Nominal System Water Flow Control; Water Flow Control Procedure - Carrier AQUASNAP 30RQ Installation, Operation And Maintenance Instructions

9 - NOMINal sYsTEM WaTER FlOW CONTROl

The water circulation pumps of the 30RQ units have been sized
to allow the hydronic modules to cover all possible configura-
tions 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°C.
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 provided in the
water leaving piping of the module (item 9 in the typical
hydronic circuit diagram).
With the pressure loss generated by the control valve in the
hydronic system, the valve is able to impose the system
pressure/flow curve on the pump pressure/flow curve, to obtain
the desired operating point. The pressure drop reading in the
heat exchanger is used to control and adjust the nominal system
flow rate.
Use this specification for the unit selection to know the system
operating conditions and to deduce the nominal air flow as well
as the 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 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.

9.1 - 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 provided to obtain the specific flow rate for this applica-
tion.
proceed as follows:
Open the valve fully (approximately 22 turns counter-clockwise).
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 hydronic circuit of the system (presence of
solid contaminants).
Read the filter pressure drop by taking the difference of the
readings of the pressure gauge connected to the filter inlet and
outlet, using valves (see typical hydronic circuit diagrams), and
comparing this value after two hours of operation.
22
If the pressure drop has increased, this indicates that the screen
filter must be removed and cleaned, as the hydronic circuit
contains solid particles. In this case close the shutoff valves at
the water inlet and outlet and remove the screen filter after
emptying the hydronic section of the unit.
Renew, if necessary, to ensure that the filter is not contami-
nated. Purge the air from the circuit using the purge valves in
the hydronic circuit and the system (see typical hydronic circuit
diagram).
When the circuit is cleaned, read the pressures at the pressure
gauge (entering water pressure - leaving water pressure),
expressed in bar and convert this value to kPa (multiply by 100)
to find out the water heat exchanger pressure drop.
Compare the value obtained with the theoretical selection value.
It is essential to carry out systematic filter cleaning at the initial
start-up, as well as after any modification in the hydronic circuit.
ATTENTION: It is essential to keep the pressure gauge purge
valve open after measuring the pressure (risk of freezing
during winter).
If the pressure drop measured is higher than the value specified
this means that the flow rate in the water 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 de reduced and the difference
between entering and leaving water temperature of the
hydronic module will be increased.
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.