Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)41

The “eco Turbo ETI” Series of High-Performance
Variable-Speed-Control Centrifugal Chillers

KENJI UEDA

YASUSHI HASEGAWA

MASAHARU NITTA

JUN KOGA|1. Introduction
Due to the growing social concern related to energy conservation and reduction of CO2
emissions, high-efficiency centrifugal chillers are now widely used, not only in industrial
applications such as heat sources in factories, but also in air conditioning system of buildings.
However, centrifugal chillers consume large amounts of energy because of the large-capacity heatpumps they contain. The reduction of CO2 emissions is now an important consideration in thetechnical improvement and product development of this equipment. The development ofuser-friendly products that are easy to install has also become a vital issue because of thewidespread application of high-efficiency centrifugal chillers in heat sources.
This paper describes recent trends and requirements for the main components in heat sources,and discusses the new “eco Turbo ETI” series of high-efficiency centrifugal chillers equipped withinverters as standard equipment, introduced in May 2008.

|2. Centrifugal chiller market and product concept
Absorption chillers using oil and gas as fuel were generally used in large-capacity heatsource equipment for air conditioning systems to help with summertime peak power reduction andelectrical load leveling after the first spike in oil prices. However, calculations of the CO2
emissions involved in producing the power required by these systems showed that the emissions
note
due to absorption chillers were approximately 1.9 times
that required by centrifugal chillers. It
is thus imperative to review conventional approaches in terms of energy conservation and CO2emission reduction. Market studies reveal that sales of absorption chillers are declining even as
domestic shipment of large-capacity chillers is leveling off, showing that the market is turning tohigh-efficiency centrifugal chillers that have found a new role as alternative heat sources.
Note: This calculation is based on the following assumptions: the COP of the centrifugal chiller is6.4, the COP of the absorption chiller is 1.35, the generating efficiency is 41.9%, andelectricity transmission loss is 4.7% based on the 2004 Tokyo Electric Power performance.

In other words, future centrifugal chillers will be primarily designed for, and integrated into,business-use air conditioning equipment with a refrigeration capacity of about 200 USRt. Reducing
installation area and shipping weight has become increasingly important as the typical installation
has changed from the factory compound to the general office building. Over the past several years,
the approach to technical innovation has shifted from offering a certain coefficient of performance(COP) under rated conditions to providing year-round efficiency even under conditions of partial
loading or low-temperature cooling water, which are more representative of how the chillers are
actually used most of the time.
Mitsubishi Heavy Industries, Ltd., (MHI) has marketed a centrifugal chiller series using
inverter-driven variable-speed controls since 2003. The present AART-I series effectively reduces
annual energy consumption. Even so, MHI concluded that it was necessary to incorporate
inverter-driven variable-speed controls into new centrifugal chiller models as standard equipment(Figure 1).
Based on market trends and user requirements, MHI developed new centrifugal chillers withthe following product features:

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)42•••

Smaller capacity (150–500 USRt)
High performance (inverters included as standard equipment)
Easy introduction (compact and lightweight)

Figure 1 Centrifugal chiller transition|3. Detailed configuration of the ETI series
3.1

High-performance design

We started with the features of large centrifugal chillers that had actually provenachievement in high efficiency, and downsized and increased the performance of the chiller bycarefully examining each feature. Typical features in this process included the following:• Two-stage compression, two-stage expansion sub-cooling cycle• High-precision machined impeller• Low-loss gears and bearings• First- and second-stage inlet guide vane control• Load and cooling-water temperature follow-up controls using six-element mathematicaloperational control• Inverter-driven compressor variable speed control• Optional correspondence to just almost nonloading control with a capacity of less than 10%
The performance of a chiller declines as the size decreases due to the relative decrease in partand assembly accuracy. However, we minimized the performance reduction through the following
technical approaches:• Reevaluation of machining accuracy, reexamination of tolerances, and review of surface
roughness criteria for each aerodynamic component• Reexamination of standard tolerances during parts assembly• Reexamination of specifications and auxiliary capacity.
Table 1 lists the specifications of the ETI-20 (title photograph) and the ETI-40 (Figure 2).
Table 1 Specifications of the ETI-20 and ETI-40
Model
Refrigerating(USRt)
capacity(kW)Chilled-water temperature (°C)
Chilled-water flow rate (m3/hr)
Cooling-water temperature (°C)
Cooling-water flow rate (m3/hr)
Power consumption(kW)
Statutory refrigeration ton
COPSize(m)RefrigerantETI-20
ETI-40200
4007031407
12 in/7 out
12 in/7 out
120.7
241.3
32 in/37 out
32 in/37 out
142.6
285.2
116.6
233.7
87.3
174.6
6.0
6.0
3.7 long × 1.5 wide × 1.8 high
4.5 long × 2.0 wide × 2.2 highHFC-134a

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)
43Rated COP is calculated based on power consumption summing inverter input power, oilpump, and the control power source. A COP of 6 is the best performance of any comparable
200-USRt-class product. The year-round efficiency, an important factor in annual power
consumption, is very high, resulting in an integrated part-load value (IPLV) of 10.2, and amaximum COP of 19.1 under partial loading. Both the IPLV and COP are high level for evaluating
year-round cooling and heating applications (Figure 3).

Figure 2 ETI-40 exterior

3.2

Figure 3 Partial load characteristics of the ETI-20 and -40

Compact and lightweight design

Models ETI-15, -20, and -25 are single-compressor units with different configurations toprovide various capacities in the range 150–250 URSt. Models ETI-30, -40, and -50 are
two-compressor units that cover the range 300–500 USRt . We managed to reduce the size by using
the same compressor for both series.
(1) Compact and lightweight compressor• We reduced the size of the motors and gears by using dedicated high-speed motors for theinverter.
• We reduced the compressor weight and volume by separating the oil tank and oil pump fromthe compressor itself.
(2) Compact and lightweight unit
• We incorporated an inverter into the chiller body and eliminated the need for a separate
inverter panel.
• We located components such as subcooler, economizer and oiltank under the condenser.
• We designed a heat exchanger optimized for the 250- and 500-USRt small-capacity class.
By optimizing the items described above, we were able to reduce the installation area for theETI-20 and ETI-40 by approximately 40% and 20%, and the equipment weight by 49% and 27%,
respectively, compared to our conventional models with the same capacity. This makes installationof new centrifugal chillers much easier.

3.3 Improvement of controllability and operability
We used the latest developments control panel technology for the ETI series of centrifugal
chillers to improve operability and visibility, and provide enhanced basic functions.
(1) Improvement of operability and visibility• We used a 10.4-inch color liquid crystal display to improve the visibility with a bright clear
digital display and large characters.
• We provided a dedicated CPU to enhance the display and reduce operator stress during theoperation of the equipment.
• The display backlight turns itself off after a period of inactivity. We also provided a detection
sensor to turn the display lighting on again without the operator having to touch the panel.
This reduces the possibility of error and decreases operator stress.
(2) Enhancement of basic functions• We were able to increase the speed and capacity of the main control CPU by transferring
control of the liquid crystal display to a dedicated CPU.
• Made up of lead-free components, the operation panel is RoHS-compliant.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)44|4. Evaluation of reduction of cost and CO2 emissions
Figure 4 compares the CO2 emissions of the ETI series, current fixed-speed AART series,
and the ART series that dates from approximately 10 years ago. A preliminary calculation showsthat the cost and CO2 emissions of the ETI series are reduced by 62% compared to those of theexisting ART series under air-conditioning loading. What is remarkable here is that the year-roundpower cost for the ETI series falls far below than that of current high-performance AART series forair-conditioning loading. This shows the value of the inverters.

Figure 4 Reduction of cost and CO2 emissions|5. Conclusion
The ETI series of high-performance compact small-capacity centrifugal chillers reflects
market demands. The series has achieved reliable performance using a balance of new concepts,time-tested technology, and a design optimized for small-capacity applications. The performance
characteristics are the same as or better than those of large-capacity high-performance centrifugal
chillers. In addition to their use in air conditioning systems for conventional industrial or
large-capacity commercial applications, the ETI series now offers substantial energy savings andreduction of CO2 emissions to customers with small air conditioning systems or who needsmall-capacity equipment.
Inverter-driven centrifugal chillers will be the basis for other models that can be used formany new applications. The ETI chillers are the first step in a series that responds to customer
needs, and we will continue our efforts to develop further products to cater to market demands.

References
1.

Wajima, K. et al., Centrifugal Chiller Maximizing Year-round Efficiency, pp.35-39, Mitsubishi Heavy
Industries Technical Review Vol. 45 No. 2 (2008)

Authors
Kenji Ueda
Manager,
Centrifugal & Absorption Chiller
Department,
Air-Conditioning & Refrigeration
Systems Headquarters

Yasushi Hasegawa
Centrifugal & Absorption Chiller
Department,
Air-Conditioning & Refrigeration
Systems Headquarters

Masaharu Nitta
Centrifugal & Absorption Chiller
Department,
Air-Conditioning & Refrigeration
Systems Headquarters

Jun Koga
Manager,
Ryoyu System Engineering/Inc.