Heat exchanger performance issues.

When running in the omotes test environment, the heat exchanger sometimes results in very slow computation times. Even in a model like the one below, it can take up to several minutes to solve.

<img width="1324" height="211" alt="Image" src="https://github.com/user-attachments/assets/3262e76f-df32-4354-b4a5-d013c542fb96" />