IBPSA2009

The paper examines the importance of using site-specific data in computer simulation of building energy performance. The CAT (Canyon Air Temperature) computer model, which is designed to predict site-specific air temperature in an urban street canyon for extended periods on the basis of data from a reference station exposed to the same meso-scale weather, was used to provide modified input to a series of Ener-Win simulations of the energy performance of a hypothetical office building.

This paper provides a brief, non-exhaustive overview of the status of the application of CFD in building performance simulation for the outdoor environment. It focuses on four topics: (1) pedestrian wind environment around buildings; (2) wind-driven rain on building facades; (3) convective heat and mass transfer coefficients at building surfaces; and (4) air  pollutant dispersion around buildings. For each topic, some specific difficulties, advantages and disadvantages of CFD are addressed.

A jet of cold air is denser then ambient air but it adheres to the ceiling of the room over the given distance when it is blown horizontally close to it. Such behaviour of fluid jets is well-known as Coanda effect and it is widely used in practice like in the case of ventilation and air-conditioning of rooms. This phenomenon is not sufficiently known both in terms of mechanism and quantitative effects.

Indoor climate has a three-dimensional spatial distribution caused by three-dimensional airflow. To obtain the accurate knowledge of building performance, it is demanded to integrate the spatial distribution into building simulations. Thus, CFD analysis is necessary in design process. However, usually only a few case of CFD could be executable in real design process, because of the large computational load.

Computational Fluid Dynamics (CFD) has been introduced to the architectural engineering and HVAC (Heating Ventilation and Air Conditioning) industry for decades. Its effectiveness in assisting the architects and engineers in the design process has been well acknowledged. However, the mesh generation process is complicated and time consuming, especially for modeling free form geometric artifacts, e.g., buildings in complex terrains or human bodies in the room. This paper presents the effort to apply quality mesh generation to CFD simulations in architectural applications.

The paper describes results from a reference study that focuses on the application of the Computational Fluid Dynamics (CFD-) technique for heat and smoke transport in practice. Goal of the study is to obtain insight into the amount and causes of the spread of CFD-results when applied by different users. In this study several CFD-practitioners have solved the same relatively well described flow problem. The obtained results have been compared. They show a clear spread which to some extent can be explained by the assumptions made for the modelling and solving of the problem.

As a cost-effective alternative to experiments, computational fluid dynamics (CFD) can provide new insight in airflow patterns and the related convective heat transfer (CHT). However, together with the governing equations, the description of the boundary conditions determines for a greater part the reliability and the accuracy of CFD simulations. In this study the sensitivity of the predicted CHT to diffuser modelling is studied. Numerical simulations of a modified version of test case E.2 of the IEA Annex 20-project are performed.

In this article, we will present a new multi-level modelling approach to obtain higher precision in HVAC plant simulation models. For this purpose, two different levels of detail in modelling, the coarse component-based approach of Modelica and the detailed physical-based approach of Computational Fluid Dynamics (CFD) were combined. In a first use case, we analysed the thermal hydraulic network of a simple heating system, both with the CFD-approach (3D-model) and the Modelica approach  (1D-model).

A simplified model was developed by use of thermal-ventilation network with the purpose of studying air environment in void space at the central portion of high-rise apartment houses when gas-fired boilers were installed in the void. First, a one-node model was studied assuming uniform temperature distribution in the void space, resulting mismatching between calculated and measured values for building surface temperature. Then, a two-node model was prepared by separating corridor region from void region.

The performance of hot water space heating systems for mild to warm temperate climates is dominated by the efficiency of boiler operation at low load (i.e. below 25% of nameplate capacity). This efficiency is influenced by a number of effects that are poorly represented in common modelling approaches, including static thermal losses from the boiler and distribution system, changes in burner efficiency at different firing rates, thermal inertia in the boiler loop and the effects of cyclic operation. In this paper, a simple model that includes these loss mechanisms is developed.