At present, direct expansion refrigeration or air conditioning equipment using a Group B1 or B2 refrigerant is prohibited for indoor use under ANSI/ASHRAE-Standard 15-1994. The use of double walled heat exchangers also poses technical and economic challenges. A successful project would be a key step toward opening up new applications for Group B1 and B2 refrigerants, and would encourage HVAC manufacturers to invest in the development of new products using these refrigerants in double walled heat exchangers.

The objectives of this research project are twofold: 1) A risk analysis will evaluate the safety of a direct, double-walled indoor evaporator (or condenser in heat pumping) with a vented annular space. The body of existing literature and regulations on Group B2 refrigerants, and on double-walled heat exchangers for potable water systems and other applications, shall be reviewed. The risks are to be compared with those of equipment installed in a machinery room constructed as per ANSI/ASHRAE Standard 15-1994. One goal is to determine whether, and under what conditions, a residential or light commercial air conditioning system with a Group B1 or Group B2 refrigerant in a direct-expansion vented double-walled indoor evaporator could be made acceptably safe. 2) Structure and design criteria for double walled heat exchangers. Design options for a double-walled refrigerant-to-air heat exchanger, consistent with the safety requirements developed under Task 1, shall be reviewed. Design criteria shall be developed from a safety standpoint, spelling out the requirements for a system using a Group B1 or B2 refrigerant in conjunction with a double walled heat exchanger.

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