What component is commonly added to a hot gas defrost system that is not used in a warm water defrost system?

In a hot gas defrost system, an accumulator is an essential component that serves a specific function. The primary role of the accumulator is to collect excess refrigerant vapor that might not have evaporated in the system during the defrost cycle. This is particularly important because the defrost cycle introduces additional heat into the system, which can lead to increased pressures and vapor flowing through the HVAC system.

During a hot gas defrost, the refrigerant is diverted to the evaporator to melt ice buildup, and without an accumulator, this vapor could cause issues, such as flooding of the compressor and potential damage or inefficiencies in the system. The accumulator ensures that only the needed vapor is sent to the compressor, maintaining system efficiency and protecting components.

In contrast, warm water defrost systems utilize heated water for melting frost and do not require the same management of refrigerant in vapor form because the operation differs significantly. The other components listed, such as the evaporator coil, expansion valve, and condensing unit, are standard in both systems, making the accumulator a key differentiator in hot gas defrost applications.