Development of a comprehensive system model for Phase Change Material Thermal Energy Storage Integrated with a Heat Pump for Nordic Residential Applications in KTH Live-in-Lab

Introduction and Project Background

Phase change materials (PCMs) offer significant potential for thermal energy storage (TES) applications in residential heating systems, particularly when integrated with heat pumps for flexible sector coupling. In Nordic climates, where space heating accounts for approximately 57% of household energy consumption (IEA, 2025), PCM-TES systems can store thermal energy during low electricity-price periods and discharge during peak demand, potentially reducing operational costs by 10% (Zhou et al., 2025) and shifting of peak loads peak loads by 25-45% (Erdemir & Dincer, 2019).

This thesis project builds upon the already installed system in Live-In-Lab, where a hierarchical control framework was developed for a 42 kWh PCM-TES system integrated with an 18 kW ground-source heat pump at KTH Live-in-Lab (LIL). The system utilises RT57HC, a bio-based PCM with a melting point around 57°C, contained in 515 encapsulated capsules with a void fraction of 0.56.

The current research gap lies in the lack of integrated system models that capture the full dynamics of PCM-TES heat pump systems across different operating conditions. Existing models typically focus on individual components, missing critical interactions among PCM storage, the heat pump, and control systems. Without comprehensive models, control strategies cannot be thoroughly tested across diverse operating scenarios, limiting optimisation potential and hindering broader deployment.

This project, conducted within the Horizon Europe HYSTORE project framework (Grant Agreement N. 101096789), aims to develop and experimentally validate a thermal energy storage system at pilot scale, serving as a platform for control strategy development and system optimisation.

Project Description

This thesis project focuses on developing a comprehensive, experimentally validated model of the integrated PCM-TES heat pump system installed at KTH Live-in-Lab. The student will work closely with the supervision team to create a dynamic system model framework that captures all relevant system dynamics and interactions.

The project begins with developing detailed thermodynamic models of each system component. For the PCM-TES, this includes implementing enthalpy-based methods for phase-change modelling and heat transfer within the encapsulated capsules. The heat pump model will incorporate performance maps. Building and HVAC components will be modelled, including the air handling unit, hydraulic networks with pumps and valves, and the shunt heat exchanger system, also illustrated in Figure 1.

Figure 1 to be published

A key outcome is a model that researchers and engineers can use for PCM-TES system design and control development. The model will include both detailed versions for analysis and simplified versions suitable for real-time control applications.

This project work is to be implemented by 1-2 thesis students

Project Learning Objectives

After the project is completed, the student should be able to/should be:

• Knowledgeable in PCM-TES systems , understanding phase change phenomena, heat transfer in encapsulated PCMs, thermal stratification effects, and integration with heat pump systems

• Capable of multi-objective optimisation, formulating optimization problems, implementing solution algorithms, and analysing trade-offs between competing objectives

• Competent in scientific programming using e.g., TRNSYS or Python (or similar) for system simulation, data analysis, and visualisation

• Critically analyse model predictions versus experimental data, perform uncertainty analysis, and identify model limitations and improvement opportunities

• Communicate complex technical concepts through comprehensive report writing, scientific publications, and technical documentation

• Contribute to developing sustainable energy solutions through understanding of sector coupling, demand response strategies, and renewable energy integration

Methodology

The proposed methodology consists of creating a system-level model and then using different operating parameters (flow rate, inlet temperature, return temperature to the condenser) to test different operating strategies for the real system.

System Modelling Development:

- Create a system model framework in e.g., TRNSYS, Python or similar.

- Develop component models for PCM-TES, heat pump, and building/HVAC (thermal networks, AHU).

- Implement flexible interfaces for integrating control strategies and exchanging data between components

Pre-requisites

• Strong foundation in thermodynamics and heat transfer

• Programming skills in TRNSYS, Python or similar (suitable for the task in hand)

• Understanding of control systems and optimisation

• Good technical writing skills in English

• Knowledge of building energy systems (advantageous)

Advantages of Being Engaged in the Project

• Hands-on experience with state-of-the-art PCM-TES system at KTH Live-in-Lab

• Development of advanced modeling skills applicable to various energy systems

• Collaboration with international HYSTORE project team

• Interaction with industry partners (Rubitherm PCM supplier, NIBE heat pump manufacturer)

• Opportunity to contribute to scientific publications (journal and conference papers)

• Development of open-source tools benefiting the research community

Main Supervisor and contact person

Examiner and co-supervisor

Project Co-supervision/Collaboration Team