The winning formula – WUFI® Plus for custom-built construction

Research in focus May 2012

As children we just loved playing with Lego bricks – placing one block on top of another to build houses or even entire cities, brick by brick. Four walls – windows and doors if you had them – a roof, and your Lego house was complete. But back then we didn't think much about the kind of forces that house had to withstand, the weather it was exposed to, and what impact all these factors have on its occupants, and, ultimately, on the house itself. But anyone that eventually turned that childhood passion for building things into a profession has to focus on precisely these issues. The aim is to clarify various fundamental questions: what impact do users or the usage of buildings have on their hygrothermal behavior and on the interaction between building envelope and the enclosed space? How can buildings be planned so that they are optimally tailored to their environment and their occupants? And more importantly, how can all the parameters and eventualities – from the outdoor to the indoor climate, through energy usage, to the requirements placed on occupants’ indoor environment – be considered before construction starts, and their impact simulated? Ultimately, the goal is to prevent building damage occurring in the first place wherever possible. Other issues arise through the increasing usage of renewable energies as main sources of energy: how can a building along with its building systems cope with fluctuations in energy availability? What impact does this relationship have on temperatures and moisture conditions within the building and components?

Florian Antretter and his team from Hygrothermal Building Analysis at the Fraunhofer Institute for Building Physics IBP analyze precisely these issues. Apart from hygrothermal building monitoring, i.e. recording and assessing temperature and moisture conditions along with user behavior, one of their core tasks is hygrothermal building simulation, which integrates the insights garnered from monitoring. Through this approach, the scientists have helped develop the WUFI ® Plus simulation tool, thus extending Fraunhofer IBP's "Wärme und Feuchte instationär – WUFI (Transient Heat and Moisture)" software family. "The earlier versions of WUFI provide realistic simulation of transient hygrothermal behavior of multilayer components under natural climatic conditions. WUFI ® Plus focuses on the building as a whole including heating and ventilation. This innovation is an important step in supporting practitioners in architects' and engineers' offices in their daily work," the Fraunhofer researcher affirms. A key goal of the software is to prevent damage to the building in the first place.

"Hygrothermal issues in the building are often dependent on several factors. Mold growth can occur as a result of critical structural details, high indoor moisture production, inadequate ventilation, or a combination of various factors," the engineer adds. The behavior of building users in response to their own comfort needs is often a primary cause of problems. Thanks to WUFI ® Plus these effects can also be simulated for various climatic regions around the globe. WUFI ® Plus can be used to evaluate the right ventilation behavior to prevent mold growth, shade strategies to reduce overheating in summer, the influence of thermal and hygric masses on building energy requirements and the indoor environment, along with the hygrothermal building behavior in the case of extreme or intermittent use.
Architects can utilize the simulation software to generate models and simulate their building under realistic conditions. "If you like, WUFI ® Plus is a decision-making tool for the optimum building," says Antretter, adding: "Solutions to prevent critical conditions, to improve hygrothermal comfort, and to reduce energy consumption can be developed with it." For example, to combat excessive humidity, a common solution is to install outsized air-conditioning systems and keep them running constantly. WUFI ® Plus, on the other hand, can easily provide a more efficient solution that substantially reduces investment and operating costs by determining the right configuration and a usage-based operating strategy.

The software developers at Fraunhofer IBP are also particularly proud of how easy WUFI ® Plus is to use. "Most of the existing tools in this segment tend to require a lengthy induction period and extensive background know-how," says Antretter. "The advantage of WUFI ® Plus is the intuitive user menus along with support for evaluating the results. Theoretically even your one-man home builder could use our software, although they would at least need some knowledge of building physics to evaluate the results." With a few adjustments, the software can be used for everything from a basic single-family home to a 50-story apartment tower. "All the standard problems you might encounter can be recorded and simulated using WUFI ® Plus," says Antretter.

In addition to its use in the planning phase of construction projects, the simulation program also provides an ideal solution for historic buildings, such as castles. Such structures are particularly susceptible to the consequences of climate change, often further compounded by other factors such as increasing utilization through tourism. Scientists from Fraunhofer IBP are therefore helping the owners and administrators of historic buildings and other conservation groups to come up with solutions to these problems. WUFI ® Plus is the key element in simulating hygrothermal conditions inside historic buildings, along with heat loss through transmission, evaporation and ventilation. It is one of the few building simulation tools capable of simulating the critical fluctuations of moisture content in the air and the associated moisture buffering effect of hygroscopic structures. Both are crucial factors when assessing historic and future building structures.

For now the scientists at Fraunhofer IBP are focusing on the new possibilities opened up by WUFI ® Plus. They are cooperating with the Fraunhofer Institute for Solar Energy Systems ISE on issues such as the integration of innovative building systems. The software is being used to develop solutions to the architectural challenges associated with the change in energy policy. Yet the software is still far from complete; new functionality will be added to Fraunhofer IBP's WUFI software family in future. Antretter already has one – albeit distant – goal in his sights: "With the opportunities that the software opens up for us, the long-term goal is to move from documenting and simulating individual buildings, to analyzing entire city districts."

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