Performance Improvement ofRefrigerating and Airconditioning Systems with 3DScroll Compressors
HAJIME SATO*1
MAKOTO TAKEUCHI*1
MAKOTO FUJITANI* 2

TAKAHIDE ITOH*1
HIROSHI YAMAZAKI*1
HIROYUKI KOBAYASHI*2

In the case of conventional scrolls, the wrap height isconstant throughout the compression process. Therefore,
refrigerant is compressed two-dimensionally from theouter side to the inner side. As for the 3D scroll, on theother hand, the outer wrap is higher than the inner one
by installing steps in scroll tips and end plates. Consequently, 3D scroll made possible to compress refrigerant
three-dimensionally, in both radial and axial direction
Fig(FigFig.. 2 ). The 3D scroll features the following:
The high compression ratio is obtained by compressing refrigerant not only radially but also axially.
The strength of scroll is improved and higher reliability is obtained by reducing the height of inner wrap
which acts heavy load.
The large capacity is obtained without extension of
the outer diameter of scroll by increasing the heightof outer wrap, and thus the 3D scroll has smaller sizeand lighter weight.
2.2 Application to MHI refrigerating and airconditioning products
Table 1 shows performance requirements of compressors and effects when the 3D scroll is introduced in eachproduct. The introduction of 3D scroll satisfies various
requirements specific to each product such as large capacity and high reliability in commercial
air-conditioners, the operation under high compression
ratio in refrigeration unit, and so on.

1. Introduction
The demand for saving energy in refrigerating and airconditioning systems is increasing in terms ofenvironmental conservation against global warming. Most
energy in refrigerating and air-conditioning systems isconsumed in compressors to compress refrigerant, so theefficiency improvement in compressors is indispensable
for saving energy in refrigerating and air-conditioning
systems. Mitsubishi Heavy Industries, Ltd. (MHI) has so
far adopted scroll compressors featuring low vibration andhigh efficiency to main refrigerating and air-conditioning
products to meet the demand for saving energy. For thepurpose of further efficiency improvement, MHI developed
three-dimensional compressors (3D scroll compressors) byadding an axial compression to the conventional radial
one. This paper describes the outline of the 3D scroll compressor and the high-performance technology.

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Note: "3D Scroll" is a registered trademark of MHI.

2. Outline of 3D scroll compressor
2.1 Features of 3D scroll
Scroll compressors compress refrigerant by orbiting
motion accompanied with mutual eccentricity of a pairof scrolls (fixed scroll and orbiting scroll) composed ofFig. 1
end plates and scroll blades (wrap) (Fig.
1).

Discharge pipe
Conventional scroll
Fixed scroll
Constant
wrap height

Fixed scroll(3D scroll)3D scrollFixed scroll Outer wrap
height: Large

Orbiting scroll(3D scroll)
Suction pipe

Motor
Orbiting scroll

Orbiting scroll

Crank shaft
Two-dimensional compression

Inner wrap
height: Small

Three-dimensional compression

Refrigerant flow
Fig. 2 Sectional views of conventional scroll and 3D scroll
Introduction of 3D scroll made possible three-dimensional compression

Fig. 1 3D scroll compressor

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)*1 Nagoya Research & Development Center, Technical Headquarters*2 Air-Conditioning & Refrigeration Systems Headquarters

1Table 1 Performance requirements for compressors and effectsof 3D scroll

Tip clearance
Orbitingscroll wrap

Side clearance
Enlarged

CommerRefrigera- RefrigeraGHP tion unit tion unit
cial airconditioner
for trucks for marinetransport

Performancerequirements

Step

High efficiency(high compression ratio)
High reliability(enhanced scroll strength)
Low-noise and low vibration
Fixed scroll wrap

Small size and light weight
Large capacity

Tip sealFig. 3 Schematic diagram of step
It is important for efficiency improvement to reduce the gas leakage at steps.

Refrigerant gas

14% loss reduction

Lubricant100
Indicative loss
(leakage loss, etc.)
12%80

Low-pressurecompression
chamberHighpressurecompressionchamber

Lubricant rate: Low
Refrigerant gas leakage

Loss (%)

Leakage flowof lubricant

Mechanical loss
(bearing loss, etc.)
15%40Motor loss
15%

20
Lubricant rate: HighClearance seal by lubricant

0Fig. 4 Visualization of Step
Optimization of clearance size and lubricant content leads to reductionof refrigerant leakage

Conventional scroll

size and lighter weight compared with conventional
scrolls. MHI has commercialized 3D scroll compressors
for commercial air-conditioners and gas heat pump (GHP)
air-conditioners, and is planning to introduce 3D scrolls
in refrigeration units, etc. in the future. MHI is determined to contribute to the conservation of the global
environment through the promotion of energy-saving activities in refrigerating and air-conditioning systems.

Since the 3D scroll has steps in the compression proFig. 3
cess (Fig.
3), it is important for efficiency improvement
to reduce the gas leakage at steps. To solve this problem, visualization tests were carried out to determine
Fig. 4the behavior of leakage flow in the step (Fig.
4). Basedon test results, clearances at steps and the lubricant
content in refrigerant were optimized, and the gas leakage at steps was minimized. Fig. 5 shows the performanceof a 3D scroll compressor for commercial air-conditioner
compared with a conventional scroll compressor, indicating that the introduction of 3D scroll results in 14%
loss reduction (5.5% improvement of efficiency).

References(1) Sato, H. et al., Efficiency Improvement Technology for 3D
Scroll Compressor, Proc. of 2005 JSRAE Annual Conf., C310
(2005).
(2) Takasu, Y. et al., Development of High Performance 3D ScrollCompressor, Proc. of 2005 JSRAE Annual Conf., C309 (2005).
(3) Kimata, Y. et al., Development of High P e r f o rma n c e R
410A S c r o l l C omp r e s s o r for Gas Engine Heat Pump,
Proc. of 2004 International Compressor Engineering Conf.
at Purdue, C028 (2004)

4. Conclusion
The development of the 3D Scroll brought dramatically improvement of efficiency and reliability, smaller

Takahide Itoh

3D scrollFig. 5 Effect of loss reduction in 3D scroll(compressor for commercial air-conditioner)
Realization of 14% loss reduction compared with the conventional type.

3. Efficiency improvement technology for 3D scroll
compressor

Hajime Sato60

Makoto Takeuchi

Hiroshi Yamazaki

Makoto Fujitani

Hiroyuki Kobayashi

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)

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