Frost/Defrost Models for Air-Source Heat Pumps with Retained Water Refreezing Considered

TL;DR

This paper introduces a comprehensive enthalpy-based frost/defrost model with fuzzy switching for air-source heat pumps, capturing phase changes, water retention, and refreezing to improve system simulation accuracy.

Contribution

It presents a novel enthalpy method and fuzzy modeling approach integrated into a heat pump system model for better simulation of frost and defrost dynamics.

Findings

Accurately captures frost formation and melting behaviors.

Models water retention and refreezing during defrost cycles.

Enhances simulation robustness with fuzzy switching.

Abstract

Cyclic frosting and defrosting operations constitute a common characteristic of air-source heat pumps in cold climates during winter. Simulation models that can capture simultaneous heat and mass transfer phenomena associated with frost/defrost behaviors and their impact on the overall heat pump system performance are of critical importance to improved controls of heat delivery and frost mitigation. This paper presents a novel frost formulation using an enthalpy method to systematically capture all phase-change behaviors including frost formation and melting, retained water refreezing and melting, and water drainage during cyclic frosting and defrosting operations. A Fuzzy modeling approach is proposed to smoothly switch source terms when evaluating the dynamics of frost and water mediums for numerical robustness. The proposed frost/defrost model is incorporated into a flat-tube outdoor heat exchanger model of an automotive heat pump system model to investigate system responses under cyclic operations of frosting and reverse-cycle defrosting.