Experimental evaluation and high-fidelity model-based optimization of a residential thermochemical heat pump water heater

Thermochemical heat pump water heaters (TC-HPWHs) offer a promising low-carbon solution for residential water heating by utilizing low-grade thermal energy sources. However, their adoption is limited by low power density and the discontinuous nature of sorption cycling, which restrict heating capacity and hot water delivery. To address these challenges, this study presents the development and evaluation of the first-of-its-kind thermally driven TC-HPWH for residential applications, integrating a condensing storage water heater with an adsorption-based heat pump cycle capable of extracting heat from ambient air. The packaged TC-HPWH was designed, constructed, and experimentally tested under standard residential operating conditions, with detailed instrumentation used to capture transient component- and system-level behavior. The prototype achieved a First Hour Rating of 51 gal, placing it within the medium draw category, and demonstrated the ability to upgrade ambient heat to meet hot water demand. A high-fidelity thermodynamic model was developed, validated against experimental data, and subsequently used for parametric optimization. The results indicate that performance improvements are primarily driven by enhancing salt accessibility and improving reactor thermal isolation, while operating conditions and component sizing are already near optimal. The modeling results showed that the TC-HPWH could achieve a Uniform Energy Factor of approximately 1.18 when key design and operating parameters are optimized. A technoeconomic analysis using Illinois, USA, as a representative location indicates that the TC-HPWH could achieve the lowest estimated annual operating cost among the compared systems, while electric heat pump water heaters provide the greatest potential for carbon mitigation.