Investigation of a multizone building with HVAC system using a coupled thermal and airflow model

In building energy simulations, the air infiltration and interzonal airflow are generally either not considered or calculated oversimplified. However, the effects of air infiltration and building airflow have an impact on the thermal comfort and the building’s energy load. The various zones in multi-zone buildings, the operation of windows, doors and mechanical ventilation make the system’s analysis complex and challenging. Building airflow affects pressure, temperature and moisture differences. Therefore, this study investigate the airflow inside a multizone building with changing user behavior, using a coupled building and system energy simulation. A decentralized air-only HVAC system provides the ventilation system with a control strategy, which variably adapts the airflow to the load in the individual zones. The effects of the air infiltration, interzonal airflow and mechanical ventilation in the building are investigated with a node and link network in TRNSYS using the airflow model TRNFLOW (COMIS). Investigating different variations of the ventilation rates and building’s airtightnesses, the results are shown by comparison with a reference model without airflow simulation. Finally, this study shows a comprehensive approach at low computational costs, determining the air quality, the thermal conditions and the airflow in a multizone building using an HVAC system.

Predicting tree damage in fragmented landscapes using a wind risk model coupled with an airflow model

Forest mechanistic wind risk models are widely applied on heterogeneous landscapes, whereas their wind load parameterizations are often derived either from homogeneous stand conditions or from simple forest edge conditions. To evaluate the impact of improving the wind flow representation of the mechanistic wind risk model HWIND on tree damage predictions when applied on heterogeneous environments, we coupled HWIND with the airflow model Aquilon. Aquilon provides to HWIND the velocity profiles and the gust factor (deduced from an approach based on the probability distribution of the wind velocity and on the turbulent kinetic energy). HWIND–Aquilon is compared with HWIND alone on different stand configurations of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) comprising newly clearcuts or shelter stands. Although both models showed the same pattern of differences in edge-tree critical wind speeds with differences in clear-cut length and shelter stand height, the model comparison reveals significant differences in the magnitude of critical wind speeds between them. This discrepancy is explained by the wind velocity and gust factor parameterizations used in HWIND alone, as in other wind risk models that exhibit weaknesses in heterogeneous configurations. This result confirms the need for improving the wind flow representation in mechanistic wind risk models when applied to heterogeneous landscapes.