Rockwell Automation FANM FanMaster Energy Saving Package - Manual (Page 13)

FanMaster Overview 1-7
Allen-Bradley® FanMaster™ Energy Saving Package Installation Manual - Publication FANM-IN001B-EN-P – December, 2009 PN-65329
Proportional Heating and Cooling Control
Proportional control of heating or cooling is used when the actual amount of
heating or cooling applied by the HVAC unit is variable. That is, the heating
or cooling element is modulated by a mechanical or electrical valve. The
valve modulates how much heating or cooling is provided and is adjusted by
the existing control system to meet the actual demand. FanMaster allows for
the selection of proportional control for either heating or cooling or both.
When selected, FanMaster runs the fan at the minimum speed when the
temperature sensors detect that heating and cooling are off, and will vary the
fan from its minimum to its maximum speed proportional to the temperature
differential detected by the temperature sensors in the air flow before and
after the heating or cooling elements. This mode allows FanMaster to
achieve energy savings during the time the HVAC unit is idle and to
modulate the fan speed based on the amount of heating or cooling requested
by the existing control system, achieving an optimum energy requirement
based on the heating or cooling load.
When in proportional mode, the “Delta T Min” and “Delta T Max” setup
values for cooling and heating determine the slope of the fan speed increase.
A typical value of five degrees for “Delta T Min” is acceptable for most
installations. The “Delta T Max” setup value should be adjusted so that the
fan can achieve its maximum speed when the proportional valve controlling
heating or cooling is at 100%. The HVAC unit manufacturer can provide the
design delta T (temperature rise) of the specific unit for both heating and
cooling modes of operation. The heating delta T is typically higher than the
cooling delta T. If the unit is older or the delta T data is unavailable,
FanMaster can be initially run with the default values. The actual delta T
values of the unit can be determined by using the existing temperature
control setpoints to force the unit into a full heating or full cooling mode.
Adjust the room temperature to a very high or low setpoint and allow the
HVAC unit to run at 100% heating or cooling for about 30 minutes or until
the maximum delta T can be observed on the FanMaster System Status
screen. Perform this test for both heating and cooling. Use the actual
measured delta T values for the “Delta T Max” settings for heating and
cooling.
TIP: Although the maximum fan speed is adjustable, there is seldom a
reason to adjust this value to less than 100%. The only exception would be
for a system that is oversized to the point that the full horsepower capacity
of the fan is not required under any conditions. This could occur if the size
of the area heated or cooled is reduced after installation or if the HVAC unit
is oversized for other reasons. In this case, the maximum fan speed can be
safely reduced, provided that adequate capacity remains for extremely hot
or cold days. For reference, a reduction of the maximum speed to 95% will
deliver 95% of the airflow with a fan energy cost reduction of 16%. A
reduction to 90% reduces the fan energy cost by 23%.