Two Italian companies working in collaboration ‒ compressor manufacturer Frascold and startup Aircodue, a spin-off of the Miri Group ‒ have developed a CO2 (R744) heat pump for railway carriage heating and cooling that offers up to 58% energy savings compared to the existing R134a system.

“The heat pump delivers savings ranging from 51% to 58% depending on the zone, with a considerable reduction in terms of tons of CO2e emissions into the atmosphere,” said Mirco Pasotti, Sales Area Manager at Frascold.

The new system ‒ designed to comply with the European F-gas Regulation and standards for fire safety and smoke control ‒ meets the underpinning goals of the partnership to save energy while enhancing reliability with low maintenance cost and low environmental impact, Frascold said in the press release. “The teamwork revolutionizes the sector by developing an innovative CO2 heat pump, featuring several technological innovations and equipped with compressors from Frascold’s transcritical series.”

“In addition to being a viable solution to the phase-out policies for fluorinated refrigerants, CO2 complies with the environmental and safety policies of the leading players in the industry,” said Giovanni Paone, Aircodue’s Chairman.

The project sought to develop a new CO2 heat pump system to replace a drop-in R134a system that would operate within the existing configuration with an outdoor unit containing primary and auxiliary circuit compressors and an indoor unit providing 28kW (7.96TR) cooling and 16.1kW (5.58TR) heating capacities for the passenger space. Frascold noted that the new system had to stay within the power requirements of the original one.

“A major design project for the railway industry, where the choice of a natural refrigerant requires careful evaluation in terms of installation and regulatory framework,” said Luigi Buttiglione, Aircodue’s Technical Manager.

The team used Frascold’s D-TK model transcritical CO2 compressor to compare theoretical performance data with a conventional system. Through dynamical simulation of the energy diagnostics of a medium-distance vehicle operating at locations representative of Italy’s main geographical areas, the analysis predicted 51% energy savings and a reduction of 6.8 metric tons of CO2e emissions annually at Brenner Pass; 57% and 3.2 at Rome; and 58% and 1.8 at Palermo.

“Once a prototype was built, a large-scale climate chamber testing program was carried out, during which the performance was verified, thereby confirming the theoretical data,” Frascold said.

“Frascold played a key role by its expertise in the field,” said Paone, adding that the manufacturer has been a long-standing partner in the development of “next-generation technologies for responsible evolution in the sector.”

Compressor technology

According to Frascold, the TX piston series in its transcritical CO2 D-TX model is known for efficiency, flexibility and reliability, with a “robust” design and up to 100bar (1,450psi) standstill pressure. 

The CapaFlex mechanical regulation of the series allows modulation of the refrigerant flow through the suction inlets. “The alternating opening and closing intervals ensure correct partialization of the compressor, resulting in an optimal load that minimizes on-off cycles,” the company said, which benefits performance.

In addition, the D-TK has low oil carry-over that minimizes leakage.

Headquartered in Milan, Frascold announced new CO2 and propane (R290) compressors and extended compressor lines in 2018, 2019 and 2020. To develop better semi-hermetic compressors, the company upgraded its testing facility in 2021, according to an article

“Frascold is, in fact, ready to support OEMs and end users in exploring the trends that will guide the future, such as the use of transcritical CO2 in the industrial sector and propane for heat pump applications,” said Marco Perri, R&D and Technical Support Manager at Frascold.

Under its Air Source Reversible CO2 Air Conditioner (ARCA) project, Aircodue aims to place “patented, innovative and sustainable products and solutions on the market,” according to the company’s website.

“The heat pump delivers savings ranging from 51% to 58% depending on the zone.”

Mirco Pasotti, Sales Area Manager at Frascold