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