Table 2: Steps To Clean, Purge, And Define A Flow Rate For Hydraulic Circuit - Riello NXHP Series Installation, Operation And Maintenance Instructions

2 - INSTALLATION OF UNIT
2.5.5 - Nominal system water flow control
The water circulation pumps of the NXHP 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 3 and 10 K.
This required difference between the entering and leaving water temperature determines the nominal system flow rate. Use this
specification for the unit selection to find the system operating conditions.
In particular, collect the data to be used for the control of the system flow rate:
■ Units with variable speed pump-control on adjustable constant speed: nominal flow rate,
■ Units with variable speed pump - control on temperature difference: heat exchanger ΔT (variable flow).
If the 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.

Table 2: Steps to clean, purge, and define a flow rate for hydraulic circuit

N°
1 No manual control valve required with Variable Speed hydraulic module
2 Set the system pump
Read the BPHE pressure drop...
3
... by taking the difference of the readings of the pressure gauge connected to the unit inlet and outlet.
4 Let the pump run for two consecutive hours to flush the hydraulic circuit of the system (presence of solid contaminants).
5
Take another reading.
Cleaning procedure
6
Compare this value to the initial value.
7 If the pressure drop...
... has decreased, this indicates that the screen filter must be removed and cleaned, as the hydraulic circuit contains
solid particles.
In this case stop the pump
8
after emptying the hydraulic section of the unit.
9
Repeat, if necessary, to ensure that the filter is not contaminated.
1 After filling with water, wait about 24h before activating the purge procedure.
Activate the purge mode
2
circuit regardless the flow switch value
Purge procedure
(3)
3 The air vent valves are field-supplied.
If the air vent valve is automatic, air will vent from circuit automatically.
If the air vent valve is manual, open the valve to vent air from the circuit
When the circuit is cleaned and purged, activate the pump in quick test
1 mode
water pressure - leaving water pressure), ...
... to find out the unit pressure drop (plate heat exchanger + internal
2
water piping).
Water flow control
Compare this value to the graph of available external static pressure
procedure 3
using the appropriate speed curve (Graphic 1 ).
If the flow rate corresponding is higher, decrease pump speed
4
vice versa.
Proceed by successively adjusting the pump speed until the expected
5
water flow rate is achieved.
(1) For configuration details, refer to table 3.
(2) CAUTION: In purge mode, the value of the flow switch is ignored, so check that there is water in the circuit, to avoid damage to the pump.
(3) CAUTION: In the unlikely case of refrigerant leak in BPHE, propane could be present in the water loop and vented out during purge procedure. Make sure during purge
procedure that environment around air vent valves is well-vented and free of ignition sources!
30
With Variable Speed hydraulic module
Adjustable constant speed
.
(1)
and close the shut-off valves at the water inlet and outlet and remove the screen filter
(1)
: water pump is requested to run continuously at maximum speed to purge the hydraulic
(1)
, and read the pressures at the pressure gauges (entering
(1)
(2) .
, and
(1)
With Variable Speed hydraulic module
ΔT
No need to adjust the flow rate because of ΔT
control.
But it is necessary to adjust the Minimum
pump speed [P563], [P564] to ensure closure
of flow switch
(1)
.