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13.2 - Units with hydronic module and fixed-speed
pump
The nominal system flow 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 flow control valve permits adjustment of the pressure/
system flow rate curve in accordance with the pump pressure/
flow rate curve to obtain the nominal flow rate at the
required operating point.
The flow rate reading in the hydronic module is used as
means of control.
The pressure of the transported fluid is measured by sensors
installed in the pump suction line and at the unit outlet
(items 7 and 10) and the system calculates the flow rate
associated with the differential pressure.
Direct access to the flow rate reading is possible via the
user interface (please refer to the 30RB/RQ 017-160
Pro-Dialog+ control manual).
As the total system pressure drop is not known exactly at
the start-up, the water flow rate must be adjusted with the
control valve to obtain the specific flow 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 difference 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 flow rate has decreased, this indicates that the
screen filter 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 filter (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 filter is not
contaminated.
Water flow control procedure
When the circuit is cleaned, read the flow rate at the user
interface and compare the value obtained with the theoretical
selection value. If the flow rate measured is higher than the
value specified 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 flow rate.
Proceed by successively closing the control valve until you
obtain the specific pressure drop that corresponds to the
nominal flow 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 flow rate cannot be obtained
(the resulting flow rate is lower) and the temperature
difference 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, options, etc.).
•
to use a correctly sized piping diameter.
•
to avoid hydronic system extensions, wherever possible.
13.3 - Units with hydronic module and variable-speed
pump - pressure differential control
The system flow rate is not controlled by a nominal value.
It is adjusted by the system (pump speed variation) to
maintain the user-selected pressure differential 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.
The system calculates the measured pressure differential
value, compares it with the user-selected set point value
and modulates the pump speed as necessary. The result is:
•
an increased flow rate, if a lower value than the set
point is measured,
•
an decreased flow rate, if a higher value than the set
point is measured.
This flow rate variation is realised, observing the minimum
and maximum admissible unit flow rates as well as the
minimum and maximum pump supply frequency values.
The pressure differential value maintained can in certain
cases be different from the set point value:
•
If the set point value is too high (achieved for a higher
flow rate than the maximum value or a higher frequency
than the maximum value), the system settles at the
maximum flow rate or maximum frequency and this
results in a lower pressure differential than the set point.
•
If the set point value is too low (achieved for a lower
flow rate that the minimum value or a lower frequency
than the minimum value), the system settles at the
minimum flow rate or minimum frequency and this
results in a higher pressure differential than the set point.
hydronic circuit cleaning procedure
First of all any possible pollution in the hydronic circuit
must be eliminated.
•
Start-up the pump using the forced start command
(refer to the 30RB/RQ 017-160 Pro-Dialog+ control
manual).
•
Set the frequency to the maximum value to achieve a
higher flow rate.
•
If a "maximum flow rate exceeded" alarm occurs,
decrease the frequency until the correct value is found.
•
Read the flow rate at the user interface (refer to the
30RB/RQ 017-160 Pro-Dialog+ control manual).
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