30
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
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.
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
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
252-452
502
Static pressure
kPa 100
200
250
100
200
250
bar 1
2
2.5
1
2
2.5
Max. water loop volume
l
Pure water
2400 1600 1200 3960 2640 1980
Ethylene glycol 10%
1800 1200 900
2940 1960 1470
Ethylene glycol 20%
1320 880
660
2100 1400 1050
Ethylene glycol 30%
1080 720
540
1740 1160 870
Ethylene glycol 40%
900
600
450
1500 1000 750
6.7 - Evaporator water flow rate
30XA
Evaporator water flow rate, l/s*
Min. flow rate
Max. flow rate**
252
3.6
37.5
302
4.0
40.5
352
4.3
40.5
402
5.3
34.1
452
6.0
36.9
504
6.7
42
502
6.7
42.0
602
8.1
45.0
702
8.9
56.1
752
9.6
59.1
802
10.4
67.1
854
11
67.1
852
11.0
67.1
904
11.8
73.9
902
11.8
73.9
1002
13.1
83.9
1112
15.1
126.5
1212
16.4
132.1
1312
17.5
118.5
1382
18.8
131.1
1402
19.3
107.4
1502
19.9
109.4
1702
22.0
107.4
* Standard evaporators with water as the heat transfer fluid.
** The maximum water flow rate corresponds to a pressure drop of 100 kPa.
Содержание Aquaforce 30XA Series
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