What are the two mechanisms that can terminate defrost in a heat pump system?

In a heat pump system, defrost termination is crucial for maintaining efficient operation and preventing frost build-up on the outdoor coil. The two primary mechanisms utilized to determine when to terminate the defrost cycle are time and temperature.

Using temperature as a termination criterion ensures that the system stops the defrost mode once the outdoor coil has reached a specified temperature, indicating that the frost has likely melted. This helps in minimizing energy consumption while allowing the system to resume heating effectively.

Time is also employed as a mechanism to terminate defrost. A predetermined time duration is set to limit how long the system will stay in defrost mode, regardless of the temperature. This prevents the system from remaining in this mode for too long, which could detract from the overall heating efficiency and comfort levels if not managed properly.

Together, these two mechanisms—time and temperature—ensure that defrost operation is managed effectively, balancing the need for efficient heat transfer with the need to remove ice build-up from the coils.