GB - 9
61 AF
E N G L I S H
Nominal system water flow control
General
The optional water circulation pumps of the 61AF units
have been sized to allow the hydronic 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.
The pump of the hydronic module is a variable speed pump.
Two different water flow controls can be selected:
- Fixed speed control
- Variable speed control based on constant temperature
difference.
The default factory setting is fixed speed and the default
speed is 100%. Settings change need to be done by a
Carrier Service representative.
For both flow control and for energy saving, the speed of the
pump will be reduced to its minimum when unit capacity is
0%.
It is essential to know the nominal system flow rate to be
able to control it, using the variable pump speed or a
manual valve that must be on the water leaving piping of
the system (item 21 in the typical hydronic circuit
diagram).
The flow control with the pump speed or with the 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.
A differential pressure gauge must be installed at the unit
inlet and outlet or using pressure gauge (item 4and 5) on
the hydronic module.
Use the specification of the unit selection to know the
system operating conditions and to deduce the nominal
flow rate and 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 with 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 in the
range of 3 to 10 K.
For domestic hot water applications (leaving water tempera-
ture above 60°C) the control cannot be made at a
∆
T
below 8 K at the condenser.
It is therefore necessary to ensure a minimum pump
entering pressure of 40 kPa (0.4 bar) during operation and
at shut-down. In order to obtain sufficient pressure, it is
recommended:
• to pressurise the hydronic circuit between 1 and 3 bars
(maximum),
• to clean the hydronic circuit before charging water
(see chapter after),
• to regularly clean the screen filter,
ATTENTION
:
The use of integrated hydronic kits in the
open loop is not permitted.
Water flow control procedure (fixed speed)
Hydronic circuit cleaning procedure
•
Open the valve fully (item 21) if present.
•
Start-up the system or unit pump (by quick test), if the
unit is equipped with a hydronic module with a pump.
•
Read the difference of pressure between the pressure
gauge connected to the unit inlet and outlet (item 3).
•
Let the pump run for two consecutive hours to clean the
system hydronic circuit (presence of solid contaminants).
•
Take another reading.
•
Compare this value to the initial value.
•
If the difference of pressure 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 1) and remove the screen
filter (item 2) after emptying the hydronic section of
the unit (item 5).
•
Purge the air from the circuit (item 6).
•
Renew, if necessary, to ensure that the filter is not
contaminated.
Water flow control procedure
•
When the circuit is cleaned, run the pump at speed
100% and read the differential pressure of the unit
(items 3)
•
Find the flow rate with the pump curve 100%
•
If the flow rate is higher than the value specified close
the control valve or reduce the pump speed.
•
Verify the minimum speed pump (when unit capacity
is 0%) is compatible with the flow switch protection
(no flow switch alarm for minimum speed).
NOTE: If the system has an excessive pressure drop in
relation to the available static pressure provided by the
system pump the nominal water flow rate cannot be
obtained (the resulting flow rate is lower) and the tempera-
ture difference between the condenser 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.
Water flow control procedure (variable speed)
61AF units with variable-speed hydronic module include a
water pump that automatically adjusts the flow to maintain
a constant temperature difference.
No control is required at start-up, but the control mode
must be selected in the unit control by a Carrier service
representant.
Verify the minimum speed pump (when unit capacity is
0%) is compatible with the flow switch protection (no flow
switch alarm for minimum speed).
