mechanical ventilation

The performance of a hybrid air-conditioning system which utilises wind-induced cross ventilation is investigated. The characteristics of flow and temperature fields are examined using CFD simulation under various conditions of inflowing outdoor air i.e. air temperature, air exchange rate and width of the opening for cross ventilation. In this simulation, the room air controlling system (VAV system) which is used to keep the task zone at a target temperature is reproduced through changing the supply airflow rate of the air-conditioning system.

There are often tradeoffs among improving IAQ (Indoor Air Quality), maintaining thethermal comfort, and reducing energy consumption for HVAC (Heating, Ventilating, and Air-Conditioning) systems. A prediction model that can simultaneously treat these factors isrequired to realize good design of sustainable buildings. For this paper, a concept of OccupantContaminant Inhalation is used for long-term assessment of IAQ. A long-term evaluationindicator for other factors such as air temperature is also introduced (Occupancy-weightedAccumulated Deviation from thresholds).

In designing thermal and ventilation systems in buildings, an examining process of exchange between the designers and analysts is needed. This study aims to expand the simulation system of thermal and ventilation into an automated process for the design of optimum thermal and ventilative conditions, based on the expertise of analysts, the analysis of the thermal environment and the modification of the design, by automating these functions.

This investigation was carried out on a mechanically ventilated office building with a high prevalence of occupant symptoms. The commonest complaints were of dry air, stuffy air and noise. Occupant symptoms, however, were most strongly associated with reports of dusty air and static electricity. Allergic and asthmatic people suffered the most. Cleaning standards were high, and upgrading the air filters failed to give improvements in occupant symptoms. Air flows to the rooms were adequate, but air movements in the rooms were poor.

Air speeds at the occupied zone were studied experimentally in seven large railway stations of space volume varying from 540- 9076 m3• The spaces are installed with mechanical ventilation systems and the air supply flow rates are from 0.455-23.67 m3 s-1• Results were analyzed by dividing the measured air speeds into different ranges. Statistical data such as the peak  value, mean value, range of the air speeds and the bandwidth are calculated. Values of the percentage of discomfort were calculated and analyzed similarly.

As thermal storage media, phase-change materials (PCMs) such as paraffin1 eutectic salts; etc. offer an order-of-magnitude increase in thermal storage capacity, and their discharge is almost isothermal. By embedding PCMs in gypsum board, plaster, or other wall -covering materials, the building structure acquires latent storage properties. Structural elements containing PCMs can store large amounts of energy while maintaining the indoor temperature within a relatively narrow range.

This paper presents results of a study where computational fluid dynamics (CFD) was the numerical tool used to analyze the ventilation performance in stations of the Buenos Aires Metro subway system. Both natural and mechanical ventilation options were studied. The study showed that although natural ventilation was sufficient to maintain the temperature criteria, it presented a potential egress problem by letting hot gases leave through the entranceways.

This Update is the first of two that discuss mechanical ventilation systems in houses. It explains why houses need to be mechanically ventilated, and examines the main characteristics of an ideal system from the standpoint of design and installation.