Heat Recovery; Series Arrangement; Series Counter Flow Arrangement; Series Evaporators Series Counterflow Condensers - York YK Manual

FORM 160.75-EG1 (519)
Application Data (Cont'd)
COND. 1 COND. 2
T
S2
S1
EVAP. 2
EVAP. 1
FIGURE 4 - SERIES EVAPORATORS SERIES COUNTERFLOW CONDENSERS
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 Arrangement (Figure 3 - Series Evaporators Parallel Condensers on page
42) – 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 one 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.
Series Counter Flow Arrangement (Figure 4 - Series Evaporators Series Counterflow
Condensers on page 43) - 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 con-
densers. 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 higher
temperature level typically provides slightly more than half the capacity. The compressor
motors and gear codes on the two chillers are often matched, such that the high tempera-
ture machine can operate at the low temperature conditions when one unit is cycled off at
part loads (as compared to series-parallel chillers which are typically not identical).
Series counter flow application can provide a significant building energy savings for large
capacity plants which have chilled and condenser water temperature ranges greater than
typical AHRI.

HEAT RECOVERY

Heat recovery may be used in buildings, where there is a need for heating and cooling
loads concurrently. By utilizing some or all of the heat rejection of a normal vapor-com-
pression cycle cooling system, overall operating energy savings result. Heat recovery
uses available heat as a by-product of the cooling function, which differs from heat pumps
where the heating can be considered the primary process. Also, the heat recovery usage
is often a winter seasonal duty, where the chiller may be expected to operate in summer
using heat rejection to a conventional cooling tower. As heating loops and cooling tower
water circuits are separate in the majority of buildings, this dictates the need for two water
circuits in the condenser of a heat recovery chiller.
JOHNSON CONTROLS 43