Ventilated Air Gap Research Articles

Measurement of Innovative Green Façades in the Central European Climate

Green structures, such as green roofs or green façades, are great examples of climate change mitigation. Their impact is mainly focused on roofs in the area of overheating reduction. In this paper, initial measurement results of a green façade experimental test setup are provided. The green façade uses an innovative board from recycled materials with vegetation rooted directly on the board. The tested green façade is divided into three segments. These segments differ from each other in their watering regimes, which are crucial for cooling effectiveness. Watering operates with the assistance of gravity; water flows from the top gutter through the boards. In this paper, these three segments are compared to each other with respect to temperatures on the surface of a regular external thermal insulation composite system façade (ETICS) during two summer days. The green façade showed an impact on the temperature in the ventilated air gap, where the temperature is almost the same as the outdoor air temperature in the morning with direct solar radiation on the façade and lower than the outdoor air temperature in the afternoon. At the peaks, the surface temperatures within the air cavity surface are up to 8 °C lower than those on a new white ETICS coating. This demonstrates a cooling potential, although the surface temperatures are always higher than the outdoor air temperatures during daylight hours.

In-use conditions of air-tightening materials applied in the air gap of ventilated building envelope constructions: A parametric study for different European climates

Materials used in the building envelope have to withstand a wide range of varying and harsh conditions over their life cycle. Particular relevance falls upon the materials used for tightening buildings, such as wind barriers and tapes, as air infiltration was found to be responsible for between 10 and 30 % of heat losses of different national building stocks in Europe. However, there is large uncertainty about the conditions a material is exposed to over a building’s service life. A validated, hygrothermal model of a zero emission office building in Trondheim, Norway was simulated with 10-year climate files from different European locations: Bergen (NO), Berlin (DE), Oslo (NO), Paris (FR), Rome (IT), Tromsø (NO), and Trondheim (NO). This was done to investigate the temperature and humidity conditions in the ventilated air gap. The results show the total and median values for temperature in the ventilated air gaps of the simulated building’s walls and roof for the investigated locations. Moreover, the maximum change compared to the previous hour and the distribution of hours in 5 °C temperature and 10 % relative humidity intervals of the roofing underlay and wall to the west are reported.

Revealing patterns of thermophysical parameters in the designed energy-saving structures for external fencing with air channels

This study reports the design of new models of energy-saving enclosing structures with air channels. To calculate the thermophysical parameters of external fences, the Maple computer algebra system was used; the value of thermal resistance of structures was determined on the basis of a finite-element method in ANSYS. The result of the structure analysis showed that the value of thermal inertia of the traditional design and the average value of the thermal inertia of the developed structures were equal. However, the vibration amplitude of the designed enclosing structures was up to 20.72 % more efficient than the traditional one. At the same time, it was revealed that the air gaps did not affect the thermal inertia of the strucure, and its parameters depended only on the total thickness of the material. The analysis showed that the vapor permeability of the inner wall of the designed structures was equal to the traditional one. However, the value of resistance to vapor permeation of the fence of the developed structures was 3.21 % more effective. At the same time, the use of a closed air layer with a heat-reflecting screen makes it possible to shift the possible condensation zone towards the outer surface of the fence. An analysis of the check for the non-condensation of condensate in the ventilated air gap showed that condensate did not fall out in the ventilated air gap in all the considered schemes, and the results of the analysis by the air permeability value showed that all fencing schemes met the requirements for air permeability. Solving the problems of energy saving in construction through the development of new energy-efficient designs of enclosing structures help reduce the cost of thermal energy of buildings, which is an urgent task all over the world today

Analysis of the Thermo-Aeraulic Behavior of a Heated Supply Air Window in Forced Convection: Numerical and Experimental Approaches

This paper presents work intended to characterize air flow and convective heat transfers within a ventilated window. This window is a device that allows for the entry of fresh air into a building while simultaneously preheating it in order to satisfy requirements in terms of air quality and thermal comfort in inhabited spaces. Therefore, this essential component of the building envelope functions herein as a heat exchanger with its own geometric characteristics and exchange conditions. In this research, a dual numerical and experimental approach has been implemented in order to highlight the temperatures, velocities and heat flux fields both at the glazing surfaces and in the ventilated air gaps. Several turbulence models were tested using CFD software (ANSYS-FLUENT®); their results were compared with each other as well as with the experimental results. This study shows that the air gap geometry in the window induces flow disturbances, recirculation phenomena and non-uniform heat exchanges, all of which prove to be important in terms of overall component performance. With regard to modeling and, in particular, at the level of turbulence models, the results obtained indicate that the model GEKO is best suited to the configuration under study when the phenomena of turbulent forced convection dominate the dynamics of the transfers. The k-ε models reveal a tremendous weakness in precisely estimating the problem’s characteristic quantities. From an experimental point of view, local measurements of thermal fluxes and temperatures demonstrate high efficiency with regard to experimental technique, which in turn could be extended to many different configurations for the local evaluation of convection heat transfer.

Experimental study of the hydrodynamic and thermal performances of ventilated wall structures

The presence of a ventilated air gap behind the external cladding in a building envelope is known to have a tangible contribution to the overall performance of the wall assembly. In the present study, the hydrodynamic and thermal performances of ventilated wall structures in a full-scale test facility are experimentally investigated using data collected during a full-year measuring campaign. In particular, the impact of varying outdoor conditions, façade orientation, and thermal inertia of the walls on the airspeed in the cavity, temperature distribution on the surfaces, heat flux through the interior space, and heat flow in the air gap are evaluated. Additionally, the discussion on transient responses of the wall structure, driving forces applied to the airflow, the overall heat gain/loss through the interior surface of the wall, and heat recovery potential from the cavity are provided. Moreover, variation of the thermal resistance caused by the ventilated air-space is analyzed. The results reveal the importance of monitoring the outdoor microclimate conditions adjacent to the wall of interest to examine the performance of the wall structure properly. It is observed that the airflow characteristics in the cavity are better correlated with outdoor temperature than other weather parameters. It is shown that the thermal resistance of the ventilated cavity dynamically varies and is generally higher in the summertime compared to the wintertime. The results highlight the potential of harvested heat flow from the ventilated cavity reaching 158 kWh/month, which could be used as an additional energy source for buildings. The optimized air change rate in the air-space obtained in this research to simultaneously provide high cavity thermal resistance and high heat recovery from the air gap shows the necessity for considering a fan system to supply specific airflow in the cavity.

Modelling and validation of hygrothermal conditions in the air gap behind wood cladding and BIPV in the building envelope

Materials used in the building envelope are exposed to a wide range of varying and harsh conditions over extended periods. Knowledge about these precise conditions allows for improving the design of testing schemes and eventually extending the durability of building materials. In this study, a numerical model in WUFI-Pro Ver. 6.5 is calibrated with field measurements in the ventilated air gap of a Zero Emission Building located in Trondheim, Norway. Measurements were taken from September 01, 2020 until August 31, 2022 and involved recording the surface temperature of the wind barrier (19 locations) and the relative humidity of the air (11 locations) in the middle of the air gap behind wood cladding and building integrated photovoltaics. Several different air change rates in the air gap are investigated in the model. Using a constant air change rate of 100 h−1 showed the overall best performance (R2 = 0.940 for the wind barrier's surface temperatures and R2 = 0.806 for the relative humidity of air in the middle of the air gap). The largest deviations between simulation results and measurements, however, can be attributed to the uncertainty of climate data input. The developed model can be used in future studies that significantly contribute to establishing better testing schemes and test conditions for building materials such as wind barriers and adhesive tapes, and eventually improve the long-term air tightness of buildings.

Simulation of Heat Transfer in Packages of Materials with Ventilated Air Gaps on the Example of Clothing for Greenhouse Workers

Simulation of Heat Transfer in Packages of Materials with Ventilated Air Gaps on the Example of Clothing for Greenhouse Workers

Numerical and experimental study of the dynamic thermal resistance of ventilated air-spaces behind passive and active façades

The variation of the thermo-hydrodynamic behavior of the airflow in the ventilated cavity behind external claddings in a wall structure could potentially affect the overall thermal resistance of the entire structure. Although the impact of an enclosed air-space in the wall on the total R-value of the assembly has been thoroughly investigated in the literature, it has not been addressed for a ventilated cavity. In the present study, as a first step, plausible definitions to determine the thermal resistance of the ventilated cavity behind external claddings in transient conditions are described. As the second step, the dynamic thermal resistance of the naturally ventilated air-spaces behind passive (i.e., brick and fiber cement) claddings and active (i.e., BIPV) facades are studied using two approaches. In the first approach, a 2-D numerical model validated against measurements is employed to compute the thermal resistance of the ventilated air gap under different conditions. Accordingly, the impact of the cladding type, seasonal variation, cavity thickness, and presence of the reflective insulation in the air gap on the dynamic change of the thermal resistance of the air-space is analyzed. In the second approach, in-field measurements are performed in a test facility to experimentally examine the contribution of the thermal resistance of the cavity to the total R-value of the wall structure. The results obtained from both approaches are compared with the design values calculated based on the ISO 6946:2017 and ISO 9869–1:2014 standards. The results reveal that the dynamic change of the thermal resistance of the air gap during a day could be captured using numerical simulations. It is shown that the daily averaged thermal resistance of the cavity could reach up to 47 times higher than the design R-value of the BIPV façade. The experimental measurements confirm that the thermal resistance of the ventilated air-space could converge to a steady-state value after a certain duration of time following the requirements provided in the standards, which could be practically used for the code-compliant analysis. It is also observed that the ventilated cavity could act as an insulation layer with higher thermal resistance compared to some of the solid materials used in the wall assembly.

Experimental analysis of the performances of ventilated photovoltaic facades

To reach the EU 2030 goals for reducing greenhouse gas emissions targets and achieving high-performing buildings, it is mandatory to increase energy generation through renewable sources. In this context, existing and new buildings should be equipped with building-integrated photovoltaic plants (BiPV). However, BiPV system integration into the building envelope could harm the electrical efficiency due to an increase in the temperature of the cells. The purpose of this work is to analyse the performance of BiPV façade naturally ventilated. With this aim, two prototypes of ventilated façade equipped with mono and bifacial PV modules have been realised. The first stage of this research presents the features of these two prototypes, the monitoring system and some preliminary experimental data. In particular, the daily temperatures of the flowing air in the cavity, on the front and the back of mono e bifacial modules are shown, during the investigated days. The observation allowed us to highlight the positive effects of the ventilated air gap, as well as the different behaviour of the two investigated PV facades. Further stages foresee the analysis of these BIPV ventilated facades through fluid dynamics simulations, as well as their electrical performance.

Measuring the effective thermal resistance of ventilated air-spaces behind common wall assemblies: theoretical uncertainty analysis and recommendations for the hot box method modifications (ASHRAE 1759-RP)

A well-designed ventilated wall that incorporates air-space behind cladding can reduce energy use for conditioning buildings by adding a thermally resistive layer. The scarcity of thermal performance data and standardized test methods is a particular barrier for practitioners to implement ventilated air gaps behind the facades. The current standardized test method to evaluate the thermal performance of a wall structure, such as ASTM 1363-19, does not consider the effect of the ventilated air-space behind external claddings. Therefore, testing and design recommendations are required to account for the impact of ventilation airflow on the thermal resistance of vertical air-spaces behind common cladding materials. In this study, the theoretical uncertainty analysis of the effective thermal resistance of the ventilated cavity is performed for a steady-state condition. The results revealed that temperature sensors with an absolute uncertainty of ±0.18 (±0.1 °C) and heat flux sensors with a relative uncertainty of 3% or lower are required to capture a wide range of the effective thermal resistance of the ventilated air gap. Thereafter, based on the uncertainty of temperature and heat flux measurements, the modifications of the ASTM C1363-19 test method to account for the airflow effects on the thermal performance of the wall assembly are proposed. A detailed description of the experimental setup is provided, and protocols for collecting, analyzing, and evaluating data are suggested. An example demonstrating how the proposed method can be practically used to measure the thermal resistance of a ventilated air-space is also presented.

Microclimate measurements in ventilated air gaps – instrumentation and first results

To achieve energy efficient buildings, the requirements for air tightness in Norway were strengthened in the recent years. Thus, the use of tape for tightening connections and overlaps in the wind barrier and vapour barrier layer has become more and more common. Since these products are covered by a façade cladding and hence difficult to access, they need to maintain their performance level over many years, usually 25 to 30 years. To design test methods to ensure the performance of tapes and other products used in the ventilated air gap, more knowledge on the climatic conditions, especially temperature conditions, is needed. The recently finished ZEB Lab building in Trondheim, Norway, has been instrumented with thermocouples to monitor the temperature conditions in the air gap. This study presents the instrumentation set up and first findings from the start of the experiment in summer 2020. First results show temperature levels up to 76°C in the upper part of the roof construction.

Thermal performance of roofs suitable for developing countries in tropical climate

Roof structures have been traditionally built from reed or straw in tropical climate locations. Now, traditional materials are often replaced by pure metal sheets. The roof construction is improved in terms of durability and cost effectiveness, but he roof built from pure metal sheets can cause excessive overheating of interior spaces. The aim of this paper is to compare dynamic thermal performance of different roof assemblies under real boundary conditions. For this purpose, a thermally insulated test box was built on the roof of the university. Six roof samples (0,9 m × 1,1 m) can be mounted on the roof. The roof covering made of pure steel sheet with Zn coating was the reference case. This assembly was then modified step-by-step either by change of colour, or by additional material layers of reed and earth boards, or by 2cm thick ventilated air cavity on the rear side of the sheet. In total, 18 different roof assemblies were tested in three consecutive test runs (approximately three-week periods between 07 – 09-2020). Ventilated air gap and white paint are the best adjustments to reduce heat flux. Dark colours of the metal sheet have the opposite effect. Influence of reed and earth boards was in many cases similar. One roof assembly was selected for use in real project.

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

The presence of an air-space within a building envelope is known to have a varying contribution to the overall thermal performance of the wall assembly due to the combined effect of convection and radiation in the air cavity. In particular, the thermal resistance of a ventilated air-space can vary significantly depending on multiple environmental and thermo-physical parameters. Although the thermal resistance of enclosed air-spaces in the building structures has been thoroughly investigated in the literature, it has not been defined for a ventilated cavity. This paper aims to introduce the plausible definitions of the thermal resistance of a vertical ventilated air-space behind external cladding systems. Both theoretical and applied formulations are provided and compared. The energy balance method is used to model the steady-state heat transfer through two types of traditional external wall systems (i.e., brick and vinyl siding) in summer and winter conditions. A range of air exchange rates in the cavity is examined, and the effect of the presence of reflective insulation in the air-space on the thermal resistance of the air gap is analyzed. The results show that the presence of a ventilated cavity in the wall assembly can influence the thermal performance of the building envelope. In particular, the effective thermal resistance of a ventilated air-space behind a brick cladding wall could be between 0.17 and 1.85 times the thermal resistance of the cladding in the range of air change rate in the cavity from 0 to 100 1/h. The effective thermal resistance of the ventilated air gap behind vinyl siding could reach up to 9 times the thermal resistance of the cladding.

Thermal Technical Analysis of Lightweight Timber-Based External Wall Structures with Ventilated Air Gap

Lightweight timber-based structures are an increasingly common part of envelopes of new buildings due to increasing requirements for their energy performance. In addition, due to the fact that wood is a sustainable material, it can be assumed that the share of these structures in civil engineering will continue to increase. The subject of this article is the thermal analysis of timber-based lightweight structures under winter conditions to expand information about thermal processes in these structures. This article deals with the lightweight timber-based external wall structures with a ventilated facade and a double-skin roof structure. Experimental temperature measurements inside the structures and ventilated air gaps are used to perform the thermal analysis. By comparing experimental and theoretical data obtained by performing numerical simulation, it was shown that for achieving an ideal match of numerical simulations and measured physical properties it is necessary to take into account not only external temperatures affecting these structures, but also other factors such as solar radiation and heat emission into the cold night sky. In the case of the external walls with ventilated facade, the benefit of a ventilated air gap has been demonstrated in relation to smaller temperature fluctuations that affect the structures.

Problems of thermal protection of two-layer external walls with hinged facade systems

Currently, in the Republic of Khakassia, much attention is paid to research aimed at reducing air pollution due to fuel combustion. In this aspect, the issue of increasing the energy efficiency of buildings is relevant. The use of ventilated facade systems with an air gap makes it possible to improve the energy efficiency class of buildings and modernize the facades. However, these facade systems have weak points that require detailed and high-quality study. Often, design solutions are used that are used in warm climates without taking into account the peculiarities of a cold climate - frequent changes in temperature, humidity, wind loads, and other influences, which can lead to negative manifestations. Facade systems with a ventilated air gap must provide the ability to monitor the operability of all system elements and, if necessary, carry out repair and reconstruction work with minimal operating costs. The article presents an analysis of the thermal properties of an external fence using a hinged facade structure. The influence of installation defects and heat-conducting inclusions on the heat-shielding properties of the building envelope is shown. It was determined that during operation the moisture-windproof membrane loses its vapor-permeable properties.

Experimental Investigation of Green Façade Components for Industrial and Storage Buildings

This paper deals with vertical greenery applied on the external side of lightweight walls for industrial and storage buildings. The greenery is expected to have some positive impacts on the building performance, in particular reduction of building energy consumption and peak cooling power. The achievable benefits are however dependent on local climatic conditions, hygro-thermal properties of the building enclosure, the requirements for the indoor environment and on the system of greenery applied on the walls. The side-by-side real-scale experiment involving three different test walls was built in two test windows with dimensions of 3.0 x 3.2 m. A climatic test room with controlled indoor environment is located behind test windows. Two reference walls present current standard technical solutions constructed as metal frame filled with thermal insulation with metal sheets on the exterior side, either in direct contact with core wall or with ventilated air gap. The third wall replaces the external metal sheets by the system of baskets filled by soil substrate and greenery with integrated irrigation pipes. The experiment was built in June 2019 and is extensively monitored since beginning of July 2019. Temperatures, relative humidity, heat fluxes, moisture content of soil substrate, inflow and outflow of irrigation water, and environmental boundary conditions are continuously recorded. Results of the first year of monitoring are presented and discussed in the paper. The measured results showed reduction of daily peak values of heat flux on the internal surface during hot summer days and evaluated power of evaporative cooling.

Development of air tightness prediction method of masonry walls

Recently, the construction of external walls of various blocks, which are externally insulated with mineral wool thermal insulation layer, with ventilated air gap and external finishing (ventilated wall structures) is becoming popular for public and office buildings. These blocks are used without internal rendering because they have a good interior surface, stable dimensions, and various filling of masonry joints provide an attractive architectural appearance. This reduces the cost and duration of construction work, however, problems with airtightness of such walls often occur. The air can penetrate through blocks or their joints, and the thermal insulation and wind protection layer does not usually provide the required air tightness of the wall. Currently, there are no standard methods to predict the air tightness of such wall, in practice, samples of particular walls are produced and their air permeability is measured at the laboratories. This is a costly job, which is only suitable for a combination of particular building materials. For the broader use of results of laboratory air permeability measurements, a methodology has been developed to predict the air permeability of block masonry walls using experimentally determined air flow resistances of the individual layers. The masonry from blocks, made of ceramic, expanded clay and aerated concrete with various joints, were used for the research; mineral wool boards of various air permeability were used for thermal insulation and wind protection layer. After measuring the air resistance of masonry units, thermal insulation and wind protection boards, the air flow resistances of the walls of different construction were calculated. The comparison of calculated and measured air permeability of wall samples showed that in cases where the nature of air movement (laminar to turbulent) through a single material remains similar with the nature of air movement through the product incorporated in the structure, the calculation and measurement data differ no more than 12-15%. In structures with building products with very different air permeability properties, especially at high thicknesses of air permeable thermal insulation products, air movement parameters change occurs and calculated and measured results have larger differences.

Research and production of prototypes of lightweight concrete panel walls with a screen

Introduction. In industrial housing construction in a dry hot climate, the issues of protecting the premises from overheating have not yet been resolved. The purpose of this study is the theoretical and experimental substantiation of the method of calculating the construction of lightweight concrete panel exterior walls with a screen for large-panel residential buildings in hot climates, with improved performance and providing technical and economic efficiency. Materials and methods. Methods have been developed for ensuring the normative amplitude of temperature fluctuations of the inner surface in the wall due to the targeted formation of material properties and design measures, lightweight concrete wall panels with a screen and suggestions for their production technology have been developed, and recommendations have been made for their operation conditions. The methods of a rational constructive solution to the sun wall consisting of a sunscreen and a supporting structure separated by an air gap have been investigated. Results. It was supposed to carry out theoretical and experimental studies of the operational properties of lightweight concrete panels of external walls with a screen in laboratory and in-situ conditions. The work was performed in stages: At the first stage, the design and production technology of panels with a screen on prototype fragments under laboratory conditions was performed. For this, experimental fragments of 1 × 2 m panels will be made in the laboratory. The parameters of the air gap were determined from the condition of ensuring sufficient natural ventilation. At the second stage, a study was made of the rational structure of lightweight concrete for exterior walls in hot climates. To find the optimal structure of lightweight concrete from a thermal point of view, a 3-factor experiment was conducted. At the third stage, a theoretical study of the temperature regime of shielded and single-layer large-panel exterior walls was performed. At the fourth stage there was a generalization of the above studies, the manufacture and installation of experimental-industrial designs of panels with a screen in the amount of 10 pieces. At the Bukhara house-building combine. Conclusions. The described study by the method of experimental design and the experimental production of sample fragments confirmed the possibility of producing panels with a screen and an air gap in a single technological cycle. Analysis of the results of theoretical calculations shows that walls with vertical screens and a ventilated air gap are quite effective means of reducing the exposure of solar radiation to buildings and reducing the cost of cooling premises.

VENTİLYASİYA OLUNAN HAVA TƏBƏQƏLİ FASADLARIN ENERJİ SƏMƏRƏLİLİYİ PROBLEMLƏRİNİN ANALİZİ

Abstract. One third of the energy expenditure in the buildings falls to their external protective constructions, and that is why their role for the energy efficient buildings is undeniable. The article focuses on the investigation of the ways in which energy efficiency problems can be solved based on the analysis of the advantages and disadvantages of the facades with the ventilated air gap. These facade systems must be calculated and designed according to the applicable building codes. Studies have shown that constructive solutions should be taken after a detailed study of the impacts of local climatic conditions taking into account key climatic parameters. The article analyzes and classifies the system advantages and energy efficiency indicators. These types of facades are considered to be the most effective physical and technical parameters for protection against adverse effects of wind and rain. Reliable functionality and long-term exploitation of the facades with the ventilated air gap can be achieved when they are properly assembled.

Investigation of the Dynamics of Solid Particles Moition Into the Ventilated Air Gap of the Cladding Façade Systems

All articles must coTheatmospheric air in cities contains a large number of pollutants in the form of solid particlesand dust. One of the most dangerous not only for humans, but also for building structures, are the particles smaller than 10 microns. They penetrate into the structures of cladding façade systems, fall and settle on the surface ofa insulation made of mineral wool, as well as on metal elements of the façade cladding system, facedinto the ventilated air layer. The author carried out a large number of experimental studies of structures of façade cladding systems, which made it possible to choose the following parameters and characteristics when performing this work.The article deals with the dynamics of the motion of dust particles with a size from 1 to 5 microns in the air interlayer of the claddingfaçade system with the Reynolds number Re ≤ 1. An equation is obtained for calculating the velocity of dust particles in a size of 10-50 µm in the air stream at its rate of 0.1-0.0, 8 m/s at various outside air temperatures, as well as the conditions under which dust particles “levitate” in the air gap are determined. At the same time, “levitating” dust particles settle on the surface of a mineral wool insulation from a stone fibber and penetrate into the thickness of the fibrous insulation, causing a change in its thermal and sorption characteristics.