Table of Contents
Advertisement
The purpose of regulation is to keep the residual ∆P constant when there is an increase in the counter–pressure, with reference
to the following graph.
Starting from nominal work point (A), the increase in counter-pressure (due, for instance to a damper closing) causes a shift in
the fan work point along the curve towards point B, with the ensuing increase in pressure. The logic tries to restore the work
point by decreasing the speed and move back towards work point C.
To avoid continuous speed adjustment without giving the fan time to adjust to the new speed value and consequently not
allowing the pressure transducer to measure the new differential pressure value, there is a "scan time" that sets the time between
the two fan signal variations.
The EC control parameters are under the "Fan" menu, accessible through the "Service" password.
The default values are are the following:
•
scan time = 60 sec;
•
step voltage = 10 (corresponds to a 0.1V
•
hyst flow = 25
•
Fan modulation delay = 120 sec.
The "Fan modulation delay" is used whenever the unit is started in order to allow the fan to start. Once this time elapses, speed
adjustment begins.
This parameter is in the "Regulations" menu that can be accessed with the "Service" password.
Version 38
Figure 11-7: constant head fan operation curve
signal increase / decrease).
DC
162
Advertisement
Table of Contents
