viastore Systems GmbH, Stuttgart


The principle of the breathing building, which is ventilated and tempered as required, has now proved its worth. The façade ventilation units not only impress with their energy efficiency, but also create a pleasant indoor climate. Neither the inductive introduction of the supply air through the floor nor the transient ventilation gave rise to any complaints – on the contrary: with the decentralized ventilation units, operating modes can be implemented that would be impossible or relatively difficult to implement with central ventilation. These include cross ventilation for night cooling (see box text) or level or room-by-room demand ventilation.

Architect SCHWARZ Architects
Project 2016
Usable area 3.200m2

Maintain thermal insulation of the façade Minimize flow short circuit

No heating of the outside air in summer. No increase in pressure losses.

Integration 115 FVP-B devices
Special feature First “breathing” office building worldwide

Thanks to the façade ventilation units, the sound attenuation of the façade could be fully maintained.

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viastore Systems GmbH, Stuttgart

Decentralized façade ventilation units were previously used more frequently in building renovation projects. However, they also offer potential savings, especially in new buildings, and in several respects: decentralized devices save space because there is no need for bulky ventilation ducts in the building, allow room-specific control and require less energy. Building owner and building user viastore has recognized this potential. The company ventilates and regulates the temperature in its new administration building in Stuttgart with 115 decentralized units with the LTG PulseVentilation system. They enable transient ventilation, making the building the first “breathing” office building.

The company viastore ventilates and regulates the temperature of its new administrative building in Stuttgart-Feuerbach, which it moved into in 2016, with 115 decentralized FVPpulse façade ventilation units from the PulseVentilation system from LTG Aktiengesellschaft. They enable transient ventilation, making the building the first “breathing” office building. The design by Schwarz Architekten from Stuttgart focused on the user and their requirements for the building: The result is a modern and aesthetic office world with contemporary and practice-oriented architecture. When constructing the new viastore, Jo Vincent Schwarz’s team focused on maximum efficiency, ecology and versatility: On the acute-angled plot in Magirusstraße in Stuttgart’s Feuerbach district, a building was created that offers plenty of work space on six floors with a building height of just 15 meters.

Façade cladding offers dual benefits

“The external appearance is based on an existing viastore building that is within sight,” explains architect Schwarz. “That’s why it was clear from the outset that we would clad the façade with smooth white aluminum sheets.” The 8 mm thick sheets enclose the parapet of each floor and offer multiple benefits: They keep solar radiation away from the walls, thus minimizing the solar cooling load, and at the same time conceal the openings of the 115 or so façade ventilation units, one of which is installed on every second axis of the building. In terms of ventilation, the sheet metal cladding provides additional weather protection, so to speak.

While the façades of the older and the new viastore administration building are very similar, the building technology itself is very different. Christoph Hahn-Woernle, who managed viastore until 2013, is also focused on efficiency in the office buildings – as he was with the company’s intralogistics. He himself provided the impetus to plan the heating technology with a CHP unit to cover the basic heat load and not to rely exclusively on natural gas condensing boiler technology. The solution proved to be more economical in the long term and so the natural gas boiler (150 kW) covers the peak demand, while the CHP unit with its 40 kW heat output meets the base load requirements.

Decentralized façade units instead of central ventilation

For ventilation and temperature control, building owner Hahn-Woernle favoured the approach rarely used to date of using decentralized ventilation units installed in the raised floor instead of central ventilation. This saves space and money in the long term. Although the decentralized façade units are not cheaper to purchase, they use less energy than central ventilation.

Pulsating ventilation units offer high performance

The decentralized ventilation units installed in the new administration building differ from conventional façade ventilation units in terms of their operating principle. They do not have a supply and an exhaust air duct, but use only one air path and alternately lead the air into or out of the building. This is why the inventor LTG also speaks of pulsating or “breathing” ventilation units. The restriction to just one air route offers advantages. The most important aspect is that an FVPpulse façade ventilation unit can move a larger volume of air and provide a higher heating and cooling capacity than conventional façade ventilation units with the same size and the same acoustics. In addition, air short circuits on the façade side are avoided as a matter of principle.

Since the flow reversal for switching between inhalation and exhalation cannot be achieved by reversing the direction of the fan, LTG has developed a patented flap mechanism that implements the changeover with a short travel time and low energy consumption. The internal damper assembly controls the four possible air paths, while the EC fan is operated at a constant speed. The appliances therefore produce a barely perceptible, constant noise. “The ventilation does not interfere with office operations in any way,” confirms the architect, whose planning also took the acoustics into account.

Only one façade opening required

As only one air path carries both supply and extract air, only one façade opening is required per device. The devices are therefore easier to integrate than two-way devices and have less impact on the architecture. Due to the metal cladding of the viastore building, this aspect is less important, but it also made planning and installation easier.

A key efficiency factor is that two air flows do not have to be passed through a recuperator in counterflow for heat recovery. In the LTG façade unit, a regenerator serves as a heat accumulator. It is alternately charged and discharged with thermal energy by the air flowing past. This type of heat recovery takes place with low pressure losses and still allows a heat recovery of up to 90 %, controllable by the breathing frequency of the device. A pleasant side effect: additional protection against icing is not required with this operating principle.

Instationary ventilation

The FVPpulse pulsating façade ventilation unit from LTG Aktiengesellschaft, Stuttgart, replicates natural air movement and allows buildings to “breathe”, so to speak. The FVPpulse thus makes the principle of transient flow usable for office buildings without great effort. In contrast to a conventional façade ventilation unit, the LTG unit uses only one fan and an opening on the façade side and uses a flap system to switch cyclically between the inhalation and exhalation functions. Such a cycle takes about 40 seconds. This leads to good mixing of the room air at low air velocities and high air volumes.

More ventilation units – “breathing” building

Breathing buildings equipped with FVPpulse do not require complex air ducts or a central exhaust air unit. Soundproofed overflow openings to the corridor areas are only required for smaller office units. These diffusers enable air exchange with the corridors, so that the CO2 concentration there is also reduced and interior zones are effectively ventilated. In a breathing building, synchronization of the individual decentralized FVP pulses is neither necessary nor desirable. Different inhalation and exhalation cycles of the individual devices support the cyclical exchange of air in the combination zones and prevent unwanted local increases in pressure in the building.

The mode of operation of the breathing façade ventilation units enables innovative ventilation concepts:

  • If on-demand ventilation is to be implemented, the breathing function is activated via a CO2 sensor, for example. This means that ventilation only takes place when people are actually present
  • For night ventilation in summer, the units on one side of the façade serve as supply air units and those on the other side as exhaust air units. The resulting cross-ventilation takes place without heat recovery and cools the building when the windows are closed.
  • On hot summer days, the alternating breathing function can be switched off and the exhaust air can escape via the façade with the window tilted. As the units then only have to convey supply air, they offer twice the ventilation or cooling capacity with the same operating noise.

For passive cooling on fresh summer nights, cross ventilation can be used instead of cyclical operation. The air then flows in through all ventilation units on one side of the façade, while all units discharge air on the other side of the façade.

The special operating mode “hybrid ventilation” can cover peak cooling loads in summer. The façade ventilation unit then operates purely as a supply air unit with almost twice the cooling capacity and the exhaust air is discharged via a tilted window, for example.

Dispensing with a second air path opens up further advantages: silencers and pressure loss-generating components such as air filters and heat recovery units can be dimensioned larger. The internal pressure losses are therefore lower than with two-way devices of the same capacity. All this results in low power consumption of the fan, which is driven by an EC motor. The electrical power required is so low that the lower electricity costs compared to a central ventilation system will have compensated for the higher investment in the decentralized devices within just a few years.

Advantages of façade ventilation units

In addition to the energy-saving potential, other factors spoke in favor of the decentralized, pulsating façade ventilation units over a central solution, above all:

  • No ventilation ducts, which saves space and floor height
  • This means that there are no pressure losses in the air distribution
  • Simple implementation of on-demand ventilation possible
  • Room-specific control of air volume and temperature

The decision-makers were also impressed by the performance of the façade units. Among other things, they offer:

  • Up to 120 m³/h air flow rate per device
  • At 90 m³/h, the fans only have an electrical power consumption of 9 W
  • Heat recovery makes over 80 % of the exhaust air heat available again during normal operation
  • Low-noise and draught-free operation
  • Simple installation in the raised floor
  • Easy integration into a four-pipe system for heating and cooling

In terms of office furniture, the use of the devices does not result in any significant restrictions. A high level of thermal comfort is ensured by introducing the supply air using the induction principle:

Due to the impulsive air flow, temperature differences are quickly reduced and there is only a relatively small temperature difference in the occupied zone,” explains Ralf Wagner, CEO of LTG. “The supply air penetrates the room in slow waves that are imperceptible to users without generating high air velocities.”

Workstations can therefore be positioned close to the ventilation grilles. No heavy pieces of furniture should be placed above the appliance, which extends further into the room than the ventilation grille under the raised floor. The maintenance flaps in the floor must remain accessible for possible repairs. Desks, mobile pedestals or lights, on the other hand, may be placed directly next to the ventilation grille.

At viastore, the façade ventilation units are equipped with stainless steel ventilation grilles. They are easy to walk on and can be easily removed for maintenance purposes. After removing the stainless steel grille, the appliances can be vacuumed or common maintenance work can be carried out. This includes maintenance work on the filter, the outside air flap, the heat exchanger and the regenerator. The electronics are also accessible after removing the grille. Service technicians can therefore simply load new parameters via a USB port using a terminal program, for example to make adjustments to air volumes or cycle times.

Pulsating ventilation for large and small rooms

The open-plan offices and the open corridors are served by several façade ventilation units. Synchronization of the devices is not necessary here – in fact, it is not even desirable (see box text). In dense office and meeting rooms with two or one device, however, it must be ensured that an appropriate air exchange takes place and that no increased air pressure builds up in the room.

The simpler case is a room with two ventilation units, as it can be controlled ex works. With the device duo, one is declared the master and the other the slave. The master then determines the duration of the breathing cycle: While the master inhales, the slave expels used air and vice versa.

Rooms with just one façade ventilation unit require a more individual solution. It must be ensured that the air space of the room is connected to the corridor. In buildings with solid walls, for example, this can be made possible by an overflow opening above the door. In the new viastore building, however, the partition walls and office doors are made of glass. “We didn’t want to destroy this light look. That’s why we had narrow, glass overflow elements installed next to the doors,” reports Schwarz. These specially manufactured, double-walled elements allow air exchange, but effectively dampen noise inside the walls thanks to special absorbers developed specifically for the building.

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