Ventilation Potential Research Articles

Study of Climatic Potential for Natural Ventilation in Buildings for Typical Indian Cities

The potential of climatic driving forces for natural ventilation to ensure acceptable indoor air quality in a conceptualised low rise building are assessed for six typical Indian cities representing all the climatic conditions of India. A simple analytical model is used for the evaluation of climatic driving forces viz. the effective wind pressure difference available for natural ventilation and the desired wind pressure difference. The concept of Pressure Difference Pascal hours (PDPH) is introduced to represent the natural ventilation potential at a location. The higher the value of PDPH the higher will be the climatic driving forces available for natural ventilation. Weather data for a typical Meteorological Year (TMY) from Transys simulation software was used in the analytical model. Monthly mean ambient temperature, monthly mean wind velocity, annual wind rose diagrams, cumulative frequency of effective pressure difference and PDPH profiles for six cities were evaluated and compared. Analysis showed that Indian climatic zones experience an effective pressure difference across indoor and outdoor in the range 0.0 - 3.0 Pa throughout a year. PDPH values assume higher values in summer (250 - 750 Pa.hrs) and low values in winter (80 - 200 Pa.hrs) for most sites except Leh. Cities on high land (Leh) and on the coast (Goa and Kolkata) have high wind velocity and PDPH, hence, theses cities have high climatic ventilation potential as compared to the other cities that were studied. The aim of this study is to help building planners at the early strategic planning of ventilation systems for indoor air quality in buildings in India.

Experimental study of the influence of a moving manikin on temperature profile and carbon dioxide distribution under three air distribution methods

The influence of occupants' movements is seldom considered in room air distribution studies. However, sedentary and walking occupants mix in many conditioned rooms, such as in an open plan office. The influence of movements on the room air distribution has been reported. In this paper, series of tests under three air distribution methods (stratum ventilation, displacement ventilation and mixing ventilation) with a moving manikin are conducted. The manikin is moving at speeds of 1.0 m/s and 0.5 m/s, along two moving routes respectively. Velocity, temperature and CO2 concentration are measured to determine the influence on air distribution. The results show that temperature profile and CO2 distribution are not influenced significantly by a short-time movement. When the movement lasts for a long time, the moving manikin produces a mixing effect and reduces the ventilation effectiveness. The influence under mixing ventilation is the smallest. The influence under stratum ventilation is smaller than that under displacement ventilation. Stratum ventilation has higher ventilation effectiveness at the occupant's head level than that of the other two air distribution methods. The results show the application potential of stratum ventilation under a condition with frequent movements.

Influence on Vertical Shading Device Orientation and Thickness on the Natural Ventilation and Acoustical Performance of a Double Skin Facade

A research showed that shading devices integrated within double skin facades (DSFs) could not only decrease direct solar heat gain but also screen unwanted sound transmission. Many researches also indicated that shading device configuration affected airflow patterns, the air velocity, and the air temperature in a DSF air cavity. At acoustical standpoints, other researches described that shading devices acted as sound barriers, however, the area of a DSF's vent opening could led to an increase in noise transmission. Therefore, the proper controls of shading devices inside a DSF air cavity can contribute to thermal and acoustical comfort with avoiding overheating and noise transmission. This study aimed at evaluating the correlation between natural ventilation potential and noise transmission loss based on the degree of orientation and thickness of vertical shading devices inside a DSF air cavity. The initial findings indicated that vertical shading devices should be controlled appropriately for balancing the requirements of thermal performance, natural ventilation efficiency and noise transmission loss.

An experimental study of the influence of a walking occupant on three air distribution methods

Most indoor air studies have not considered the influence of walking occupants. However, the occupants of many air conditioned rooms are a mixture of sedentary and walking occupants, such as in an opening plain office. In this paper, a series of tests are conducted under three air distribution methods (stratum ventilation, displacement ventilation and mixing ventilation) with a real walking occupant. The occupant walks at a speed of 1.5 m/s along two different walking routes. Velocity, temperature and CO2 concentration are measured to find the influence on air distribution. The results show that a short walk does not change the temperature or CO2 concentration profiles. When the walk lasts for a long time (30 min in this study), the walking occupant causes mixing effect. The influence under mixing ventilation is the smallest. The influence under stratum ventilation is smaller than that under displacement ventilation. The ventilation efficiency of stratum ventilation is still higher than that of mixing ventilation. Stratum ventilation and mixing ventilation recover from the influence more quickly than displacement ventilation. The results show the application potential of stratum ventilation with frequently walking occupants.

CFD analysis of cross-ventilation of a generic isolated building with asymmetric opening positions: Impact of roof angle and opening location

The position of window openings and roof inclination are important parameters determining the effectiveness of wind-driven cross-ventilation in buildings. Many studies on natural ventilation have been performed in the past, however, a detailed review of the literature indicates that the majority of these studies focused on flat roofs with symmetric opening positions. There is a lack of research that analyzes the impact of asymmetric opening positions and roof inclination on natural ventilation potential. This paper presents Computational Fluid Dynamics (CFD) simulations to analyze the natural ventilation flow in a generic isolated building with different vertical positions of the outlet opening – yielding asymmetric opening positions – and five different roof inclination angles. The simulations are performed using the 3D steady Reynolds-Averaged Navier–Stokes (RANS) equations. They are based on a grid-sensitivity analysis and on validation with previously published wind-tunnel measurements using Particle Image Velocimetry. The results show that the shear-stress transport (SST) k-ω and the Renormalization-group (RNG) k-ε turbulence models provide the best agreement with the experimental data. It is also shown that the roof inclination angle has a significant effect on the ventilation flow; the volume flow rate increases by more than 22%. The maximum local indoor air velocity increases considerably when the inclination angle is increased, however, the differences in the average velocity in the occupied zone are only around 7%. The vertical position of the outlet opening has a relatively small impact on the volume flow rate (less than 4%), and a small influence on the average velocity in the occupied zone (<5%).

Experimental research of the thermal characteristics of a multi-storey naturally ventilated double skin façade

This study presents the results of the actual thermal behaviour of a multi-storey naturally ventilated double skin facade. Governed by lack of experimentally measured data, a field of detailed measurements were performed during the 2013/2014 season in the office building located in Belgrade, Serbia. The uniqueness of this building is that the first facade layer is made in the tradition manner. Apart from studying classical environmentally influenced air cavity behaviour, the methodology incorporates a detailed analysis of the air cavity enthalpy flow. The main purpose of this research is to examine the current state of the building facade and how it affects energy performance. To this effect, measurement data was used in order to analyse transmission losses and gains and to quantify enthalpy change of the cavity air linked to the airflow established within the facade. Analyse of the transmission losses and gains were described by a series of diagrams of vertical and horizontal temperatures trends for selected typical days in each regime. For investigation of the natural ventilation potential, an adequate indicator based on the enthalpy change was established. Overall, the experiment results highlight that the use of a double skin facade does not necessarily reduce energy consumption.

Energy savings modelling of re-tuning energy conservation measures in large office buildings

Today, many large commercial buildings use building automation systems to manage a wide range of equipment. This paper investigates the energy savings potential of several common heating, ventilation, and air conditioning (HVAC) system re-tuning measures on a typical large office building using the EnergyPlus software. Individual re-tuning measures simulated include automatic schedule adjustments, damper minimum flow adjustments, thermostat adjustments, as well as dynamic resets to static pressure, supply-air temperature, condenser chilled- and hot-water temperatures, and chilled and hot water differential pressure set points. All individual measures and combinations were simulated in 16 locations representative of different climates in the USA. Many of the demand-side individual measures were capable of reducing annual HVAC energy consumption by over 20% in most cities. Supply-side measures affecting HVAC plant conditions were only modestly successful (less than 5% annual HVAC energy savings). Some of the combinations revealed between 35% and 75% HVAC energy savings.

Outdoor ventilation performance of various configurations of a layout of two adjacent buildings under isothermal conditions

This paper explores the pedestrian-level wind environment around two buildings of unequal heights for the effects of ratio of height of upwind building to that of downwind building, referred to as buildings height ratio, spacing distance between the buildings, and direction of ambient wind, on the outdoor air ventilation. The objective is to propose appropriate spacing distances for various configurations of this type of buildings layout in a suburban area of Kuala Lumpur, which would enable harnessing the full ventilation potential of the local wind conditions. A three-dimensional numerical technique employing computational fluid dynamics simulation of continuity and Reynolds-Averaged Navier-Stokes equations was used to study the turbulent flow field around the full-scale sizes of the buildings. Results indicate the influence of spacing distance between buildings, relative heights of the buildings and direction of ambient wind on outdoor ventilation. Results also show that 3-D turbulent flow processes such as lateral and secondary flows play significant roles in defining the wind flow pattern and ventilation availability. The perpendicular wind direction presents remarkable adverse effects compared to the inclined direction, while a higher upwind building height which would ordinarily be expected to proportionally obstruct wind flow could be of advantage, at low values of building height ratios, in enhancing outdoor ventilation. The findings established the need to give consideration to climatic factors such as wind flow and direction in planning urban cities, as it affects buildings to be situated in close proximity, especially when there is height difference.

Inversions and air pollution in Istanbul

Owing to the rapidly growing and inefficient usage of fuel, air pollution has increased in Istanbul. The levels are affected by the weak dispersion conditions in the city. The strength of the inversion can be explained by the temperature difference between the top and bottom boundaries and their height. In this study, nighttime surface inversion heights have been found to range between 84 m and 419 m. The mean height of the inversions was found to be less than 300 m in winter months. This behaviour indicates a poor ventilation and high pollution potential in the city.

Natural ventilation potential of high-rise residential buildings in northern China using coupling thermal and airflow simulations

Natural ventilation is regarded as one of the most energy-efficient ways of ventilating a building. Suitable methods for predicting ventilation performance are essential for regulating indoor air parameters in buildings. This study establishes a method to predict the natural ventilation potential for residential buildings. The average annual ventilation rate (N) and annual cooling load saving ratio (ACSR) for the top six types of residential buildings were measured and analyzed under different conditions. The N calculation formula was summarized to calculate the natural ventilation air change rate for each of the designated buildings. In addition, the logarithmic regression curves of the ACSR (with N) were also obtained and then used to predict the natural ventilation potential for specific climatic conditions. The simulation results could be used to guide engineers in deciding when and where natural ventilation can be incorporated as an energy-efficient feature without affecting indoor comfort. Moreover, accurate strategic analysis could also be used to assist architects evaluate the potential of natural ventilation at the architectural pre-design stage.

Energy saving potential of utilizing natural ventilation under warm conditions – A case study of Mexico

The objective of this article is to show the potential of natural ventilation as a passive cooling method within the residential sector of countries which are located in warm conditions using Mexico as a case study. The method is proposed as performing, with a simplified ventilation model, thermal–airflow simulations of 27 common cases of dwellings (considered as one thermal zone) based on the combination of specific features of the building design, occupancy and climate conditions. The energy saving potential is assessed then by the use of a new assessment method suitable for large-scale scenarios using the actual number of air-conditioned dwellings distributed among the 27 cases. Thereby, the energy saving is presented as the difference in the cooling demand of the dwelling during one year without and with natural ventilation, respectively. Results indicate that for hot-dry conditions, buildings with high heat capacity combined with natural ventilation achieve the lowest indoor temperature, whereas under hot-humid conditions, night ventilation combined with low heat capacity buildings present the best results. Thereafter, an average aggregated saving potential of 4.2TWh for 2008 is estimated, corresponding to 54.4% of the Mexican electric cooling demand for the same year. The practical implications of the study are that the results contribute to an assessment of the economic and environmental benefits for using natural ventilation rather than an active method such as air conditioning. Thereby, the average economic saving is estimated at US$ 900M and the environmental benefit at an annual average mitigation of 2 Mt CO2eq, both for 2008.

Natural Ventilation Potential in Portuguese Residential Buildings under Winter Conditions – An Opportunity for Hybrid Ventilation

This paper presents a study of the potential for the use of natural ventilation systems in Portuguese multi-family residential buildings under winter climatic conditions. The behaviour of various natural ventilation systems is tested in a standard residential dwelling, using the TRNSYS 15 and COMIS 3.1 software programs. This study leads to the conclusion that the use of hybrid ventilation systems can save a considerable amount of the energy normally spent on continuously operating mechanical ventilation systems. Hybrid ventilation systems will not be adequate if there are no ventilation inlets in the façade and air intake is only by means of infiltration, especially in the case of certain modern windows with better seals; in such situations, the use of continuous mechanical ventilation systems is recommended. Therefore, it is essential to equip buildings with air inlets in the façades, preferably self-adjustable grilles, to ensure the best use of hybrid systems.

Study on Natural Ventilation Potential for Residential Buildings in Southern China

Existing methods for natural ventilation potential analysis are reviewed and discussed in this paper. Based on related research results, a simple natural ventilation potential prediction model for two-opening room is developed considering climatic conditions, local terrain conditions, building opening area and thermal comfort zone. In this model, several major cities in southern China are selected and the natural ventilation potential is analyzed by using the evaluation index of effective hours and effective air change rates. It shows that residential buildings in the south of China are suitable for natural ventilation generally, while effect differ significantly by region and season. The analysis results can help the designers to formulate the proper ventilation strategy and to make assessment of energy-saving effect.

Natural cross ventilation in buildings on Mediterranean coastal zones

Abstract Natural ventilation of buildings is a common way to improve indoor air quality, thermal comfort in summer and reduce energy consumption due to air conditioning. However, efficiency of such a system is highly dependent on climatic conditions. This paper investigates the use of thermal breezes, characterized by moderate speeds and well-defined direction, to improve natural cross ventilation technique on Mediterranean coastal zones. The interest of this phenomenon is highlighted by the development of climate indicators with meteorological data from various places in Corsica (France). A statistical wind rose is used to give more information on main wind sectors and speed fluctuations. The natural ventilation potential is assessed by a radar plot which groups the main climate indicators for comfort ventilation and passive cooling. Tracer gas measurements on a seaside building in Corsica show that high air change rates are reached by cross ventilation during day (higher than 25 ACH). Night ventilation gives more moderate results for passive cooling with air change rates close to 10 ACH. As the comfort in building is related to the airflow, it is necessary to be able to control it. The issue of controlling openings to maintain a satisfying airflow is treated with the help of an empirical model. Due to the regularity of thermal breezes, it shows that even if the airflow varies greatly during the day, a minimal control on opening surface is sufficient to maintain the airflow rate on a comfortable range.

Energy saving potential of night ventilation: Sensitivity to pressure coefficients for different European climates

The suitability of night ventilation to reduce the cooling demand in buildings can be evaluated by coupling Airflow Network Models to Building Energy Simulation tools. To estimate wind-induced ventilation, pressure coefficients (Cp) on the building envelope are key inputs, as well as local wind speed and direction. Cp data obtained by primary sources such as measurements or CFD simulations are considered the most reliable but can be difficult to obtain. An easy alternative are Cp secondary sources, such as databases providing literature data correlations. Therefore an issue arises regarding the choice of the source of pressure coefficients.This paper investigates the effects of Cp from primary and secondary sources on the predicted energy saving potential of night ventilation of an isolated office building for several European climates and some relevant design conditions and simulation parameters. Different Cp sources produce a dispersion of Cp data and differences in the calculated night ventilation rates up to 15%. Contrary to what might be expected, these differences influence only marginally the resulting passive cooling effects. Overall a stronger impact is observed for the colder climates, where higher temperature differences occur between desired indoor temperature and night-averaged outdoor temperature. Finally, for the building under study, the choice of the Cp source appears less crucial than the choice of other building simulation parameters, such as the internal Convective Heat Transfer Coefficient. This study can support building designers towards accurate energy simulations of naturally ventilated buildings.

Assessment of emergencies in return air system design

The upside potential of an underground mine ventilation by return air systems is analyzed in the article. It is shown that subsidiary air supply depends on the ratio of the pressure head of a recirculating draught producer to the mine depression at the recirculating draught producer site. By calculation of the actual example, the authors prove that air leaks can cause emergencies due to drastic reduction of fresh air supply in working areas.

Simulation of Natural Ventilation Taking into Account the CO2 Concentration and Room Temperature

The operating mode of the building, its occupancy and user behaviour has a significant impact on the CO2 concentration and on the internal temperature of the room and therefore on the quality of the indoor environment and on the overall energy performance of the building. This paper summarises results from dynamic thermal modelling software combined with an air flow model for the assessment of a natural ventilation potential in office premises of the building not only with regards to the internal temperature, but also to the CO2 concentration.

Potential of natural ventilation in temperate countries – A case study of Denmark

The objective of this article is to investigate the energy performance of natural ventilation as a passive cooling method of buildings within houses located in temperate countries using Denmark as a case study. The method consists in running simulations with a thermal–airflow program of a household located in Vejle, Denmark during the months of June, July and August calculating the indoor air temperatures during this period. The dwelling belongs to a Danish project of passive houses named Komfort Husene where its users claim there are periods of overheating during the summer time. Then, after the simulations are validated with measured data, and by applying a new assessment method presented in this article as the cooling rate due to natural ventilation instead of a constant mechanical ventilation rate in the thermal balance within the dwelling, the energy saving is calculated. Results show that there is a reduction of 90% of hours of a possible use of mechanical ventilation, showing the feasibility to achieve thermal comfort within the house by using passive ventilation. The conclusion is therefore that the results contribute to an assessment of the economic and environmental benefits of using natural ventilation rather mechanical one on large-scale scenarios located in temperate conditions. Finally, as a practical implication example, an assessment for Denmark is carried out.

A review of the potential of attic ventilation by passive and active turbine ventilators in tropical Malaysia

Abstract The strategy of attic ventilation represents one of the techniques to reduce heat build-up in indoor spaces. Its benefit helps to control high energy consumption and improve indoor environment. On the other hand, this approach cannot entirely stop the transfer mechanism of heat from the roof to the attic. Despite this, it is able to reduce its effect depending on the method adopted and the existing environment conditions. The aim of this review is to explore the potential of passive and active turbine ventilators as a technique to overcome heat build-up in tropical buildings. As turbine ventilators represent outlet vents, a ventilated attic would require two systems which are inlet and outlet vents to complete its function. Thus, these two types should be discussed broadly. Through the review, it shows that the hybrid system provides a better solution for Malaysian environment. Therefore, adopting a system that consists of an inlet vent from the gable and an outlet vent using a turbine ventilator with curved vanes comprising of an internal duct, an opening cap with solar panel are preferable. This is due to the fact that this combination creates constant air flow and provides uniform distribution to extract heat effectively.

Effect of urban geometry on pedestrian-level wind velocity

The orientation of the streets and the height of continuous buildings cut off summer breezes and the prevailing wind in Izmir, Turkey. Compared with the northern parts of Turkey, the summer period in Izmir is relatively hot, humid and long. Due to the dense urban structure and the expansion of hard surface materials, the temperature in the city centre is higher than this centre's surroundings and this effect is called the urban heat island. Consequently, pedestrian comfort in the city drops dramatically especially in locations where the wind flow is obstructed by buildings. In addition, natural ventilation through the building façades is weakened due to the low average wind speed in the streets. For better outdoor and indoor comfort the citizens in Izmir should benefit from the prevailing wind and summer breezes locally named ‘imbat’ in the sea-land direction. Therefore, the existing situation is examined through the field study in order to understand the natural ventilation potential at the pedestrian level in the selected main streets in Izmir.