CFD

This paper presents a validation of airflow network (AFN) and computational fluid dynamics (CFD) simulations for a naturally ventilated office building using wind tunnel measurements as the reference for external pressure coefficients and effective airflow rate prediction. The CFD simulation model is also used to study the effect of partially open windows on the effective flow rate. This study also includes a design exercise for a naturally ventilated office building that analyses the differences in predicted average window open area for a typical weather year.

Cross-ventilation flows (CV) are characterized by significant inflow momentum conservation as fluid flows across an enclosed rectangular volume as a confined jet. When the inflow area is smaller than the volume cross-sectional area the CV flow has distinct jet and recirculation flow regions. The simplified model presented in this paper characterizes the CV flow as the result of a confined axisymmetric jet driving one or two recirculation regions, each of which is a lid-driven cavity flow.

Japan will have to further reduce CO2 emissions to meet its obligations under the Paris Agreement negotiated at the 2015 United Nations Climate Change Conference. Society is increasingly demanding higher energy-efficiency standards and zero-energy buildings because general commercial buildings have high energy costs, especially for air conditioning.

Outdoor air change qualifies the air that enters into the buildings. The outdoor air moves freely along the urban mesh favoured by the wind forces and stresses. Buildings, trees and other constructions alter the natural air flow pattern inside the cities, creating stagnated air masses in those wind-protected regions. Some outdoor spaces such as light shafts and confined light shafts inhibit the correct exchange of the stagnated air with fresh air coming from the outskirts and suburban areas. 

Recently, many studies have focused on the adsorption of pollutants as a method for improving indoor air quality. In Korea, the Health-Friendly Housing Construction Standards specify requirements for the installation of pollutant-absorbing materials. It is recommended that at least 10% of the total area of the living room and bedroom walls be covered. However, current guidelines regarding the installation locations of the adsorption material are unclear.  

Airtightness is the most important property of building envelopes to understand the ventilation. Airtightness refers to the flow measurement through the building envelope as a function of pressure across the building envelope. This relationship often fits to a power law, which is the most common way of expressing data. However, pressure homogeneity during airtightness tests can crop up, especially in large buildings.

The Royal Wanganui Opera House (RWOH), in Whanganui, New Zealand, was constructed in 1899, and now seats 830 people. This building was designed with a natural ventilation system; however, this system is no longer in operation and the RWOH has received regular complaints from patrons regarding indoor thermal comfort. Various options for mechanical systems to improve indoor comfort during summer performances have been considered, but have been deemed too costly. The RWOH is listed with Heritage New Zealand as a Category 1 heritage building.

The aim of this study is to analyse the behaviour of natural ventilation techniques in low-rise commercial buildings in terms of Indoor Air Quality (IAQ).

A VAV (Variable Air Volume) air conditioning system without reheat of the air supplied is generally regarded as energy efficient. Re-heat can be avoided when induction VAV controllers are used instead of conventional controllers since primary airflow can be reduced to about 10−20% of its nominal value without a draught risk.

The paper investigates the possibility for using a traditional ventilation system with ceiling mounted diffusers to provide heating under winter time conditions in relatively cold climates – in buildings with low transmition losses such as “passive houses”. The analysis is done through a number of CFD simulations of a simplified office. It is shown that even small over-temperatures reduce the Air Change Efficiency substantially. On the other hand even very small internal heat sources increase the efficiency.