Thermal comfort: standard compliant modelling of natural ventilation in adaptive time step solvers

Natural ventilation can help maintain thermal comfort during summer periods. In simulation models for thermal comfort analysis, occupant behaviour related to natural ventilation is often included through definition of ventilation rule sets. For example, windows are opened when room temperature exceeds a given limit while outside temperatures remain below a threshold. Such rules are included in building codes, such as DIN 4108-2 [1]. However, these rules are defined with respect to fixed step time integration methods, often using hourly step sizes. Straight-forward implementation of such rules in error controlled adaptive time step integration solvers (including drivers for Modelica models) fails. The article discusses strategies and model variants that work with such modern solvers and discusses new model parameters such as the delay time or dead-band size. The impact of these parameter choices is illustrated with sensitivity studies using the thermal room model THERAKLES [3-5].