Research in focus

A software family conquers the construction industry

Structural damage and its consequences are a matter of increasing concern in the construction industry: The number of building damage incidents has increased by more than 400 percent from 2002 to 2013, and the total loss amounts are also continuously on the rise. These are the findings of a joint project initiated by property owner interest group Bauherren-Schutzbund e.V., professional liability insurer Berufshaftpflicht AIA AG, and construction research organization Institut für Bauforschung e.V. The objectives of the project included the study of structural damage incidence growth during this time period. It is not uncommon for construction projects of all sizes to end up on the desks of appraisers, professional liability insurers, attorneys or even on courtroom dockets in the worst cases due to incidences of significant structural damage. But who is at fault? Were the mistakes made during planning, or did they occur during the construction phase? Could there even have been unsuitable building materials in use? Were there any environmental factors which were perhaps not sufficiently considered? At any rate, the technical requirements for buildings have increased enormously in recent years: They should be cost and energy efficient as well as conveniently user-controllable, and of course a healthy, comfortable atmosphere inside the rooms is a must nowadays as well. However a common complaint is that the inside air is too hot in the summer and often too dry in the winter. “The demands for healthy, sturdy, and energy-efficient buildings represent a major challenge for architects, planners and contractors”, says Prof. Dr. Klaus Peter Sedlbauer, director of the Fraunhofer Institute for Building Physics IBP, who brings us to an important point: “Robust planning is impossible without taking into account complex hygrothermic processes and interactions.” Fraunhofer IBP researchers were already aware of this by the mid-nineties, which is when they began development of the WUFI® simulation software. This successful application is now celebrating its 20th anniversary.

The name WUFI stands for "Wärme und Feuchte instationär”, or "Transient Heat and Moisture" in English. The program transparently models the basic principles and interactions of heat and moisture transfer for building components under natural climate conditions, and provides valuable insights into the processes taking place within the component itself. The necessity of such information for solid planning was already obvious to Fraunhofer IBP Hygrothermics department head Dr. Hartwig Künzel and his colleague Prof. Dr. Krus in 1995. Operating from different points of emphasis, the two researchers focused on heat and moisture transfer inside construction components, which are closely correlated with one another. Dr. Künzel developed the computational model, and Prof. Krus developed the measurement methodology for determining the necessary material characteristic values. Elevated levels of moisture in building components lead to increased heat losses, and conversely, temperature conditions affect the moisture transfer characteristics in building components. The study of this interdependency, and the work of deriving standards from the results, formed the cornerstone for the development of WUFI ®. To this end, the worldwide one-of-a-kind outdoor testing site in Holzkirchen offered the ideal conditions for scientifically corroborating the calculations with outdoor and laboratory data. By continuously comparing measured and calculated data, a reliable process was created for verifying fitness of use of buildings, construction materials and construction methods.
For a long time, the so-called Glaser method was the standard tool for measuring the moisture characteristics of construction components. However this method only permits stationary, which is to say highly simplified, assessment of winter condensation risk. Factors such as trapped moisture, driving rain, rising ground moisture, hygroscopic moisture or summer condensation are not accounted for with this method. Hygrothermic simulation with WUFI ®, on the other hand, provides a realistic depiction of transient heat and moisture characteristics subject to recorded outdoor climate and real-world usage scenarios which encompass all of the above-mentioned factors. The software thus allows assessment of building component moisture characteristics in any climate conditions and usage scenarios, not only over the course of a year but also long-term over the life of the building. It can provide information on damage mechanisms such as frost, mold, wood rot, material destabilization, condensation formation on component surfaces and inside components and corrosion on metal parts. Furthermore, with WUFI ® it is possible to optimize components and systems for various usage areas and climates, or to address questions regarding drying times of new components, or components saturated due to water damage. Because the WUFI computational kernel based on Computational Fluid Dynamics (CFD) has always been very fast, it was and still is superior to competing products in a number of ways. This Fraunhofer IBP software is standardized in DIN EN 15026 as of 2007, and it is also accepted for use in the measurement of moisture characteristics in accordance with DIN 4108.
A multifaceted family
The WUFI®-Family has been continuously enhanced over the years, and today it covers all aspects of hygrothermic construction component and building simulation: With WUFI® Pro und WUFI® 2D, users can determine whether damage can be ruled out in the standard cross-section as well as in critical locations such as the connection areas of specific building structures. WUFI® Plus und WUFI® Passive, on the other hand, cover building simulation with a stronger emphasis on indoor hygiene and comfort. Fraunhofer researchers are elated at the success of their software. "In the first year we had a mere five customers for WUFI ® Pro, but now since 2012 alone we've sold more than 3000 licenses." Today, the various products in the WUFI ® family are used in over 40 countries by planners, architects, building product manufacturers, construction firms and technical experts, in addition to a multitude of educational institutions and universities.
Version 6.0 will be released in late November for the 20th anniversary of WUFI ® Pro. This basic program of the WUFI family, which has been continuously enhanced since its inception, will become even more stable, versatile and user-friendly. Key enhancements in recent years include improving building component moisture resistance properties by accounting for typical convection and precipitation leakages, as well as simplified results assessment using so-called post-processors. These allow for functionality such as detailed mold growth risk prognoses (WUFI ® Bio und WUFI ® VTT), assessment of hygiene requirements based on transient u-values, or corrosion rate forecasts of metal parts embedded in mineral materials (WUFI ® Korr). Further additional programs, including those for forecasting wood rot processes and wood connection corrosion, as well as for evaluating interior insulation and wood components in accordance with the new WTA data sheets, are currently in development.
"Transient building simulation is the future, as it will be the basis for the development of comfortable and hygienic zero-energy and energy-plus houses," says Florian Antretter, head of the hygrothermic building analysis group of the Hygrothermics department, with an air of certainty. Hygrothermal building simulations realistically reproduce the interactions that occur at interfaces between building envelopes, building services, types of use and user behavior. This enables experts to simulate various ventilation strategies and evaluate how these affect comfort levels within the room. It is also possible to compare a range of passive measures designed to reduce energy consumption (insulation, windows, storage masses, etc.). As well as analyzing the energy efficiency of components and buildings, it is equally important to look at their hygrothermal performance under different climate conditions. Designed with these objectives in mind, the WUFI ® Plus and WUFI ® Passive software applications were upgraded this year to version 3.0. WUFI ® Plus is the most full-featured tool in the WUFI ®-Family, with functionality for indoor climate simulations including hygrothermic conditions in components. In 2004, the software was enhanced and validated as a part of a research project conducted by the German Federal Ministry for Economic Affairs. Because it models transient indoor moisture conditions more effectively than conventional building simulation models, it can provide exceptionally realistic data in response to questions regarding comfort, energy requirements and indoor climates.
Passive homes feature very low energy requirements. Dynamic models are necessary to properly duplicate the hygrothermic characteristics of buildings when high dynamic fluctuations in the outside climate are present, or when cooling and dehumidification of indoor air play an important role. They make it easier to measure thermal and hygric storage masses with the aim of further optimizing energy requirements and eliminating negative comfort factors such as excessive heat. Furthermore, dynamic-hygrothermic assessment is necessary to ensure damage-free functioning of extensively insulated components which are transferred to other climate zones. For this reason, Fraunhofer IBP and the Passive House Institute US (PHIUS) co-developed the WUFI ® Passive software application in 2012. The software can be used for assessing homes for standard passive house certification, and also for hygrothermic simulation of certified homes.
But WUFI ® software is not only used to address questions regarding new building construction and renovation of residential and nonresidential buildings. These Fraunhofer IBF programs are also utilized by planners, energy consultants, building product manufacturers and other construction contractors for tasks such as damage assessment and analysis, building renovation, and for unusual building types far outside standard usage scenarios. This includes structures such as historic buildings, cold storage units and swimming pools.
Today, the WUFI ® family is an indispensable part of the planning and construction work routines at many offices and factories. The high attendance rate of the seminars and training courses organized by Fraunhofer IBP and its partners in 20 countries at present is but one indicator of its popularity. Interested parties may also download free versions of WUFI® software for noncommercial/restricted use via our webshop.