Zehnder EASY 5.0
74
It is usually necessary to modify P and/or I when the setpoints configured (fan, temperature, etc.) deviate significantly
from the factory setpoints, and/or when the installation (network volume/length, size/volume of the building, etc.) has
an unconventional design, as well as if the machine is under/oversized with an operating point that is far from the
nominal operating point. For example, it is possible to:
■
Increase P supply air fan in LOBBY if the supply pressure setpoint is significantly increased
■
Increase the I supply air fan in LOBBY if the supply network is very short and uneven.
■
Oversizing: increase P and I
■
Undersizing: decrease P and I
The first prerequisite before changing the settings of a PID is to check whether the measurement of the variable to be
controlled (e.g. supply pressure in LOBBY) is stable. If it is unstable, the cause must be determined and rectified. Typical
causes include:
■
The sensor (temperature, pressure, volume flow, etc.) is incorrectly installed and is subject to interferences
(turbulence, radiation, leaks, etc.). In this case, one should try to move the sensor to a more remote place or to calm
the conditions by installing specific devices
■
Presence of an external disturbance that generates air volume instabilities in the machine (e.g. 90° curved air duct
immediately after leaving/entering the unit, gusts of wind, etc.).
■
External disturbance such as dampers or vents opening/closing too quickly - change the opening and closing speeds
of the dampers and leave a minimum opening.
Factory settings of the PID parameters of the LOBBY version fans
P
I
D
Supply air fan VAS
500 Pa
20 seconds
There is no derivative
Return air fan VAR
500 Pa
20 seconds
Definition
Details
Example of a general equation
Influence
P
Proportional
strip
It is the gain reflection; the
output signal is directly
proportional to the
difference between the
setpoint and the
measurement
1/P×(Setpoint-
measurement)
↑P = the output signal
decreases for the same
error
↓ P = the output signal
increases for the same error
If P is too low, the system
becomes unstable.
If P is too high, the system is
slow.
I
Integral
Cancels the static error
(error that the P term cannot
cancel) when the operating
conditions are stable.
1/I×∫
0
t
(Setpoint-
measurement)dt
↑ I = the output signal
decreases for the same
error
↓ I = the output signal
increases for the same error
D
Derivative
Pre-emptive term, not
generally used in ventilation
and air handling because it
causes instabilities in “slow”
systems
The derivative is not used.
Z-MASTER-V1122-CSY-INM-Zehnder Easy5.0
