22-82 Work Point Calculation
Option:
Function:
Example 1
: Speed at System Design Working Point is known:
From the data sheet showing characteristics for the specific equipment at different speeds, simply
reading across from the H
DESIGN
point and the Q
DESIGN
point allows us to find point A, which is the
system design working point. The pump characteristics at this point should be identified and the
associated speed programmed. Closing the valves and adjusting the speed until H
MIN
has been
achieved allows the speed at the no flow point to be identified.
Adjustment of par. 22-81
Square-linear Curve Approximation
then allows the shape of the control
curve to be adjusted infinitely.
Example 2:
Speed at System Design Working Point is not known: Where the Speed at System Design Working
Point is unknown, another reference point on the control curve needs to be determined by means
of the data sheet. By looking at the curve for the rated speed and plotting the design pressure
(H
DESIGN
, Point C), the flow at that pressure Q
RATED
can be determined. Similarly, by plotting the
design flow (Q
DESIGN
, Point D), the pressure H
D
at that flow can be determined. Knowing these two
points on the pump curve, along with H
MIN
described above, allows the adjustable frequency drive
to calculate the reference point B and thus to plot the control curve that will also include the system
design working point A.
VLT
®
HVAC Drive Instruction Manual
7 How to Program the Adjustable Frequency
Drive
MG.11.AB.22 - VLT
®
is a registered Danfoss trademark
7-47
7
