Greenheck DFD Series Installation, Operation And Maintenance Manual page 71

®
Programming Sure-Aire™
Greenheck's Sure-Aire™ Differential
Pressure Controller provides either a
2-10 Vdc or 4-20 mA electrical output
signal. The output signal is linearly
proportional to the pressure range of
differential pressure controller. The
ranges for Greenheck's Sure-Aire
controllers are listed in the table.
Calculating Flow from Differential Pressure
The volumetric flow through the fan (cfm) can be calculated from the equation:
∆P
CFM = K

where K is the K-factor for the specific fan model and size, ∆P is the measured differential pressure across the
inlet cone (inches W.C.), and  is the air density (lb/ft
this document.
Calculating Flow from Voltage Signal
If using a 2-10 Vdc output signal from a differential pressure controller, this equation can be used to calculate the
flow:
(V - 2) P
max
CFM = K
8 
where V is the output voltage of a 2-10 Vdc transmitter and P
being used (inches W.C.).
Calculating Flow from Current Signal
If using a 4-20 mA output signal from a differential pressure controller, this equation can be used to calculate the
flow:
(mA - 4) P
CFM = K
16 
where mA is the output current of a 4-20 mA transmitter and P
controller being used (inches W.C.).
Density Corrections
Air density, , is affected by elevation and temperature. The Greenheck Sure-Aire Differential Pressure Controllers

allow the user to input the elevation for the application. This elevation input automatically updates the density
used for the flow calculation.
The Remote Temperature Sensor will adjust the air density value in the controller based on the sensor
measurement when Temperature Compensation is set to 'Yes'. This density compensation will affect the flow rate
displayed on the controller. If Temperature Compensation is set to 'No', the air density value will be a function of
standard air (70°F/21°C).
The density being used by the Sure-Aire controller can be viewed on the main menu by scrolling up or down
through the settings.
®
Greenheck Part Number
100-240 VAC
384799
384800
384801
384802
384803
max
Controller ∆P Range
24 VAC / VDC
384986
384987
384988
384989
384990
3
). K-factors for Greenheck models are found on the back of
is the maximum pressure range of the controller
max
is the maximum pressure range of the
max
Document 478758
Programming Sure-Aire™
P max
(inches W.C.)
(inches W.C.)
0-8.30 8.30
0-22.14 22.14
0-41.52 41.52
0-83.04 83.04
0-138.40 138.40
Programming Sure-Aire™
1