Increased Efficiency in CO₂ Plants with Alchemist Subcooler
Torraval Cooling Demonstrates the Impact of Adiabatic Cooling on CO₂ Systems Using Real Data
This time, Torraval Cooling presents real-world results showing the benefits of adiabatic cooling through the use of the Alchemist subcooler—an innovative solution designed for transcritical CO₂ cycle plants.
Developed by MITA (patent no. 17194148.7) and currently marketed by our company, the Alchemist is designed to be integrated just after the gas cooler and optimizes performance in transcritical CO₂ systems, particularly in the demanding commercial refrigeration environment.
Objective of the Adiabatic Subcooler Study
The aim of this case study is to showcase the benefits of the Alchemist subcooler, including:
- Reduction in energy consumption.
- Lower working pressures in the refrigeration circuit.
System Installation Features
- Location: Vicenza province, Italy.
- Maximum design power of the MT line: 164 kW.
- Central refrigeration system configuration:
- 4 Dorin compressors, model CD 300 H (one with frequency inverter).
- 1 Dorin compressor, model CD 300 H (with inverter, parallel compression).
- 1 Alchemist adiabatic subcooler, model 4000 SR.
Collected Data on Subcooler Operation
The hottest period of the year was chosen to collect real operational data over six consecutive days in summer 2022, from 01:00 Monday to midnight Saturday. The Alchemist was automatically turned on and off to compare the following parameters:
- Refrigerant outlet temperature.
- Operating pressure.
- Evaporation temperature.
- Total electrical consumption (including fans from the gas cooler and the Alchemist).
- Water consumption by the Alchemist subcooler.
Based on this data, the following were calculated:
- Thermal energy provided by the system.
- COP (Coefficient of Performance) evolution, including the energy use of the gas cooler and Alchemist fans.
During the analysis week, outdoor temperatures peaked at 35°C.
Key Results
- Refrigerant Temperature Drop
Using the Alchemist significantly reduced refrigerant outlet temperature. Over the six-day test, the average drop was 8°C when the subcooler was active.
- Reduced Working Pressure
Pressure correlates with refrigerant outlet temperature: the lower the temperature, the lower the required pressure. With the Alchemist in operation, a mean pressure reduction of 6.4 bar was achieved, directly improving efficiency.
The system operated in a transcritical regime (> 73.5 bar) almost all the time, except for a brief period late Friday when the Alchemist was deactivated.
- Energy Savings
The most relevant parameter is total energy consumption, including all fans. Comparing days with and without the Alchemist showed significant savings:
- Over 1,100 kWh saved in just three days (~27%).
- Associated water consumption: 3.8 m³.
- Considering more standard conditions (e.g., high relative humidity >75%, where the system is recommended to be turned off), the adjusted average saving would be 22%, with water consumption around 3.2 m³.
Energy Performance (COP)
Based on collected data (pressures, temperatures, and Dorin-provided formulas), the system’s overall efficiency was calculated:
- Average COP with Alchemist on: 2.54 (very high, considering an average ambient temperature of 30.6°C).
- Average COP with Alchemist off: 1.90 (with only a 0.2°C higher average temperature).
During the hottest hours of the day, the COP dropped below 2 without the subcooler.
Conclusions
The study conducted during the hot summer of 2022 shows that using the Alchemist significantly reduces the electrical consumption of refrigeration systems, with very low water usage.
Additionally, it has been confirmed that its effectiveness remains even in subcritical operating conditions, making its installation advisable for all transcritical CO₂ systems, regardless of location.
At Torraval Cooling, we are committed to solutions that improve energy efficiency and reduce environmental impact, and Alchemist is one of the most effective tools in this regard.