By Jay Fox

With a footprint of 3,600 m² and 7,700 m² (82,900 ft²) of conditioned space, the House of Bavarian History (Haus der Bayerischen Geschichte) is currently the largest Passive House certified museum in the world. The museum is located on the southern banks of the Danube River, just steps from the historic core of Regensburg and is designed to provide visitors with two types of immersive experience. On the one hand, it explores the cultural and economic history of Bavaria through the clever presentation of myriad commercial products, cultural memorabilia, and everyday items from the age of Napoleon to the present. The narrative reveals how the Bavaria transformed over the course of the nineteenth and early twentieth centuries to become one of the leading economic powerhouses of Central Europe.

On the other, visitors are allowed to walk around and experience the comfort and peace achieved through thoughtful engineering, energy efficiency, and Passive House levels of performance.

Context is just as important for the massing of the museum, even though this may not be apparent at first glance. Given its curtained façade, it is no doubt distinct from Regensburg’s medieval core, but the architecture firm that won the competition to design the museum, Frankfurt-based wörner traxler richter planungsgesellschaft mbH (WTR), painstakingly researched the several dozen buildings that had previously existed on the site. They then incorporated the historic rooflines into the design and profile of the museum to make the building feel like a continuation of the cityscape rather than a disruption. This same kind of thinking influenced the layout of the museum, as the central atrium and concourses on the first floor recreate the alleyways, streets, and plazas that once oCccupied the space.

In addition to being a celebration of Bavaria’s past, the museum also represents the climate ambitions of the State of Bavaria, as the local government enacted a law in 2011 requiring all administrative buildings and some selected public projects to undergo Passive House certification through the Passive House Institute (PHI). According to Raphaël Vibert, Passive House Certifier and Senior Designer at Herz & Lang, the museum was even considered “a flagship project for the Bavarian state to showcase its commitment to sustainability and energy efficient building practices through the Passive House standard.”

Shortly after winning the competition to design the museum in 2013, WTR decided to partner with Herz & Lang. They were tasked with conducting the energy modeling and dynamic simulations necessary to ensure the museum ultimately met its performance targets.

This is not the first time that the two firms have worked together, nor is it the first time they have had to apply the principles of Passive House to a unique building typology. The two firms were also on the team that designed and built varisano Klinikum Frankfurt Höchst first. Located in the German city of Frankfurt, it is the first hospital in the world to be certified by PHI.

Identifying Key Challenges

Construction of the museum began in 2015 and was completed in 2019. However, well before site excavation even began, the team recognized that internal heat gains were going to be a concern for several reasons.

First, the museum is designed to maintain a comfortable interior even with up to 1,620 occupants at any given time, and it can accommodate up to 300,000 visitors per year, according to white paper produced by Vibert. However, no two days are going to be exactly the same. Extreme fluctuations can occur not only in the number of total visitors to the museum, but also in the number of occupants in any one room. This could be due to a large tour group exploring the permanent collection area or should the museum host an event in the 1,000-m² Danube Hall, a space on the museum’s ground floor that houses special exhibitions and events. Such sudden spikes in occupancy and/or density can lead to high heat and moisture loads that can be very difficult for even the most sophisticated systems to manage.

Second, was the issue of waste heat. Even seemingly simple exhibits need elaborate lighting setups, while more complicated exhibits can often contain multiple electronic components. When the museum contains approximately 1,000 items and hundreds of individual exhibits, as the House of Bavarian History does, all those relatively small internal heat gains begin to add up.

Finally, and perhaps most crucially, the climate within the museum is required to remain within extremely narrow parameters. As Vibert explains, these parameters were set to create an environment conducive to the preservation of the artifacts, and the museum is contractually obligated to maintain that environment. The target air temperature is set at 19°C in winter and 24°C in summer, and the designers were allowed only +/- 1°K in play regardless of season. The target level for relative humidity was set at 50% +/- 5% (from floor level to 3m above the floor).

Given these restrictions and the need to ensure stability without rapid or significant fluctuations in temperature and humidity, a strategy like night flushing was simply not viable. Instead, the design team leveraged the passive principles of Passive House construction to enhance the efficiency of the HVAC system, creating a precise, dynamic, and extremely thermal-resistant enclosure.

In addition to the atrium, the ground floor also includes Danube Hall, a gift shop, a permanent video installation housed in a panoramic theater, and the museum’s Wirsthaus (tavern). The permanent exhibit space is on the second floor and consists of 2,500 m² (26,900 ft²). The layout is designed in such a way so that visitors see the many generations of Bavarian history in chronological order. Guests begin their journey in the year 1800, and then they stroll through 225 years of history with 1,000 specific artifacts serving as guides. These cultural snapshots track the evolution of Bavaria from a largely agrarian economy to one of Germany’s primary industrial engines.

In the permanent exhibit area on the upper floor, the amount of glazing is limited to ensure protection of the artifacts. However, there is an opening to the southwest that provides a spectacular view of the medieval cityscape and St. Peter Cathedral, an exemplar of High Gothic style dating to the thirteenth century. This triple-paned curtainwall, also by RAICO, faces to the west and is divided into three sections of 25 square meters each.

Limited use of glazing certainly helped the museum’s performance, but it would not have reached its targets without using passive principles to inform the design of the foundation, wall, and roof assemblies.

The foundation is based on a load bearing concrete slab insulated with 200 mm of extruded polystyrene (XPS), as well as 30-70 mm of EPS insulation between the slab and the screed. Some parts of the foundation are supported with underground piles that do penetrate the insulation layer, leading to limited thermal bridging, but the foundation still has a solid average U-value of 0.17 W/(m²K). The below grade walls are also insulated with 200 mm of XPS, while the above grade walls are insulated with 280 mm of mineral wool. The ceramic façade is clipped to the assembly using thermally broken fasteners made of stainless steel. The average U-value of the wall assembly is 0.138 W/(m²K).

The non-skylit portion of the roof is steel-framed and insulated with 370 mm of mineral wool with a high-compressive strength when compared to the walls. It does use similar stainless-steel fasteners. The U-value of this assembly is 0.124 W/(m²K).

“The Passive House envelope played a significant role in guaranteeing the indoor climate,” Vibert says. “Thanks to the well-insulated and airtight envelope, the museum is kind of independent from outdoor, changing conditions. As designers, we only have to focus on what is happening in the building itself.”

The building’s HVAC system relies on an innovative heat pump system that is connected to the central wastewater pipe of the city of Regensburg. When compared to the nearby Danube, the wastewater system is not only more consistent with respect to temperature; it is also warmer in the winter and cooler in the summer. This novel approach involving the use of “free” energy from municipal wastewater systems is very efficient, Vibert says, but it is likely only feasible for large-scale projects.

Vibert also stresses the importance of system optimization following initial occupancy. While the museum opened its doors on June 5, 2019, the team continued to monitor how the system was performing and recognized that something was amiss. While the system was sized correctly and the envelope was performing as anticipated, the mechanical systems were effectively fighting one another, leading to significantly higher than anticipated energy use.

“There are always optimizations needed, even in a simple residential building,” Vibert says. However, the level of savings that the optimization achieved is astounding, as depicted in Figure 1. When the museum opened, the mechanical systems for the permanent exhibition space were consuming between 22,000 and 22,500 kWh per month. Through the innovative combination between PHPP modeling software and detailed dynamic simulation, Vibert’s team at Herz & Lang was able to steadily bring down energy use over the course of two years. As an example, within two years of opening, the mechanical systems’ monthly energy use of the permanent exhibition had fallen to approximately 3,000 kWh. Even more amazing, Vibert says the resultant savings amounts to €16,000 each month for the whole museum!

The museum’s energy consumption also stands out when compared to other museums (see Figure 2). When compared to more than 100 other museums, archives, and storage facilities across Germany, the House of Bavarian History had the fourth-lowest level of energy consumption. Vibert says they are even outperforming some facilities that are unheated.

Lessons Learned

The museum’s final certification was issued in 2024, demonstrating the universality and adaptability of Passive House principles. This harmonization between envelope and mechanical systems that makes certification possible is never easy to achieve, but Vibert says that one of the steps that teams can take to make it easier is by bringing the Passive House designer on board as early as possible. “Involving the Passive House designer at such an early stage is always very important,” Vibert says. “Not only to make sure that the Passive House standard will be reached in the end, but also that it will be reached with the highest possible cost efficiency. The later we come [on board], the more it costs if we have modifications to make.”

Additionally, Vibert advises that designers invest time in the beginning of the design phase to assess the user profiles and internal heat gains within the building. Understanding these two factors can go a long way in ensuring the proper sizing of mechanical systems and allowing the team to make realistic assumptions about energy use. Perhaps most importantly, having faith in the Passive House envelope’s performance and fine-tuning the mechanical systems following initial occupancy, especially in buildings with variable and dynamic internal heat gains, can have a tremendous impact on comfort levels, energy use, and operating costs.