27
Variable evaporator ow can be used in standard 30HXC chillers.
The chillers maintain a constant leaving water temperature under
all ow conditions. For this to happen, the minimum ow rate
must be higher than the minimum ow given in the table of
permissible ow rates and must not vary by more than 10% per
minute.
If the ow rate changes more rapidly, the system should contain
a minimum of 6.5 litres of water per kW instead of 3.25 l/kW.
Whichever the system, the water loop minimum capacity is given
by the formula:
Capacity = Cap (kW) x N litres
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
bafed in order to ensure proper mixing of the liquid (water or
brine). Refer to the examples below.
5.2 20.8
100 6.5 25.9
110 7.4 29.6
120-130 8.3 33.4
140-155 9.4 37.8
11.5 45.9
200 14.1 56.3
230 16.3 65.2
18.3 73.4
310 20.9 83.7
345-375 23.0 91.9
* Basedonawatervelocityof0.9m/s.
** Basedonawatervelocityof3.6m/s.
2.3 7.0 28.2
120-130 3.1 9.3 37.1
140-155 3.7 11.1 44.5
4.3 13.0 51.9
200 4.9 14.8 59.2
6.7 20.1 80.4
310-375 8.0 24.0 95.9
* Basedonawatervelocityof0.3m/sinaclosedloopand0.9m/sinanopen
loop.
** Basedonawatervelocityof3.6m/s.
Bad
Bad
Good
Good
NOTE: The compressor must not restart more than 6 times in an
hour.
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