Dynamic modelling of a high-temperature latent heat store for stable compressor operation in a solar-assisted thermo-mechanical vapour compression cooling system

Solar-assisted thermo-mechanical vapour compression cooling delivers part of the compression work by heating the refrigerant at constant volume using solar-heated water at 98–120 °C. However, operation beyond sunset relies on sensible hot-water storage, whose declining temperature causes the thermal compressor to switch repeatedly in and out of the circuit, imposing step load changes on the mechanical compressor. The integration of a high-temperature latent heat store with such a cycle has not previously been reported. This study presents such a system, using erythritol (melting point 117 °C) in a shell-and-tube configuration. A transient two-dimensional model of the store, validated against experimental and numerical benchmarks to within 6%, is dynamically coupled with a stratified sensible store, a solar collector field, and the cooling cycle serving a residential building in Baghdad, Iraq, with a peak cooling load of 521 kW. Without latent storage, the mechanical compressor undergoes 45 load swings per night with step changes of up to 30 kW; a 20 mm PCM layer eliminates these fluctuations by holding the supply temperature above the thermal compressor threshold throughout the 5.7-h night-time discharge, extending solar-driven operation at a system COP of 3.83. Heat penetration saturates at approximately 17.5 mm, identifying 20 mm as the design thickness. Seasonally, the integrated system reduces compressor electricity consumption by 20.5% relative to a conventional vapour compression baseline, up to 24% on the July design day. The results establish operational stability, rather than energy savings alone, as the principal value of high-temperature latent storage in solar-driven cooling.