18
Installation, operation and maintenance instructions - VMGFE102
12 NOMINAL SYSTEM WATER FLOW CONTROL
The water circulation pumps of the AR05 units have been
sized to allow the hydronic modules to cover all possible
confi gurations based on the specifi c installation conditions,
i.e. for various temperature diff erences between the entering
and the leaving water (∆T) at full load, which can vary
between 3 and 10 K.
This required diff erence between the entering and leaving
water temperature determines the nominal system fl ow rate.
Use this specifi cation for the unit selection to fi nd the system
operating conditions.
In particular, collect the data to be used for the control of the
system fl ow rate:
•
Unit without a hydronic module: nominal unit pressure
drop (plate heat exc internal piping),
•
Unit with fi xed-speed pump: nominal fl ow rate,
•
Unit with variable-speed pump, controlled by a diff e-
rence in constant pressure between the unit inlet and
outlet: nominal fl ow rate,
•
Unit with variable-speed pump, controlled by the heat
exchanger temperature diff erence: nominal temperature
diff erence at the heat exchanger.
If this information is not available at the system start-up,
contact the technical service department responsible for the
installation to get it.
These characteristics can be obtained from the technical
literature using the unit performance tables for a ∆T of 5 K at
the water heat exchanger or with the Electronic Catalogue
selection program for all ∆T conditions other than 5 K in the
range of 3 to 10 K.
12.1 - Units without hydronic module
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 (see example for unit size AR05 078).
The pressure drop reading in the unit (plate heat exc
internal piping) is used as means of control.
This reading can be taken with pressure gauges that must be
installed at the unit inlet and outlet (item 19).
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 pressure drop 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 18) 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 pressures at the
pressure gauges (entering water pressure - leaving water
pressure), to fi nd out the unit pressure drop (plate heat
exc internal water piping).
Compare the value obtained with the theoretical selection
value. If the pressure drop measured is higher than the value
specifi ed this means that the unit fl ow rate (and thus system
fl ow rate) is too high. The pump supplies an excessive fl ow rate
based on the global pressure drop of the application. In this case
close the control valve and read the new pressure diff erence.
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
system pump the nominal water fl ow rate cannot be
obtained (the resulting fl ow rate is lower) and the tempe-
rature 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.
