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74
Variable Air Volume Option — This option can be
used in conjunction with the CO
2
sensor option (ordered
separately). Outside air and exhaust air blower speeds are
independently controlled by variable frequency drives and
modulated based upon space occupancy, which can be
measured by CO
2
. The more people in the space the greater the
CO
2
levels, the more outside air is introduced. This option
eliminates over ventilating the space in less than full condi-
tions. The ERV unit has completely different electrical charac-
teristics when used with a variable air volume option. Refer to
Tables 2 and 3.
Operating Sequence
OCCUPIED MODE — While in occupied mode, the 62M
ERV will operate per the ERV Timer option (scheduling
program), the CO
2
sensor input, a combination of the schedul-
ing option and CO
2
input, or the economizer accessory.
Additionally, the low temperature lockout (LTLO) function
locks out the 62M ERV if the outdoor-air temperature entering
the wheel is below the set point. The LTLO is factory set at
–10 F, and can be field adjusted from –30 F to 100 F.
Occupied Mode, with CO
2
Sensor — When the CO
2
sensor
is used, it will measure the space CO
2
levels in parts per
million (ppm). The 62M ERV CO
2
setting is factory set at
1,000 ppm but can be adjusted from 0 ppm to 2,000 ppm.
When either the scheduling program and/or the CO
2
sensor
calls for ERV operation, the ERV will activate the following:
• ERV wheel
• Outdoor air blower motor
• EXH blower motor
• Two-position damper opens
NOTE: The two-position damper option may slightly delay
activation of the ERV blower motor.
Occupied Mode, with Frost Protection
— In the occupied
mode, the frost protection option will eliminate frost build-up
on the ERV wheel using exhaust air. It is activated via a
pressure differential across the ERV wheel. This set point is
field set from 0.2 in. wg to 2.0 in. wg and must be set to 150%
of the normal static pressure across the wheel. The frost protec-
tion feature is automatically locked out above 35 F.
NOTE: If the outdoor-air temperature is below 35 F, a dirty
wheel may incorrectly activate the frost control feature if the
differential pressure across the wheel exceeds the set point.
When the frost protection option is activated the following
will occur:
• ERV wheel turns on.
• Outdoor air blower motor turns off.
• EXH blower motor is on.
Occupied Mode, with the Pre-Heat Option
— In the occu-
pied mode, the pre-heat option provides frost protection for the
ERV wheel and slightly warms the outdoor air. This feature is
factory set to activate at –5 F, and can be field adjusted from
–30 F to 100 F. It is recommended that this set point be set at
the frost threshold for the region in which it is used.
If desired, this feature may also be activated via a field
supplied pressure differential switch to determine if frost build
up has occurred on the ERV wheel.
Occupied Mode, with the Economizer Accessory
—When
using the economizer option, this allows for up to 100%
outside air to be brought in for free cooling. During free
cooling, the rooftop unit mechanical cooling may or may not
be operating depending on the set points used with the rooftop
unit. When using the economizer accessory, it is recommended
that the minimum position be set to the closed position and the
ERV should be set such that it is locked out when the econo-
mizer opens far enough to bring in the same level of outdoor air
as the ERV.
If desired, this feature may also be activated via a
field-supplied pressure differential switch to determine if frost
build- up has occurred on the ERV wheel.
During free cooling, the following occurs:
• ERV wheel is turned off.
• Outdoor air blower is turned off.
• EXH blower motor turns on.
• Two-position outdoor-air damper is closed (if used).
• Two-position EXH damper is opened (if used).
• Stop/jog option will periodically rotate the ERV wheel
to clean it during wheel bypass operation. This feature is
factory set to activate every 10 minutes, for 20 seconds
of operation. Both settings can be adjusted from 0 to 10
minutes.
Wheel Bypass Option
— When using the wheel bypass option
(with the stop/jog option), this allows free cooling through the
wheel limited by the ERV airflow cfm limits. With this option
the unit can be in free cooling or not depending on the tempera-
ture of the outdoor-air compared to the set point. When not in
free cooling, the ERV will not operate. When in free cooling:
• ERV wheel is turned off.
• Outdoor-air blower is turned on.
Fig. 81 — Blower Motor Pulley Adjustment
Fig. 82 — Belt Alignment