A SH / S-TRAC MANUAL
20 of 29 Feb 06
Dump mixing valve
During each dump cycle a mixing valve is energised to add cool water to the drain, as the hot tank water is
drained, to reduce the leaving water temperature. As supply water pressure and temperature varies from
location to location, the amount of water the mixing valve can supply to the drain will also vary. If the
mixing water volume is too low, or the mixing water temperature is too high, the resulting drain water
temperature will be too high. To overcome this several things may have to be done.
1. Increase the supply water pressure.
2. Increase the size of the mixing water valve.
3. Reduce the tank drain valve flow rate.
Note: If the drain valve flow rate is reduced too much, the velocity of the water may not be enough to flush
the system of residual minerals.
Tank High Limit
This limit will protect the heat exchanger from firing in the event of a ‘dry’ tank. Set at 400°F (200°C), this
sensor will disable the heating until manually reset. It is located on the heat exchanger primary drum at
approximately the 10:00 or 2:00 o’clock position.
Overflow Protection
When the S-TRAC and humidifier are operating normally (not in a dump cycle) the drain temperature will
always be cool. If the drain temperature becomes hot this is an indication that the tank has overflowed
either with water or steam (leaking drain or fill valve, plugged or kinked steam line, water level too high).
All of these conditions will cause the S-TRAC to lock out on tank overflow.
HUMIDITY CONTROL FUNCTIONS
Humidity setpoint
The S-TRAC has two different methods to set the desired room humidity set point (requested set point).
The setpoint source can either the face mounted setpoint dial or from an external 0-10Vdc source
(10V=100%RH).
The actual setpoint may not match the requested setpoint. As an option the S-TRAC will override the
requested setpoint when external conditions such as low outside ambient temperatures or duct humidity
levels approaching 80% (modulating high humidity limit). The requested humidity setpoint and the actual
setpoint can be measured using the two test points marked REQUESTED RH SP and OPERATING RH
SP using a DC voltmeter from the test points to ground (1V=10%RH).
If a BMS 0-10Vdc input is used to directly modulate the S-TRAC burner output, note that the actual
S-TRAC response range is 2 - 8Vdc. The burner will be at high fire above 8Vdc. No external resets are
activated when the S-TRAC is under direct control.
Control
Dip switch #3
Dip switch #4
Stand Alone
off
off
Remote
on
off
Direct
off
on
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