Miljøprojekt, 1143 – Teknisk udvikling af chiller med CO2 som kølemiddel

Teknisk udvikling af chiller med CO2 som kølemiddel

2 English summary

2.1 Objective

The new Danish legislation puts a ban on the use of HFC in units with refrigerant charges above 10 kg in new equipment installed after Jan 1, 2007.

New solutions with natural refrigerant are demanded by the industry and currently quite a few viable solutions already exist and have proven well. However, in chiller applications in the capacity range from 80-400 kW viable solutions might be missing. Ammonia and hydro carbons may be applied, but the issue of price, toxicity and flammability, respectively, does represent an obstacle for the implementation of these refrigerants.

For this reason a technical and economical feasibility study has been carried out to investigate the potential of applying carbon dioxide in medium sized chillers.

Compared to other refrigerants carbon dioxide is non-toxic and non flammable (group L1 refrigerant in EN-DS-378). Furthermore, carbon dioxide may have benefits from a thermodynamic point of view if low ambient temperatures can be exploited throughout the majority of the operating hours. On the other hand, the higher pressure and the trans-critical operation may cause challenges in practice.

The objective of the project is to evaluate how CO₂chillers through design analysis and optimisation of operating strategies can be made competitive alternatives HFC in the range from 80-400 kW.

2.2 Conclusion

A detailed analysis of the operating conditions using hour by hour statistical Danish weather data reveals that the yearly average COP for CO₂chiller can be improved by up to 20% compared to conventional HFC chillers. The conclusion is based on a fully optimised gas cooler design which together with the proper operating strategy is outmost important.

This results is important because it incorporates an economical advantage of CO₂ along with the obvious environmental benefit. In other words, a buying motivation can be stimulated if CO₂chillers can be manufactured at prices comparable to HFC chillers.

A thorough analysis of assembly methods, skid arrangements and selection of optimised components indicate that the challenge in reducing cost is to a lesser degree associated with the high operation pressure compared to the cost influence of lower production volumes.

In conclusion, the potential exist to manufacture competitive chiller solutions with carbon dioxide for the Danish market. A commercial breakthrough is highly dependent on reduced prices trough simplified design and, hopefully production of scale benefits.