Triple rotary compressor pushes VRF boundaries

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Published: 03 June 2021


Reduced vibration with triple rotary compressor

David McSherry, TCUK's sales manager for Toshiba and DX, highlights the role of Toshiba's pioneering new compressor in delivering exceptional efficiency and other performance benefits in the company's latest Variable Refrigerant Flow system, SMMS-u.

At the heart of Toshiba’s latest VRF, the SMMS-u, is a ground-breaking new triple rotary compressor developed in-house, which significantly improves energy efficiency and overall reliability. And with a refrigerant pre-charge almost 50 per cent less than the previous model, it also offers significant safety and environmental benefits.

In recognition of its efficiency, the Japanese government-backed Energy Conservation Centre has awarded SMMS-u the country's highest technology award for innovation in this product and business segment. 

Volumetric efficiency

One of the keys to the new compressor's efficiency is its new multi-port design, which results in a significant reduction in pressure losses within the system. The previous generation of two-stage rotary compressors had just two ports; the new Toshiba triple unit has six.

The increased number of discharge valves smooths out the dynamics of gas flow within the compressor. It enables the higher volumes of refrigerant passing through the larger unit to be discharged much more efficiently, without consequential losses incurred with a conventional arrangement.

The discharge ports themselves are in two forms: the main valve and a sub-valve, with the size of each optimised to reduce losses due to over-compression and to handle large volumes of refrigerant vapour.
This design maximises compressor efficiency at both high and low load. This is important since air conditioning in most climates – and indeed in the UK and other Northern latitudes – tends to operate at part-load most of the time.

Reduced vibration

Another significant benefit of the triple rotary design is reduced vibration. The three compression chambers are positioned above one another on the vertical drive-shaft at perfectly offset 120-degree angles. 

This results in a very balanced configuration, with the forces generated during rotation and compression countering each other and enabling the assembly to rotate smoothly on the drive shaft. The result is a significant reduction in mechanical vibration. It also reduces wear on bearings and leads to improved reliability and extended operational life.

With three compression chambers arranged vertically on top of one another, the design creates a highly compact unit capable of delivering high cooling capacity in a small space. For example, a single Toshiba triple rotary compressor can displace up to 120 cubic centimetres and deliver up to 20 horsepower (56 kW). 

Special treatment

Reliability and efficiency are enhanced further with Diamond-like Carbon (DLC) treatment on key contact and wear points such as compressor vanes. DLC was developed for use in high-tech and extreme performance applications such as Formula 1 racing and aviation.

When combined with the new chassis design of SMMS-u, this results in an exceptionally compact unit that allows more cooling and heating capacity than ever before to be delivered from a restricted space. It also helps installers with logistics on site.

Further benefits include:

  • A new oil management system ensures continuous compressor lubrication and overcomes the need for piping for an oil balance circuit, speeding up installation on site.
  • A sensor-based defrost system that only initiates defrost when necessary, maintaining up to five hours of continuous heating, ensuring the comfort of building occupants at all times. In applications with multiple systems, the intelligent control system staggers defrost cycles across the systems to maintain overall performance, ensuring occupants' comfort.