© 2013
400_D - 09/13
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Domestic Hot Water Tank Operation
Section C
A DHW Call is required in order for the control to provide
heat to a DHW tank. Once the control registers a DHW Call,
it will display the “DHW” icon under Calls in the display.
This can be done in three ways:
DHW Tank Aquastat
If a DHW aquastat (mechanical switch) is used to
apply a DHW Call, the tank is heated to the aqua-
stat temperature setting. A dry contact or 24 V (ac)
signal is applied across the DHW Call terminals on the
House Control.
DHW Tank Sensor
A DHW tank sensor provides superior temperature
control of the tank compared to an aquastat. The
House Control automatically detects whether a DHW
sensor is installed. The upper limit of the DHW tem-
perature is set by the DHW setting. The DHW tank dif-
ferential is fixed to 6°F (3°C).
•
•
DHW
Calls
DHW Call
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DHW Mode
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The control has five different settings available for DHW
Mode 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 the DHW tank
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 DHW tank temperature
recovery.
DHW MODE 1 - DHW in Parallel no Priority
When a DHW Call is present, the DHW pump is activated.
The boiler system pump does not turn on, but may operate
based on either a Boiler or Setpoint Call.
It is assumed that the DHW pump will provide adequate
flow through the heat exchanger and the boiler.
DHW MODE 2 - DHW in Parallel with Priority
When a DHW Call is present, the DHW pump is activated.
The boiler system pump and all boiler temperature zones
are shut off through tekmarNet
®
communication to achieve
DHW priority.
It is assumed that the DHW pump will provide adequate
flow through the heat exchanger and the boiler.
DHW - Boiler Target
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When a DHW Call is present, a boiler target is
determined.
When using a DHW Tank Aquastat, the boiler target is
set to the DHW Exchange setting.
When using a DHW Tank Sensor, the boiler target is
set to the DHW Occupied setting plus 40°F (22°C).
•
•
ON Or OFF
ON
DHW
Pump
ON Or
OFF
Zone
Valve
Boiler System
Pump
DHW Mode = 1
OFF
ON
DHW
Pump
OFF
Zone
Valve
Boiler System
Pump
DHW Mode = 2
When using a tekmarNet
®
Setpoint Control, the boiler
target is set to the devices Exchange Supply setting.
If there are multiple devices calling for heat, the boiler target
is set to the highest temperature requirement.
•
tekmarNet
®
Setpoint Control with Sensor
A DHW Call is provided through the tekmarNet
®
system. This can be done through the Boil Expansion
tN4 terminals with a tekmarNet
®
setpoint device such
as a Setpoint Control 161.
•
