit is similar to a radiator, but has
a low profile and is installed at the base of the wall. The
proportion of heat transferred by radiation from a baseboard
is greater than that from a fin-tube convector.
Boiler Terminal Unit Defaults
When a terminal unit is selected for boiler zones, the
control loads default values for the boiler design, boiler
maximum supply, and boiler minimum supply temperatures.
The factory defaults can be changed to better match the
installed system. Locate the Boiler Terminal Unit setting in
the Adjust menu.
Fancoil (COIL)
A fancoil terminal unit or air handling unit (AHU) consisting
of a hydronic heating coil and either a fan or blower. Air is
forced across the coil at a constant velocity by the fan or
blower and is then delivered into the building space.
Fin–tube Convector (CONV)
A convector terminal unit is made up of a heating element
with fins on it. This type of terminal unit relies on the natural
convection of air across the heating element to deliver
heated air into the space. The amount of natural convection
is dependant on the supply water temperature to the heating
element and the room air temperature.
Terminal Unit
High Mass Radiant
Low Mass Radiant
Fancoil
Fin-Tube Convector
Radiator
Baseboard
BOIL DSGNBOIL MAXBOIL MIN
120°F (49°C)140°F (60°C)OFF
140°F (60°C)160°F (71°C)OFF
190°F (88°C)210°F (99°C)140°F (60°C)
180°F (82°C)200°F (93°C)140°F (60°C)
160°F (71°C)180°F (82°C)140°F (60°C)
150°F (76°C)170°F (77°C)140°F (60°C)
Room Setting in Adjust Menu
The Room setting is the desired room air temperature, but
it is not measuring a room temperature sensor. Instead,
the Room setting parallel shifts the heating curve up or
down to change the target water temperature. Adjust the
Room setting to increase or decrease the amount of heat
available to the building. Once the heating curve has been
set up properly, the Room setting is the only setting that
needs to be adjusted. The default Room setting is 70°F
(21°C), and it can be adjusted for both the occupied and
unoccupied periods.
The outdoor design temperature is typically the coldest
outdoor air temperature of the year. This temperature is
used when doing the heat loss calculations for the building
and is used to size the heating system equipment. If a cold
outdoor design temperature is selected, the supply water
temperature rises gradually as the outdoor temperature
drops. If a warm outdoor design temperature is selected,
the supply water temperature rises rapidly as the outdoor
temperature drops.
Boiler Indoor Setting in Adjust Menu
The boiler indoor design temperature is the indoor
temperature the heating designer chose while calculating the
heat loss for the boiler water heated zones. This temperature
is typically 70°F (21.0°C). This setting establishes the
beginning of the boiler characterized heating curve.
Boiler Design Setting in Adjust Menu
The boiler design supply temperature is the boiler water
temperature required to heat the zones at the outdoor design
temperature, or on the typical coldest day of the year.
(Default automatically changes based on terminal unit
setting)
Warm Weather Shut Down (WWSD) Setting in Adjust
Menu
Warm Weather Shut Down disables the heating system when
the outdoor air temperature rises above this programmable
setting. When the control enters into WWSD, the LCD will
indicate this in the status field. WWSD is only available
when the DIP switch = Demands. The boilers will operate
when a Domestic Hot Water (DHW) demand or a Setpoint
Demand is present.
Boiler Operation Section C
The 274 is able to operate up to four on/off boilers as a heat
source. For proper operation of the boilers, the 274 must be
the only control that determines when a boiler is to fire.
*Important note: The boiler operator, or aquastat, remains
in the burner circuit and acts as a secondary upper limit
on the boiler temperature. The boiler aquastat temperature
setting must be adjusted above the 274’s boiler maximum
setting in order to prevent short cycling of the burner.
Mode
The 274 control is capable of staging single stage, two
stage, three stage and four stage on/off heat sources. As
well, in certain modes of operation, the control is capable
of controlling the individual boiler pumps. The control has 6
modes of operation based on the type of staging and pump
operation that is desired. The following describes the modes
of operation.
Mode 1: 4 Single stage boilers and primary pump.
Mode 2: 2 Single stage boilers with individual boiler
pumps and primary pump.
Mode 3: 2 Two stage boilers and a primary pump.
Mode 4: 1 Two stage boiler and individual pump.
Mode 5: 1 Three stage boiler and individual pump.
Mode 6: 1 Four stage boiler and primary pump.
Relay 1Relay 2Relay3Relay 4
Mode 1
Mode 2
Mode 3
Mode 4
Mode 5
Mode 6
Boiler 1Boiler 2Boiler 3Boiler 4
Boiler 1Boiler 1
Boiler 1
Stage 1
Boiler 1
Stage 1
Boiler 1
Stage 1
Boiler 1
Stage 1
Supply
Supply
Sensor
Sensor
Primary
Primary
Pump
Pump
Return
Return
Sensor
Sensor
Pump
Boiler 1
Stage 2
Boiler 1
Stage 2
Boiler 1
Stage 2
Boiler 1
Stage 2
Boiler 2Boiler 2
Boiler 2
Stage 1
Boiler 1
Pump
Boiler 1
Stage 3
Boiler 1
Stage 3
Boiler
Boiler
Pumps
Pumps
Pump
Boiler 2
Stage 2
not used
Boiler 1
Pump
Boiler 1
Stage 4
Boiler Target Temperature
The boiler target temperature is determined by connected tN4
devices or by a Boiler, DHW or Setpoint demand received
by the control. An Energy Management System (EMS) can
also give a boiler target. The tN4 devices determine the
highest water temperature required and then request 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.
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. The MIN segment is displayed in
the LCD while viewing the boiler supply or target and when
the boiler target is boiler minimum and the boiler supply is
less than boiler minimum plus 5°F (2.5°C). Set the Boiler
Minimum setting to the boiler manufacturer’s recommended
temperature.
Boil MIN + 5°F (2.5°C)
Boiler Differential
e
e
r
B
B
o
o
i
i
l
l
W
W
a
a
e
e
T
T
t
t
e
e
r
r
MIN segment on
r
u
u
t
t
a
a
r
r
e
e
p
p
m
m
Boil MIN
MED
The MED setting is selected if the boiler that is used has
a medium thermal mass. This means that the boiler either
has a large water content and a low metal content or a
low water content and a high metal content. This is typical
of many modern residential cast iron boilers or steel tube
boilers.
The Med mass setting provides a moderate response to
the heating system.
HI
The HI setting is selected if the boiler that is used has a
high thermal mass. This means that the boiler has both
large water content and a large metal content. A boiler that
has a high thermal mass is relatively slow in coming up to
temperature. This is typical of many commercial cast iron
and steel tube boilers.
The Hi mass setting provides a slow response to the
heating system.
Boiler Maximum Setting in Adjust Menu
The boiler maximum is the highest temperature that the
control is allowed to use as a boiler target temperature.
The MAX segment is displayed in the LCD while viewing
the boiler supply or target and when the boiler target is
boiler maximum and the boiler supply is greater than boiler
maximum minus 5°F (2.5°C). Set the boiler maximum
setting to the boiler manufacturer’s recommended temperature. At no time does the control operate the boiler
above 248°F (120°C).
MAX
segment
on
B
B
o
o
i
i
l
l
W
W
a
a
e
e
T
T
t
t
r
r
e
e
e
e
p
p
m
m
e
e
r
r
u
u
t
t
a
a
r
r
MAX
segment
on
Boil MAX
Boil MAX – 5°F (2.5°C)
Boiler Differential
Stage Delay Setting in Adjust Menu
The Stage Delay is the minimum time delay between the
firing of each stage. After this delay has expired the control
can fire the next stage if it is required. This setting can be
adjusted manually or set to an automatic setting. When the
automatic setting is used, the control determines the best
Rotation
The Rotate feature changes the firing order of the boilers
whenever one boiler accumulates 48 hours more run time
than any other boiler. Rotation will be forced if any boiler
accumulates 60 hours more run time. After each rotation,
the boiler with the least running hours is the first to fire and
the boiler with the most running hours is the last to fire.
This function ensures that all of the boilers receive equal
amounts of use. When the Rotate / Off DIP switch is set
to the Off position, the firing sequence always begins with
lowest boiler to the highest boiler.
12
720 hours
672 hours
21
672 hours
720 hours
To reset the rotation sequence (without regard to historical
running hours), toggle the Rotation DIP Switch Off for 3
seconds and on again. Note that the running hours (see
Run Time) in the View menu also need to be reset if you
want the rotation sequence and running hours display to
be synchronized.
stage delay based on the operation of the system.
Boiler Mass Setting in Adjust Menu (per boiler)
Match the boiler mass setting with the thermal mass
characteristics of each boiler. The boiler mass settings
also adjusts the inter-stage delay time when operating with
an automatic differential.
LO
The LO setting is selected if the boiler that is used has
a low thermal mass. This means that the boiler has very
small water content and has very little metal in the heat
exchanger. A boiler that has a low thermal mass comes
up to temperature quite rapidly when fired. This is typical
of many copper fin-tube boilers.
The Lo mass setting provides a fast response to the heating
system.
In some applications, it may be desirable to have the last
boiler fire last at all times while the firing sequence of
the remaining boilers is changed using Equal Run Time
Rotation. This configuration is typical of installations where
the boiler plant includes higher efficient boilers and a single
less efficient boiler. The lesser efficient boiler is only desired
to be operated when all other boilers in the plant are on
and the load cannot be satisfied. This rotation option is
selected by setting the Fixed Last / Off DIP switch to Fixed
Last. With a fixed last rotation, the last boiler is the last to
stage on and the first to stage off.
Fixed Lead & First On / First Off
In some applications, it may be desirable to have the first
boiler fire first at all times while the firing sequence of the
remaining boilers is changed using Equal Run Time Rotation.
This rotation option is selected by setting the Fixed Lead /
Off DIP switch to the Fixed Lead position.
When using the Fixed Lead rotation option, a selection must
be made between First On / Last Off and First On / First Off
using the DIP switch.
When First On / First Off is selected, the lead boiler is always
staged on first and staged off first. This configuration is typical
of installations where the boiler plant includes similar boilers
but the first boiler is required to be the first to fire in order to
establish sufficient draft for venting.
Fixed Lead & First On / Last Off
When First On / Last Off is selected, the lead boiler is always
staged on first and staged off last. This configuration is typical
of installations where the boiler plant includes a single higher
efficient boiler with lesser efficient boilers. The lead boiler
is the high efficiency boiler, therefore it is the last boiler to
be sequenced off.
Boiler Run Time in View Menu
The running time of each boiler is logged in the view menu.
To reset the running time, select the appropriate Boiler Run
Time in the View menu and press and hold the Up and Down
buttons simultaneously until CLR is displayed.
Boiler Differential Setting in Adjust Menu
An On/Off heat source must be operated with a differential
in order to prevent short cycling. The boiler differential can
be fixed or automatically determined by the control. The Auto
Differential setting balances the amount of temperature swing
in the boiler supply temperature with boiler on times, off times,
and cycle times. This reduces potential short cycling during
light load conditions.
Manual Differential
Differential = 10°F (6°C)
165°F (74°C)
160°F (71°C)
155°F (68°C)
Boiler
On
Boiler
On
Target + 1/2 Differential
Target
Target – 1/2 Differential
Automatic Differential
Off
Differential
Time
On
Heating Load
Boiler Staging Mode - Lo/Hi or Lo/Lo in Adjust Menu
When using multi-stage boilers, a selection must be made
regarding the staging order of the boiler(s). This adjustment
is made in the ADJUST menu of the control.
Lo/Hi: If the Lo/Hi staging option is selected the control stages
in sequence all of the stages in a single boiler. Once all of the
stages are turned on, the control then stages in sequence all
of the stages of the next boiler in the rotation sequence.
Lo/Lo: If the Lo/Lo staging option is selected, the control
stages all of the Lo stage outputs in all of the boilers first.
Once all of the boilers are operating on their Lo stages, the
control then operates the second stage in each boiler in the
same order.
Boiler Fire Delay Setting in Adjust Menu
(per boiler)
The Boiler Fire Delay sets the time it takes for the boiler to
generate flame from the time the boiler turns on.
Boiler Contact Closed
Fire Delay
Burner On
Time
Combustion Air and Alert Settings Section D
Relay Setting in Adjust Menu (C.A. Damper / Alert)
The control includes an auxiliary relay that can be used either
for a combustion damper/venting device or an Alert. Selection
is made through the Relay item in the Adjust menu.
When the Relay is set to Alert, terminals 15 and 16 close
whenever a control or sensor error is detected, or when a
warning or limiting condition is detected. When the alert
contact closes, refer to the Error Messages section of this
brochure to determine the cause of the alert and how to
clear the error.
Boiler Alarm
For the Boiler Alarm item to appear in the Adjust menu, the
Relay must be set to Alert. If no temperature increase is
detected at the boiler supply sensor within this delay period,
the Alert relay will close and the control will display the Boiler
Alarm error message. All boilers continue to operate if this
error is present. To clear the error, press and hold the up and
down buttons simultaneously for 5 seconds while viewing the
error message in the View menu.
Combustion Air (C.A.) Damper
When the Relay is set to Damper, terminals 15 and 16 operate
a combustion air damper / fan motor or power vent motor. The
Relay closes once a demand is received and the control has
determined that one or more boilers need to be turned on.
Combustion Air Proof Demand Setting in Adjust Menu
The proof demand can be used to prove a combustion air
or venting device if set to C.A. Boiler operation cannot occur
until the proof demand is present. If the proof demand is lost
during operation, the boiler plant is sequenced off.
Combustion Air Proof Demand Delay Setting in Adjust
Menu
The control includes a time delay that is associated with
the proof demand feature in order to determine if the proof
device is functional. Once the C.A. relay closes, the control
allows for this delay to receive the proof demand. If the proof
demand is not received within the delay time, the control will
display an error message.
Combustion Air Damper Delay Setting in Adjust Menu
If the Proof Demand function is set to F P (flow proof) or
OFF, boiler sequencing only occurs once a user adjustable
time delay elapses.
Combustion Air Post Purge
There is a fixed 15 second post purge of the C.A. relay
after the last boiler has turned off, or demand is removed. If
there is a heat demand still present once the last boiler has
turned off, the control can look at the error and determine
if sequencing is to occur in a “short” period of time. If the
control does anticipate staging, the C.A. relay will remain
on. Otherwise, the C.A. relay will be turned off once the 15
second post purge elapses.
Combustion Air Proof Demand Test
The control includes a C.A. proof demand test in order to
determine if the proving device has failed. If the C.A. damper
contacts are opened, the flow proof demand should not be
present after 4 minutes. If the flow proof demand remains,
the control will display an error message.
Domestic Hot Water Operation Section E
DHW operation is only available when the Pump Sequencer
DIP Switch is set to Off.
DHW Demand
DHW Demands come from one of three sources: an external
aquastat, a DHW tank sensor, or a tN4 DHW control.
Once the control detects a DHW Demand, the DHW Demand
segment is displayed in the LCD. If an External Powered
DHW Demand is applied while the DHW sensor is enabled
in the 274, an error message is generated and both demands
are ignored.
A DHW demand from a tN4 Setpoint Control can coexist with
another DHW demand without generating an error message.
The 274 will then use the higher of the two targets.
Powered DHW Demand
The control registers a DHW Demand when a voltage
between 20 and 260 V (ac) is applied across the DHW
Demand terminals 23 and 24. An aquastat or setpoint control
is used to switch the DHW Demand circuit. Program a DHW
Exchange temperature for the Occupied and UnOccupied
events in the Adjust Menu.
• DHW Sensor must be set to Off.
DHW Sensor
The control can register a DHW Demand when A DHW
Sensor is wired to terminals 5 and 6. Once the DHW Sensor
drops 1/2 of the DHW Differential setting below the DHW
Setpoint, the control registers a DHW Demand. Program a
DHW Tank temperature for the Occupied and UnOccupied
events in the Adjust Menu.
The DHW Sensor must be set to On. There cannot be
•
an externally powered DHW demand when using a DHW
sensor.
tN4 Setpoint Control in DHW Mode
The control can register a DHW Demand when a tN4 Setpoint
Control in DHW Mode is wired to terminals 1 and 2. The
DHW Demand is sent over the tN4 communication bus when
the Setpoint Control calls for heat. Program a DHW tank
temperature for the Occupied and UnOccupied events and
the desired supply water temperature required on the tN4
bus in the Adjust Menu of the tN4 Setpoint Control.
Due to large differences between the heating load and the
DHW load, a separate DHW differential should be used
whenever a DHW Demand is present. This will improve
staging and boiler cycling. When using a DHW Sensor, a
DHW Demand is registered when the DHW sensor drops 1/2
of the DHW Differential setting below the DHW setting. The
DHW Demand is satisfied once the DHW Sensor rises 1/2
of the DHW Differential setting above the DHW setting.
OFF
DHW
Differential
ON
DHW Target
Mode OFF / No DHW Generation
All DHW demands are ignored. If this mode is selected while
DHW generation is underway, all DHW operation stops.
Mode 1 - DHW in Parallel with No Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) turns on. The primary pump can operate
when a Boiler Demand is present. It is assumed that the
DHW pump will provide adequate flow through the heat
exchanger and the boiler. Heating zones are unaffected
by DHW operation.
Mode = 1
Boiler Target Temperature during a DHW Demand
If a Powered DHW Demand is present, the boilers are
operated to maintain the DHW Exchange temperature. If a
DHW sensor demand is present, the boilers are operated
to maintain a temperature 40°F above the DHW tank
temperature. If a tN4 demand is present, the primary
pump is turned on according to the device’s reported
requirements and the boilers are operated to maintain the
devices requested target on the bus. The DHW Demand
overrides the boiler reset target temperature, except when
the boiler reset target is higher than the DHW target.
Regardless of DHW settings and requested targets, the
boilers will maintain a supply temperature no higher than
the Boil MAX setting.
DHW During UnOccupied
When using a Powered DHW Demand, the control has a
DHW Exchange UnOccupied setting that allows the installer
to select On or Off. When set to On, and the control receives
a DHW Demand during an UnOccupied or Sleep period,
the control continues operation of the DHW system as it
would during the Occupied and Wake periods. When set to
Off, the control will ignore a DHW Demand for the duration
of the UnOccupied and Sleep periods.
When using a DHW Sensor, a second DHW temperature
setting is available for the UnOccupied or Sleep period.
DIP Switch must be set to Setback to view UnOccupied
items.
During the Away Scene, DHW demands are ignored.
DHW
Pump
Primary
Pump
Mode 2 - DHW in Parallel with Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) turns on. The primary pump can operate
when a Boiler Demand is present. If the boilers are unable
to maintain the boiler target temperature, space heating
zones are shut off sequentially using tN4 communication
in order to provide priority to the DHW tank. For non-tN4
systems, the primary pump shuts off to provide priority. It
is assumed that the DHW pump will provide adequate flow
through the heat exchanger and the boiler.
Mode = 2
OFF
DHW
Pump
Primary
Pump
DHW Mode Setting in the Adjust Menu
The control has six different DHW Modes that affect pump
operation. The required DHW Mode setting will depend on
the piping arrangement of the DHW tank and whether or
not priority for DHW is necessary. DHW Priority stops or
limits the delivery of heat to the building heating system
while the DHW tank calls for heat. This allows for quick
recovery of the DHW tank.
Mode 3 - DHW in Primary/Secondary with No Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) and Primary Pump relay (terminal 18) turn
on. Heating zones are unaffected by DHW operation. This
mode can be used if the DHW tank is piped in parallel and
a DHW valve is installed (need to use an external relay to
power the valve with 24 V (ac) since the DHW pump output
is a 120 V (ac) powered output).
Mode = 3
DHW
Pump
Primary
Pump
Mode 4 - DHW in Primary/Secondary with Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) and Primary Pump relay (terminal 18) turn
on. If the boilers are unable to maintain the boiler target
temperature, space heating zones are shut off sequentially
using tN4 communication in order to provide priority to the
DHW tank.
Mode 5 - DHW in Parallel / Last Boiler with Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) turns on and boiler pump 4 turns off. The control
uses the DHW Exchange Supply Sensor in order to measure
the boiler supply temperature supplied to the indirect tank.
There are two boiler target temperatures, one for the heating
system (BOIL TARGET) and one for the indirect DHW system
(BOIL DHW TARGET). In this mode, the DHW Demand can
only be provided from an External Powered Demand or tN4
Setpoint Control in DHW mode.
All boilers are used for space heating requirements
•
Boiler 2 is used for DHW when there is a DHW demand
•
The dedicated DHW boiler is always boiler 2 (relay 3),
•
even if there are less than 4 boilers.
If boiler 2 is disabled and mode 5 is selected then the
•
dedicated DHW boiler (boiler 2) will not operate.
This DHW mode is only available when control is in
•
Mode = 2
Mode = 5
DHW Exchange
Supply Sensor
DHW Pump
ON
Boiler
OFF
Supply
Sensor
Mode = 4
DHW
Pump
Primary
Pump
OFF
Primary
Pump
Mode 6 – Dedicated DHW
When a valid DHW Demand is present from the DHW
Sensor, the primary pump relay turns on. The DHW Relay
in this mode is used as the DHW recirculation pump and
operates continuously in the Occupied period and cycles
with the primary pump in the UnOccupied period. The boiler
plant is sequenced based only on the DHW Sensor.
All boilers are used for DHW requirements
•
Requires DHW demand from DHW sensor
•
DHW Pump Relay is used for DHW recirculation pump
DHW Priority Override applies to DHW MODE 2 and 4, as
well as Mode 5 if there is a tN4 device with DHW. It prevents
the building from cooling off too much or the possibility of
a potential freeze up during DHW priority.
When set to auto, the priority time is calculated based
on outdoor temperature. At or below the design outdoor
temperature, 15 minutes are allowed for DHW priority. At
or above 70°F, 2 hours are allowed for DHW priority. The
time allowed for DHW priority varies linearly between the
above two points. There is a manual setting also available
in the adjust menu.
The priority timer does not start timing until priority is selected
and both a DHW Demand and a Boiler Demand exist together.
Once the allowed time for priority has elapsed, the control
overrides the DHW priority and resumes space heating.
Automatic Priority Override
2 hours
15 mins
70°F (21°C)
Design Temperature
Conditional DHW Priority
If the boiler supply temperature is maintained at or above
the required temperature during DHW generation, this
indicates that the boilers have enough capacity for DHW
and possibly heating as well. As long as the boiler supply
temperature is maintained near the target, DHW and heating
occurs simultaneously.
DHW Post Purge
After the DHW Demand is removed, the control performs
a purge. The control shuts off the boilers and continues to
operate the DHW Pump and the primary pump if applicable.
This purges the residual heat from the boilers into the
DHW tank. The control continues this purge until one of
the following occurs:
1. A Boiler Demand is detected
2. The boiler supply drops 20°F (11°C) below the DHW
target temperature
3. The DHW tank temperature rises above the DHW
setpoint plus 1/2 DHW Differential
4. Two minutes elapse
DHW Mixing Purge
After DHW operation, the boiler is extremely hot. At the same
time, the heating zones may have cooled off considerably
after being off for a period of time. When restarting the
heating system after a DHW demand with priority, the
control shuts off the boiler and continues to operate the
DHW pump while the primary pump is turned on. This allows
some of the DHW return water to mix with the cool return
water from the zones and temper the boiler return water.
DHW with Low Temperature Boilers
If DHW heating is to be incorporated into a low temperature
system such as a radiant floor heating system, a mixing
device is often installed to isolate the high DHW supply
temperature from the lower system temperature. If a mixing
device is not installed, high temperature water could be
supplied to the low temperature system while trying to
satisfy the DHW demand. This may result in damage to
the low temperature heating system.
The control is capable of providing DHW heating in such a
system while minimizing the chance that the temperature
in the heating system exceeds the design supply water
temperature. In order to do this, the following must be true:
tN4 Present
•
DHW MODE 2 or 4
•
Boil MIN OFF
•
On a call for DHW, the control provides DHW priority by
sending a message on the boiler temperature bus to the tN4
thermostats to shut off the heating zones for a period of time.
The length of time is based on the outdoor air temperature as
described in the DHW Priority Override section. However, if
the DHW Demand is not satisfied within the allotted time, the
boiler shuts off and the heat of the boiler is purged into the
DHW tank. A DHW mixing purge occurs in order to reduce
the boiler water temperature and once the boiler supply
temperature is sufficiently reduced, the DHW Pump contact
shuts off. The heating system zones are allowed to turn on for
a period of time to prevent the building from cooling off. After
a period of heating, and if the DHW Demand is still present,
the control shuts off the heating system and provides heat
to the DHW tank once again.
DHW Boilers Setting in Adjust Menu
Select the number of boilers to use for DHW generation.
Setpoint operation is only available when DHW Mode is
set to Off.
The control can operate to satisfy the requirements of a
setpoint load in addition to a space heating load. A setpoint
load overrides the current outdoor reset temperature in
order to provide heat to the setpoint load.
Setpoint Demand
Setpoint Demands come from one of two sources: a
Powered Setpoint Demand, or a tN4 Setpoint Control.
Powered Setpoint Demand
The control registers a Setpoint Demand when a voltage
between 20 and 260 V (ac) is applied across the Setpoint
Demand terminals 23 and 24. An aquastat or setpoint
control is used to switch the Setpoint Demand circuit.
Program a Setpoint target for the Occupied and UnOccupied
events in the Adjust Menu.
• DHW Mode must be set to Off.
tN4 Setpoint Control
The control can register a Setpoint Demand when a tN4
Setpoint Control is wired to terminals 1 and 2. The Setpoint
Demand is sent over the tN4 communication bus when
the Setpoint Control calls for heat. Program a Setpoint
temperature for the Occupied and UnOccupied events and
the desired supply water temperature required on the tN4
bus in the Adjust Menu of the tN4 Setpoint Control.
• DHW Mode must be set to Off.
A demand from a tN4 Setpoint Control can coexist with another
setpoint demand without generating an error message. The
274 will then use the higher of the two targets.
DIP Switch must be set to Setback to view UnOccupied
items.
During the Away Scene, Setpoint demands are ignored.
Setpoint Mode Setting in the Adjust Menu
The control has four different Setpoint Modes that affect
pump operation. The required Setpoint Mode setting will
depend on the piping arrangement and whether or not
priority is necessary. Setpoint Priority stops or limits the
delivery of heat to the building heating system while the
Setpoint load calls for heat. This allows for quick recovery
of the Setpoint load.
Mode OFF - No Setpoint Operation
All Setpoint demands are ignored. If this mode is selected
while Setpoint operation is underway, all Setpoint operation
ceases.
Mode 1 - Setpoint in Parallel with No Priority
Whenever a Setpoint Demand is present, the boilers are
operated to maintain the setpoint target. The primary
pump does not turn on, but may operate based on a Boiler
Demand. It is assumed that the Setpoint pump will provide
adequate flow through the heat exchanger and the boiler.
Mode = 1
Setpoint
Primary
Pump
Boiler Target Temperature during a Setpoint Demand
If a Powered Setpoint Demand is present, the boilers are
operated to maintain the Setpoint target. If a tN4 demand
is present, the primary pump is turned on according to
the device’s reported requirements and the boilers are
operated to maintain the devices requested target on the
bus. The Setpoint Demand overrides the boiler reset target
temperature, except when the boiler reset target is higher
than the Setpoint target. Regardless of Setpoint settings
and requested targets, the boilers will maintain a supply
temperature no higher than the Boil MAX setting.
Setpoint During UnOccupied
When using a Powered Setpoint Demand, the control has
a Setpoint UnOccupied setting that allows the installer to
select On or Off. When set to On, and the control receives
a Setpoint Demand during an UnOccupied or Sleep period,
the control continues operation of the Setpoint system as
it would during the Occupied and Wake periods. When set
to Off, the control will ignore a Setpoint Demand for the
duration of the UnOccupied and Sleep periods.
Mode 2 - Setpoint in Parallel with Priority
When a Setpoint Demand is present, the boilers are
operated to maintain the setpoint target. The primary
pump can operate when a Boiler Demand is present. If the
boilers are unable to maintain the boiler target temperature,
space heating zones are shut off sequentially using tN4
communication in order to provide priority to the Setpoint
Load. For non-tN4 systems, the primary pump shuts off to
provide priority. It is assumed that the Setpoint pump will
provide adequate flow through the heat exchanger and
the boiler.
Mode 3 - Setpoint in Primary/Secondary with No Priority
Whenever a Setpoint Demand is present, the primary pump
is turned on and the boilers are operated to maintain the
setpoint target.
Mode = 3
Setpoint
Automatic Priority Override
2 hours
15 mins
Primary
Pump
Mode 4 - Setpoint in Primary/Secondary with Priority
Whenever a Setpoint Demand is present, the primary
pump is turned on and the boilers are operated to maintain
the setpoint target. Space heating zones will be shut
off if the boilers are unable to maintain the boiler target
temperature.
Mode = 4
Setpoint
OFF
Primary
Pump
Setpoint Priority Override Setting in Adjust Menu
Setpoint Priority Override applies to SETPOINT MODE 2 and
MODE 4. To prevent the building from cooling off too much or
the possibility of a potential freeze up during setpoint priority,
the control limits the amount of time for setpoint priority.
When set to auto, the priority time is calculated based
on outdoor temperature. At or below the design outdoor
temperature, 15 minutes are allowed for Setpoint priority.
At or above 70°F, 2 hours are allowed for Setpoint priority.
The time allowed for Setpoint priority varies linearly
between the above two points. There is a manual setting
also available in the adjust menu.
The priority timer does not start timing until priority is
selected and both a Setpoint Demand and a Boiler Demand
exist together. Once the allowed time for priority has
elapsed, the control overrides the Setpoint priority and
resumes space heating.
Design Temperature70°F (21°C)
Conditional DHW Priority
If the boiler supply temperature is maintained at or above
the required temperature during setpoint generation, this
indicates that the boiler has enough capacity for setpoint
and possibly heating as well. As long as the boiler target
temperature is maintained, setpoint and heating occur at
the same time.
Setpoint Post Purge
After a tN4 Setpoint Demand is removed, the control
performs a purge. The control shuts off the boilers and
continues to operate the Setpoint Pump and the primary
pump if applicable. This purges the residual heat from the
boilers into the Setpoint load. The control continues this
purge until one of the following occurs:
1. A Boiler Demand is detected
2. The boiler supply drops 20°F (11°C) below the Setpoint
target temperature