Natural Ventilation Modelling of Building

This work proposes a new model to evaluate the air changes per hour (ach) due to natural infiltrations in buildings. This modeling already exists at building scale, but the new model will implement the hourly ventilation load in a physical-based modeling for space heating and cooling in buildings at urban scale. The proposed improvement considers the wind and buoyancy effects in the calculation of hourly achs in a high-density urban context. A three-zone air flow lumped modeling is applied to describe the air flow in buildings; the air flow rate due to infiltrations is calculated depending only on leakages’ characteristics and pressure variations in various climate conditions. The non-linear equations system of mass and energy conservation is solved by an iterative procedure using the Newton-Raphson numerical method. Besides, two different  methodologies are compared to evaluate the external dynamic and static pressure conditions on building façades: experimental values (pressure coefficients Cp) and CFD simulations. For the latter, the air flow field in the urban canyons is described by the windy conditions and by imposing a temperature gradient due to solar irradiation between the windward
and leeward facades. This methodology is applied to three urban canyons in Turin, with typical aspect ratios and orientations for some local climate conditions considering both heating and cooling seasons. Comparing the results of hourly ach obtained from the Cp method, the CFD technique allows to modulate the ach considering the impact of the canyon dimension, wind and buoyancy effect of non-isothermal condition,  in varying the wind speed on the façades of buildings for different scenarios.  t also overcomes the limit of field of applications of Cp, especially in high-density built urban environments. The encouraging results of this work will  ead to future developments of the three-zone lumped model and its numerical solution techniques.

This study uses wind tunnel experiments to investigate the wind-driven ventilation for buildings with two openings on a single wall. The exchange rates are measured by the tracer gas decay method under different external wind speeds, directions and opening sizes. The experimental results indicate that the time-averaged pressure difference across the openings is much larger than the fluctuating pressure when the wind direction is  = 22.5-45 • , and the ventilation rate can be predicted by the orifice equation. When the wind direction is  = 0 • and 67.5-180 • , the pressure difference across the openings is insignificant and the fluctuating pressure entrains air across the openings. The exchange rate is proportional to the root-mean-square of the pressure fluctuation. Furthermore, the dimensionless exchange rate of the shear-induced ventilation (wind is parallel to the openings) is found to be independent of the wind speed, opening area and location. The exchange rate for buildings with an internal partition is lower than that without a partition when the wind direction is  = 0-90 •. A semi-empirical prediction model is proposed to calculate the exchange rate by incorporating the time-averaged pressure difference and pressure fluctuation. The application of the prediction model to compute the air change rate (ACH) is also discussed.

The rising cooling energy demand, caused by the increase in global average temperature and the frequency of heat waves, is currently leading to a significant increase in global electricity consumption. Passive cooling strategies, such as ventilative cooling, can provide acceptable indoor thermal comfort with no or minimal energy consumption, offering an alternative to air conditioning systems in buildings. This paper investigates the effectiveness of natural ventilation in an iconic post-modernist high-rise building in India: Charles Correa's Kanchanjunga Apartments. The research, employing CFD simulation paired with building energy simulation, demonstrates how cross-ventilation can improve the ventilative cooling efficiency in buildings, ensuring affordable indoor thermal conditions even in adverse climatic conditions like the Indian one. Thanks to nighttime structural cooling, a maximum reduction in the operative temperature of up to 5.3 • C was achieved compared to the scenario without natural ventilation and up to 6.4 • C compared to the outdoor temperature peak on the hottest day. Consistently with the Indian Model for Adaptive Comfort, cross-ventilation ensures a reduction in discomfort hours of up to 58 % on the hottest day and a total reduction in discomfort hours on a typical monsoon and winter day. The paper aims to assist architects and policymakers in quantifying the cooling potential of natural ventilation in high-rise buildings, suggesting passive solutions for cooling energy saving.

The introduction of the Energy Performance of Buildings Directive (EPBD) in Poland established minimal building energy performance requirements for new and retrofitted buildings without changing the U-value requirement for the building envelope in the building code. This change in the Polish law has sometimes caused investors to draw the wrong conclusions about thermal standards for single-family residences. With this in mind, this paper seeks to optimise the thermal performance of buildings using both fuzzy sets and Zadeh probability with simple hourly 6R1C building energy simulation. An optimal design is important especially for victims of a recent flood who are constructing new housing and face multiple objective constraints.

Urban-scale evaluations of aerodynamic and morphological parameters allow to correct the wind speed within the urban boundary layer, as the wind profile is strongly influenced by the presence of roughness elements. This can have important implications in defining urban strategies for the reduction of buildings’ energy consumption and the improvement of air quality and liveability of outdoor spaces. Among the current models for assessing the air flow rate by natural ventilation in buildings at urban scale, this study aims to define a GIS-based methodology, using existing databases and an open source QGIS plug- in. From a digital surface elevation dataset, and considering prevalent wind directions, the displacement height (zd) has been determined. The wind speed has been corrected, applying the logarithmic or turbulent laws of wind profile, respectively above and below zd. This method can determine the spatial distribution of wind speed, considering each building façade characteristics and its surrounding. Resulting wind pressure on windward and leeward facades drives the air flow rate inside the buildings. Further developments of this work will improve the air flow modelling in buildings with other tools for applications at urban scale.

Data-driven models, either simplified or detailed, have been extensively used in the literature for energy assessment in buildings and districts. However, the uncertainty of the estimated parameters, especially of thermal masses in resistance–capacitance (RC) models, still remains a significant challenge, given the wide variety of buildings functionalities, typologies, structures and geometries. Therefore, the sensitivity analysis of the estimated parameters in RC models with respect to different geometric characteristics is necessary to examine the accuracy of identified models. In this work, heavy- and light-structured buildings are simulated in Transient System Simulation Tool (TRNSYS) to analyze the effects of four main geometric characteristics on the total heat demand, maximum heat power and the estimated parameters of an RC model (4R3C), namely net-floor area, windows-to-floor ratio, aspect ratio, and orientation angle. Executing more than 700 simulations in TRNSYS and compar...

Buildings are responsible for one-third of the UK's greenhouse gas (GHG) emissions. The move to reduce emissions has resulted in recent stringent building regulations primarily aimed at reducing heating and associated energy use, often by improving the building fabric's airtightness. However, internal gains dominated, highly-insulated and airtight non-domestic buildings will likely overheat in the projected warming climate, requiring energy-intensive cooling, thus diminishing the effectiveness of heating efficiency focused regulations. This research investigated the effects of the warming climate on overheating and energy use and resulting emissions in representative urban office spaces in London in the present-day and projected future climates using hourly dynamic thermal simulations. Findings suggest that airtight and highly-insulated office buildings in the temperate UK will overheat in the 2050s. Heating demand reduces by at least 36% in the 2050s but electricity consumption and summertime space conditioning will increase by at least 13% and 55% respectively when hybrid cooling is adopted to ameliorate overheating. Despite the increase, a mixed-mode ventilation strategy is one of the ways of achieving overall energy efficiency while meeting benchmark overheating and emissions targets. Current heating-focused legislation needs to be re-evaluated to account for the effects of the warming climate and overheating risks.

Many colonial office buildings are located in the Old City of Semarang, Central Java, Indonesia have a passive cooling system. These office buildings are characterized by high ceilings and roof angles, thick wall panel and normally used as a gallery under sun shading. The Djakarta Lloyd office room was selected to determine the correlation between the width of sun shading and percentage of wall opening toward thermal comfort parameters such as indoor air temperature and percentage difference of relative humidity. The calibration and validation graph of temperature versus time was conducted between data measured at site and computer simulation using Energy Plus program. The results showed that 3.6m width of sun shading and 40% of the wall opening is significant toward the indoor air temperature and percentage differences of relative humidity. Whereas, 0m together with 1.8m and 1.8m with 3.6m of width of sun shading and 10% together with 20% and 10% together 40% of wall opening were i...

Generally, the models for evaluating the energy performance of buildings have a ventilation thermal load that depends on the type of building and its occupancy rate. The models apply a constant rate of air changes and therefore the ventilation load depends on this value and on the temperature gradient between internal and external environments. In this work, a single zone air flow model is presented to modify monthly the air changes according to the climatic data, the air permeability, shape and orientation of the building and the urban morphology. The results of this work, show how the air change rates vary with the building floor and with the wind direction and velocity. For both case studies, the air changes per hours vary monthly with minimum values in wintertime and with monthly differences of 41%. Of course, if the building is not well exposed and there is no wind, the air infiltrations are not sufficient to ensure good air quality conditions and it will be necessary to open the windows. In these first two case-studies, a very simple single zone evaluation of air flow rate by natural ventilation improved the existing energy performance placebased model. The results of this work encourage the application of this model at district-urban scale, taking into account the characteristics of each single building and its surroundings.

Generally, the models for evaluating the energy performance of buildings have a ventilation thermal load that depends on the type of building and its occupancy rate. The models apply a constant rate of air changes and therefore the ventilation load depends on this value and on the temperature gradient between internal and external environments. In this work, a single zone air flow model is presented to modify monthly the air changes according to the climatic data, the air permeability, shape and orientation of the building and the urban morphology. The results of this work, show how the air change rates vary with the building floor and with the wind direction and velocity. For both case studies, the air changes per hours vary monthly with minimum values in wintertime and with monthly differences of 41%. Of course, if the building is not well exposed and there is no wind, the air infiltrations are not sufficient to ensure good air quality conditions and it will be necessary to open the windows. In these first two case-studies, a very simple single zone evaluation of air flow rate by natural ventilation improved the existing energy performance placebased model. The results of this work encourage the application of this model at district-urban scale, taking into account the characteristics of each single building and its surroundings.

Wider application of heat recovery ventilation in residential buildings brings attention to knowledge and regulatory gaps which call for research and other actions. In many technical questions there is no consensus in national regulations of EU Member States (MS). This applies for instance for air flow rates, i.e. how much ventilation is needed, restrictions of the use of some heat exchangers types, connection of cooker hoods to ventilation system and placement of exhaust air devices. While European standards are well detailed in these aspects for non-residential ventilation, there is very limited information available for residential ventilation systems. Recent European Guidebook REHVA GB No 25 has made an attempt to collect evidence based best practice technical solutions and design principles for residential ventilation. In this paper a recent evidence and common assumptions behind REHVA airflow rate selection procedure is discussed. Best practice solutions and open research ques...

Most current building thermal codes impose upper limits to the predicted annual building energy demand for heating, ventilation and air conditioning. In the building design phase these predictions are obtained using thermal simulations with variable complexity. The simplest approach uses a single lumped thermal capacitance to model the high thermal mass building elements, combined with five thermal resistances (known as the 5R1C model proposed in EN ISO 13790 standard). This model is used by many European countries as the reference simplified methodology to assess overheating risk and calculate yearly building energy demand. This paper presents a successful extension of this model that allows for its application to the prediction of the internal air temperature of free-running buildings with double skin faç ades. The extension consists in an increased number of thermal resistances used to model the double skin faç ade zone. The extended model is validated using a set of detailed thermal measurements obtained in a free-running double skin test cell. For the case analysed the simplifications used in the RC model do not reduce the overall accuracy: the mean absolute error for room air temperature is approximately 1 • C, the same order of magnitude of more detailed EnergyPlus simulations (1.2 • C).

In this 1992 study, nine computerized design and analysis tools were compared for their capabilities at modeling cooling loads and seven different passive cooling strategies. Also, a test house was modeled using a rule-of-thumb method, a detailed hand calculation method on a computerized spreadsheet, and a computerized hourly thermal network analysis model.