Hygrothermal Building Simulation

In order to elaborate the most substantial risks of changing climate conditions on historic artefacts in specific regions, CLIMATE FOR CULTURE has taken the innovative approach of correlating high resolution climate change scenarios with building simulation tools. By doing so, the impact on historic buildings can be evaluated and possible effects on the indoor environment including collections be identified.

Historic buildings usually show a broad variation of indoor humidity levels and climatic conditions which might be dangerous to cultural heritage materials. How much ventilation and additional heat energy is required to ensure safe indoor conditions for cultural heritage when a historic building is exposed to extreme climate conditions or to a high amount of visitors? What will happen to the hygrothermal behaviour of walls and ceilings if the use of a for example historic cellar changes? How do the indoor air conditions and the envelope of buildings in temporary use react to different heating and ventilation strategies?

These questions exemplify that identifying precise indoor humidity fluctuations and moisture profiles in the building envelope is essential for a sound damage and risk assessment, taking into account complex hygrothermal interactions between the indoor air, usage, furnishing and the building envelope. The hygrothermal behaviour of components exposed to different weather parameters is an important aspect of the overall performance of a building. In the present state of the art such interactions of different parts of the envelope can be calculated, allowing a realistic assessment of all relevant effects. However, the total behaviour of the whole building has not yet been considered which expresses the need to apply models that combine thermal building simulation with hygrothermal component simulation.

For this purpose, different thermal and hygrothermal building simulation tools are evaluated for their applicability to simulate the indoor environment and hygrothermal transport mechanisms in historic building materials, taking also into account the type of use and HVAC climatisation components. This approach has never been performed before as computational models are usually used for simulating water and temperature distributions in modern building components like insulated walls or roofs. To date, the applicability of building models to historic buildings with often unknown constructions and material properties is still limited.

The most suitable tools are then applied to model the predicted impact of climate change using high resolution climate data from the Max Planck Institute for Meteorology to predict the future indoor environment of the case study buildings which are then assessed by applying various damage functions. In addition, these simulation models are also used to evaluate effects of innovative active and passive mitigation measures.

Building simulation models

For adapting existing tools for hygrothermal building simulation, the following existing software is evaluated during CLIMATE FOR CULTURE. The building model WUFI® PLUS is a combination of a thermal building simulation with the hygrothermal envelope calculation model WUFI®. This holistic model takes into account the main hygrothermal effects deriving from moisture sources inside a room, the moisture input of the envelope due to capillary action and diffusion as well as vapour ad- and desorption as a response to exterior and interior climate conditions. In addition, different indoor heat sources coming from the envelope and the solar energy input through walls and windows as well as hygrothermal sources due to natural or mechanical ventilation are incorporated. Also carefully tested are common software tools such as Hambase /5/, ESP-r /6/, Energy Plus /7/, DA-ICE /8/ and TRNSYS with regard to their applicability for historic buildings.

These different tools are expected to have strengths and weaknesses as to their level of performance matches the aims to be achieved, e.g. some simulate the combined heat and moisture transport through porous materials, whereas others only use simplified models for these processes or have higher possibilities in accurately modelling different HVAC systems. Therefore, missing features for appropriate climate change impact modelling on complex historic buildings are developed during the project and implemented into software tools.

St.Margaretha's Church, Roggersdorf, Germany (left) and simulation model of the church using
WUFI®plus software (right)