Hygrothermal

The term 'hygrothermal' refers to the movement of heat and moisture through buildings.

Repeated wetting, drying, freezing and thawing of the fabric of a building can cause problems such as damp, condensation, mould growth and loss of thermal performance, and may even result in premature failure.

Computer-based hygrothermal modelling simulates the movement of heat and moisture, generating information relating to temperature, water content and relative humidity within multi-layer building elements.

Buildings can be affected by water through a number of mechanisms, including:

• Water leaks.
• Wicking of groundwater.
• Penetrating and rising damp.
• Air infiltration and condensation through the building fabric.
• Vapour diffusion.
• Drainage.
• Ventilation.
• Evaporation.

By simulating the performance of building assemblies, the risks of problems associated with these mechanisms can be evaluated and minimised. By understanding risks such as condensation, moisture entrapment, fungal growth, material degradation, and so on, the correct balance between heat and moisture can be achieved.

Physical testing may also be used to test the performance of materials or assemblies under a range of hygrothermal conditions.

NB Energy Efficiency and Historic Buildings, How to Improve Energy Efficiency, Published by Historic England in 2018, defines hygrothermal behaviour as: ‘…the movement of heat and moisture through buildings. Permeable materials tend to be hygroscopic because of the reduction in vapour pressure in the pores that occurs as a result of condensation, capillarity and salt action.’

[edit] Related articles on Designing Buildings Wiki

• A Practical Guide to Building Thermal Modelling.
• CFD.
• Cold bridge.
• Computational fluid dynamics in building design: An introduction FB 69.
• Condensation.
• Convection.
• Conventions for calculating linear thermal transmittance and temperature factors.
• Damp in buildings.
• Dynamic thermal modelling of closed loop geothermal heat pump systems.
• Heat transfer.
• The thermal behaviour of spaces enclosed by fabric membranes (Thesis).
• Thermal behaviour of architectural fabric structures.
• Thermography for traditional buildings.
• Understanding dampness.
• U-values.
• Ventilation.
• Wall insulation and moisture risk.
• Water vapour.

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