R744 innovations from Japan Part 1: pressure adjusted control and multiple compressors improve system efficiency

By Janaina Topley Lira, Feb 11, 2015, 18:24 6 minute reading

At ATMOsphere Asia 2015, presentations during the Commercial Refrigeration Technology Case Studies session by Panasonic and Sanden showcased the unique features and benefits of their respective CO2 systems for convenience stores (CVS). Whether it is Panasonic’s new “pressure adjust control” system or Sanden’s system with three compressors in cascade, each is smaller, lighter and cheaper than comparable conventional models.

From the 3-5 February leading HVAC&R stakeholders gathered in Tokyo for the second ATMOsphere Asia conference to discuss the latest technology trends in natural refrigerants. R744 was in the spotlight, with a number of presentations focused on the latest technological breakthroughs for CO2, including for convenience store applications and warm ambient temperatures, and on the challenges that remain to further expand the market for climate friendly CO2 systems. In part 1 of our reporting we focus on the presentations from Panasonic, Lawson and Sanden.
Improved efficiency through 2-stage compression and split system
In his presentation Hidekazu Tachibana, General Manager at Panasonic discussed the company’s various innovations to improve the efficiencies of its CO2 refrigeration systems. The first of these innovations is a two-stage compression solution, which has the following benefits:
  • Reduces pressure differential, thereby reducing leakage
  • Improves compression efficiency
  • Weight and cost of casing is reduced, as it is designed for intermediate pressure
  • Vibration and noise reduced
  • Temperature of the sliding parts and oil reduced thanks to cooling the discharge gas in the intercooler reduces
The second innovation Tachibana presented was Panasonic’s CO2 split system, whereby the refrigerant is partially branched off from the gas cooler and decompressed to intermediate pressure in a split expansion devices. A split heat exchanger then cools the refrigerant in the main circuit. Because the refrigerant discharged by the outdoor unit is cooled off to a lower temperature, then ambient temperature, the cooling capacity of the unit increases. 
Smaller, lighter and easier to install, Panasonic’s “Pressure adjust control” system
Panasonic's third innovation is its “Pressure adjust control” CO2 refrigeration system, in which the transfer pressure from the condensing unit, is automatically controlled. This solution addresses the fact that a change in outdoor temperature has a significant impact on the output pressure to the showcase, which can vary from 5-9MPa. The “pressure adjust control” type means the pressure to the showcase is maintained at about 6MPa in all seasons. 

In addition to being smaller, lighter and easier to install than current models, other system benefits include:
  • 34% reduction in CO2 unit size for 20 and 15 HP models, and 35% reduction in CO2 unit size for 10HP models
  • 20% decrease in weight for 20 and 15 HP models, and 23% reduction in weight for 10HP models
  • 1 fan, as opposed to 2, which reduces noise levels
  • 59% decrease in piping weight thanks to the adoption of thinner, high-strength copper piping
Panasonic will have four of the new “pressure adjust control” type models in 2015. In addition, a new 2HP model will be made available in May. The company will also offer 651 different showcase models, up from today’s 271 models.

Lawson striving to be ‘the world’s number one natural refrigerant retailer’
Japanese convenience store operator Lawson is making big strides with their adoption of CO2 solutions. In his presentation, Lawson's director Shinichirou Uto talked about the Japanese convenience store's plans to install CO2 in all new outlets and reduce energy consumption by 20% across all stores compared with 2010 FY (Fiscal Year). 
Lawson, which operates 12,000 stores, adopted CO2 refrigeration as its standard technology for all new stores, in 2014, and has stated its desire to become ‘the world’s number one natural refrigerant retailer’. Lawson is rapidly approaching the international benchmark set by Denmark, of 712 CO2 stores, with the retailer currently at 461 CO2 stores.
For each new store Lawson introduces it will implement two CO2 systems, a 10HP and 2HP CO2 transcritical compressor, including the following benchmarks:
  • Lawson expects to have opened 570 stores by the end of February 2015
  • The CO2 technology will save 27% in energy costs
  • With newer generation CVS (15HP and 2HP compressors) energy savings of 21%
Lawson director Shinichirou Uto said the main problem facing the company’s CO2 goals was the lack of technical training in Japan.
“It has been a long road and we have overcome many challenges. The biggest problem was the lack of training, so we had to provide training to Lawson’s refrigeration technicians, for which we received the cooperation of the system manufacturers,” he said.
Sanden’s micro channel gas cooler and unique CO2 system with three compressors
Sanden’s Yukio Yamaguchi, General Manager within the Department of CO2 Refrigeration, presented a number of his company’s CO2 products, which include five models of CO2 reciprocating compressor and vertical and horizontal scroll compressors. In addition to these Sanden has developed an all aluminium micro channel gas cooler, which compared to a fin and tube gas cooler features:
  • 15% increase in capacity
  • 75% smaller size
  • 58% lighter 
  • 60% cheaper
Sanden has also developed 6HP and 2HP CO2 transcritical units, as well as CO2 plug-in showcases and CO2 open front drink coolers. Sanden’s outdoor CO2 units are unique in that they have three compressors installed in a cascade system. This enables Sanden to reduce the refrigerant charge. What is more, in the event of a compressor failure the redundancy in the system means the temperature can be maintained. According to Yamaguchi, thanks to Sanden’s CO2 system it is theoretically possible to improve COP by 1.5 times compared with a standard system. 
Other merits of the Sanden system include:
  • Easy installation
  • Smaller copper tube dimensions, reducing system costs
  • No need for ventilation system or CO2 sensor 

Emerson's iPro and evaporator expansion valve control (EXV)
Emerson Technologies presented its improved controls designed to optimise CO2 system pressure by improving flash tank pressure stability, evaporator pressure, and temperature stability.
The iPro CO2 high pressure controller functions in both subcritical and transcritical temperature ranges, enhancing flash tank pressure stability in the following ways:
  • Subcritical operation: helps maintain subcooling in the condenser by subcooling at the outlet of the gas cooler, based on a point the user sets
  • Transcritical operation: controls gas cooler pressure
  • Transient operation: ensures hard switch into either sub or transcritical operation to avoid system destabilisation at the ‘rapid density change zone’
  • Original controller pressure varied within 7 bar, I-pro enhanced to within .7 bar 
Emerson’s evaporator expansion valve control (EXV), which has been widely adopted in Australia since 2013, has two control points to maintain a more steady case temperature and pressure. To achieve this, the valve modulates on a set time cycle in fully open and closed positions. In conventional control methods, the EXV pulse width modulation (PWM) is determined by the target super heat, while in continuous control mode, it is determined by the target super heat and case temperature. Essentially, because there are two control points in continuous control mode, the controller ‘knows’ the capacity needed and rarely drops to 0% PWM.


By Janaina Topley Lira

Feb 11, 2015, 18:24

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