In Heidelberg, an office building is being constructed that maintains thermal comfort without conventional heating, cooling, or ventilation systems. The project demonstrates how principles of building physics can ensure a stable indoor climate and exceptional longevity.
While typical office buildings are designed for a lifespan of around 50 years, the “Speicherschmid” aims for a service life of up to 200 years. The longer a building remains in use, the lower its ecological and economic costs for new construction, renovation, or demolition throughout its life cycle.
Early in the planning phase, it became clear that the technical building services (HVAC systems – heating, ventilation, and air conditioning) represent the highest costs over the life cycle due to:
Reducing or even eliminating technical building systems therefore not only lowers costs but also significantly extends the usable life of the building itself.
To ensure thermal comfort without conventional heating or cooling systems, the building must be optimized from a building physics perspective so that the architecture itself provides comfort conditions.
Commissioned by Heinrich Schmid Immobilien GmbH, Müller-BBM Building Solutions advises on all aspects of building physics – including thermal and moisture protection, building and room acoustics, daylight, and holistic building simulations. Architectural design is provided by Florian Nagler Architekten of Munich.
The thermal balance of a building can be described as the sum of heat sources and sinks: solar gains and internal loads from occupants and equipment act as sources, while transmission and ventilation losses act as sinks.
The main challenge for the project was to demonstrate that comfortable indoor conditions – in terms of operative temperature, humidity, and CO₂ concentration – can be maintained for every hour of the year.
Standardized monthly balance methods, such as those defined in the Building Energy Act, are insufficient because they fail to represent system dynamics. Therefore, an innovative approach based on dynamic, holistic building simulations was chosen to evaluate room conditions on an hourly basis under realistic boundary conditions.
In a first step, extensive parameter studies were carried out to investigate the influence of individual measures, such as:
Based on these studies, an integrated whole-building simulation was conducted to validate the overall concept and identify potential weaknesses.
Visualizations: Florian Nagler Architekten
Whole-building simulation: Müller-BBM Building Solutions
A key challenge was the six-lane road running directly north of the site, producing daytime noise levels of up to 74 dB(A). Under such conditions, conventional window ventilation on the north façade would be unacceptable for future users.
In collaboration with Florian Nagler Architekten, an innovative façade and ventilation concept was developed:
The main occupied spaces are oriented to the south, while ancillary rooms are placed on the north side. Generous south-facing windows allow for solar gains and deep daylight penetration, while the north façade has been limited to the minimum area required for daylighting. This minimizes both noise and air quality impacts from the adjacent road, as well as winter heat losses.
To enable natural cross-ventilation, vertical exhaust shafts are provided at regular intervals along the north façade, extending from each unit up through the roof. Thermal buoyancy generates a pressure difference, allowing the shafts to act as exhaust outlets.
On the south side, automatically controlled ventilation flaps provide fresh air intake. These are operated according to a control scheme developed by Müller-BBM Building Solutions, based on continuous monitoring of indoor temperature and CO₂ concentration. The result is a self-regulating building that adapts automatically to external conditions without user intervention.
Ventilation concept: Fresh air enters through the façade, circulates within the occupied zones, and is exhausted through the roof shafts.
A central finding from the thermal simulations was the significant contribution of the thermal mass in the concrete floor slabs to indoor climate stability. The massive slabs can absorb, store, and release large amounts of heat energy over time.
This means internal loads – such as heat from people, equipment, and solar gains – do not immediately translate into temperature peaks but are distributed evenly over several hours.
In winter, this effect helps maintain a comfortable indoor temperature without the need for conventional heating. In summer, the ceiling mass cools down overnight through natural ventilation and serves as a thermal buffer against overheating during the day.
Thus, the thermal mass performs a dual function: it replaces parts of traditional heating and cooling systems while ensuring consistent thermal comfort throughout the year.
In addition to thermal building physics, Müller-BBM Building Solutions also provided comprehensive advice on building and room acoustics. The objective was to achieve acoustic quality in all occupied areas according to state-of-the-art standards – ensuring both speech intelligibility and user comfort.
The “Speicherschmid” concept posed special challenges, as conventional acoustic solutions such as suspended ceilings, carpets, or acoustic panels could not be used. Although effective acoustically, these would have interfered with the thermal exchange and radiant performance of the solid ceilings.
In most rooms, the required sound absorption was achieved through targeted wall design. Furthermore, a synergy was created with a measure originally intended for thermal reasons:
In front of the south-facing post-and-beam façade, a heavy, automatically controlled curtain is installed. Closed at night, it reduces heat losses; during the day, it also provides an acoustic function. When drawn across the interior walls, it allows daylight to enter while acting as a large-area sound absorber, significantly reducing reverberation times.
Left: curtain (pink) parked along the interior wall during the day. Right: curtain closed at night to minimize heat losses.
The Speicherschmid project demonstrates that consistently building-physics-based design can produce buildings that operate without conventional heating, cooling, and ventilation systems.
Its foundations lie in a highly efficient building envelope, the use of solar gains through south orientation, demand-based natural ventilation, and – most importantly – the thermal mass of the concrete slabs. Acoustic requirements are addressed through integrative solutions, such as sound-absorbing curtains, without compromising thermal performance.
The greatest challenge was to verify comfort conditions throughout the entire year, hour by hour – in terms of both temperature and indoor air quality. Standardized verification methods proved insufficient, so dynamic building simulations were employed to validate the concept under realistic boundary conditions.
Project-specific challenges – such as the high external noise levels from the six-lane road to the north – were successfully addressed through innovative solutions, including a closed north façade with exhaust shafts.
Simulation results show that operative indoor temperatures exceed 21 °C in winter, while 26 °C is rarely exceeded in summer.
Annual progression of outside air temperature and operative room temperature.
Presentation of hourly weighted frequencies: operational indoor temperature in a room over one year.
Relationship between outside air temperature and operating temperature.
Müller-BBM Building Solutions continues to provide consultancy through to the start of construction, focusing on transferring the simulated concepts into practical application and ensuring the design’s robustness against potential disruptions – such as extreme weather events (prolonged heat waves or cold spells) or unpredictable user behavior (e.g., permanently open windows, high internal loads from equipment).
A successor project based on the Speicherschmid concept is already in planning at a site in Karlsruhe.
Further information is available at speicherschmid.de.
Authored by Arvand Vaghari Fard, Carolin Uhlenbrock, and Domenic Hampel, Müller-BBM Building Solutions GmbH
