Integrated CO2 solutions
Bitzer’s Oliver Javerschek was another to promote integrated CO2 solutions (MT and LT compressors, heat recovery, air conditioning) during his technology case study along with CAREL Japan and Bitzer, who are working closely together at a laboratory in Germany to improve the efficiency of integrated systems through suction optimisation and an MP optimisation system.
“CO2 is the ideal refrigerant for integrated solutions,” he argued. “Integrated systems offer high annual energy efficiency and reduce or even avoid combustion of fossil energy for heating.”
Javerschek’s claim that CO2 is safe, devoid of regulation and a ‘naturally superior’ refrigerant in moderate climates was backed up by performance figures from case studies cited. A small booster system using parallel compression in a Tokyo supermarket (1,600m2 heating area) with LT / MT / heating capacities of 15 kW / 60 kW / 50 kW respectively saved as much as €10,600/annum (JPY 1,350,000) based on variable fossil fuel and electricity prices.
In addition, he noted, the use of waste heat for heating the supermarket can supply the AC to achieve high seasonal efficiencies, while ejectors can achieve further energy efficiency improvements.
CAREL’s high efficiency integrated CO2 system using parallel compressor incorporates an MT compressor, an LT compressor, a heat recovery heat exchanger, a gas cooler, TC and flash gas valves, suction optimisation valves, and an MP dynamic optimisation system.
The parallel compression is used to reduce use of the excess flash gas valve and help stabilise the temperature in high ambient conditions, while the suction increases interaction between the compressor lines, in turn increasing efficiency. The optimisation system allows for dynamic control of the medium pressure inside the receiver.
CAREL is the only company currently on the market offering an expansion valve for CO2 transcritical and ammonia systems. With parent company Shibata Welding Construction, it introduced a TC booster at an R&D centre in Japan. With energy saving results of 9% (traditional booster) and 4% (booster + parallel compression), the company hopes to spread the technology to high ambient regions in Japan, as it has already proven effective in Europe.
Sanden CO2 compressors show variety
Sanden’s Yukio Yamaguchi highlighted the 50% decrease in initial costs the company has seen for its CO2 compressors in the past five years and a move to develop the technology for air conditioning (AC) for machines. In regards to showcases for commercial applications Sanden achieves around 15% in energy savings, while Yamaguchi quoted figures of around 23% for machine AC with CO2 compressors.
In 2015, Sanden reached sales of 1.5 million CO2 compressors (since 2010), a huge step towards further cost reductions. “Going forward we are expecting to see further impact as the volume increases, so the cost parity with HFCs can be achieved,” Yamaguchi said.
For CVS, Sanden’s CO2-CO2 cascade system with pressure control is achieving excellent efficiencies in high ambient temperatures, and as a result the company would like to conduct a demonstration in a hot climate in 2016 to share relevant market data with the industry. The water-loop system, which can be stopped in winter and features heat recovery supplying hot water, was introduced into a store in Switzerland and will be fitted in a further 300 stores by March.
Affordable, efficient, compact
In his case study, Abel Gnanakumar of Emerson Climate Technologies described cost, efficiency and compactness as the three main priorities for the continued development of CO2 systems.
Emerson’s CO2 booster system mixing scroll and piston compressor technology has been very popular in Australia and New Zealand, and Gnanakumar said it was looking to roll it out in Japan and China. “We believe the technology is applicable in Japan. Very close collaboration is required with customers to ensure success,” he said.
Gnanakumar said the company did not find any specific engineering requirements to mix the compressor technology in one pack, which can “easily” be paired with parallel compression and even an adiabatic cooler to mitigate the lower efficiencies in high ambient temperatures.
More broadly, Gnanakumar said a market-wide shift to CO2 realistically required 100% cost parity with HFC systems. 50 of Emerson’s booster systems are currently operating in the UK, but even after seeing 21% cost reductions, the technology remains 35% more expensive than a comparable HFC pack. The CO2 booster achieves energy savings of 3%, and 10% with heat reclaim.
Yamato’s Toshiaki Hosono presented case study data on the performance of its Ultra Eco-Ice system with a new CO2 pressure adjust control system based on the first prototype developed in August 2015.
The brine ice thermal storage-equipped system differs from standard direct expansion CO2 systems in that it is more compact. The benefit of using the brine (secondary coolant) system to produce and store ice and cool the store’s display cases include reducing daytime electric power demand (peak cut), higher energy efficiency, and greater safety due to the thermal storage.
Yamato will continue to improve the technology in 2016 with the goal of achieving a further 10% reduction in energy consumption.