Rockwell Automation FANM FanMaster Energy Saving Package - Manual (Page 11)

FanMaster Overview 1-5
Allen-Bradley® FanMaster™ Energy Saving Package Installation Manual - Publication FANM-IN001B-EN-P – December, 2009 PN-65329
Demand Ventilation Mode
A second source of energy savings is achieved by FanMaster's Demand
Ventilation mode. A typical Constant Air Volume HVAC unit is equipped
with a damper that allows a small percentage of outside air to be mixed with
the return air, maintaining an adequate CO
2
level for the building's
occupants. The damper is typically set during installation for a fixed volume
of fresh air, adequate for the worst case condition of full occupancy. The
outside air drawn in through this damper adds to the heating and cooling
load of the HVAC unit, since the outside air is seldom at the required
temperature for the building's occupants. In fact, depending on the local
conditions, the amount of heating or cooling energy which must be supplied
to this air can be quite costly.
When FanMaster reduces the fan speed as described above, it will also
reduce the amount of outside air brought into the HVAC unit. FanMaster's
demand ventilation technique monitors the amount of CO
2
in the return air
and will override the reduced fan speed at any time the CO
2
level rises
above a user specified setpoint. This feature maintains an adequate level of
ventilation while reducing the cost of heating and cooling excess outside air
whenever possible.
The energy savings can be further enhanced by an optional feature which
allows FanMaster to fully close the outside air damper up to 50% of the
time when the CO
2
level does not require additional ventilation. By closing
the damper fully, FanMaster further reduces the cost of heating and cooling
the outside air. The typical outside air damper has a spring return-to-close
mechanism and the existing controls are providing a signal maintaining the
10% open position. FanMaster provides an adjustable duty cycle electrical
relay which can interrupt the electrical signal to the damper allowing it to
close up to 50% of the time. This feature is overridden automatically by the
demand ventilation mode when the CO
2
level exceeds the user specified
setpoint.
Variable Ventilation Mode
This mode allows FanMaster to reduce the HVAC unit fan speed and
includes the option of allowing the damper to be overridden and closed 50%
of the time, exactly as with the Demand Ventilation mode. The difference is
that with the Variable Ventilation mode there is no CO
2
sensor and the fan
speed and damper operation are never overridden by the demand for
additional ventilation. This mode is designed for spaces such as warehouses
or manufacturing with limited occupancy or staffing relative to the volume
of the space and thus no opportunity for buildup of excessive CO
2
.