Understanding and predicting the performance of passive heat and moisture exchangers using a numerical model.

Background: To improve the understanding of the thermodynamics and performance of small passive hygroscopic Heat and Moisture Exchangers (HMEs), a computer model simulating HME function is required.

Methods: We developed a numerical HME model to calculate the HME's water and heat exchange. The model was tuned and verified with experimental data and validated by applying it to HME design variations.

Results: Verification of the model's results to the experimental data shows that the tuned model yields reliable results. The mass of the core, which determines the HME's total heat capacity, is the most important parameter influencing the performance of passive HMEs.

Conclusions: Increasing the HME's diameter is an effective way to improve an HME, as it yields higher performance and lowers breathing resistance. HMEs intended for use in warm or dry climates should contain more and those for use in cold humid climates should contain less hygroscopic salt.