Outdoor Test Cell Research Articles

Experimental assessment of the energy performance of microfluidic glazing components: The first results of a monitoring campaign carried out in an outdoor test facility

Microfluidic glazing is a newly developed, adaptive, transparent component characterized by micro-channels filled with a circulating liquid, functioning as a heat exchanger and controlling the heat transfer through a façade. The performance of this glazing depends on its design and operation on site. The aim of this study is to present the results of an in-situ performance evaluation of microfluidic glazing components obtained from an experimental campaign in outdoor test cells, and to explore their potential and limitations under realistic working conditions. A case study has been conducted in Turin, Italy, in which two small south-oriented triple glazing units, upgraded with different functional elements, including a laminated semi-transparent Perovskite solar cell and microfluidic glazing, have been investigated under different operating conditions. Overall, the experimental campaign has shown a reduction in the heat exchange through the façade of about 70%. Moreover, this technology allows the temperature in the Perovskite solar cell to be decreased by as much as 10 °C, and the central glazing temperature to be reduced by as much as 41 °C, when set as the central panel, thereby effectively decreasing the risk of thermal degradation or thermal shocks. A temperature difference of 12 °C and 16 °C was recorded, depending on the modules, between the inlet and outlet temperatures.

Monitoring of a Living Wall System in Santo Domingo, Dominican Republic, as a Strategy to Reduce the Urban Heat Island

Given the current need to reduce the Urban Heat Island (UHI) worldwide, one of the strategies that can contribute to this mitigation is green façades. In this context, the aim of this research is to evaluate a Living Wall System (LWS) as a strategy to reduce the urban heat island in Santo Domingo, Dominican Republic, using outdoor test cells. This research was focused on the monitoring of two different façades, an LWS and a reference façade, during the warmer months. For the comparison, the parameters measured were air temperature, relative humidity, surface temperature and environmental variables. In addition, thermal images were taken. Results reveal that during the days selected, the average outdoor air temperature difference between the LWS compared to the reference façade was 5.3 °C, whereas during the day, the average was 3.3 °C. Concerning surface temperature, in the case of the LWS, the temperature was higher and had greater fluctuations than the reference façade. This behavior was confirmed by the results obtained with thermal images. In conclusion, using an LWS in a tropical climate helps the urban microclimate, which contributes to urban heat island effect mitigation during the warmer months.

Modelling and validation of a single-storey flexible double-skin façade system with a building energy simulation tool

Double skin façades are adaptive envelopes designed to improve building energy use and comfort performance. Their adaptive principle relies on the dynamic management of the cavity's ventilation flow and, when available, of the shading device. They can also be integrated with the environmental systems for heating, cooling, and ventilation. However, in most cases, the possible exploitation of the ventilation airflow is not fully enabled, as the adoption of only one or two possible airpath limits the possibility that this façade architecture offers, meaning that flexible interaction with the environmental systems cannot be planned. This work aims to develop, using an existing software tool for building energy simulation, a numerical model of a flexible double-skin façade module capable of fully exploiting the adaptive features of such an envelope concept by switching between different cavity ventilation strategies. Leveraging the “Double Glass Facade” component available in IDA ICE, a new model for a flexible double-skin façade module was developed, and its performance in replicating the thermophysical behaviours of such a dynamic system was assessed by comparison with experimental data collected through a dedicated experimental activity using one the outdoor test cells of the TWINS facility in Torino (Italy). The accuracy of the predictions of the new model for a flexible double-skin façade was in line with that obtained by the conventional “Double Glass Facade” component to simulate traditional double-skin facades. The mean bias errors obtained were lower than 1.5 °C and 4 W/m2, for air and surface temperature values and for transmitted long-wave or short-wave heat flux values, respectively. By establishing a new archetype model to study the performance and optimal integration of a large class of double-skin façade modules, including fully flexible ones, this work demonstrates the possibility of modifying existing models in building energy simulation tools to study unconventional building envelope model solutions such as adaptive façade systems.

Experimental study on the impact of double tilted Venetian blinds on indoor daylight conditions

One of the most important concerns when designing buildings as liveable spaces is the indoor comfort. This depends on different factors, including daylight availability and discomfort glare conditions.The increasing use of glazing areas in the building's envelopes can lead to high energy consumption and problems such as visual discomfort. The use of shading devices stands out as a sustainable design strategy to reduce energy consumption in the buildings. This work presents an experimental analysis of the impact of an innovative shading device, a double-tilted venetian blind (DTVB) with different positions of upper and lower slats, on the indoor daylight conditions. Moreover, discomfort glare evaluation, through DGPs metric, is performed.The experimental campaign was conducted in an outdoor test cell during three periods of the year: summer solstice, winter solstice and autumn equinox. Experiments were carried out with both white and grey DTVBs, for several positions of upper and lower slats, under clear and overcast sky conditions. This comprises the measurement of indoor and outdoor horizontal and vertical illuminances and irradiances and solar and visible transmittance of the fenestration. It was concluded that DTVBs can achieve a higher performance, regarding solar protection, daylighting and glare control, when compared with more traditional venetian blinds systems.

Living wall system for improved thermal performance of facades located in tropical climate. Case study in Dominican Republic

The tropical climate of the Dominican Republic generates a high energy demand for cooling buildings. In this respect, façade improvements as passive techniques can significantly reduce cooling energy needs and green walls are considered to be one of the most appropriate sustainable solutions. In addition, it is important to characterize the real behavior of Living Wall Systems (LWS) to know the effectiveness in terms of energy reduction. Therefore, the present paper aims to evaluate the thermal performance of a LWS with outdoor test cells located in a tropical climate. This work was focused on the evaluation of two different facades, a LWS and a reference façade in two scenarios, one using air conditioning and the other without air conditioning as a passive system. The samples are located in the city of Santo Domingo (Dominican Republic), which is a location characterized by a very high level of solar radiation, high temperatures, and wet and dry seasons. For the comparison, the parameters measured were air temperature, relative humidity, surface temperature, heat flux and energy consumption. In addition, a meteorological station was used to record environmental variables. Results demonstrate that the LWS in such climate conditions, helps to improve the internal thermal behavior of the buildings in comparison with the reference façade, presenting a maximum difference in air temperature between them of 7.43 °C in passive and 9 °C in active. In addition, LWS has a lower energy consumption with respect to the reference facade, thus contributing to energy savings in the Dominican Republic.

Experimental validation of a dynamic numeric model to simulate the thermal behavior of a facade

The process of analysis and design of energy saving measures aimed to reduce building energy consumption, both in the design of new constructions and in the refurbishment of existing ones, has led to the need to solve increasingly complex problems with the consequent demand to develop complex models and new calculation tools, which often entails the coupling of different models each one of them to solve a specific task and always under the requirement of obtaining accurate and reliable results. This article presents a modular dynamic model based on a finite difference scheme with matching conditions between wall layers to record the different thermophysical properties of layer materials and accurately compute the heat flux through the building envelope. The aim of this model is to simulate the energy behavior of building envelopes and to allow the connection, via a co-simulation procedure, with other codes based in models for addressing complex issues usually not included in standard Building Energy Simulation (BES) tools. For that, the simulation model was designed with a modular structure in order to facilitate its connection, when required, to other codes written in C++. The thermal model has been validated experimentally, using data from two full-scale outdoor test cells with different façade constructive solutions for different ventilation and blind opening regimes. An additional code-to-code comparison was also performed between the developed model and the Energy-Plus software to complement the results of the experimental validation. The results obtained in the validation process show the ability of the proposed numerical model to simulate the energy performance of the envelope and of the test cell globally in a wide variety of situations, predicting internal air temperature and envelope internal surfaces temperatures which meet the requirements usually established for the validation of building energy simulation tools. The numerical formulation of the introduced model and its characteristics that combine flexibility, modularity and accuracy for the calculation of the thermal behavior of a façade and is able of an easy connection to external codes written in C++ to solve more complex problems, allow to consider the present work as innovative and novelty on the literature.

Empirical and Numerical Analysis of an Opaque Ventilated Facade with Windows Openings under Mediterranean Climate Conditions

In recent years, there has been growing concern regarding energy efficiency in the building sector with energy requirements increasing worldwide and now responsible for about 40% of final energy consumption in Europe. Previous research has shown that ventilated façades help to reduce energy use when cooling buildings in hot and temperate climates. Of the different ventilated façade configurations reported in the literature, the configuration of ventilated façade with window rarely has been studied, and its 3D thermodynamic behavior is deserving of further analysis and modeling. This paper examines the thermal behavior of an opaque ventilated façade with a window, in experimentally and numerical terms and its impact in energy savings to get indoor comfort. Field measurements were conducted during the winter, spring and summer seasons of 2021 using outdoor full scale test cells located in Seville (southern Spain). The modeling of the ventilated façade was carried out using a three-dimensional approach taking into account the 3D behavior of the air flow in the air cavity due to the presence of the window. The validation and comparison process using experimental data showed that the proposed model provided good results from quantitative and qualitative point of view. The reduction of the heat flux was assessed by comparing the energy performance of a ventilated façade with that of an unventilated façade. Both experimental and numerical results showed that the ventilated façade provided a reduction in annual total energy consumption when compared to the unventilated façade, being compensated the winter energy penalization by the summer energy savings. This reduction is about 21% for the whole typical climatic year showing the ability of the opaque ventilated façade studied to reduce energy consumption to insure indoor comfort, making its suitable for use in retrofitting the energy-obsolete building stock built in Spain in the middle decades of the 20 century.

Thermal Performance of Facades Based on Experimental Monitoring of Outdoor Test Cells in Tropical Climate

The high cost of energy consumption in buildings highlights the importance of research focused on improving the energy efficiency of building’s envelope systems. It is important to characterize the real behavior of these systems to know the effectiveness in terms of energy reduction. Therefore, the aim of this paper is to characterize the thermal performance of facades based on experimental monitoring of outdoor test cells in tropical climate. To carry out this research, a case study was presented to compare two construction systems. One of them is a light façade (M1) and the other a reference façade (M2). A thermal simulation was performed for the opaque and glazed facades. In addition, several parameters were measured with different types of sensors, as well as environmental variables to evaluate the thermal and lighting behavior of multiple facades systems under real conditions. The findings show that light façade behavior was the opposite of what was expected, since by incorporating a window in the façade it has allowed solar radiation to increase the interior temperature in both modules. In the case of the light facade the penalization was higher than the reference facade, which has a lower thermal transmittance than M1. Doi: 10.28991/cej-2021-03091773 Full Text: PDF

Experimental characterisation of a smart glazing with tuneable transparency, light scattering ability and electricity generation function

Daylighting control technologies have become an essential part of sustainable building design to reduce overheating, glare and energy consumption in buildings. In this paper, a smart glazing system where a Building Integrated Photovoltaic (BIPV) glazing is coupled with an optically switchable thermotropic hydrogel layer is proposed to improve the daylighting control and electricity generation performance of traditional BIPV glazings. Thermotropic (TT) hydrogels made of various weight percentage combinations of hydroxypropyl cellulose (HPC) polymer, gellan gum and sodium chloride (NaCl) salt were synthesised and first evaluated by visible-near-infrared spectroscopy. Subsequently, small-scale prototypes of the proposed BIPV thermotropic (BIPV-TT) laminated glazing based on these TT hydrogels were fabricated and characterised experimentally under controlled laboratory conditions. The TT hydrogel, which was synthesised of 6 wt% HPC, 0.5 wt% gellan gum and 4.5 wt% NaCl, was selected for further experimental characterisations in a dynamic outdoor environment, due to its appropriate transition temperature of 30.7 °C for use in mild climates with a wide modulation range of solar transmittance from 85.8% (in the transparent state) to 9.6% (in the light-scattering state). The outdoor tests were conducted in Nottingham, the UK, on typical summer days with sunny and partial cloudy conditions. The results showed that using the prototype BIPV-TT laminated glazing can reduce up to 80% of the solar radiation transmitted into the outdoor test cell, while providing up to 12% higher electrical power outputs, compared to its counterpart system with no thermotropic hydrogel applied.

Energy performance of PVC-Coated polyester fabric as novel material for the building envelope: Model validation and a refurbishment case study

Tensile materials are concurrently becoming more and more utilized in contemporary architecture design, despite a lack of experimental testing and numerical model development to assess their actual effect on the building behavior, even more, if considered integrated in a second-skin system. In this research, the PVC-coated polyester fabric has been selected and tested as tensile second-skin material by using two outdoor comparative test cells to evaluate its performance and to calibrate and validate a numerical model in TRNSYS 18. Then, the validated numerical model has been used in a case study as a second layer in a flexible façade system. In particular, a simulation refurbishment of a typical three-story office building, located in southern Italy, has been investigated with the aim to evaluate its potential benefits from an energy point of view. The results showed that the refurbishment by means of a second-skin system always allows for an energy saving, up to a maximum of 6.1%; also, by exploiting the semi-transparency and the flexibility offered by this material to implement a continuous whole-façade design on the south wall, thus covering with the second-skin both the walls and the openings, the solar gains across the year can be modulated, by minimizing the gains during the summer and maximizing them during the winter, consequently leading to a reduction of the cooling and heating energy demands, for an overall heating energy demand reduction of about 9.8%.

The contribution of a solar air heater collector to the cooling load in a building

Over the last few decades, there is a clear target for reducingenergy needs in the building sector. The above objective can be achieved both by renovating the existing building stock and/or by constructing new buildings that will meet the characteristics of zero or nearly zero energy buildings. In order to construct or renovate a building into a zero or almost zero energy building, different passive, active and hybrid systems can be used. One such system is a solar air heater collector. The above system was installed in the south facade of the outdoor test cell (ZED-KIM (Zero Energy Demand – Kimmeria)), located at the Campus of the Environmental Engineering School, DUTH at Xanthi (Greece). In the present study, the monitoring results of the solar air heater collector and its contribution to cover the cooling load of a building will be presented. The system was monitored under real weather conditions for the period June 2017 to August 2017. This period was separated in two sub-periods. In the first one, the system operated as a solar air heater and with the appropriate modifications air from inside the test cell was passed through solar collector and hot air was rejected out. In the second sub-period, a ventilation inlet was added in the north facade of the test cell, and the system operated as a solar chimney. The heating load that rejected out in the first sub-period was 12 KWh and in the second sub-period was 58.5 KWh. In other terms the cooling load of the test cell was reduced by 70.5 KWh for the whole period of measurements. In addition the cooling load for the specific climate zone of Greece and for 20 m2 cooling space was 488 KWh so there was a reduction of 15 percent. Furthermore, it was noticed that the thermal efficiency of the system increased above 50 percent between 1st and 2nd sub period, with values being 16% and 34% respectively. Based on the above results, it is concluded that even in hot weather conditions prevailing in northern Greece, the use of a solar air heater collector with the appropriate modifications can cover, in a significant degree, the cooling load of a building and in conjunction with other passive and active systems it can lead at a nearly zero energy building.

The effect of PCM layer on the natural air flow movement in the façade cavity of BiPV system

The incorporation of a phase change material (PCM) in building integrated photovoltaic (BiPV) façade can be applied to improve its thermal performance including more effective electrical conversion, however their real interaction needs to be investigated at adequate level. The aim of the presented paper is focused on the application of a material with high latent heat capacity based on PCM in the structure of double-skin BiPV façade. The key aspect concerns on an analysis of natural air flow movement affected by the storing/releasing heat energy from the PCM during daytime/night-time of days. The experimental campaign was performed using an experimental outdoor test cell where two full-scale façade samples (reference BiPV and experimental BiPV/PCM) were investigated. The strong effect of thermal inertia of the PCM identified by experimental measurements was observed on the façade air cavity temperature and air flow movement. Experimental results revealed that natural air flow regimes in façade cavities are nearly equal in the daytime, but in the night-time are totally different. The thermal emission from PCM increase the air temperature in the façade cavity and increase the velocity of air flow movement (PCM started solidified), mainly in the night-time.

Thermal performance of semitransparent CdTe BIPV window at temperate climate

Semi-transparent photovoltaic (PV) technology is attractive for building-integrated photovoltaics (BIPV) due to its ability to lower the admitted solar heat gain, to control the penetrating daylight and to generate onsite benevolent direct current power. In this work, semi-transparent cadmium telluride (CdTe) based BIPV as window was experimentally characterized using outdoor test cell in temperate UK climate. Spectral measurement confirmed its 25% visible transmission and 12% solar transmission. Thermal transmission and solar heat gain coefficient were calculated from measured thermal data. Overall heat transfer coefficient (U-value) of 2.7 W/m2 K was found for outdoor and indoor characterization of CdTe BIPV window. A comparison with single glazed window has been produced emphasis its feasibility for Facade buildings.

Thermal and visual comfort analysis of adaptive vacuum integrated switchable suspended particle device window for temperate climate

In this work, thermal and visual comfort of low heat loss switchable suspended particle device-vacuum (SPD-vacuum) glazing was investigated for less energy-hungry adaptive building’s glazing or façade integration at temperate climate. This SPD-vacuum glazing had 38% visible transmittance in the presence of 110 V applied an alternating voltage and 2% visible transmittance in the absence of electrical power. Outdoor test cell characterisation was employed to measure the thermal and daylighting parameters of this glazing. Solar heat gain or solar factor was calculated using non calorimetric methods and varied between 0.38 (Switch OFF/opaque) to 0.51 (Switch ON/transparent). Test cell indoor and ambient parameters (incident solar radiation and ambient temperature) were engaged for thermal comfort analysis by using PMV and PPD methods. Visual comfort was analysed from glare potential, useful daylight index, and colour properties. The comfortable thermal environment was attainable using both states of this glazing for a clear sunny day. Acceptable daylight throughout the day was possible for a clear sunny day for opaque state; however clear state offered allowable/comfortable correlated colour temperature (CCT) of 5786.18 K and colour rendering index (CRI) of 94.83.

Outdoor Test Cell Modelling with Modelica

The experimental setup implements a simplified PASSYS test cell construction, which is combined with a detailed simulation to reduce measurement effort. To analyze the cell’s dynamic behavior, the test cell was closely monitored with thermal sensors, and different static and dynamic heating modes were applied during a three-week calibration period. Co-heating tests were performed for steady-state measurements and cyclic heating periods account for the transient behavior of the test cell. The cells response was compared to the results of transient simulations with the software packet Modelica. The equation based Modelica framework allowed a detailed transient thermal simulation of the test cell’s dynamic to be set up that shows close agreement with the measurements. In addition, the flexibility of Modelica allowed unforeseen events affecting the experimental setup to be replicated, thereby ensuring an uninterrupted heat flow history of all surfaces. More than 96% of the predicted air temperatures (1 min resolution) match the experimental values within an error band of ±1.5 K, and 90% of all predictions are within ±1.0 K.

The effect of airflow rate control on the performance of a fan-assisted solar air heating façade

Solar Air Heating Façades (SAHF) can exploit solar radiation to partially fulfil the building heating and ventilation demand. This study was developed starting from an experimental campaign on a full scale fan-assisted SAHF applied to an outdoor test cell (TWINS) located in Torino (Italy). The data gathered from the monitoring activity were used to validate a white box model, developed in EnergyPlus. An axial fan drives the airflow through the façade; therefore, the supplied air temperature can be controlled by changing the fan speed. For this purpose, a PID (Proportional Integrative Derivative) controller was developed. This study demonstrates that the application of different control strategies significantly affects the façade overall performance and behaviour. Results highlight that the system can reach an average seasonal solar efficiency of up to 30%. Furthermore, by operating the system in heating-mode only and controlling the supply air temperature at 25°C, the system operates for 30% of the heating season, while at 40°C the system can provide fresh pre-heated air with an higher exergy level for the 10% of the winter period. Fan-assisted SAHF represent a valuable retrofit strategy solution in all buildings that present space limitations for the installation of centralised ventilation systems, helping to address the nZEB target requirements.

The Influence of the Initial Condition in the Transient Thermal Field Simulation Inside a Wall

The envelope structures of buildings are exposed to heat-humidity conditions. The heat and humidity flow through these structures depends on the boundary conditions of the indoor and outdoor environments. This paper shows different initial conditions for the determination of temperature spread. The aim is to bring certain results of temperature calculated considering the initial conditions. When temperature changes, heat flow also rapidly changes. In certain specific cases, it is necessary to consider the initial conditions of temperature—for example; when transient energy simulations of real buildings are carried out. The reasons as to why it is necessary to consider the initial conditions, are shown in the examples of one-layer assemblies. The test walls exposed to the transient hygrothermal conditions are placed in the outdoor test cell. The cell has a stable temperature and relative humidity, and outdoor weather conditions change. The measured data on these walls and the calculated values of the temperatures in the wall structure, according to the different initial conditions, are compared. The average difference of the mean by the simulation and the measured values is significant. For a simulation time of about five days, the initial condition for calculating the temperature in the center of the masonry is necessary.

Experimental comparison of green facades with outdoor test cells during a hot humid season

We used outdoor test cells during a hot humid period to analyse the surface temperatures behind the following four types of green walls: a felt layer wall; a planter boxes wall; a direct climbing plants wall, and; an indirect climbing plants wall. We compared these temperatures with temperatures of a bare wall and we found that all four types of green facades were able to maintain lower temperatures than the bare wall, and that the felt layer and planter boxes wall had lower temperatures than the other walls for the majority of the study period. In particular, the daily average and peak surface temperatures behind the felt layer wall were by 1.9 °C–4.8 °C and by 7.1 °C–13.4 °C respectively lower than the bare wall. We undertook a significance analysis and produced Pearson coefficients to better understand the relationship between average daily weather conditions and the surface temperatures on all five test cells. We noted that the average daily solar radiation flux did not affect the surface temperatures behind the planter boxes and felt layer walls, but the daily average ambient air temperature was significantly correlated with the average and peak surface temperatures behind all four green facades. Finally, we concluded that the cooling potential of the felt layer and the planter boxes walls increases with higher amounts of solar radiation and higher ambient temperatures. In addition, from the analysis of the diurnal temperature variations and the time series trends we illustrated that the temperatures behind the felt layer and planter boxes walls fluctuated less than the other walls, which lead to a slower rate of surface temperature reductions during a cooler day than the other wall types of the study.

Experimental assessment of thermal performance of three passive cooling techniques for roofs in a semi-arid climate

Three passive techniques for air cooling in buildings are tested in the real conditions of Marrakech (Morocco) whose climate is hot semi-arid (BSh type according to the Köppen–Geiger climate classification). The passive techniques, that are white painting, shading and thermal insulation, are applied to the roofs of three outdoor test cells. Thermal performance of these techniques are assessed simultaneously via a 29 summer days monitoring of four test cells, including a reference cell with bare roof. Measurements concerned the cells indoor air temperature, the roof slab inside (ceiling) and outside surface temperature, as well as the heat flux through the roof slab. Moreover, all the local climate parameters were recorded by means of a weather station installed near the test cells. The results show that the studied passive techniques have a significant impact on the heat flux through the roof and consequently on the cells ceiling and indoor air temperature. The white painted roof has the highest thermal performance as it lowers the ceiling temperature by up to 13.0 °C relatively to the reference cell; while this temperature reduction was always less than 9.9 °C and 8.9 °C respectively for the thermally insulated and the shaded roofs. Moreover, the white painted roof reduced the heat flux through the roof slab by up to 66%.

Solar Heat Gain Reduction of Ventilated Double Skin Windows without a Shading Device

With global efforts to strengthen various energy-saving policies for buildings to reduce greenhouse gas emissions, in South Korea, new laws and regulations have been in force since May 2015 to install shading devices in public buildings and to include the solar heat gain coefficient (SHGC) reduction performance of shading devices in the evaluation of building performance. By making a ventilated air layer outer glass and inner glass to lower the temperatures of the air layer and glass surface, it is possible to reduce the amount of heat flowing into the building while maintaining the same level of light transmission as plain window systems. This study proposes a double-skin façade window with a 20 mm ventilated air cavity, and assumes that insolation inflow indoors would be reduced through ventilation in the air cavity. The artificial solar lab test results show that the SHGC can be lowered through ventilation by 28% to 52.9%. Additionally, in an outdoor test cell experiment, the results show that the mean temperature was 0.6 K and the peak temperature was 0.9 K lower with ventilation in the air cavity than that without ventilation in the air cavity.