Mexican manufacturer of industrial refrigeration equipment and systems Frigus Bohn de Mexico has delivered a large custom-built ammonia (R717) and CO₂ (R744) combined HVAC&R system for a food production facility in Mexico.

The unorthodox system comprises two ammonia-based chillers for medium- and high-temperature applications at the facility and a glycol-cooled subcritical CO₂ system – the glycol delivered by medium-temperature ammonia chiller – to meet its low-temperature needs.

Once the facility is operational, the customer, which has not been named by the manufacturer, will produce 23,000 baked goods per day for around 70 retails sites across three Mexican states.

R717 and CO₂ for multiple temperatures

According to Xavier Flores, Application Engineer at Frigus Bohn, the combined system includes OSKA-series compressors from German manufacturer Bitzer and chillers from Finland-based Vahterus.

The first of the two chillers serves the facility’s HVAC and has a total capacity of 756kW (215TR) with one 200HP compressor. It will supply 7°C (44.6°F) water to 54 water-cooled diffusors to provide thermal comfort in the site’s process rooms and offices.

For medium-temperature applications such as cold rooms, the second ammonia-based chiller has a total capacity of 992kW (282TR) that is divided into two 200HP compressors. It will serve 32 circuits including glycol diffusors – with glycol at -4°C (24.8°F) that will also cool the CO₂ system’s condensers.

The R744 system serves low-temperature storage at the facility, as well as its “quick-chill tunnels” for cooling goods after they are baked, with operating temperatures around -24°C (-11°F). The total capacity of CO₂ system – which includes three Bitzer subcritical compressors with a total of 65HP – is 218kW (62TR).

The CO₂ system uses the three compressors – one at a -8°C (17.6°F) suction temperature and condensing at 4°C (39.2°F) –  with three plate-and-shell heat exchangers (PSHEs) condensers (one for each compressor) using cold glycol from the medium-temperature ammonia chiller. A small stainless-steel air-cooled gas cooler is also used to reduce the temperature coming from the discharge of each CO₂ compressor, preventing the condensers from suffering “high thermal stress,” said Flores.

But the main heat transfer takes place in the condensers, which use the ammonia-chilled glycol to keep lowering the discharge CO₂ temperature “until the condensing point and the condensing process,” he added.

Growing demand for NatRefs

Frigus Bohn (Bohn Mexico) was established in 1994 as a joint venture between the Mexican company Frigus and U.S.-based Heatcraft Worldwide Refrigeration, of which Bohn is a brand. Frigus Bohn has traditionally focused more on HFC-based systems. However, over the past five or six years, the manufacturer has noticed a growing interest in CO₂ and ammonia, explained Flores.

To meet this increase in demand for natural refrigerants, in 2016 Frigus Bohn created a division to work on ammonia-based products for industrial applications, he added.

For commercial refrigeration, the company manufactures transcritical CO₂ booster systems for supermarkets and cascade systems for smaller applications.

When discussing the company’s newly built ammonia-CO₂ system, Eloy Espinosa, Director of Engineering at Frigus Bohn noted that for the company and its customer this was an “important step into the world of natural refrigerants.”

Frigus Bohn had installed the ammonia-CO₂ configuration in two projects before this one, both for the same application – cold-storage rooms for rent, said Flores. Frigus Bohn is aware that industrial refrigeration companies in Europe have used this solution “to keep the ammonia inside the chiller and avoid ammonia installation and piping entering into the storage rooms,” he noted.

In the region, the growing interest in natural refrigerants is driven partially by regulation, such as the Montreal Protocol and its Kigali Amendment, and partially by corporate sustainability concerns, said Flores.

“Smaller businesses tend to be driven almost exclusively by regulation,” Flores said. “Whereas larger businesses have a greater interest in the additional benefits associated with natural refrigerant-based systems, like lower refrigerant charges and higher energy efficiency.”

“Larger businesses have a greater interest in the additional benefits associated with natural refrigerant-based systems, like lower refrigerant charges and higher energy efficiency.”

Xavier Flores, Frigus Bohn

While the company has a strong engineering base in “traditional” synthetic refrigerants, it is now interested in expanding into newer systems that use ammonia and CO₂, Flores added, noting it would be good to “get ahead of the market before it becomes mandatory.”