The series A chillers only have 1 compressor.
Therefore, the minimum volume required for a temperature differential of 5 deg. C is:
V
min
= 860 * 11.72 * 4 = 134 litres
5 * 60 * 1
With an internal buffer tank of 32 litres, the remaining volume of (134 - 32) = 102 litre
must be from the external piping and fan coil units.
Therefore, it is important for a calculation check to be made for this total water volume to ensure a
proper operation. Too short a piping (e.g. back-to-back installations) may cause the compressor
to cycle ON/OFF too frequently during low loading conditions.
It is recommended that the compressor do not switch ON/OFF for more than 8 cycles per
hour.
The above recommendations are applicable for close piping systems
. In the case of open
systems, whereby there is an external tank, there should be no problem of having the compressor
short cycling as the additional volume of water in the external tank will take a much longer time to
pull down the temperature.
With the series-C chillers, no buffer tank is required. This is because of the chiller control
algorithm used to control the two compressors in the chiller (i.e. two capacity load steps).
By having a sequential ON/OFF of the compressors (i.e. first ON, first OFF) and anti-short cycling
timer in the controller, the compressors are prevented to ON/OFF too frequent beyond the
specified cycles.
Thus, it is not necessary to perform similar minimum water volume calculations for these chillers.
Section 6 Page 88
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