14
5.4 - Variable flow evaporator
Variable evaporator flow can be used in standard chillers.
The chillers maintain a constant leaving water temperature
under all flow conditions. For this to happen, the minimum
flow rate must be higher than the minimum flow given in
the table of permissible flow rates and must not vary by
more than 10% per minute.
If the flow rate changes more rapidly, the system should
contain a minimum of 6.5 litres of water per kW instead of
3.25 l/kW.
5.5 - system minimum water volume
Whichever the system, the water loop minimum capacity is
given by the formula:
Capacity = Cap (kW) x N litres
application
N
Normal air conditioning
3.25
Process type cooling
6.5
Where Cap is the nominal system cooling capacity (kW) at
the nominal operating conditions of the installation.
This volume is necessary for stable operation and accurate
temperature control.
5.6 - Evaporator flow rate
30hZ/hZV
Min. water flow rate, l/s
Closed loop
043
4.1
052-065
5.0
091
6.0
101-121
8.5
141-161
9.9
195-280
12.0
Bad
Bad
Good
Good
It is often necessary to add a buffer water tank to the circuit
in order to achieve the required volume. The tank must
itself be internally baffled in order to ensure proper mixing
of the liquid (water or brine). Refer to the examples below.
NOTE: The compressor must not restart more than 6 times
in an hour.
Evaporator pressure drop curves, standard units
Pressure drop, kPa
legend
1 30HZ/HZV 043
2 30HZ/HZV 052-065
3 30HZ/HZV 091
4 30HZ/HZV 101-121
5 30HZ/HZV 141-161
6 30HZ/HZV 195-225
7 30HZ/HZV 250-280
Water flow rate l/s