In an indirect refrigeration system, which of the following is NOT used as a cooling medium for building spaces?

In indirect refrigeration systems, the cooling medium typically consists of substances that can carry heat away from the refrigerated space and transfer it to another medium that is ultimately used to cool the building spaces. The use of R22 refrigerant as a cooling medium is generally classified under direct refrigeration systems rather than indirect ones.

Ammonia, water, and brine solutions are suitable for use in indirect systems. Ammonia is commonly used for its efficiency in industrial applications, while water acts as a common heat transfer fluid in many cooling systems. Brine solutions, which are mixtures of water and salt or other antifreeze solutions, serve as effective coolants, particularly when temperatures need to be lowered beyond the freezing point of water.

Given the context of indirect refrigeration systems, the use of R22 refrigerant does not align with the conventional practices of cooling as it typically serves as the refrigerant in direct systems, where it absorbs heat directly from the building space. Thus, R22 is not used as a cooling medium for building spaces in the context of an indirect refrigeration system.