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Integrating Latent Heat Storage into Residential Heating Systems

This project experimentally and numerically investigated the performance of thermal energy storage (TES) tank with phase change material (PCM). The experimental analysis has been conducted on a test rig that is designed and built within this project at the Energy Technology Department at KTH. The test rig’s experimental capacity covers wide range of heating and cooling/refrigeration applications; it can run in the temperature range of - 10 to 90°C with a heating capacity of about 20kW and cooling capacity of about 10 kW. The test rig is fully equipped with highly accurate measurements that facilitate detailed analysis of the PCM-TES tank performance.

Funded by:

The studies have been financed by Swedish Energy Agency and the KTH-CSC Programme, which is based on the agreement between KTH and the China Scholarship Council (CSC)

Time period: 2015-2021

Project partners:

Svensk Energi & Kylanalys (EKA)

Danfoss Värmepumpar AB

Vesam AB


Buildings are responsible for about 40% of total energy use in Sweden and Europe. The increasing rate of constructing new buildings and the rate of refurbishment of the large old building stock offer valuable opportunity to introduce highly efficient energy systems.

Thermal energy storage (TES) as one of key technology options for energy-efficient heating and cooling in buildings. Phase Change Material based Thermal Energy Storage (PCM-TES) could replace sensible heat storage solutions. Such an innovative concept utilizes the phase change of a substance to store and release energy at a narrow range of temperature change, resulting in 5-15 times larger storage density than with the commonly used sensible heat storage. This makes it possible to design a compact system that fits in the limited space available in buildings but with much greater storage capacity, thereby allowing for an increased use of renewable energy and waste heat.

Project content

The general aim of this project is to experimentally and theoretically investigate the integration of PCM into the built environment for space heating and domestic hot water production.

The comprehensive study in this project demonstrated a multi-level investigation on the techno-economic feasibility of using three off-the-shelf, macro-encapsulated technologies for residential heat load shifting, focusing on the application of storage integration with heat pump (HP)-based heating systems. The investigations are conducted on three levels (material, component, and system), mainly consisting of the following four aspects:

1) Selection of PCMs and measurements of their thermo-physical properties.

2) Development and characterization of three full-scale LHTES components.

3) Development and validation of numerical heat transfer models for predicting and optimizing the storage thermal performance.

4) Techno, economic, and environmental evaluation of load shifting operations with LHTES-HP integrated systems.


Journal papers:

  1. Xu, T., Chiu, J. N.-W., Palm, B., & Sawalha, S. (2019). Experimental investigation on cylindrically macro-encapsulated latent heat storage for space heating applications. Energy Conversion and Management, 182, 166-177.
  2. Xu, T., Gunasekara, S. N., Chiu, J. N.-W., Palm, B., & Sawalha, S. (2020). Thermal behavior of a sodium acetate trihydrate-based PCM: T-history and full-scale tests. Applied Energy, 261, 114432.
  3. Xu, T., Humire, E. N., Chiu, J. N.-W., & Sawalha, S. (2020). Numerical thermal performance investigation of a latent heat storage prototype toward effective use in residential heating systems. Applied Energy, 278, 115631.
  4. Xu, T., Humire, E. N., Chiu, J. N.-W., & Sawalha, S. Latent heat storage integration into heat pump-based heating systems for energy-efficient load shifting. Energy Conversion and Management, 236, 114042.
  5. Xu, T., Humire, E. N., Trevisan, S., Ignatowicz, M., Sawalha, S., Chiu, J. N.-W. Experimental and numerical investigation of a latent heat thermal energy storage unit with ellipsoidal macroencapsulation. Energy, Available online 21 August 2021, 121828.

Conference papers:

  1. VIII. Xu, T., Sawalha, S., Mazzotti, W., & Palm, B. (2016). Performance Evaluation of a Large Capacity Air-Water Heat Pump Using Propane as Refrigerant. In Proceedings of 12th IIR-Gustav Lorentzen Conference on Natural Refrigerants Edinburgh UK - GL2016, 21-24 August 2016.
  2. IX. Xu, T., Navarro-Peris, E., Piscopiello, S., Sawalha, S., Corberán, J. M., & Palm, B. (2018). Large-Capacity Propane Heat Pumps for DHW Production in Residential Buildings. In Proceedings of 13th IIR Gustav Lorentzen Conference on Natural Refrigerants: Valencia, Spain, 18-20 June 2018
  3. X. Xu, T., Hao, Y., & Sawalha, S. (2019). Comparing integrating configurations of latent heat storage in heat pump heating systems. In Proceedings of the 25th IIR International Congress of Refrigeration: Montréal, Canada, August 24-30, 2019.
  4. XI. Xu, T., Chiu, J., & Sawalha, S. (2019). Numerical Study of a Latent Heat Storage Unit with Cylindrically Encapsulated PCMs. In SUPHER’19 Conference, Sanova, Italy, 4-6 September 2019.

Project contact persons

Project leader:

PhD student (graduated):

Other senior researchers:

PARMENIDES – Plug & plAy EneRgy ManagEmeNt for hybriD Energy Storage
HYSTORE - Hybrid services from advanced thermal energy storage systems
Open-source models for holistic building energy system design at scale
Tank to Grave Management of new Low-GWP Refrigerants (Hantering av nya låg-GWP köldmedier från installation till destruktion)
Novel tool and guidelines for designing ground source heat pumps (GSHPs) in densely populated areas
Data driven lab for building energy systems
Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family buildings
Smart Control Strategies for Heat Pump Systems
Open-source models for holistic building energy system design at scale
Control systems for hybrid solutions based on biomass fueled Stirling engines, solar and wind for rural electrification
Prosumer-Centric Communication for Solar PV Diffusion (completed)
Towards Sustainable (Fossil-free) Heating System in Small Residential Buildings
Solar energy and ground source heat pumps for Swedish multi-family housing (completed)
Solar photovoltaic systems in Swedish cooperative housing (completed)
Smart Control Strategies for Heat Pump Systems (completed)
Creating and Understanding Smart Innovation in Cities
Building heating solutions in China
Accelerating innovation in buildings
High-Resolution GIS District Heating Source-Load Mapping
Digitalization and IoT technologies for Heat Pump systems
Sustainable combined systems for heating of buildings (completed)
Cost- and Energy-Efficient Control Systems for Buildings
Situation of Opportunity in the Growth and Change of three Stockholm City Districts (completed)
Wuxi Sino-Swedish Eco-City Project (completed)
Smart Renovation Strategies for Sustainable Electrification
Future Secondary Fluids for indirect refrigeration systems
Smart Fault Detection and Diagnosis for Heat Pumps
Performance indicators for energy efficient supermarket buildings
Magnetic Refrigeration
High-Resolution GIS District Heating Source-Load Mapping
Smart Solar Hybrid Solutions for Sustainable European Buildings (completed)
Building state-of-the-art (SotA) supermarket: Putting theory into practice
Efficient utilization of industrial waste heat by low temperature heat driven power cycles – an integrated approach for Swedish Industry
Cooperation between Supermarkets and Real Estate Owners; Energy Efficiency and Business Models
Digitalization and IoT technologies for Heat Pump systems
Capacity control in Heat Pump systems
Alternative secondary fluids
Functional surface coatings for energy efficient heat pumps
Two-phase flow in flat channels
Two phase heat transfer & pressure drop with new environment friendly refrigerants in minichannels (completed)
Numerical Study on flow boiling in micro/mini channels (completed)
Distributed Cold Storages in District Cooling
Integrating Latent Heat Storage into Residential Heating Systems
Simulation of temperature distribution in borehole thermal storages supported by fiber optic temperature measurements (completed)
Solar energy and ground source heat pumps for Swedish multi-family housing (completed)
Neutrons for Heat Storage, NHS, (completed)
4D Monitoring of BTES (completed)
Aquifer Thermal Energy Storage (completed)
Deep Borehole Heat Exchanger (completed)
Combined Heat and Power plants in combination with borehole thermal energy storage (completed)
Improved borehole technology for Geothermal Heat Pumps development (completed)
Compact Minichannel Latent Energy Storage for Air Related Cold Storage Applications
Building heating solutions in China
Toward Sustainable (Fossil-free) Heating System in Small Residential Buildings
Renewable Energy Park, RE-Park (completed)
Efficient use of energy wells for heat pumps (completed)
Efficient design of geothermal heating systems (completed)
SPF (completed)