YZ Engineering Guide
Form: 161.01-EG1 (0618)
4
Introduction
The YORK® YZ Magnetic Bearing Centrifugal Chiller is a revolutionary advancement that challenges everything about
conventional chiller design. The result is a chiller fully optimized for ultimate performance with a next generation low-
GWP (global warming potential) refrigerant, delivering superior real-world performance and a new definition of
sustainability. The YORK® YZ Chiller is available from multiple global factories to
meet regional customers’ needs.
EFFICIENCY
Johnson Controls pioneered the term “real-world efficiency” to illustrate the energy-saving potential of focusing on chiller
performance during off-design conditions. Off-design conditions are not only seen at part-load, but at full-load operation
as well, by taking advantage of reduced entering condenser water temperatures (ECWTs). These conditions are where
chillers operate up to 99% of the time, and where operating costs add up. YZ chillers are designed to operate on a
continuous basis with cold ECWT and full condenser flow at all load points, taking full advantage of real-world conditions.
YZ chillers offer the most efficient real-world operation of any chiller, meaning lower operating costs and an excellent
return on your chiller investment.
Actual chiller efficiency cannot be determined by analyzing the theoretical efficiency of any one chiller component. It
requires a specific combination of heat exchanger, compressor, and motor performance to achieve the best system
efficiency. YZ technology matches chiller system components to provide maximum chiller efficiency under actual
– not
just theoretical
– operating conditions. Now with the YORK® YZ, efficiency is improved up to an impressive 7% at part-
load and as much as an additional 5% at full-load versus our most efficient previous designs.
BETTER EFFICIENCY IN EVERY OPERATING CONDITION
The YZ chiller has been designed to take full advantage of colder cooling tower water temperatures, which are naturally
available during most operating hours. Considerable energy savings are available by letting tower water temperature
drop, rather than artificially holding it above 19°C (65°F), especially at low load, as some chillers require.
Since the vast majority of its operating hours are spent at off-design conditions, a chiller should be chosen not only to
meet the full-load design, but also for its ability to perform efficiently at lower loads, lower tower water temperatures, and
even higher leaving evaporator water temperatures. It is not uncommon for chillers with the same full-load efficiency to
have an operating cost difference of over 10% due to differences in part-load efficiencies.
Part-load is
important to an owner’s operating budget, this information has been standardized within the AHRI
Certification Program in the form of an Integrated Part Load Value (IPLV), and Non-Standard Part Load Value (NPLV).
Additionally, looking at annual energy costs that use weather data specific to your city, you can get a better understanding
of the efficiency benefits the YORK® YZ offers across a wide range of operating conditions. This more detailed analysis
also takes into account actual building load profiles to provide a more accurate view of chiller operating cost. Part-load
performance data should be requested by the customer for each job using its own design criteria.