Thermal flexibility of buildings – potential, methods and findings
The building sector plays a key role in the energy transition: it accounts for around 47% [1] of final energy consumption in Germany, while at the same time the ramp-up of heat pumps will place a greater strain on the electricity sector in the future [2]. This is why a previously underutilised potential is becoming increasingly important: the thermal flexibility of the buildings themselves. With their inherent thermal mass – in the form of walls, floors, ceilings – buildings can store heat and shift it over time. This allows them to function as decentralised thermal storage units that can cushion peak loads in the electricity grid and support the integration of renewable energies.
The study systematically examines the flexibility potential of typical German residential buildings. The methodological basis is a 5R1C network model in accordance with DIN ISO 13790 [3], which maps the calculation procedure of thermal behaviour of buildings on an hourly basis. Representative building types (single-family houses (SFH), multi-family houses or apartment buildings (AB)), three building age classes and various renovation states are analysed based on the TABULA building typology [4]. Annual simulations are used to calculate temperature profiles, heating loads and heat requirements. Based on this, it is determined how buildings react to flexibility events, in particular grid-side power reductions in accordance with Section 14a of the German Energy Industry Act (EnWG) [5].
Key findings:
Thermal stability and building envelope:
- Unrenovated old buildings have higher mass capacities but cool down quickly due to poorer insulation – their flexibility potential is therefore practically limited.
- Modern or renovated buildings have less storage mass, but significantly better insulation. This increases usable flexibility because heat remains in the building longer.
- Apartment buildings exhibit particularly stable temperature behaviour due to more favourable geometries and lower envelope area ratios and are well suited for providing flexibility.
Shifting energy potentials:
A 12-hour reduction to 19°C or 18°C results in, among other things:
- SFH 1910, unrenovated: up to 12.6 kWh (≈4.3% of daily requirement)
- SFH 2005 renovated: 9.9 kWh (≈13.3%)
- AB 1960 unrenovated: up to 206 kWh (≈6.5%)
- AB 2005 renovated: approx. 134 kWh (≈13.5%)
The results show that renovation significantly increases flexibility potential, up to a factor of 2–3.
Comparison with conventional heat storage systems:
In SFHs the building mass corresponds approximately to the volume of a 700-litre combination storage tank. In MFHs, the inherent building mass potential can even correspond to a heat storage capacity that is 12 times greater than that of a typical storage system.
Relevance for the energy transition and the electricity sector:
The analysis shows that thermal building flexibility is an important short-term and decentralised storage resource for the energy system. It supports:
- the stabilisation of the electricity grid,
- the integration of volatile renewable energy,
- the targeted control of heat pumps,
- and – particularly important – energy-efficient renovation, which not only reduces heat demand but also increases the flexibility potential of a building.
The study thus provides a methodological framework and indicative results that enable an initial classification of relevant dimensions for system analyses, political decisions and future network strategies.
Weitere Informationen:
Literatur:
[1] AGEE-Stat, „Zeitreihen zur Entwicklung der erneuerbaren Energien in Deutschland“. 17. November 2025. [Online]. Verfügbar unter: https://www.umweltbundesamt.de/dokument/zeitreihen-zur-entwicklung-der-erneuerbaren
[2] Fraunhofer IWES/IBP, „Heat Transition 2030. Key technologies for reaching the intermediate and long-term climate targets in the building sector“. Agora Energiewende, Februar 2017
[3] DIN, DIN EN ISO 13790: Energieeffizienz von Gebäuden – Berechnung des Energiebedarfs für Heizung und Kühlung, Berlin., September 2008
[4] T. Loga, B. Stein, und N. Diefenbach, „TABULA WebTool“. Zugegriffen: 8. Dezember 2025. [Online]. Verfügbar unter: https://webtool.building-typology.eu/#bm
[5] Bundesamt für Justiz, Gesetz über die Elektrizitäts- und Gasversorgung (Energiewirtschaftsgesetz – EnWG) § 14a Netzorientierte Steuerung von steuerbaren Verbrauchseinrichtungen und steuerbaren Netzanschlüssen; Festlegungskompetenzen. 2024.
