Design Considerations for an NH3 System Utilizing CO2 as a Secondary Refrigerant in Tokyo, Japan
Author: Kuniaki Kawamura, S. Akaboshi, Akito Machida, Nelson Mugabi, Quinn Vo, and Kelly Sasaki
Ammonia is one of the oldest refrigerants in industrial use today. It is a natural refrigerant with excellent thermal properties. However, most ammonia refrigeration systems in Japan are of the indirect type using secondary refrigerants such as propylene glycol or water. Most of the conventional secondary refrigerants have poor heat transfer characteristics and high pressure losses at low temperatures thus offering low system coefficients of performance (COPs). Carbon dioxide is being promoted as a secondary refrigerant because carbon dioxide is a natural refrigerant (ODP=0, GWP=1), non toxic, non-flammable and has good transport properties which results in low pressure losses in the pipes. The COP of the system, therefore, can be improved. This paper reports on development and application of a 2000kW (569 TR) ammonia refrigeration system with carbon dioxide as the secondary refrigerant which operates at three different temperatures.