Designed by Italian-based manufacturer SCM Frigo to “optimize” low-temperature (LT) demand, a CO2 (R744)-based system at a cold storage warehouse located in Santiago, Chile, has achieved an 8% energy efficiency improvement over a system with parallel compression.
The optimized system uses medium-temperature (MT) satellite compression, high-temperature (HT) compression, vapor ejection and adiabatic gas cooling.
The design and performance of the system at the Chilean facility ‒ owned by Friosan, a global investment fund group ‒ was presented by Mirko Bernabei, Technical Director and R&D Manager at SCM Frigo, and Pier Zecchetto, CEO of Chilean system installer Pórtan, at the ATMOsphere America Summit 2023, held June 12–13 in Washington, D.C. The event was organized by ATMOsphere, publisher of R744.com.
The warehouse, located in the commercial Pudahuel area, required 247TR (868.7kW) of -0.5°F (-18.1°C) LT cold storage for 16,000 pallet positions ‒ roughly 4 million cubic feet (113,276m3) ‒ and 76TR (267.3kW) of 32°F (0°C) MT capacity for a loading bay area, covering 262,000ft3 (7,419m3). Friosan wanted a sustainable, technologically advanced solution with high operational efficiency, Bernabei said.
Chile has a current deficit of 100,000 pallet positions for frozen logistic storage, according to Bernabei. “The Friosan project will cover 16% of the deficit, with the objective of being the lowest cost operator by using robotized and automated systems operation.”
Design parameters in Santiago required the system to operate efficiently in 95°F (35°C) ambient temperatures with 54% relative humidity during the summer and meet seismic construction codes for up to a 9᠆degree magnitude earthquake.
For safety, sustainability and reliability reasons, Friosan chose to go with CO2, said Zecchetto. “This customer didn’t look to make a simple CO2 system but instead wanted to optimize cost and keep reliability.”
The warehouse met design parameters for five LT cold rooms, individually built and separated by 6ft (1.8m) to meet seismic codes, and one MT loading bay, Zecchetto said.
Two triple-temperature CO2 systems
Two CO2 booster systems, each using LT, MT and HT compressors, provide each cold room with 50TR (175.8kW) at -13°F (-25°C) saturated suction temperature (SST), said Bernabei, adding that every room contains eight LT cubic evaporators operating with dry expansion and two fans.
As part of the multiple-compressor rack, a MT “satellite compressor” connects to the loading bay that operates at 76TR capacity at 17.6°F (-8°C) SST. The loading bay uses eight MT cubic evaporators with dry expansion and three fans, he added. “The satellite compressor shares a common discharge and gas cooler with the rack, but it has an independent suction line from the loading bay and operates with a lower SST than the other MT suction groups.”
The satellite compressor does not receive the flash gas generated on the expansion of the high-pressure valve, Bernabei said in response to an inquiry. “All the flash gas produced in the unit is managed by the HT compressor, which acts as a parallel compressor with a 46.4°F [8°C] SST to optimize the energy efficiency.”
“We optimized the design of the LT, the major load of the system, to bring the interstage pressure at the best pressure possible for efficiency,” Bernabei said. “The combination of systems, especially with the satellite compressor configuration, gains 8% of energy efficiency in the design compared to a parallel compression system with less complexity.”
In ambient temperatures above 68°F (20°C), a vapor ejector lifts part of the MT mass flow (at -8°C SST) to the liquid receiver (at 8°C SST) and then to the HT compressor. “This lifting is generated free of charge by the ejector, allowing the lifted mass flow to be compressed at the higher temperature,” said Bernabei. “When in operation, the vapor ejector can improve efficiency up to [an additional] 12% on average.”
The facility is running with less than 50l (13.2gal) of oil and a CO2 charge below 3,500lbs (1,578.6kg), Zecchetto said.
At the time of the presentation, four LT cold rooms and the MT loading bay were operating, with the fifth cold room expected to be operational in early July.
Resale plans
As an investment group, Friosan plans to resell this cold storage facility within five years, Zecchetto said, with the price linked to efficiency and good practices. Since fats and proteins are better preserved in certain conditions, the investment hinges on receiving a “premium” price for exported high-quality animal proteins based on guaranteed temperature control.
From data collected in January, with temperatures ranging from 95°F (35°C) during the day and down to 65°F (18.3°C) at night, the system “provided a narrow difference of 3.3°F [1.8°C], between the temperature coming out of the evaporator and the temperature in each control point in the cold room,” Zecchetto said, which assures quality around the cold room.
The robotics complicated the installation, with a 5ft (1.5m) maximum vertical space left to place the evaporators. The sloped roof required the installer to design a tiltable system for the evaporator installation near the top of the 75ft (22.9m)-high ceiling, Zecchetto said.
In addition, water discharge had to be carefully controlled to prevent electrical issues; the robots and heaters were relocated and individually alarmed.
Energy consumption data from January 1 to late April of 2023 showed the facility spent 2.2W of electrical energy per cubic yard (2.8W/m3). “If we apply it specifically to LT storage, it’s more like 1.7 or 1.8W per cubic yard [2.2‒2.4kW/m3],” Zecchetto said.
Friosan’s commitment to sustainability calls for the system to run solely off renewable energy, Bernabei said. The building is LEED (Leadership in Energy and Environmental Design) certified, with the sectioned cold rooms using robotic openings to “optimize” the electricity.
The cooling and condensing systems use air and adiabatic cooling via micro-sprayed tap water to conserve water resources, Bernabei said. Gray water from the system is treated and used to irrigate sustainable green areas that contain native flora.
Located in Santiago, Chile, Pórtan has 30 years of experience installing HVAC&R systems. “We have been working in CO2 transcritical installation for the last eight years,” Zecchetto said.
Founded in 1979, SCM Frigo produces CO2 subcritical packs, cascade systems, transcritical chillers and booster systems. The Piove Di Sacco, Italy-based company is part of the Swedish Group Beijer Ref.
“We optimized the design of the LT, the major load of the system, to bring the interstage pressure at the best pressure possible for efficiency.”
Mirko Bernabei, Technical Director and R&D Manager at SCM Frigo
