Which type of refrigeration system is least likely to allow refrigerant leakage into the building space being cooled?

The indirect refrigeration system is designed in a way that minimizes the risk of refrigerant leakage into the space being cooled. In this system, a secondary fluid—typically water or a glycol solution—is used to absorb heat from the space and transfer it to the refrigerant. This separation between the refrigerant and the building's interior significantly reduces the likelihood of any refrigerant escaping into the occupied areas.

By utilizing this method, even if there were a failure in the cooling mechanism, the refrigerant is contained within a closed loop that does not directly communicate with the air or environment of the building. This design principle is crucial for maintaining safety and ensuring that any potential leaks do not endanger occupants by exposing them to refrigerants, which can be harmful.

In contrast, the other types of refrigeration systems, such as direct expansion systems, often involve refrigerants circulating directly in the areas being conditioned, which increases the risk of exposure should a leak occur. The gravity feed and open loop systems can also present similar risks, as their designs can allow refrigerants easier access to the occupied space. Thus, the indirect system stands out as the best option for minimizing the risk of refrigerant leakage.