Transpired Solar Collectors Research Articles

Energy and exergy analysis and performance optimization of buildings integrated with transpired solar collectors and phase change materials

Transpired solar collectors (TSCs) are one of the cost-effective air heating technologies that can be easily installed on building facades to provide heated fresh air to condition indoor space. The economics of TSCs can be further enhanced by integrating with phase change materials (PCMs). This study presents the performance investigation and optimization of a building-integrated TSC and PCM system (TSC-PCM). The interactions between PCM thermal properties, their locations in the building envelope, and TSC design parameters were investigated. Based on the modeling of the TSC-PCM by using energy balance and enhanced enthalpy method, a series of orthogonal tests, which varied PCM type, thickness, and location within building envelopes, and TSC suction flow rate were conducted. Multivariate testing, through the Taguchi method, was then applied to identify the optimal design combination. The results showed that the suction flow rate of the TSC-PCM on the external wall showed the highest influence on enhancing indoor thermal performance (up to 77.6%), followed by PCM location on the external wall (up to 9.2%). The optimized TSC-PCM system improved the thermal comfort increase index (TCI) to 3.7 and achieved a maximum thermal efficiency of 401.8%, with an exergy improvement of 26.9% in comparison with the use of the TSC-only. The optimized TSC-PCM system increased the average indoor room temperature to 18.8 oC, which was 6.8% and 18.2% higher than the use of the TSC-only and a baseline without using PCM and TSC, respectively.

Simulation study of dynamic building insulation with transpired solar collectors

This study conducts a comprehensive numerical analysis using Ansys Fluent to investigate the thermal behaviour of transpired solar collectors (TSCs) focusing on temperature distribution, airflow dynamics, and heat recapture capabilities. The research evaluates TSC performance across various environmental conditions. A significant observation from the study is the TSCs' ability to recapture heat losses from the enclosures during nighttime, particularly under higher airflow conditions, where TSCs effectively redirect heat back into building spaces, contributing to energy conservation. Subsequently, the study reveals an inverse relationship between solar radiation levels and TSC efficiency in heat loss recapture. As solar radiation increases from 200 W/m2 to 1000 W/m2, the recaptured wall heat loss decreases by a percentage, ranging from 125 % to 241 % compared to the maximum observed during nocturnal periods. Additionally, the temperature analysis of the TSC backplate demonstrates a complex thermal response under different operational conditions. Solar radiation, airflow rates, and environmental properties influence this interplay. The study also uncovers a consistent linear increase in airflow velocity from the inlet to the outlet within the TSC air cavity, suggesting efficient airflow management. This insight is crucial for optimizing TSC design for improved heat exchange efficiency. In conclusion, the findings of this research offer valuable insights into the operational dynamics of TSCs, highlighting the importance of environmental factors in their design and functionality.

Harnessing Nanomaterials for Enhanced Energy Efficiency in Transpired Solar Collectors: A Review of Their Integration in Phase-Change Materials

The building sector plays an important role in the global climate change mitigation objectives. The reduction of CO2 emissions and energy consumption in the building sector has been intensively investigated in the last decades, with solar thermal energy considered to be one of the most promising solutions due to its abundance and accessibility. However, the discontinuity of solar energy has led to the study of thermal energy storage to improve the thermal performance of solar thermal systems. In this review paper, the integration of various types of phase-change materials (PCMs) in transpired solar collectors (TSC) is reviewed and discussed, with an emphasis on heat transfer enhancements, including nanomaterials. Thermal energy storage applied to TSC is studied in terms of design criteria, materials technologies, and its impact on thermal conductivity. This review highlights the potential of nanomaterial technology integration in terms of thermal performance improvements. The utilization of nanomaterials in solar walls holds the potential to significantly enhance their performance. The integration of diverse materials such as graphene, graphite, metal oxides, and carbon nanoparticles can pave the way for improving thermal conductivity.

Effect of displacing the separation plate on the heat exchange effectiveness of unglazed double skin transpired solar collector

Achieving zero-carbon or low-carbon buildings is possible by implementing innovative approaches and incorporating renewable energy sources into the building infrastructure. Thermal energy collection has become critical amid challenges such as climate change, global warming, and environmental pollution. One such thermal energy collection system is Transpired Solar Collector (TSC). TSCs are a well-proven and readily available technology and are a green energy alternative for large space heating. The utilization of Computational Fluid Dynamics (CFD) analysis for the optimization of TSC is a robust and cost-effective approach. A recent variant of TSC, the Double Skin Transpired Solar Collector (DTSC), has been studied for optimisation. The numerical simulations targeted one single parameter: distance of separation plate from the main absorber plate.

Enhancing solar façade thermal performance with PCM spheres: A CFD investigation

To improve building energy efficiency and address thermal storage challenges during periods without a heat source, such as cloudy weather or night-time, a range of solutions is required. Innovative technologies and sustainable practices are essential for combating climate change and reducing carbon emissions. This study primarily focuses on Thermal Energy Storage (TES) systems, specifically those using Phase Change Materials (PCMs), to increase energy efficiency for Transpired Solar Collectors used in buildings applications. During the last 30 years Transpired Solar Collectors (TSC) have been extensively investigated. However, a primary concern still exists regarding thermal storage when the heat source is unavailable, such as during periods of cloudy weather or at night. Thus, a Thermal Energy Storage (TES) system coupled with the TSC is a potential solution. In this study we are investigating using numerical simulation the arrangement of encapsulation for TES, integrating phase change materials (PCM) in spherical elements when compared with plate encapsulation elements. The model reproduces a part of a real scale thermal energy storage inserted in a Double Skin TSC. The model consists of a Plexiglas duct in which four different arrangements for the spherical encapsulated PCM were studied. For each of the arrangements the heat transfer between the TES elements and the air passing through the collector was analyzed. The primary finding of the study indicates that the hexagonal arrangement offers better passive airflow control, thus enhancing the heat transfer up to 12.3% compared to the rectangular arrangements

Corrugated transpired solar collectors: Mathematical modeling, experimental investigation, and performance analysis

This paper developed a new mathematical model for transpired solar collectors (TSC) which better considered radiative heat transfer of the corrugated absorber. The model offers flexibility to simulate different scenarios, such as using flat plate or corrugated absorbers, and the introduction of extra airflow from outdoor or indoor air. The model was first validated against the experimental data and was then used to quantify the impact of different influential factors on the thermal performance of the TSC. The model can provide reliable estimates with an average R-squared of 0.96. The opening angle of the corrugated absorber and the introduction of indoor air to the air channel of the TSC showed the largest impact on the overall performance among the factors considered. Using corrugated TSCs with an opening angle of 60° could result in average thermal efficiency of 82.31% while that using the flat plate TSC was 80.80%. The introduction of indoor air (i.e. 24 °C) to the air channel improved the outlet air temperature of corrugated TSCs by 1.5 °C during the daytime when the total flow rate was 300 L/s. The findings from this work could be used to facilitate the design and optimization of TSCs with corrugated absorbers.

Flat Unglazed Transpired Solar Collector: Performance Probability Prediction Approach Using Monte Carlo Simulation Technique

Engineering applications including food processing, wastewater treatment, home heating, commercial heating, and institutional heating successfully use unglazed transpired solar collectors (UTCs). Trapping of solar energy is the prime goal of developing an unglazed transpired solar collector. The UTC is usually developed in and around the walls of the building and absorbs the solar energy to heat the air. One of the key challenges faced by the UTC designer is the prediction of performance and its warranty under uncertain operating conditions of flow variables. Some of the flow features are the velocity distribution, plate temperature, exit temperature and perforation location. The objective of the present study was to establish correlations among these flow features and demonstrate a method of predicting the performance of the UTC. Hence, a correlation matrix was generated from the dataset prepared after solving the airflow over a perforated flat UTC. Further, both strong and weak correlations of flow features were captured through Pearson’s correlation coefficient. A comparison between the outcomes from a linear regression model and that of computational simulation was showcased. The performance probability for the UTC was interlinked with correlation matrix data. The Monte Carlo simulation was used to predict the performance from random values of the flow parameters. The study showed that the difference between the free stream value of temperature and the value of temperature inside the UTC’s chamber varied between 15 and 20 °C. The probability of achieving system efficiency greater than 35% was 55.2%. This has raised the hope of recommending the UTC for drying and heating where the required temperature differential is within 20 °C.

Numerical Simulation Investigation of a Double Skin Transpired Solar Air Collector

Transpired solar collectors (TSC) are one of the most popular solar thermal technologies for building façades. TSC use solar energy to heat the absorber surface, which transmits thermal energy to the ambient air. A variant of TSC, namely, a double skin transpired solar collector (DSTSC), has been analyzed in this paper, thus providing guide values and a technical point of view for engineers, architects, and constructors when designing such transpired solar collectors. Three important parameters were addressed in this study through numerical simulation: the influence of a separation plate introduced in a TSC, turning it into a DSTSC; the air layer thickness influence on the performance of the collector; and the influence of the used absorber materials for the separation plate material. Greater heat exchange efficiency was noticed for the DSTSC at every imposed airflow rate compared with the TSC. Regarding the thickness of the collector, the efficiency gradually increased when increasing the solar collector thickness until it reached a value of 20 cm, though not varying significantly at a thickness of 30 cm.

Comprehensive Evaluation of a Landscape Fabric Based Solar Air Heater in a Pig Nursery

Supplementing fossil fuels with solar air tempering for brooding young livestock could reduce energy use and improve indoor air quality. Metal transpired solar collectors (TSC) are effective but too expensive for heating livestock buildings. An inexpensive 12.7 m2 dark grey landscape-fabric-based transpired solar collector (fTSC) was evaluated in a swine nursery with two herds of pigs. A fraction of the fTSC area was underlain with phase change material (PCM) to store excess heat. The Test room with the fTSC was compared with an adjacent identical Control room, each with 120 piglets. The fTSC provided supplemental heating, e.g., with a suction velocity (Vs) of 0.027 m/s during a 9 h period, air temperature was increased by 11.6 °C (mean irradiance of 592 W/m2). Between 4 pm and 9 pm that same day, the PCM increased air temperature by 3.9 °C. The fTSC did not reduce propane use or improve pig performance. Higher Vs, operational changes and controller modifications could improve system performance and reduce cost. Modeling could be used to optimize PCM use. Hence, this very low-cost fabric-based solar air heater offers potential for considerable reduction in heat energy use in livestock barns.

Modelling and experimental performance investigation of a transpired solar collector and underground heat exchanger assisted hybrid evaporative cooling system

Despite of being solar assisted, evaporative cooling devices in hot arid regions consume a substantial amount of electricity to produce sufficient cooling effect. This paper presents the design and performance analysis of a novel hybrid evaporative solar cooling system, aided by underground heat exchanger. A fan-assisted chamber composed of two vertical plenum space is intended to be cooling façade; the first plenum space is made up of black aluminum transpired plate and the second plenum space is shaped from the sand tile wall. The sand tile wall is used as an evaporative pad and sand wall with a perforated aluminum plate as a solar collector to evaporate the sprayed water. Simulation model of this system is built in MATLAB and it has been validated through experimental investigation carried in the hot and dry regions of Tikrit, Iraq. Experimental outcomes agree reasonably well with simulation results with only 2.3% incongruity. When the cooling system is powered only with transpired solar collector (TSC), indoor air temperature reduces 5 °C less and relative humidity 15% higher than ambient. In contrast, when TSC is assisted by underground heat exchanger, indoor air temperature falls 12 °C below and relative humidity 26% higher than ambient. Hence, using underground heat exchanger reduces cooling load by 50%. This passive evaporative cooling system is found to maintain room temperature between 2° to 6 °C below the ambient. This hybrid evaporative cooling system ensures enhanced comfort at lesser energy consumption.

Study of novel solar assisted heating system

The potential for energy, carbon dioxide equivalent (CO2e) and cost savings when using low emissivity (low-ε) transpired solar collectors (TSCs), combined with heat pumps in a range of configurations, has been investigated using computer modelling. Low-ε TSCs consist of metal solar collector plates with a spectrally sensitive surface, perforated with holes. Ambient air is drawn through the holes and heated by convection from the solar collector plate, increasing the air temperature by up to 25 K. The heated air can be used for e.g. space heating, or pre-heating water in buildings. The models developed have been used to compare the performance of low-ε TSC/heat pump heating systems in small and large buildings, at a range of locations. The model results showed savings in energy, CO2e and costs of up to 16.4% when using low-ε TSCs combined with an exhaust air heat pump compared with using the exhaust air heat pump alone. Practical application: If the UK is to meet its target of reaching net zero greenhouse gas emissions by 2050, it will be necessary to adopt low or zero carbon heating technologies. The novel low emissivity transpired solar collector device investigated can contribute to this. Its advantages include: (i) utilising solar radiation; (ii) readily integrated with existing heating systems e.g. heat pumps; (iii) significant energy, CO2e emissions and cost savings; (iv) low cost device; (v) minimal energy input i.e. one small fan; (vi) can be retrofitted to existing buildings; (vii) its benefits were applicable at all of the (wide range of) locations tested.

Wall heat loss recapture evaluation of transpired solar collectors for different climates: A European case study

In the present paper, the performance of the transpired solar collector (TSC) is evaluated for several European cities with different climates. Two primary outputs, the solar air heating, and the recapture of transmission heat loss through the walls were analysed. The wall heat loss recapture can be considered as an important factor for energy saving in buildings, which has not been studied before. RETScreen and SWift are two building simulation tools available for the design and evaluation of transpired solar collectors. Another primary aim is to investigate the detailed mathematical approach that describes the heat transfer process of the physical model for each simulation tool. Results of the models were analysed to predict the performance of TSC in delivering heated air for ventilation applications, and the ability of the partial recapture the transmission heat loss from the warm building interior. Solar radiation, heating degree days, wall thermal transmittance, and air flowrate are the key parameters that influence the heat transfer process. The findings indicate a promising result of using TSC as a dynamic insulation solution for energy savings which can reach up to 55 [kWh/(m2·year)] at high air flowrate 180 [m3/(h∙m2)] for some climates besides the main duty which is the solar air heating.

PEM fuel cell performance with solar air preheating

Proton Exchange Membrane Fuel Cells (PEMFC) have proven to be a promising energy conversion technology in various power applications and since it was developed, it has been a potential alternative over fossil fuel-based engines and power plants, all of which produce harmful by-products. The inlet air coolant and reactants have an important effect on the performance degradation of the PEMFC and certain power outputs. In this work, a theoretical model of a PEM fuel cell with solar air heating system for the preheating hydrogen of PEM fuel cell to mitigate the performance degradation when the fuel cell operates in cold environment, is proposed and evaluated by using energy analysis. Considering these heating and energy losses of heat generation by hydrogen fuel cells, the idea of using transpired solar collectors (TSC) for air preheating to increase the inlet air temperature of the low-temperature fuel cell could be a potential development. The aim of the current article is applying solar air preheating for the hydrogen fuel cells system by applying TSC and analyzing system performance. Results aim to attention fellow scholars as well as industrial engineers in the deployment of solar air heating together with hydrogen fuel cell systems that could be useful for coping with fossil fuel-based power supply systems.

Geometrical optimisation of Transpired Solar Collectors using design of experiments and computational fluid dynamics

Transpired Solar Collectors (TSCs) are simple low maintenance air heating systems which have been widely used for agricultural and industrial applications. In spite of their potential, these systems have not been yet widely employed in residential buildings as they are unable to generate high grade heat for moderate and low ventilation demands. Hence there is an opportunity for optimisation studies in order to enhance the thermal performance of these systems.Optimisation and parametric studies can be costly and time consuming if carried out by physical experiments. CFD models however offer a more flexible and less expensive tool to carry out such studies. This research has aimed to optimise the geometry of the solar absorber plate using a validated CFD model which accounts for a wide range of the key factors affecting TSC performance.A 2nd order polynomial predictive model was developed based on the CFD results with Root Mean Squared Error (RMSE) of 3.8%. The predictive model was used to identify an optimal geometry which delivers a Heat Exchange Effectiveness (HEE) of 0.739. The optimised geometry demonstrated 43% increase in HEE whilst using 28% less material compared to the baseline geometry under the same operating conditions. This geometry can be integrated with other performance enhancement techniques to further improve the thermal performance of TSCs.

Numerical Simulation of Flow over a Flat Unglazed Transpired Solar Collector (UTC) and it’s Performance Prediction

An unglazed transpired solar collector is a system that can leverage the abundant solar energy for various purposes. The solar collector is available in flat or corrugated form and is seen to be installed as an exterior layer of building facades. The cladding thus made absorbs radiation from the sun and heats up air being sucked by fan and flowing through perforations. In this research the focus has been to understand the correlation of plate temperature, exit temperature, the velocity distribution in the chamber and perforation location when air flows past an unglazed transpired solar collector (UTC). The establishment of correlations was carried out in the dataset of flow variables obtained after solving the problem using Navier-Stokes (NS) equations along with standard two-equation (k-ε) turbulence models and Shear Stress Transport (SST ) k-ω models for turbulent flow. The same problem was also solved using NS equation using laminar model. An attempt has also been made to compute Pearson’s correlation coefficient of any two variables to understand their strong and weak correlations. A linear regression analysis was done through an open source software Rstudio for a dataset produced during the computational modeling using a commercial CFD solver, Ansys® Fluent. At the end a Monte Carlo simulation has been done to predict the likelihood of using the flat UTC for drying as well as to understand the dependency of system efficiency on plate exit temperature, suction velocity and freestream temperature.

Experimental study on heating characteristics and parameter optimization of transpired solar collectors

Abstract It is necessary to improve indoor air quality while meeting the indoor thermal demand of buildings during winter. The transpired solar collector (TSC) is a solar energy integration technology in buildings, which usually consists of a heat collecting plate with infiltration holes, an air layer, an insulation wall, air outlet and other appurtenances. It not only provides preheated fresh air for the indoor environment, but also reduces the cold wind infiltration heat load in winter. In this paper, the heat transfer process of each component of the transpired solar collectors was analyzed comprehensively. Findings on, the heat collection efficiency, heat exchange efficiency indexes and optimized parameters of the transpired solar collectors are presented. Moreover, an integrated and detailed performance test platform for the transpired solar collectors heating characteristics and optimization parameters was developed. Additionally, a comprehensive and multi-condition experimental study was carried out. One important finding is that the non-uniform distribution of infiltration holes at the top and bottom of the transpired solar collectors significantly influence on the preheating effect of fresh air and the overall efficiency of the system. Moreover, an increase in the uniformity of the infiltration holes, increase the heat collection efficiency and heat exchange efficiency by 25% and 10% respectively. Furthermore, the heat collection gain per unit of heat collecting plate area increased by about 34.7 W, and the outlet temperature could be improved by about 15 °C. These findings provide a critical design reference for the high-performance application of the transpired solar collectors in buildings.

Mesh independency study for an elementary perforated panel part of an air solar collector

In order to achieve the numerical model of a transpired solar collector (TSC) with integrated phase changing materials (PCM) it is mandatory to study the impact of the orifice geometry on the entire system. The numerical simulation of the entire solar collector absorber metal plate (1000x2000mm and 5000 orifices) is not feasible thus resulting a huge number of cells for the numerical grid for which we will need very high computational resources and a very large amount of time to be solved. By taking these aspects into account we decided to simulate only four equivalent orifices and then to transpose the results to the actual case for further studies. The present paper aims to analyse the mesh independency study for an elementary perforated panel with four equivalent lobed orifices which is part of a real case TSC. This analysis represents one of the most important stages within the construction of the TSC numerical model and doesn't need an experimental validation. The study was conducted in Ansys Fluent CFD software and the results were processed directly by using Tecplot software. Six different meshes were analysed (from 0.2 to 7.3 million cells), boundary conditions were imposed, and k-ε RNG turbulence model was used according to the literature. After comparing velocity and temperature fields in longitudinal and transverse planes we concluded that from 5.3 million cells the solution is independent of the meshing quality.

Preliminary numerical studies conducted for the numerical model of a real transpired solar collector with integrated phase changing materials

Solar energy has a great potential to reduce the worldwide energy consumptions thus mitigating the impact of building systems on the global warming. Transpired solar collectors (TSC) are cost-effective solutions and phase changing materials (PCM) implemented within them could store the energy during the periods when solar radiation is available. The current paper is part of comprehensive numerical studies and analyses the mesh independency studies conducted in ANSYS Fluent with SST k-Ω viscous model and the numerical model preliminary results (3.3ºC rise in temperature). The results emphasise that the 5 million cells mesh is the feasible option for the studied case.

The Potential of Solar Air Heating in the Turkish Industrial Sector

Transpired solar collector (TSC) systems are simple solutions for the preheating of ventilation air with solar energy. Their performance is a function of several environmental factors, so the climatic conditions of the location play an important role. In this paper, the effect of different climatic zones on the thermal performance of the TSC is investigated. To exclude other sources of influence, the same reference industrial building is examined in four Turkish locations (Antalya, Istanbul, Ankara and Sivas) representing different climatic conditions. RETScreen simulation is carried out for all four regions to obtain the drop of conventional heating requirement in case absorber azimuth of 0°, 45° and 90°. To illustrate the performance, temperature rise, heating energy savings and annual solar fraction are presented. Generally, it can be stated that a location with cold climate and high solar radiation at the same time benefits most from the use of a TSC system. A mathematical correlation has been found showing the solar fraction's dependence on solar radiation and heating degree days. Finally, simulation results have been compared to a set of measurement data from an industrial building's TSC system near Istanbul.

A systematic review on parametric dependencies of transpired solar collector performance

Zero or low-carbon buildings can be achieved through novel technology solutions and integrating renewable energy into the buildings. One method of reducing the fossil fuel dependency of buildings and limiting greenhouse gas emissions is integrating the solar thermal system into the built environment. Recently, transpired solar collector has been identified as 1 of the most efficient solar thermal conversion technologies where a very high efficiency can be achieved. The proposed review paper investigates the performance of transpired solar collectors (TSCs) and discusses the relevant case studies in this context. This paper introduces the background and concept of TSCs. It mainly focuses on the study of parametric dependency of the performance of TSCs. The paper also investigates various mathematical models, experimental study, and numerical simulations particularly CFD used for TSC performance analysis. This proposed paper concluded that wind speed and airflow rate are the most dominant factor in TSC performance but solar irradiation, hole diameter, hole geometry, and pitch size have limited effect on TSC performance; also, profile with longer pitch tends to lower the collector efficiency and heat transfer coefficient. However, profile with shorter pitch tends to reduce the wind effect.