Watts tekmar 289 - Sequence of Operation; Central Heating Operation Cycle; Establishing Steam Phase; Minimum On Time Setting

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Sequence of Operation
Central Heating Operation
The control operates either one or two steam boilers to heat a
building using an Outdoor Reset algorithm to progressively run
the steam boiler longer when the outdoor air temperature is
colder. In this way the building heat loss is replaced by heat from
the boilers.
The central heating operates on a cycle that consists of four
phases:
1. Establishing Steam
2. Heat On
3. Heat Off
4. Cool Down
The cycle repeats until the central heating system is shut off
when the outdoor air temperature exceeds the Warm Weather
Shut Down (WWSD) setting. The Cool Down phase requires
the installation of a condensate return sensor and this phase
will be skipped when not installed.
Establishing Steam
In steam heating systems, there is a time delay between
when the steam boiler or steam valve is turned on and when
the steam reaches the furthest radiator in the system. It is
important for the control to determine this time delay to ensure
proper heating in all rooms. The control uses either a con-
densate return sensor or a minimum run time to complete the
Establishing Steam phase.
Condensate Return Sensor
The best method to determine establishing steam is to measure
the condensate return temperature when steam enters the
furthest radiator in the building. If possible, install condensate
return sensor on the return pipe of the furthest radiator.
Alternatively, the condensate return sensor may be installed in
the boiler room. It is important that the Universal Sensor 071
be strapped to the bottom of the return pipe in order to
measure the condensate return temperature.
To set the Establishing Steam setting, use the Max Heat
Override at 100% output to operate the system. Record the
Condensate sensor reading when steam reaches the furthest
radiator. Then exit the Max Heat Override, and enter the
recorded condensate return temperature into the Establishing
Steam setting in the System menu.
Minimum on Time
In cases where a condensate return sensor cannot be
installed, a Minimum On Time can be set to account for the
establishing steam time period. Setting a Minimum On Time for
a steam system can be problematic because a system takes
more time to reach operating temperature from a cold start
than when it is hot from a previous cycle.
To set the Minimum On Time setting, use the Max Heat
Override at 100% output to operate the system. At the same
time, start a stopwatch timer. Measure the amount of time
required for steam to reach the furthest radiator. Then exit
the Max Heat Override and enter the recorded time as the
Minimum On Time setting.
Last Radiator
One Pipe System:
Radiator
Vent
Best
Main
Air Vent
OK
Supply Main
Condensate Return
Sensor Location
Two Pipe System:
Most Distant Radiator
Thermostatic
Trap
Best
Supply
Air Vent
Return
Air Vent
Condensate Return
Sensor Location
Float and
Thermostatic
Trap