The demonstration project has received support from the government of Japan, noted Gaku Shimada, Manager, SANYO Electric Co., Ltd. during the presentation he provided at the ATMOsphere Europe 2011 workshop on natural refrigerants (October 2011). Moreover, Lawson’s will endeavour to have 500 stores with CO₂ by 2016.

Mr Shimada also presented a theoretical approach for measuring CO₂ unit efficiency that was in line with the trends found when measuring real performance of the units that have already been installed by Lawson in a store in the Kyoto Prefecture.

The CO₂ units

The candidate standard technology foreseen for 2015 to cover the needs of a typical 200m² Lawson store will encompass 2 CO₂ units:

• a 10 horsepower outdoor unit for refrigeration and
• a 2 horsepower unit for the freezers

Measured performance of first convenience store with CO₂ units

The first convenience store with CO₂ outdoor units has been operating since December 2010 at a Lawson’s convenience store located in the Kyoto Prefecture.

Measurement data have showed that the CO₂ split cycle performs better than the original R404A system by:

• 16-26% at LT application and
• 0-30% at MT use

The cross point exists at high ambient temperature of more than 32°C average daily temperature (corresponding to day temperature of at least 40°C).

“So we can confirm that CO₂ performed very well in the field”, said Mr Shimada.

A new theoretical approach for measuring CO₂ performance

The measurement data found the CO₂ performing better than what theoretical comparisons between CO₂ and R404A would typically denote. Several reasons could explain this including:

1. CO₂ performs relatively better in cold climates, hence AT 32°C comparison may not be fair.
2. Components are different (e.g. HX, DC inverter motor, ...).
3. The refrigeration cycle is different, and what is a good cycle for R404A is not the best for CO₂ and vice versa.

Using an alternative theoretical approach for calculating CO₂ performance

To address the third reason for which there is a notable discrepancy between the theoretical and actual measured performance, namely the cycle difference, SANYO used an alternative theoretical approach to calculate performance.

Whereas the “performance of COP can be underestimated when using the same outlet temperatures, […] instead we divided the gas cooler in 100 pieces and applied the same heat transfer coefficient for each piece”.

Theoretically calculating the efficiency based on the same heat transfer coefficient denoted the same trend as measurement data and showed that the CO₂ split cycle is better than the original R404A system:

• by 3-7% at LT use and
• is about the same at MT use

The remaining gap of efficiency comparison (measured v.s. calculated) could be attributed to improved components such as DC inverter motor. 

About SANYO

SANYO Electric Co., Ltd. was founded in 1947. It currently employs about 86,000 people around the globe and has more than 230 subsidiaries and affiliates worldwide. Its products and services are divided among four business segments: consumer, commercial, components, and other. SANYO\'s Brand Vision "Think GAIA" reflects a threefold approach focusing on the environment, energy and lifestyle.