b. Use a Variable Speed Drive for the Secondary Water Pump.
LOAD
LOAD
LOAD
∆
P
INV
primary loop
When the differential pressure becomes higher, the inverter will slows
down the water pump to maintain the head pressure. If no demand,
the water pump will stop running.
c. Modify the Control Wiring for Chiller and Fan Coil Unit.
The above two methods will incur high cost due to the extra piping, pressure transmitter and
other necessary fittings/equipment.
An easier method is to change the control wiring of the system. Conventionally, when the
fan coil unit thermostat cuts-off, the power supply to the control 2-way valve will be off.
It is possible to run a line from the thermostat to the chiller remote switch whereby
when the thermostat cuts-off, the chiller unit (and the pump) will also switch off.
See Section 11 on 'Electrical Wiring Control' for more details.
However, the disadvantage with this method is that the chiller cycle on-off more frequently
and the water supply temperature will fluctuate up and down.
d. In view of the difficulties mentioned above, it is recommended that 3-way
diverting valves to be used in the mini chiller hydronic system.
Since the 3-way valve gives a constant flow system, there will not be any problem when
there is no load demand since the water will bypass through the valve when it is in the
fully closed position (with respect to the load).
Section 3 Page 50
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