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Consider adding additional piping and isolation valves to
isolate each chiller to allow for service on the machine, and
still allow for partial capacity from the other chiller.
Even if evaporators are piped in series, parallel con-
denser piping should be considered on constant speed
chillers to maximize capacity and efficiency while minimiz-
ing condenser pressure drop and saturated condensing
temperatures. If the condensers are piped in series, ensure
that the leaving fluid temperature does not exceed 122 F
(50 C) for standard units, or 140 F (60 C) for high con-
densing or heat machine condensers.
Electric utility interests
Energy management — Use of energy management
practices can significantly reduce operating costs, espe-
cially during off-peak modes of operation. Demand limiting
and temperature reset are two techniques for accomplish-
ing efficient energy management. See Demand Limiting
(also called load shedding) section below for further details.
Demand limiting (load shedding) — When a utility's
demand for electricity exceeds a certain level, loads are
shed to keep electricity demand below a prescribed maxi-
mum level. Typically, this happens on hot days when air
conditioning is most needed. The energy management
module (EMM) option can be added to accomplish this
reduction. Demand may be limited on the unit by resetting
water temperature, or by unloading the chiller to a given
predetermined percentage of the load. Demand limit may
also be driven by an external 4 to 20 mA signal. These fea-
tures require a signal from an intelligent central control.
Duty cycling — Duty cycling will cycle an electrical load
at regular intervals regardless of need. This reduces the
electrical demand by "fooling" demand measuring devices.
Duty cycling of the entire compressor is NOT recom-
mended since motor windings and bearing life will suffer
from constant cycling.
Remote on-off control — Remote on-off control may be
applied by hard-wired connection (see the Controls,
Start-Up, Operation, Service and Troubleshooting guide)
or by connection to the Carrier Comfort Network
®
(CCN)
system.
Application data (cont)