Watts tekmar 294 - DHW Operation - Calls and System; DHW Call Methods; System Pump Operation for DHW; DHW Application Types

IOM-T-294 2205 © 2022 tekmar
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Domestic Hot Water (DHW) Operation
DHW Call
A domestic hot water (DHW) call operates the boilers at a fixed
temperature to heat a DHW storage tank. The DHW call status
is displayed in the System Inputs on the display. A DHW call
can be created in one of three ways:
DHW Tank Aquastat
If a DHW Tank Aquastat (mechanical switch) is used to apply
a DHW Call, the tank is heated to the aquastat temperature
setting. A dry contact or 24 V (ac) signal is applied across the
DHW Call terminals.
DHW Sensor
A DHW Tank Sensor 078 (not included) is installed in a
temperature well to measure the tank temperature. A DHW
call is created when the tank temperature falls to the DHW
Tank Occupied minus the DHW Differential. The DHW call
is removed when the tank reaches the DHW Tank Occupied
setpoint.
DHW
Differ
ential
DHW Tank Setpoint
ON
OFF
tekmarNet
®
Setpoint Control
A DHW call is provided through the tekmarNet
®
system by
using a tekmarNet
®
Setpoint Control 161 or 162.
Boiler Target Temperature during a DHW Call
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 fixed
at the DHW Tank Occupied (or Unoccupied when using a
schedule) setpoint plus 40°F (22.0°C).
• When using a tekmarNet
®
Setpoint Control, the boiler target
is set to the device’s Exchange Supply setting.
If there are multiple devices calling for heat, the boiler target is
set to the highest temperature requirement.
Programmable Schedule and Away Scene
When the programmable schedule is On, additional setpoints
for the unoccupied period become available.
When using a DHW tank aquastat, select DHW Exchange
Unoccupied to On to heat, or select Off to not heat the DHW
tank during the unoccupied time periods.
When using a DHW Sensor, the control heats to the DHW
Tank Unoccupied setpoint.
During the Away scene, DHW calls are ignored.
DHW Application Type
The DHW Type setting selects the piping configuration. Three
options are available:
• System
• Side Arm
• Dedicated
DHW Type System Operation
The indirect DHW tank is piped in the boiler system loop. When
a DHW call is present, the DHW Pump turns on.
Heating System
Loop
System Pump
The DHW System Pump setting selects the operation of the
system pump during DHW calls.
Off
The system pump does not turn on during indirect DHW
operation. Select Off when an indirect DHW tank is piped in
parallel to the central heating system and located the boiler
system loop.
DHW
Pump
ON
System
Pump OFF
ON
The primary pump turns on during indirect DHW operation.
Select On when the indirect DHW tank piped is piped in
primary/secondary in the boiler system loop.
DHW
Pump
ON
System
Pump ON