A Study on Daylighting Performance of Split Louver with Simplified Parametric Control

A split louver consists of two sections with their slat angles to be adjusted separately for glare protection and redirection of sunlight, respectively. The upper section works in conjunction with the lower section to enhance daylight availability and uniformity throughout the year. The study aims to improve the daylighting performance of the split louver by applying a simplified parametric control, which predetermines the angle difference between adjacent slats in the upper section for a chosen solar altitude and then keeps this difference fixed during operation. The slats in the upper section can be changed parametrically using the Grasshopper to reflect daylight onto the ceiling and then illuminate the rear zone of a space. The lower section of the split louver can control the daylight in the front space area and may affect the amount of light in the back. The performance indicator in evaluating the proposed split louver design for the chosen typical days is the percentage coverage of the work plane area for the illuminance range of 150~750 lux, which was achieved up to 100% in some cases. The proposed split louver with the simplified parametric control has the potential to provide relatively consistent and distributed daylight coverage of the floor area and a glare-free environment

Daylighting performance improvements using of split louver with parametrically incremental slat angle control

Different shading device systems and control strategies can be employed in different parts of a window system to perform different functions, particularly for fully glazed façades. A split louver with various improvements was proposed in this study as an innovative daylighting device to improve daylighting distribution and uniformity. An 8 m deep office room in Jordan was chosen for a case study, where it is south-oriented with a high window-to-wall ratio (WWR: 95%). The split louver system features two sections with different functions that can affect the quality and quantity of daylighting performance in the deep room space. Four types of parametrically controlled reflective slats, i.e., unanimous, incremental, fully parametric, and parametrically incremental, were investigated for the upper section of the split louver. While the daylighting performance of the four systems is extremely similar in terms of illuminance level but different in distribution, the parametrically incremental control is the preferred one attributed to its practicality and distribution performance. The upper section of the split louver includes blind integration, and different slat surface materials (diffuse, semi-mirrored, and mirrored) were evolved through various improvement phases. Simultaneously, the lower section of the split louver was investigated in order to adjust the overall illuminance level. The proposal of scheduled angles of split louver in both sections presented the most optimal combinations to achieve balanced daylighting levels in both the front and back of the space. This resulted in a free-glare indoor with accepted daylight uniformity levels of up to 0.60 and high percentage coverage within UDI150∼750 lx for most of the working hours throughout the year are realized (between 90% and 100% at noontime and no less than 50% along the rest of the working hours)

Daylighting performance assessment of a split louver with parametrically incremental slat angles: Effect of slat shapes and PV glass transmittance

Advanced shading systems, including light redirecting systems, may cause undesirable glare and affect the quality of the transmitted daylight. Therefore, it is important to integrate different building components, such as shading and glazing, to comprehensively assess daylighting performance and ensure a comfortable, luminous environment. This study proposes an advanced daylighting design based on a parametrically controlled split louver with reflective slats to redirect sunlight onto a ceiling and integrated PV glazing to control the illuminance levels. A special contoured slat design (retro shape) was evaluated and compared to different slat shapes (flat, curved, and oval) of the upper section. In addition, the effect of the PV glass transmittance (30 %, 50 %, and 70 %) on the daylighting performance was investigated. The daylight analysis was performed using Grasshopper software as a parametric tool to predict the daylighting performance through advanced dynamic metrics including Useful Daylight Illuminance (UDI), Daylight Glare Probability (DGP), and Illuminance Uniformity (Uo). It is found that the retro-shaped slat design can significantly improve the daylight distribution and level without using the common blind system for more than 90 % of the work plane area within the recommended acceptable UDI range (150 ∼ 750 lx) for a longer period of the day (including the early morning and late afternoon). Furthermore, retro-shaped slats can improve the Uo throughout the space to achieve the recommended level (0.70), while PV glazing can reduce the risk of daylight glare

Feasibility of an innovative amorphous silicon photovoltaic/thermal system for medium temperature applications

Medium temperature photovoltaic/thermal (PV/T) systems have immense potential in the applications of absorption cooling, thermoelectric generation, and organic Rankine cycle power generation, etc. Amorphous silicon (a-Si) cells are promising in such applications regarding the low temperature coefficient, thermal annealing effect, thin film and avoidance of large thermal stress and breakdown at fluctuating temperatures. However, experimental study on the a-Si PV/T system is rarely reported. So far the feasibility of medium temperature PV/T systems using a-Si cells has not been demonstrated. In this study, the design and construction of an innovative a-Si PV/T system of stainless steel substrate are presented. Long-term outdoor performance of the system operating at medium temperature has been monitored in the past 15 months. The average electrical efficiency was 5.65%, 5.41% and 5.30% at the initial, intermediate and final phases of the long-test test, accompanied with a daily average thermal efficiency from about 21% to 31% in the non-heating season. The thermal and electrical performance of the system at 60 °C, 70 °C and 80 °C are also analyzed and compared. Moreover, a distributed parameter model with experimental validation is developed for an inside view of the heat transfer and power generation and to predict the system performance in various conditions. Technically, medium temperature operation has not resulted in interruption or observable deformation of the a-Si PV/T system during the period. The technical and thermodynamic feasibility of the a-Si PV/T system at medium operating temperature is demonstrated by the experimental and simulation results

Modelling analysis of a solar-driven thermochemical energy storage unit combined with heat recovery

Solar-driven thermochemical energy storage (TCES) can address the mismatch between solar heat production and heating demand and contribute to decarbonisation in buildings. In many studies of typical salt hydrate TCES systems, massive heat carried by the discharged humid airflow during the charging phase is not well-utilised but directly dissipated to the ambient. Therefore, a solar photovoltaic/thermal-powered TCES system integrating a heat exchanger (PV/T-TCES-HEX system) is proposed in this study for recovering this part of heat. To study the effect of adding the PV/T collector and heat exchanger (HEX) on the performance of the TCES system, the thermal performance of the PV/T-TCES-HEX system is compared with other two TCES systems via COMSOL modelling. Results suggest that the PV/T-TCES-HEX system requires an additional external electricity input of 11.86 kWh on a typical summer day in Nottingham, which is only 40.53% of the TCES-only system. The overall thermal efficiency of the PV/T-TCES-HEX system is 56.00%, indicating an efficiency enhancement of 146.80%. A lower mass flow rate leads to higher thermal efficiency and storage energy. The system has the highest overall thermal efficiency when the reactor bed thickness is 0.04 m (57.55%) and when the reactor bed length is 0.5 m (58.73%)

Performance study of a thermochemical energy storage reactor embedded with a microchannel tube heat exchanger for water heating

Thermochemical energy storage (TCES) provides a promising solution to addressing the mismatch between solar thermal production and heating demands in buildings. However, existing air-based open TCES systems face practical challenges in integrating with central water heating systems and controlling the supply temperature. To overcome these limitations, a novel water-based TCES-HEX-HRU system is proposed in this study, which integrates a water-to-air microchannel tube heat exchanger (HEX) and an air-to-air heat recovery unit (HRU). A comprehensive evaluation of the TCES-HEX-HRU system is conducted numerically using a COMSOL model, including a comparative assessment for different TCES system configurations. The results demonstrate that the TCES-HEX-HRU system achieves an overall thermal efficiency of 82.35 %, marking a substantial 69 percentage points improvement over the TCES-HEX system. Although slightly lower than the typical air-based TCES system without HEX and HRU by 15.44 percentage points, the TCES-HEX-HRU system can be a practically promising and viable choice for applications in central heating systems. Numerical investigations indicate that the thermal performance of the system is influenced by the inlet conditions of airflow and waterflow. Moreover, increasing the number of water channels in the HEX of the TCES-HEX-HRU system enhances heat transfer but reduces the amount of heat released by TCES composite materials, resulting in a maximum overall thermal efficiency of 92.09 % with 35 channels and a peak outlet water temperature of 33.67 °C at with 30 channels. However, further increases in the number of channels lead to a decline in overall thermal efficiency and outlet water temperature. Changes in the width of water channels in the HEX have a minor impact on the highest outlet water temperature and overall thermal efficiency, while affecting the volume of the TCES composite materials

Implementation of Passive Radiative Cooling Technology in Buildings: A Review

Radiative cooling (RC) is attracting more interest from building engineers and architects. Using the sky as the heat sink, a radiative cooling material can be passively cooled by emitting heat to the sky. Thanks to the development of material technology, RC research is now revived, aiming at increasing the materials' cooling power as well as finding reliable ways to utilize it in cooling for buildings. This review identifies some issues in the current implementation of RC technologies in buildings from an architectural point of view. Besides the technical performance of the RC technologies, some architectural aspects, such as integration with architectural features, aesthetic requirements, as well as fully passive implementations of RC, also need to be considered for buildings application. In addition to that, performance evaluation of a building-integrated RC system should begin to account for its benefit to the occupant's health and comfort, alongside the technical performance. In conclusion, this review on RC implementation in buildings provide a meaningful discussion for the direction of the research

Exploring a novel tubular-type modular reactor for solar-driven thermochemical energy storage

Thermochemical energy storage (TCES) has gained extensive attention as a potential solution to address the mismatch between solar thermal energy production and demand. In this study, a novel tubular-type modular TCES reactor is introduced. COMSOL modelling of the system is developed and experimentally validated using a laboratory-scale TCES system. Both types of reactors show similar temperature increases, intensifying with higher inlet relative humidity. Their maximum temperature lifts exceeding 26 °C at 90 % RH. Tubular designs offer better axial flexural strength and dispersion of TCES composite materials compared to plate structures. This property of tubular structures beneficial reducing bed thickness and pressure drop and enhancing equivalent thermal efficiency. Simulations show tubular-type modular reactors reduce pressure drop by 4–5 times compared to plate-type modular reactors, increasing equivalent thermal efficiency by nearly 7% points. Increasing the number of reactor beds and inner tube radius improves equivalent thermal efficiency due to reduced bed thickness and pressure drop. As the number of matrix rows and columns in the reactor bed increases from 2 to 10, bed thickness decreases from 0.058 m to 0.012 m, reducing pressure drop from 845.53 Pa to 38 Pa and increasing equivalent thermal efficiency from 78.82 % to 96.61 %

Effect of the spectrally selective features of the cover and emitter combination on radiative cooling performance

Radiative cooling (RC) shows good potential for building energy saving by throwing waste heat to the cosmos in a passive and sustainable manner. However, most available radiative coolers suffer from low cooling flux. The situation becomes even deteriorated in the daytime when radiative coolers are exposed to direct sunlight. To tackle this challenge, an idea of employing both a spectrally selective cover and a spectrally selective emitter is proposed in this study as an alternative approach. A comparative study is conducted among four RC modules with different spectral characteristics for the demonstration of how the spectral profiles of the cover and the emitter affects the RC performance. The results under given conditions show that the RC module with a spectrally selective cover and a spectrally selective emitter (SC/SE) reaches a net RC power of 62.4 W/m2 when the solar radiation is 800 W/m2, which is about 1.8 times that of the typical RC module with a spectrally non-selective cover and a spectrally selective emitter (n-SC/SE). When the ambient temperature is 30°C, the SC/SE based RC module realizes a daytime sub-ambient temperature reduction of 20.0°C, standing for a further temperature decrement of 9.2°C compared to the n-SC/SE based RC module

Parametric study of a novel combination of solar chimney and radiative cooling cavity for natural ventilation enhancement in residential buildings

The application of radiative cooling (RC) is expanding to a diverse research field, with some current studies trying to apply RC for natural ventilation. One proposed strategy is to use RC for the enhancement of solar chimney (SC) ventilation, and this strategy has been proven in a dry temperate climate. However, geographical locations and other design parameters may affect the performance of this natural ventilation strategy, and the conditions in which SC-RC ventilation performs best need to be investigated. This parametric study examines the performance of a novel SC-RC ventilation with six different parameters. The six parameters are the RC emitter's convection cover, building's thermal mass, RC cavity gap, internal heat gain, climate, and fan usage. Transient 2D computational fluid dynamics (CFD) simulations with Ansys Fluent were conducted to analyse the SC-RC ventilation's optimal design and working conditions. A convection cover on the RC emitter, a thermal mass wall material, a smaller RC gap, and a relatively low internal heat gain help the SC-RC achieve a cooler room and higher ventilation flow rate. Overall, the novel SC-RC ventilation performance is better than a conventional SC, except in humid climates. In dry climates, the SC-RC has the potential to create a maximum 2 °C temperature reduction, with a daily average room temperature of 0.56 °C lower than ambient. This cooling performance of the passive SC-RC ventilation is better than the fan-assisted SC-RC. Also, the SC-RC can achieve a daily average of 2.1 ACH, which is 0.4 ACH more than the conventional SC