Filter
Top Products
TRG-TRC011-EN 43
period three
Capacity Control
notes
Special consideration must be given to controlling the chiller at very low load
conditions combined with low cooling water temperatures. Under these
conditions, the chiller reaches equilibrium with a very low solution
concentration in the absorber. There is a possibility that the chiller might not
have enough refrigerant to dilute the solution this much. As a result, the lithium
bromide solution absorbs all of the refrigerant in an attempt to achieve this very
dilute concentration, causing the evaporator to run dry.
The loss of refrigerant from the evaporator automatically stops the chiller.
Additionally, if refrigerant is used to cool and lubricate the pump motors, a
safety switch may shut the chiller off to protect the motor and pump.
One solution to this problem is to charge the chiller with additional refrigerant.
During operation, this extra refrigerant is simply stored in the evaporator pan or
a supplemental storage tank where it has no adverse effect on chiller operation.
When low-load and cold-cooling-water conditions are encountered, this
additional amount of refrigerant is available to effectively dilute the solution in
the absorber. This allows the chiller to operate throughout its capacity range
without the need for additional control devices.
An alternative solution is the use of controls to avoid this potential problem
area. A float arrangement can be used to sense a low level of refrigerant in the
evaporator, and in response, open a valve to divert solution from the absorber
sprays directly back into the absorber sump. This reduces chiller capacity by
slowing the rate of absorption and, therefore, the rate at which refrigerant is
vaporized inside the evaporator.
refrigerant
refrigerant
storage tank
storage tank
evaporator pan
evaporator pan
Figure 51