The project focused on the design, modelling, and experimental validation of a flexible heat‑pump system that incorporates a latent‑heat storage unit. The core idea is a cascade concept in which the latent‑heat storage is integrated directly into the heat‑pump loop. This arrangement allows the system to absorb excess heat during periods of low demand and release it when the load rises, thereby smoothing the operating curve of the heat‑pump and improving overall efficiency. A key technical contribution is the development of a thermodynamic model that captures the phase‑change behaviour of the storage medium and its interaction with the heat‑pump components. The model was built using a combination of numerical simulation techniques and analytical expressions for heat‑transfer coefficients, latent‑heat capacity, and pressure‑temperature relationships. It was then applied to the sizing of the storage volume and to the optimisation of the heat‑pump operating parameters. The model predicts that, for a typical commercial building load profile, the integrated storage can reduce the peak electrical demand by up to 30 % and increase the coefficient of performance (COP) by roughly 10 % compared with a conventional heat‑pump without storage.

Experimental work was carried out on a laboratory test rig that replicated the cascade configuration. The rig included a variable‑speed compressor, an evaporator, a condenser, and a custom‑designed latent‑heat storage chamber filled with a phase‑change material (PCM) that has a melting range around 30 °C. Sensors measured temperature, pressure, mass flow, and electrical power. The results confirmed the model predictions: the storage chamber maintained a stable temperature during the charging phase and released heat during discharging, allowing the heat‑pump to operate closer to its optimal point for longer periods. Energy‑efficiency measurements showed a reduction in total energy consumption of about 15 % over a 24‑hour cycle, and the system demonstrated robust operation under varying ambient conditions. The validation also highlighted the importance of the capillary‑tube design for controlling the PCM flow and ensuring uniform heat distribution.

In addition to heating, the project explored a cooling application. A test storage was integrated into a variable‑refrigerant‑volume (VRV) system, and a three‑media latent‑cooling storage was constructed. The cooling storage used a PCM that melts at 10 °C, enabling the absorption of excess cooling capacity during low‑load periods. Experimental data showed that the VRV system with the latent‑cooling storage achieved a 20 % lower compressor power draw during peak cooling demand compared with a conventional VRV unit. The three‑media design, which combined PCM with a sensible‑heat medium, further improved the system’s ability to maintain a constant indoor temperature while reducing the need for compressor cycling.

The research was carried out in collaboration between a university research group and several industry partners who supplied components and provided practical insights into system integration. The project was funded through a German research grant, and the work spanned several years, culminating in a series of peer‑reviewed publications and conference presentations. The outcomes demonstrate that integrating latent‑heat storage into heat‑pump and VRV systems can deliver measurable gains in energy efficiency and operational flexibility, offering a promising pathway for meeting stringent building‑energy‑efficiency standards.