19
Installation, operation and maintenance instructions - VMGFE102
Example: AR05 078 at Eurovent conditions of 3.7 l/s
Water fl ow rate, l/s
P
ressur
e dr
op
, kP
a
Legend
1
‘’Unit pressure drop (including internal water piping)/fl ow rate’’ curve
2
With the valve open the pressure drop read (111 kPa) gives point A on the curve.
A
Operating point reached with the valve open.
3
With the valve open the fl ow rate achieved is 4,8 l/s: this is too high, and the valve
must be closed again.
4
If the valve is partially closed, the pressure drop read (65 kPa) gives point B on the
curve.
B
Operating point reached with the valve partially closed.
5
Wih the valve partially closed the fl ow rate achieved is 3,7 l/s: this is the required
fl ow rate and the valve is in an adequate position.
12.2 - Units with hydronic module and fi xed-speed pump
The nominal system fl ow rate is controlled by a manual valve
that must be on the water leaving piping of the system (item
20 in the typical hydronic circuit diagram).
Due to the pressure drop it generates in the hydronic system
this fl ow control valve permits adjustment of the pressure/
system fl ow rate curve in accordance with the pump pressure/
fl ow rate curve to obtain the nominal fl ow rate at the
required operating point.
The fl ow rate reading in the hydronic module is used as
means of control.
The pressure of the transported fl uid is measured by sensors
installed in the pump suction line and at the unit outlet
(items 7 and 10) and the system calculates the fl ow rate
associated with the diff erential pressure.
Direct access to the fl ow rate reading is possible via the user
interface (please refer to the control manual).
As the total system pressure drop is not known exactly at the
start-up, the water fl ow rate must be adjusted with the
control valve to obtain the specifi c fl ow rate for this system.
Hydronic circuit cleaning procedure
•
Open the valve fully (item 20).
•
Start-up the system pump.
•
Read the plate heat exchanger pressure drop by taking
the diff erence of the readings of the pressure gauge
connected to the unit inlet and outlet (item 19).
•
Let the pump run for two consecutive hours to clean the
hydronic circuit of the system (presence of solid
contaminants).
•
Take another reading.
•
Compare this value to the initial value.
•
If the fl ow rate has decreased, this indicates that the
screen fi lter must be removed and cleaned, as the
hydronic circuit contains solid particles. In this case close
the shut-off valves at the water inlet and outlet (item 17)
and remove the screen fi lter (item 1) after emptying the
hydronic section of the unit (item 6).
•
Purge the air from the circuit (items 5 and 15).
•
Renew, if necessary, to ensure that the fi lter is not
contaminated.
Water fl ow control procedure
When the circuit is cleaned, read the fl ow rate at the user
interface and compare the value obtained with the theoretical
selection value. If the fl ow rate measured is higher than the
value specifi ed this means that the total system pressure
drop is too low compared to the available static pressure
generated by the pump. In this case close the control valve
and read the new fl ow rate.
Proceed by successively closing the control valve until you
obtain the specifi c pressure drop that corresponds to the
nominal fl ow rate at the required unit operating point.
NOTE: If the system has an excessive pressure drop in
relation to the available static pressure provided by the
unit pump, the nominal water fl ow rate cannot be obtained
(the resulting fl ow rate is lower) and the temperature
diff erence between the water heat exchanger entering and
leaving water will increase.
To reduce the pressure drops of the hydronic system, it is
necessary:
•
to reduce the individual pressure drops as much as
possible (bends, level changes, accessories, etc.).
•
to use a correctly sized piping diameter.
•
to avoid hydronic system extensions, wherever possible.
12.3 - Units with hydronic module and variable-speed
pump - pressure diff erential control
The system fl ow rate is not controlled by a nominal value.
It is adjusted by the system (pump speed variation) to
maintain the user-selected pressure diff erential between the
unit inlet and outlet.
The pressure sensor at the unit outlet (item 10 in the typical
hydronic circuit diagram) is used as the means of control.
