It is difficult to design a naturally ventilated indoor environment because there is insufficient knowledge to evaluate the effect of the natural ventilation space quantitatively. Especially, natural ventilation rate is not yet fully understood. In this paper, the properties of natural ventilation with large openings are examined mainly from the results of measuring ventilation rate.
Cross ventilation to reduce cooling energy is one of the most important techniques for maintaining acomfortable indoor environment in hot and mild seasons. However, at present, it is difficult to design the indoor environment under cross ventilation because there is insufficient knowledge to evaluate the effect of cross ventilation quantitatively.
The aim of the work was to investigate the effect of upstream geometry of the nozzle on the turbulence mixing and temperature distribution in still air large enclosed spaces. Prototype experiments were carried out with the JETs (Jet Environmental Techniques) existing nozzle geometry in a test room. These were used to validate, under steady state conditions, the application of an RNG kappa-epsilon turbulence model. In the next stage a range of nozzle profiles of similar inlet and contraction diameters were tested under identical conditions similar to the prototype test room.
The assessment of building thermal comfort quality in the Mediterranean context necessitates an accurate knowledge of air temperature and velocity fields inside the space. Also, these thermal and airflow aspects must be considered in combination because of their very strong interdependence. In this particular context, a three-dimensional calculation model of coupled heat transfer and airflow calculation has been developed, which enables the evaluation of temperature field and airflow pattern inside unconditioned buildings under transient conditions, taking into account external conditions.
The present study investigates the effect of alteration in the building shape due to some common remodelling practice on the wind pressure differences delta-p for cross-ventilation of a semi-detached low-rise building using Computational Fluid Dynamics (CFD). A commercial code ANSYS CFX was employed to solve the flow governing equations. The standard k-e, renormalisation group (RNG) k-e and Shear Stress Transport (SST) turbulent models were adopted for comparison and the computed velocity was validated against full-scale measurement data.
This paper describes the classical approach for calculation of wind driven airflow through large openings in buildings and discusses the fulfilment of the limiting assumptions. It is demonstrated that the limiting assumptions are not fulfilled for large openings in buildings for cross ventilation, and therefore, the classical approach is not appropriate for prediction of airflow through large openings in buildings in the cross ventilation case. Using the approach for real openings and estimating the discharge coefficient for window openings has also not been very successful.
Measurements of the unsteady flow in a ventilation stack of a school have been made at model scale in an environmental wind tunnel. The results confirm the expectation that the stack is well-sited, in that it was difficult to induce flow reversal except over a narrow range of wind directions and the amount of reversal was small (reversal percentage < 5 %). The results also show that the technique is capable of reliably detecting such small reversal percentages.
Age-of-air is a technique for evaluating ventilation that has been actively used for over 20 years. Age-of-air quantifies the time it takes for an elemental volume of outdoor air to reach a particular location or zone within the indoor environment. Age-of-air is often also used to quantify the ventilation effectiveness with respect to indoor air quality. In a purely single zone situation this use of age-of-air is straightforward, but application of age-of-air techniques in the general multizone environment has not been fully developed.
Several studies have suggested that recommended ventilation rates are not being met within schools. However these studies have not included an evaluation of whether or not this failure might have an impact on pupil performance and learning outcome. The work reported here was designed as an initial investigation into this question. Using the Cognitive Drug Research computerised assessment battery to measure cognitive function, this study demonstrates that the attentional processes of school children are significantly slower when the level of CO2 in classrooms is high.
This paper reports on tracer gas measurements of the ventilation flow within a low-energy building.Constant-concentration, decay and homogenous tracer gas emission methods were used. Low-energy buildings are airtight constructions; effective ventilation is thus very essential for the indoor climate. The results of this study show an airflow rate between 0.42 and 0.68 air exchanges per hour (ac/h), which should be compared to the minimum requirements in Sweden of 0.5 ac/h.
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