Variable Flow Evaporator; System Minimum Water Volume; Maximum System Water Volume; Evaporator Water Flow Rate - Carrier Aquaforce 30XA302 Installation, Operation And Maintenance Instructions

6.4 - Variable flow evaporator

Variable evaporator flow can be used in standard 30XA
chillers. The chillers maintain a constant leaving water
tem-perature 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.

6.5 - System minimum water volume

Whichever the system, the water loop minimum capacity is
given by the formula:
Capacity = Cap (kW) x N litres
Application
Normal air conditioning
Process type cooling
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.
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.
Connection to a buffer tank
Bad
Bad
30
N
3.25
6.5
Good
Good

6.6 - Maximum system water volume

Units with hydronic module incorporate an expansion
tank that limits the water volume. The table below gives
the maximum loop volume for pure water or ethylene
glycol with various system concentrations, as well as the
static pressures. If the maximum volume is insufficient,
compared to the minimum system water loop volume, an
additional expansion tank must be added to the system.
30XA
Static pressure kPa
bar
Max. water loop volume l
Pure water
Ethylene glycol 10%
Ethylene glycol 20%
Ethylene glycol 30%
Ethylene glycol 40%

6.7 - Evaporator water flow rate

30XA Evaporator water flow rate, l/s*
Min. flow rate
252 3.6
302 4.0
352 4.3
402 5.3
452 6.0
504 6.7
502 6.7
602 8.1
702 8.9
752 9.6
802 10.4
854 11
852 11.0
904 11.8
902 11.8
1002 13.1
1112 15.1
1212 16.4
1312 17.5
1382 18.8
1402 19.3
1502 19.9
1702 22.0
* Standard evaporators with water as the heat transfer fluid.
** The maximum water flow rate corresponds to a pressure drop of 100 kPa.
252-452 502
100 200 250 100 200
1 2 2.5 1 2
2400 1600 1200 3960 2640
1800 1200 900 2940 1960
1320 880 660 2100 1400
1080 720 540 1740 1160
900 600 450 1500 1000
Max. flow rate**
37.5
40.5
40.5
34.1
36.9
42
42.0
45.0
56.1
59.1
67.1
67.1
67.1
73.9
73.9
83.9
126.5
132.1
118.5
131.1
107.4
109.4
107.4
250
2.5
1980
1470
1050
870
750