This code applies to refrigerating systems and heat pumps used in the occupancies defined in Section 3. It does not apply where water is the primary refrigerant. Application: This Code shall apply to refrigerating systems installed subsequent to its adoption and to parts replaced and components added after its adoption. Equipment listed by an approved nationally recognized testing laboratory is deemed to meet the design, manufacture, and factory test requirements section of this Code, for the refrigerant or refrigerants for which such equipment is designed. Exceptions: In cases of practical difficulty or unnecessary hardship, the authority having jurisdiction may grant exceptions from the literal requirements of this Code or permit the use of other devices, materials or methods, but only when it is clearly evident that equivalent protection is thereby secured.