Passive House Hospital Opens Doors

More than a decade ago the State of Hesse in Germany approached the Passive House Institute (PHI) about conducting a study on how to get a new building type to meet Passive House targets— a hospital. Hospitals are notoriously high energy users, and across Germany, many hospital buildings are reaching the end of their useful life.That exhaustive study and many years of careful planning paid off earlier this year, when the new 700-bed, 79,000-m2 Klinikum Frankfurt Höchst opened its doors. It’s the first Passive House-certified hospital in the world, and a leading example for hospitals worldwide of how to prioritize energy efficiency and sustainability.

Wörner traxler richter planungsgesellschaft mbh is the architectural firm responsible for the design of this complex structure, which was developed by Zentrale Errichtungs Gesellschaft mbh (ZEG) with the prime builder being ZECH Hochbau AG and the Max BöglBauservice GmbH & Co. KG, acting under the consortium name of ARGE KFH. The hospital includes 10 operating theaters and an entire floor devoted to expectant parents and children, with one of the delivery rooms featuring a birthing bath. All of the features in this new facility are state of the art, and the highest quality patient comfort was built into it, thanks to the advantages that flow from its Passive House design.

Today, new, conventionally built hospitals in Germany have an average annual final energy demand of about 240 kWh/m2. Bringing that high use down at the Frankfurt property to just 130 kWh/m2 required all of the usual Passive house approaches—such as a robust thermal envelope, high performing windows and doors, and ventilation with heat recovery—plus a minute scrutiny of all operations conducted and equipment used at the hospital. As Berthold Kaufmann, senior scientist at PHI, pointed out in his presentation at PHI’s 2023 conference in Wiesbaden, Germany, a hospital building encompasses uses that are typical of residential buildings, office buildings, and medical facilities. So, layered onto the energy uses required to keep patients comfortable in their rooms is the substantial energy use associated with the robust ventilation system needed to satisfy hygiene requirements, all of the computing equipment for administrative tasks, and the medical equipment that allow the providers to deliver excellent care. To further complicate planning, most of the equipment throws off excess heat, which also has to be accounted for, especially when devising the building’s cooling strategy.

Furthermore, hospital occupants’ requirements exceed those of typical building users. Patient rooms are kept to 22ºC to ensure comfort for people who are often sparsely dressed or elderly, and operating rooms have their strict ventilation specifications. All of these demands—and their optimization—factor into the final energy balance.

With the first pilot now in operation, though, the experience gained will smooth the path for future hospital developers. As Raphaël Vibert from Herz & Lang, the Passive House consultant who led the certification of this pilot hospital building, says, “The most important lesson is that it is worth it. Targeting Passive House has a huge impact on the energy consumption of a building over its lifetime and is highly cost-efficient over that period.” For hospital developers, he adds this challenge, “They should dare to do it.”

In issuing this challenge, Vibert speaks from extensive experience. He was the one tasked with figuring out the details that would get Klinikum Frankfurt Höchst to successfully meet the performance targets set by PHI for this pilot project, while also keeping within the developer’s budget limits. Provisional data from ZEG peg the extra investment cost for this innovative Passive House building to be a reasonable 6%.

This building was more complex than others Vibert has worked on, for many reasons, including a hospital’s strict hygiene and fire requirements—but not that far outside the realm of his typical projects. He explains, “Twenty percent of the challenges we had were hospital specific. Eighty percent of the challenges were Passive House-specific challenges that we have in every building.”

The real difficulties arose from an issue that is not unique to a hospital project: “The biggest challenge was the fact that it had to be designed parallel to the execution,” notes Vibert. When Herz & Lang started on this project seven years ago, the developer consortium had already chosen the builder, and initial construction was beginning, even though the design details had not been worked out yet. He says Herz & Lang led many workshops with the designers and with the builders and subcontractors, teaching them about Passive House and how to attain the performance targets they had agreed to reach. He emphasizes, though, that despite this non-ideal work flow, the project ultimately is a huge success.

One example of the very typical Passive House-related tasks that had to be managed was sourcing the optimal windows. PHI had originally specified in its PHPP model window frames with a U-value, or Uf, of 0.75—a value that represents the highest end of the market and is quite expensive. At the time when PHI recommended that framing value, glazing with low Ug-values was hard to source. In the meantime, better glazing has become more readily available, and frames with a Uf of 1.0 are on the order of 20% to 30% less expensive than those with the lower Uf of 0.75. So, Herz & Lang suggested changing the approach, opting to use better glazing and allowing the windows to fit within the developer’s budget. “We took more cost-efficient frames with higher U-values and compensated for those with better glazing,” Vibert says. He then successfully argued the case for this revised package with PHI, showing that, for the whole installed window, the resulting comfort-related properties would be the same.

Airtightness was another hurdle that was both within the realm of an ordinary Passive House challenge and more complicated than usual. Herz & Lang led many trainings on connection details for the builder and also drove many times to the hospital to test specific areas to check whether the airtightness details had been installed correctly.  “We would measure a room, gather information on the quality of the executed connections, and then optimize measures based on this feedback. We would then communicate with the contractor about how to improve the airtightness concept to be sure that, in the end, we could succeed the first time,” Vibert explains. It helped that the hospital is a concrete building, so that only the penetrations and connections were what was needed to be optimized.  The day for the final airtightness test of the whole eight-story building revealed the success of Herz & Lang’s coaching. The building achieved an airtightness of 0.13 ACH50.

Sourcing a heat-recovery ventilation system that met both PHI’s efficiency requirements and the hospital’s hygiene requirements presented similar difficulties. No certified ventilation systems met the hygiene needs, particularly for the operating rooms where very high airflow rates would be needed. Minimum ventilation requirements in the patient bed rooms are 30 m3/h per bed, or 60 m3/h for the typical two-bed rooms. In the children’s wards these requirements increase to 90 m3/h, while the intensive care room requirements are 150 m3/h. The operating rooms’ needs jump to 1,200 m3/h, with each operating room supplied by a separate HRV for hygiene reasons. Higher airflow rates mean higher pressure drops through the filtration system, which requires higher electricity use. One part of the solution was tailoring the filters’ depth and area to reduce the pressure drops and increase the system’s overall energy efficiency.

Given all of the internal heat gains from all of the hospital’s equipment, meeting the PHI’s heating demand was not as challenging as it might be in other buildings. To maintain comfort in winter, heat is being distributed through hot-water radiators. The cooling demand was more of a concern, and ultimately relies on a three-pronged approach. Operable windows throughout the hospital allow for nighttime ventilation; the ventilation system’s supply air can be pre-cooled in summer; and there is an additional water-based surface cooling system mounted in the ceiling. The reaction time of this latter system is very slow, due to the high mass of the concrete ceiling, so managing it requires careful controls. “We are quite sure the systems will run well with respect to indoor climate and thermal conditions,” says Kaufmann.

As part of completing the original hospital study, PHI’s Oliver Kah and a team of colleagues had visited the old hospital that Klinikum Frankfurt Höchst replaced, and they had taken electrical power use measurements of as many medical devices as they could get their hands on. These data were paired with detailed schedule information on how often each type of equipment was being used and for how long. These calculated equipment loads had helped determine the building’s heating and cooling loads. However, it turned out that optimizing the actual equipment power use was quite difficult, due to limitations in the market availability and choice of medical devices. PHI made suggestions to medical device manufacturers, says Kaufmann, on how to improve the energy efficiency of their products, but medical equipment purchases ultimately were driven mainly by the services provided. Many more choices exist in the information technology market, so it was both feasible and practical to select computing equipment with lower-than-average electrical consumption.

This Passive House hospital has generated quite a bit of interest, with many visitors requesting tours. ”It is helpful to show that it did not require so much special effort,” says Kaufmann. Each new building type that gets certified gives rise to new challenges, and demands dedicated teamwork—and maybe even some daring—to arrive successfully. Still, the payoff is substantial, especially for a medical facility serving people in high-need situations: a building that operates efficiently and delivers optimal comfort now and into a future made less predictable by a shifting climate.