A Comparative Experimental Analysis of a Cold Latent Thermal Storage System Coupled with a Heat Pump/Air Conditioning Unit

Claudio Zilio, Giulia Righetti, Dario Guarda, Francesca Martelletto and Simone Mancin ()
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Claudio Zilio: Department of Management and Engineering, University of Padova, 36100 Vicenza, Italy
Giulia Righetti: Department of Management and Engineering, University of Padova, 36100 Vicenza, Italy
Dario Guarda: Department of Management and Engineering, University of Padova, 36100 Vicenza, Italy
Francesca Martelletto: Department of Management and Engineering, University of Padova, 36100 Vicenza, Italy
Simone Mancin: Department of Management and Engineering, University of Padova, 36100 Vicenza, Italy

Energies, 2025, vol. 18, issue 13, 1-15

Abstract: The decarbonization of residential cooling systems requires innovative solutions to overcome the mismatch between the renewable energy availability and demand. Integrating latent thermal energy storage (LTES) with heat pump/air conditioning (HP/AC) units can help balance energy use and enhance efficiency. However, the dynamic behavior of such integrated systems, particularly under low-load conditions, remains underexplored. This study investigates a 5 kW HP/AC unit coupled with an 18 kWh LTES system using a bio-based Phase Change Material (PCM) with a melting temperature of 9 °C. Two configurations were tested: charging the LTES using either a thermostatic bath or the HP/AC unit. Key parameters such as the stored energy, temperature distribution, and cooling capacity were analyzed. The results show that, under identical conditions (2 °C inlet temperature, 16 L/min flow rate), the energy stored using the HP/AC unit was only 6.3% lower than with the thermostatic bath. Nevertheless, significant cooling capacity fluctuations occurred with the HP/AC unit due to compressor modulation and anti-frost cycles. The compressor frequency varied from 75 Hz to 25 Hz, and inefficient on-off cycling appeared in the final phase, when the power demand dropped below 1 kW. These findings highlight the importance of integrated system design and control strategies. A co-optimized HP/AC–LTES setup is essential to avoid performance degradation and to fully exploit the benefits of thermal storage in residential cooling.

Keywords: latent thermal energy storage; PCM; heat pump; residential air conditioning (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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