WP-BiLatent – Heat pump with integrated latent heat storage units for space heating and domestic hot water
Heat transformation: heat pumps & refrigeration units
Electric heat pumps are a key element of the future heat supply, enabling electrical energy to be efficiently converted into useful energy for the heating and cooling of buildings as part of sector coupling. As an electrically powered heat supply system, heat pumps play a crucial role in load management within the electricity supply system and in the use of electricity from renewable sources. The use of heat storage tanks allows the provision and use of heat to be decoupled, meaning that the heat pump can be operated flexibly in terms of timing as a heat generator. This flexibility helps to prevent the electricity supply from becoming overloaded as a result of peak demand for heating. In addition to the temporal flexibility of the heat pump heating system’s operation in conjunction with the electricity supply, a heat storage system also enables the utilisation of favourable ambient conditions for particularly energy-efficient operation of the heat pump heating system. The aim of this project is to utilise latent heat storage tanks in a heat pump heating system for space heating and domestic hot water production. The objective is to achieve improved storage performance and increased energy efficiency compared with conventional heat pump systems incorporating heat storage tanks.
Project description
The use of latent heat storage tanks in heat pump systems offers a number of advantages over conventional heat storage tanks filled with heat transfer fluid.
- As heat absorption and release during the phase change of the storage material take place at an approximately constant temperature, it is possible to achieve particularly efficient coupling with the heat pump, whose internal cycle is also characterised by constant temperatures during the evaporation and condensation of the refrigerant.
- Latent heat storage systems exhibit a high energy density within a narrow temperature range. This allows the heat storage system to be well suited to the space heating requirements of residential buildings, which are typically operated with temperature differences between the heating circuit flow and return of around 10 K: By maintaining the temperature settings of the heating system, the heat pump can be operated at high efficiency – as expressed by the coefficient of performance (COP) – even whilst charging the storage tank. At the same time, the storage tank can be designed to be very compact, thanks to the high specific heat capacity during the phase change. Conventional storage tanks result in higher electrical power consumption by the heat pump as the storage temperature increases, leading to a correspondingly lower coefficient of performance. Conversely, whilst maintaining the temperature settings of the heating system, this approach yields a storage volume approximately five times greater than that achieved using a latent heat storage tank.
- In domestic hot water systems, the temperature at which heat is stored can be set to match the desired tap temperature when using a latent heat storage tank. Heating the contents of the storage tank to 60°C to prevent the growth of Legionella – as stipulated by the relevant technical regulations for the use of domestic hot water storage tanks – is not necessary if heat is extracted from the latent heat storage tank on a continuous flow basis. Accordingly, due to the lower temperature at which heat is stored, the use of latent heat storage tanks allows a higher heat pump coefficient of performance to be achieved compared with the use of domestic hot water storage tanks.
Project Management
Team members
other team members
Niklas Fellner
Dept 05 – Utilities and Building Services Engineering
CENERGIE – Research Center for Energy-Efficient Buildings and Districts
Alternativ Heat Energy Ltd
Cabero Wärmetauscher GmbH & Co. KG,
November 2024 – October 2027
The German Government’s 7th Energy Research Programme, the ‘Energiewendebauen’ research initiative