YZ Engineering Guide
Form: 161.01-EG1 (0618)
20
Depending on the number of units and operating characteristics of the units, loading and unloading schemes should be
designed to optimize the overall efficiency of the chiller plant. It is recommended to use an evaporator bypass piping
arrangement to bypass fluid around evaporator of any unit which has cycled off at reduced load conditions. It is also
recommended to alternate the chiller cycling order to equalize chiller starts and run hours.
Series/Parallel Arrangement
-
Chillers may be applied in pairs with chilled water circuits connected in series and
condenser water circuits connected in parallel. All of the chilled water flows through both evaporators with each unit
handling approximately half of the total load. When the load decreases to a customer selected load value, one of the
units will be shut down by a sequence control. Since all water is flowing through the operating unit, that unit will cool the
water to the desired temperature.
Figure 2
– Series/Parallel Arrangement
Series Counter Flow Arrangement
- Chillers may be applied in pairs with chilled water circuits connected in series and
with the condenser water in series counter flow. All of the chilled water flows through both evaporators. All of the condenser
water flows through both condensers. The water ranges are split, which allows a lower temperature difference or "head"
on each chiller, than multiple units in parallel. For equal chillers, the machine at the higher temperature level will typically
provide slightly more than half the capacity. The compressor on each chiller is often matched, such that the high
temperature machine can operate at the low temperature conditions when one unit is cycled off at part load (as compared
to series-parallel chillers which are typically not identical).
Figure 3
– Series Evaporators (Evap.) Series-Counter Flow Condensers (Cond.)
Cond. 1
Evap. 1
Cond. 2
Evap. 2
S1
S2
T
S
- Temperature Sensor for Chiller Capacity Control
- Thermostat for Chiller Capacity Control
T
Cond.
1
Evap. 1
Cond. 2
Evap. 2
T
S1
S2
T
S
- Temperature Sensor for Chiller Capacity Control
- Thermostat for Chiller Capacity Control
