Italian manufacturer Carel has worked with a small Danish servicing company B Cool to develop a new fully modulating CO2 (R744) refrigeration rack specifically for maritime applications, and the prototype, which was retrofitted to a vessel in April, has shown a 20% improvement in COP.

This result and more insight into how the system works was presented during the Transport and MAC session of 2022 ATMO Europe Summit by Federico Ferrari, Sales & Marketing – Application Specialist at Carel, together with Ejner Brodersen, Chief Executive Officer at B Cool A/S. ATMO Europe was held in person in Brussels on November 15–16 and was hosted by ATMOsphere, publisher of R744.

Although natural refrigerants and especially CO2 is rapidly growing in commercial and industrial applications, the same has unfortunately not been true for the maritime sector, explained Ferrari. That is why Carel was happy to get involved with a “creative project” such as the one proposed by B Cool, explained Ferrari.

A slide from Carel showing the increase in natural refrigerant projects.

Recognizing the gap for “green” refrigeration

B Cool is a small marine service company in Denmark. It used to service the HVAC&R systems on cruise ships as its main business. However, when the pandemic hit, this market disappeared totally for them. The company decided to look at something different and change course. That’s when they decided to act on the need they identified in the maritime for “greener” HVAC&R, explained Brodersen.

B Cool then spent two years during the pandemic to develop this system with Carel, who now had the opportunity to enter the maritime sector by providing the components needed. After two years of testing at B Cool’s facility, the prototype was installed in a vessel in Kalundborg, Denmark, in April 2022.

For the prototype, two identical units were designed and installed to ensure 100% redundancy. The rack serves one cold room and one freezer room and includes two medium-temperature (MT) compressors and two low-temperature (LT) compressors at a load of 1.6kW (0.5TR) MT at -6°C (21°F) and 3.5kW (1TR) LT at -28°C (-18°F).

To address the challenge of changing ambient temperatures as the vessel moves around the world, a plate heat exchanger (PHE) gas cooler was installed. It is cooled by the process water of the ship with a temperature of 20–38°C (68–100°F), depending on geographical location.

Thanks to the compact nature of the system, installation was relatively easy, explained Brodersen. The entire installation took only 10 days from start to finish.

Benefit to the owner

One of the reasons the vessel owner agreed to be the first to trial this new system was to improve its image as being more “green,” said Brodersen. The owner wanted to be HFC-free as he had a big problem with leaks (around 20%) and was concerned about the availability and cost of f-gases. By retrofitting to CO2, emissions equivalent to 35 metric tons are saved.

Another big plus was an efficiency improvement of 20% over the system that was retrofitted. The new system also had a smaller footprint and resulted in space saving.

The CO2 rack comes with remote troubleshooting and service capabilities – very beneficial for a vessel that travels around the world. This gives the customer great peace of mind. Live training and support for the vessel’s crew is even available through the use of smart glasses. The only challenge is the lack of internet while on the sea. Though once at a port, this is no longer an issue.

Brodersen confirmed that more companies are now interested in retrofitting their vessels with this CO2 solution.

A closer look at the system

Together with Carel, B Cool developed this compact multiDC booster rack for complete with rotary compressors from Toshiba. In addition to the compressors, Carel also provided the controls and inverter probes with the possibility to also supply evaporator controllers, supervisory systems and electrical panels if needed.

The modular compressor setup can support up to six MT compressors and two LT ones. It has an extremely wide modulating range between 5 and 100% ,and its compact nature makes it ideal for retrofits.

Carel’s DC inverter technology is at the core of this solution, explained Ferrari. Compared to the standard AC compressor, it has a wider capacity modulation and can also reach higher cooling capacities, he said.

Because of the wide modulation range, the critical point is the oil separation. As such, Carel invented a patent-pending oil management system. Fully developed by Carel’s R&D team, the multiDC oil management function is fully integrated in the solution with dedicated oil check valves, software logics and a custom design for Toshiba’s DC rotary compressors.

The new prototype rack installed in the vessel (on right) shows the space saved versus the original system (on left).