2.7.5 Example with Varying Flow over 1 Year
The example below is calculated on the basis of pump
characteristics obtained from a pump datasheet.
The result obtained shows energy savings in excess of 50%
at the given flow distribution over a year. The payback
period depends on the price per kWh and price of
Adjustable frequency drive. In this example, it is less than a
year when compared with valves and constant speed.
Energy savings
P
shaft
=P
shaft output
Flow distribution over 1 year
500
[h] P
1000
1500
2000
200
100
300
[m
3
/h]
400
Q
175HA210.10
Table 2.4
Figure 2.11
m
3
/h
Distri-
bution
Valve regulation
Adjustable frequency
drive control
% Hours Power Consump-
tion
Power
Consump
tion
A
1
- B
1
kWh
A
1
- C
1
kWh
350
5
438
42.5
18.615
42.5
18.615
300
15
1314
38.5
50.589
29.0
38.106
250
20
1752
35.0
61.320
18.5
32.412
200
20
1752
31.5
55.188
11.5
20.148
150
20
1752
28.0
49.056
6.5
11.388
100
20
1752
23.0
40.296
3.5
6.132
Σ
100 8760
275.064
26.801
Table 2.5
2.7.6 Better Control
If a Adjustable frequency drive is used for controlling the
flow or pressure of a system, improved control is obtained.
A Adjustable frequency drive can vary the speed of the fan
or pump, thereby obtaining variable control of flow and
pressure.
Furthermore, a Adjustable frequency drive can quickly
adapt the speed of the fan or pump to new flow or
pressure conditions in the system.
Simple control of process (flow, level or pressure) utilizing
the built-in PID control.
2.7.7 Cos
φ
Compensation
Generally speaking, the VLT
®
HVAC Drive has a cos
φ
of 1
and provides power factor correction for the cos
φ
of the
motor, which means that there is no need to make
allowance for the cos
φ
of the motor when sizing the
power factor correction unit.
2.7.8 Star/Delta Starter or Soft-starter not
Required
When larger motors are started, it is necessary in many
countries to use equipment that limits the start-up current.
In more traditional systems, a star/delta starter or soft-
starter is widely used. Such motor starters are not required
if a Adjustable frequency drive is used.
As illustrated in the figure below, a Adjustable frequency
drive does not consume more than rated current.
Introduction to VLT® HVAC D...
VLT
®
HVAC Drive Design Guide
2-12
MG11BB22 - VLT
®
is a registered Danfoss trademark
2
2
