CIAT DYNACIAT LG 080, Инструкция по эксплуатации

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10 - NOMINAL WATER FLOW CONTROL WITH FIXED-SPEED PUMP
10.1 - General
The water circulation pumps of the units have been sized to allow
the hydraulic modules to cover all possible configurations based
on the specific installation conditions, i.e. for various temperature
differences between the entering and the leaving water (∆T) at
full load, which can vary between 2.5 and 7 K for evaporators
and 3 and 18 K for condensers.
This required difference between the entering and leaving water
temperature determines the nominal system flow rate. It is above
all absolutely necessary to know the nominal system flow rate
to allow its control via a manual valve.
Manual control valves for the unit are not supplied and must be
installed upstream and downstream of the evaporator and
condenser water loops to ensure correct flow control.
With the pressure loss generated by the control valve in the
hydraulic system, the valve is able to impose the system
pressure/flow curve on the pump pressure/flow curve, to obtain
the desired operating point (see example).
The pressure drop reading in the plate heat exchanger is used
to control and adjust the nominal system flow rate. The pressure
drop is measured with the pressure sensors connected to the
heat exchanger water inlet and outlet.
Use this specification for the unit selection to know the system
operating conditions and to deduce the nominal air flow as well
as the plate heat exchanger pressure drop at the specified
conditions. 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 or the Electronic
Catalogue selection program for all conditions.
10.2 - Water flow control procedure
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 application.
Proceed as follows:
Open the valve fully.
Start-up the pump using the forced start command (refer to the
controls manual) and let the pump run for two consecutive hours
to clean the hydraulic circuit of the system (presence of solid
contaminants).
Read the hydraulic module pressure drop by taking the difference
of the readings at the machine connected to the hydraulic module
inlet and outlet. Compare this value after two hours of operation.
Entering water pressure reading
O
F F
Leaving water pressure reading
O
F
F
O Open
F Closed
Water inlet
Water outlet
Pressure gauge
If the pressure drop has increased, this indicates that the screen
filter must be removed and cleaned, as the hydraulic circuit
contains solid particles. In this case, in units with Safety hydraulic
component option, close the shutoff valves at the water inlet and
outlet and remove the screen filter after emptying the hydraulic
section of the unit. In units without Safety hydraulic component
option, clean the screen filter on hydraulic circuit out of the unit.
Renew, if necessary, to ensure that the filter is not contaminated.
When the circuit is cleaned, read the pressures at the unit
(entering water pressure - leaving water pressure), expressed
in kPa to find out the plate heat exchanger pressure drop.
Compare the value obtained with the theoretical selection value.
If the pressure drop measured is higher than the value specified
this means that the flow rate in the plate heat exchanger (and
thus in the system) is too high. The pump supplies an excessive
flow rate based on the global pressure drop of the application.
In this case close the control valve one turn and read the new
pressure difference.
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.
-
If the system has an excessive pressure drop in relation to
the available static pressure provided by the pump, the
resulting water flow rate will be reduced and the difference
between the input and output water temperature of the
hydraulic module will be increased.
To reduce the hydraulic system pressure drops, 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 hydraulic system extensions, wherever possible.
EN-47 Dynaciat LG/LGN