Integration of Thermochemical Heat Storage and Heat Pump Performance Study for Sustainable Building Applications

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Chinese explanation / 中文解读

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Original abstract

Thermochemical Energy Storage (TCES) offers high-density thermal storage for building applications, but the thermal delivery limitations of conventional subcritical heat pumps usually restrict system performance. In this study, a new integration of a low-GWP transcritical R1234yf heat pump for charging a 50gram Vermiculite-Calcium Chloride (CaCl₂) composite bed is numerically studied. A transient lumped parameter model with linear driving force (LDF) reaction kinetics was developed and extensively validated against experimental subcritical R134a baseline data. A detailed sensitivity analysis shows that the thermodynamic results are robust against realistic hardware degradation. The results indicate that the intrinsic limitation of isothermal condensation in the baseline subcritical R134a cycle restricts the maximum bed temperature to 52.0°C, which traps residual moisture and limits the material energy storage density to 658.0 kJ/kg. In contrast, the phase-change plateau in the gas cooler is replaced by a sensible temperature glide when operating the R1234yf cycle at a transcritical discharge pressure of 3.8 MPa. This steep thermal gradient drives the composite bed to 54.8°C, forcing a significantly deeper moisture desorption. It is found that the transcritical system attains the energy storage density of 923.6 kJ/kg, which is a significant 40.4% increase over the baseline. The mechanical charging efficiency (COP = 2.70) is inevitably lower than the subcritical cycle (COP = 3.58) because of the extreme transcritical compression. However, this loss in mechanical energy is fundamentally compensated for by a disproportionate gain in latent chemical storage. A reasonable thermal penetration approach, rather than instantaneous compressor efficiency, best realises the ultimate objective of maximising the TCES capacity. In conclusion, this work provides a mathematical proof that the combination of low-GWP R1234yf heat pumps and vermiculite-CaCl₂ composites is a very efficient, high-capacity and structurally resilient architecture for sustainable building decarbonisation.

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