Bell & Gossett P86272B VS Variable Speed Pump Control - Manual (Page 11)

11
Setback and Boost (Sbc )
• The Setback (Sbc ) setting has no effect if the VS is in
Thermostat mode (see pg. 6).
• When the VS is initialized to run in the Setback mode, the
EXT Input can be connected to an external clock or switch
(see Fig. 5). When the E X T to C O M terminals are
shorted/closed, the VS will switch to Setback mode and
reduce the temperature of the Secondary loop by the
number of degrees selected. The VS switches from Setback
mode back to Boost mode when the E X T
to C O M
terminals are opened. In the Boost mode, the VS will
increase the secondary loop temperature by the number of
degrees selected in the setback for a period of one hour to
allow faster heat recovery to the zone.
Example: If the calculated Secondary water temperature is
130°F and the Setback (Sbc) is set to 10°F, when the EXT
Input is shorted/closed, the calculated water temperature
would immediately change to 120°F. When the EXT input is
opened, the VS will go into boost mode and the calculated
water temperature would immediately change to 140°F for
a period of one hour. After the one hour of operation, the
calculated water temperature will return to the standard
operating mode of 130°F.
• The rule of thumb for adjusting the Setback (Sbc) with
baseboard radiation is to decrease the water temperature
4° for each degree you wish to lower the ambient space
temperatures. Therefore, if you wish the space
temperatures to be 5° colder at night or when the building
is not occupied, adjust the Setback (Sbc) to 20°. With
radiant heat, adjust the Setback (Sbc) only 1 or 2 degrees
for each degree you wish to lower the space temperature.
OPERATION SETTINGS
Gain (GAn)
• The Gain (GAn) controls how aggressive the VS will change
the injection pump’s speed.
• A higher Gain (GAn) setting will generate larger changes. A
lower Gain (GAn) setting will generate smaller changes.
• If the system tends to stay below the set point, increase the
gain. If the system overshoots and undershoots the set
point rapidly, decrease the gain.
Low Return (LOr ) Available with Return Sensor
Mode only (Startup menu r option)
• The Low Return (LOr) setting is designed to help speed
recovery in the event of low boiler return water tempera-
tures. The boiler manufacturer may require a minimum
return water temperature to protect the boiler. Check with
the boiler manufacturer for the specified temperature.
• If the VS registers that the temperature of the water
returning to the boiler is below the Low Return (LOr ), the VS
will immediately reduce the Injection pump speed by half
and not allow the speed to increase again until the return
temperature rises to the Low Return (LOr ) setting. This
means that the VS will decrease the load on the Primary
loop, but will still provide some heat to the Secondary loop.
NOTE: If a minimum return water temperature is not specified
by the boiler manufacturer, or if the Secondary loop size is
such that it will have little impact on the Primary loop
temperature, the Boiler Return sensor (see Figure 2) may not
be installed. If the return sensor is not connected, the control
will ignore the LOr setting and no error will be displayed.
TROUBLESHOOTING
No Display:
Check the 120VAC power into the Blue input wires. If power is
present, turn the power to the VS off and then back on.
Display shows or flashes OPn or SHt :
Follow the procedure for Sensors on next page.
OUTPUT light is OFF when heat is required:
Check the Outdoor Cutoff (COF ) setting (see pg. 9). If the
outdoor temperature sensor reading is above the setting, the
VS will not give heat. Also check if the VS is in the Thermostat
(tt ) mode (see pg. 6). In the Thermostat (tt ) mode, the VS will
never give heat if terminals EXT and COM are not shorted
together.
OUTPUT light is FLASHING when heat is required:
The Output light flashes when the Secondary loop pump is on
but the Injection pump is off. This will occur when the VS is
satisfied with the temperature of the Secondary loop. See
Insufficient Heat conditions below.
OUTPUT light is FLASHING or ON but Secondary loop
pump is not running:
Turn off the power to the Secondary loop pump. The VS
power must remain connected. Then disconnect all wires
attached to the VS Black wires. Test for continuity across the
Black wires. If the wires are continuous, the VS is working
properly. Check the Secondary loop pump and its power.
OUTPUT light is ON but Injection pump is not running:
If the Output light is on, the Injection pump should be running.
However, if it is running at a very low speed, it may be hard to
detect. It is possible to test the Injection pump output with a
voltmeter which can read at least 120VAC.
Place the leads of the voltmeter across the power inputs of the
Injection pump. At the highest speed, the AC Volt reading will
be approximately 120VAC. As the speed is decreased, the
reading will decrease. At the lower speeds, the reading may
fluctuate by several Volts. This is considered to be normal.
OUTPUT light is OFF or FLASHING but
Injection pump is running:
When the Output light is off or flashing, the Injection pump
should not be running. Check the wiring to see if any other
control, a HOA switch, or other switch input is causing the
pump to run. Turn the power off to the VS. If the Injection
pump continues to run, the VS is not the cause of the pump
running.
WARNING: This Bell & Gossett control is strictly an
operating control; it should never be used as a pri-
mary limit or safety control. All equipment must have its
own certified limit and safety controls required by local
codes. Failure to follow these instructions could result in
serious personal injury, death and/or property damage.
WARNING: This test can only be performed with the
Injection Pump power connected. This test should
only be performed by a qualified electrician or electrical
contractor. Failure to follow these instructions could result
in serious personal injury, death and/or property damage.