What effect do non-condensables have on discharge pressure in a refrigeration system?

Non-condensables, such as air or other gases that do not change phase in the refrigeration cycle, can significantly influence the performance of a refrigeration system. When non-condensables are present in the system, they occupy space in the condenser and the evaporator. Due to their inability to condense like the refrigerant, these gases increase the overall pressure within the system, particularly at the discharge side of the compressor.

As the compressor continues to operate, it must work against this increased pressure, which can lead to a higher discharge pressure. This situation can reduce the efficiency of the system, cause overheating, and possibly lead to compressor failure if not addressed. Moreover, maintaining high discharge pressure may also result in higher energy consumption due to the increased load on the compressor.

In contrast, the other options do not align with the principles of refrigeration thermodynamics regarding the behavior of non-condensables. They do not lower discharge pressure, create a variable discharge pressure, or have no effect, as non-condensables consistently contribute to increased pressure in the system. Understanding this concept is critical for diagnosing issues within refrigeration systems and ensuring they operate efficiently.