Energies

Research

18 pages, 3878 KiB

Open AccessArticle

Energy Consumption Verification of SPD Smart Window, Controllable According to Solar Radiation in South Korea

by Yujin Ko, Hyogeun Oh, Hiki Hong and Joonki Min

Energies 2020, 13(21), 5643; https://doi.org/10.3390/en13215643 - 28 Oct 2020

Cited by 13 | Viewed by 2499

Between 60% and 70% of the total energy load of a house or office occurs through the exteriors of the building, and in the case of offices, heat loss from windows and doors can approach 40%. A need for glass that can artificially [...] Read more.

Between 60% and 70% of the total energy load of a house or office occurs through the exteriors of the building, and in the case of offices, heat loss from windows and doors can approach 40%. A need for glass that can artificially control the transmittance of visible light has therefore emerged. Smart windows with suspended particle device (SPD) film can reduce energy consumption by responding to environmental conditions. To measure the effect of SPD windows on the energy requirements for cooling and heating in Korea, we installed a testbed with SPD windows. With TRNSYS18, the comparison between measurements and simulation has been made in order to validate the simulation model with respect to the modeling of an SPD window. Furthermore, the energy requirements of conventional and SPD-applied windows were compared and analyzed for a standard building that represented an actual office building. When weather for the city of Anseong and a two-speed heat pump were used to verify the simulation, the simulated electricity consumption error compared with the testbed was −1.0% for cooling and −0.9% for heating. The annual electricity consumption error was −0.9%. When TMY2 Seoul weather data were applied to the reference building, the decrease in electricity consumption for cooling in the SPD model compared with the non-SPD model was 29.1% and the increase for heating was 15.8%. Annual electricity consumption decreased by 4.1%. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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24 pages, 3183 KiB

Open AccessArticle

Shaping High Efficiency, High Temperature Cavity Tubular Solar Central Receivers

by Ronny Gueguen, Benjamin Grange, Françoise Bataille, Samuel Mer and Gilles Flamant

Energies 2020, 13(18), 4803; https://doi.org/10.3390/en13184803 - 14 Sep 2020

Cited by 14 | Viewed by 3047

Abstract

High temperature solar receivers are developed in the context of the Gen3 solar thermal power plants, in order to power high efficiency heat-to-electricity cycles. Since particle technology collects and stores high temperature solar heat, CNRS (French National Center for Scientific Research) develops an [...] Read more.

High temperature solar receivers are developed in the context of the Gen3 solar thermal power plants, in order to power high efficiency heat-to-electricity cycles. Since particle technology collects and stores high temperature solar heat, CNRS (French National Center for Scientific Research) develops an original technology using fluidized particles as HTF (heat transfer fluid). The targeted particle temperature is around 750 °C, and the walls of the receiver tubes, reach high working temperatures, which impose the design of a cavity receiver to limit the radiative losses. Therefore, the objective of this work is to explore the cavity shape effect on the absorber performances. Geometrical parameters are defined to parametrize the design. The size and shape of the cavity, the aperture-to-absorber distance and its tilt angle. A thermal model of a 50 MW hemi-cylindrical tubular receiver, closed by refractory panels, is developed, which accounts for radiation and convection losses. Parameter ranges that reach a thermal efficiency of at least 85% are explored. This sensitivity analysis allows the definition of cavity shape and dimensions to reach the targeted efficiency. For an aperture-to-absorber distance of 9 m, the 85% efficiency is obtained for aperture areas equal or less than 20 m² and 25 m² for high, and low convection losses, respectively. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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11 pages, 2982 KiB

Open AccessArticle

Hybrid Microencapsulated Phase-Change Material and Carbon Nanotube Suspensions toward Solar Energy Conversion and Storage

by Jun Li, Lisi Jia, Longjian Li, Zehang Huang and Ying Chen

Energies 2020, 13(17), 4401; https://doi.org/10.3390/en13174401 - 26 Aug 2020

Cited by 11 | Viewed by 1920

Abstract

In this study, a new type of functional hybrid suspension for solar energy conversion and thermal energy storage was prepared by adding carbon nanotube (CNT) and microencapsulated phase-change material (MEPCM) into deionized water. MEPCM with octadecane as the core material and titania (TiO [...] Read more.

In this study, a new type of functional hybrid suspension for solar energy conversion and thermal energy storage was prepared by adding carbon nanotube (CNT) and microencapsulated phase-change material (MEPCM) into deionized water. MEPCM with octadecane as the core material and titania (TiO₂) as the shell material was synthesized by the sol–gel method. The MEPCMs were spherical particles with diameters of 2–4 μm, and the thickness of the shell was about 100 nm. The MEPCM achieved better thermal stability and thermal conductivity than the pure octadecane due to the TiO₂ shell. The melting and solidification latent heats of the MEPCM were about 154.24 and 154.26 J/g, respectively. The encapsulation efficiency of octadecane was calculated to be 65.84%. Most of all, the novel hybrid CNT and MEPCM suspensions exhibited remarkable dispersion stability owing to the stable reticular structure composed of CNT in the suspension. Compared with pure water, the thermal conductivity, specific heat of the MEPCM/CNT suspension improved by 34.48 and 43.57%, respectively and the photo-thermal conversion efficiency reached a high value of 86.0%. This work provided a new type of hybrid functional suspension towards direct absorption solar collector for solar energy conversion and storage. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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31 pages, 907 KiB

Open AccessArticle

Adsorption Isotherm Modelling of Water on Nano-Tailored Mesoporous Silica Based on Distribution Function

by František Mikšík, Takahiko Miyazaki and Kyaw Thu

Energies 2020, 13(16), 4247; https://doi.org/10.3390/en13164247 - 17 Aug 2020

Cited by 14 | Viewed by 6239

Abstract

A new model of adsorption isotherms Type IV and V is proposed as a basis for theoretical calculations and modelling of adsorption systems such as adsorption heat storage and heat pumps. As the current models have decent yet limited applicability, in this work, [...] Read more.

A new model of adsorption isotherms Type IV and V is proposed as a basis for theoretical calculations and modelling of adsorption systems such as adsorption heat storage and heat pumps. As the current models have decent yet limited applicability, in this work, we present a new combined model with universal use for micro-mesoporous silica/water adsorption systems. Experimental measurement of adsorption isotherm of water onto seven different samples of micro and mesoporous silica and aluminium-silica were used to fit new adsorption models based on a combination of classical theories and a distribution function related to the pore-size distribution of the selected materials. The fitting was conducted through a repeated non-linear regression using Trust Region Reflective algorithm with weighting factors to compensate for the scalability of the adsorption amount at low relative pressure with optimization of the absolute average deviation fitting parameter. The results display a significant improvement for most of the samples and fitting indicators compared to more common models from the literature with average absolute deviation as low as AAD =

0.0025

g

g

⁻¹ for material with maximum uptake of q =

0.38

g

g

⁻¹. The newly suggested model, which is based on a combination of BET theory and adjusted normal distribution function, proved to bring a higher degree of precision and universality for mesoporous silica materials with different levels of hydrophilicity. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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13 pages, 1830 KiB

Open AccessArticle

Greenhouse Gas Reduction Effect of Solar Energy Systems Applicable to High-rise Apartment Housing Structures in South Korea

by Chang-Hyun Park, Yu-Jin Ko, Jong-Hyun Kim and Hiki Hong

Energies 2020, 13(10), 2568; https://doi.org/10.3390/en13102568 - 19 May 2020

Cited by 13 | Viewed by 3108

Abstract

In South Korea, we are aiming for net zero energy use apartment home structures. Since the apartment structure in South Korea is generally a high-rise of 10 or more floors, the types of renewable energy applicable are limited to photovoltaic (PV) panels, solar [...] Read more.

In South Korea, we are aiming for net zero energy use apartment home structures. Since the apartment structure in South Korea is generally a high-rise of 10 or more floors, the types of renewable energy applicable are limited to photovoltaic (PV) panels, solar collectors installed on the wall, or a photovoltaic thermal (PVT) hybrid panel combining both. In this study, the effect of PV, ST (Solar Thermal), and PVT systems on greenhouse gas reduction was analyzed using TRNSYS18. All three systems showed maximum CO₂ reductions at 35° facing south. PV, ST, and PVT showed CO₂ reductions of 67.4, 114.6, and 144.7 kg_CO₂/m²·year, respectively. Compared to those values, when installed on a wall (slope of 90°), CO₂ reduction is about 35–40% less and about 20% less at a slope of 75°. ST and PVT installed on the vertical wall have a greater greenhouse gas reduction effect than the PV installed at the optimal slope of 35°. Since the CO₂ reduction difference among SW, SE, and azimuthal S is within 10%, ST and PVT are recommended for installation on high-rise apartment structure walls or balconies with the azimuthal angle of ± 45° with respect to south. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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16 pages, 3854 KiB

Open AccessArticle

Performance Investigation of a Two-Bed Type Adsorption Chiller with Various Adsorbents

by Jung-Gil Lee, Kyung Jin Bae and Oh Kyung Kwon

Energies 2020, 13(10), 2553; https://doi.org/10.3390/en13102553 - 18 May 2020

Cited by 18 | Viewed by 2534

Abstract

In this study, the performance evaluation of an adsorption chiller (AD) system with three different adsorbents—silica-gel, aluminum fumarate, and FAM-Z01—was conducted to investigate the effects of adsorption isotherms and physical properties on the system’s performance. In addition, the performance evaluation of the AD [...] Read more.

In this study, the performance evaluation of an adsorption chiller (AD) system with three different adsorbents—silica-gel, aluminum fumarate, and FAM-Z01—was conducted to investigate the effects of adsorption isotherms and physical properties on the system’s performance. In addition, the performance evaluation of the AD system for a low inlet hot-water temperature of 60 °C was performed to estimate the performance of the system when operated by low quality waste heat or sustainable energy sources. For the simulation work, a two-bed type AD system is considered, and silica-gel, metal organic frameworks (MOFs), and ferro-aluminophosphate (FAPO, FAM-Z01) were employed as adsorbents. The simulation results were well matched with the laboratory-scale experimental results and the maximum coefficient of performance (COP) difference was 7%. The cooling capacity and COP of the AD system were investigated at different operating conditions to discuss the influences of the adsorbents on the system performance. Through this study, the excellence of the adsorbent, which has an S-shaped isotherm graph, was presented. In addition, the influences of the physical properties of the adsorbent were also discussed with reference to the system performance. Among the three different adsorbents employed in the AD system, the FAM-Z01 shows the best performance at inlet hot water temperature of 60 °C, which can be obtained from waste heat or sustainable energy, where the cooling capacity and COP were 5.13 kW and 0.47, respectively. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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13 pages, 6572 KiB

Open AccessArticle

Validation and Numerical Sensitivity Study of Air Baffle Photovoltaic-Thermal Module

by Yu-Jin Kim, Kwang-Seob Lee, Libing Yang, Evgueniy Entchev, Eun-Chul Kang and Euy-Joon Lee

Energies 2020, 13(8), 1990; https://doi.org/10.3390/en13081990 - 17 Apr 2020

Cited by 13 | Viewed by 2611

Abstract

Photovoltaic-Thermal (PVT) is a type of technology that generates electricity and heat simultaneously at the point of use. The generated electricity could be used on site or exported to the grid while the thermal output could be utilized for space and water heating. [...] Read more.

Photovoltaic-Thermal (PVT) is a type of technology that generates electricity and heat simultaneously at the point of use. The generated electricity could be used on site or exported to the grid while the thermal output could be utilized for space and water heating. There is a lot of research for solar air heating with experiment or CFD (Computational Fluid Dynamics), but CFD has the disadvantage that it would indicate impractical results. In this paper, a numerical PVT baseline model was developed and validated with Separate Effect Test (SET) data to increase reliability. The numerical study was conducted by considering the effect of baffle lengths and baffle slopes on outlet temperature, total heat transfer and pressure drop inside PVT air module. An optimum PVT baffle length and slope design were suggested. The baseline numerical PVT model agreed well with the test data set as indicated by 1.25% error for inlet–outlet temperatures difference. The sensitivity study was conducted by changing the PVT baffle length and slope. The optimum baffle design was concerned with both heat transfer and pressure drop at the same time with ratio. The baffle length should be kept under 150 mm and baffle slope should be greater than 30° to achieve better air mixing in PVT air channel and unit heat transfer compared to baffle slope less than 30°. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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14 pages, 3429 KiB

Open AccessArticle

Effects of Evaporator and Condenser in the Analysis of Adsorption Chillers

by Woo Su Lee, Moon Yong Park, Xuan Quang Duong, Ngoc Vi Cao and Jae Dong Chung

Energies 2020, 13(8), 1901; https://doi.org/10.3390/en13081901 - 13 Apr 2020

Cited by 5 | Viewed by 4698

Abstract

In a survey of the literature from the last 20 years, 20% of the numerical models used to analyze the performance of adsorption chillers assumed the evaporator and condenser were ideal, with a fixed evaporation temperature and condenser temperature, and ignored interactions between [...] Read more.

In a survey of the literature from the last 20 years, 20% of the numerical models used to analyze the performance of adsorption chillers assumed the evaporator and condenser were ideal, with a fixed evaporation temperature and condenser temperature, and ignored interactions between the adsorption bed and evaporator/condenser. Even when the interaction with the evaporator and condenser was included, the other 80% of studies modeled the adsorption bed based on the LPM (lumped parameter method), which ignores the geometry effect and contact resistance of the bed, and thus reduces the accuracy of the analysis. As a consequence, these earlier numerical studies overestimated the system performance of the adsorption chiller. In this study, we conducted a refined numerical approach which avoids these limitations, producing estimates in close agreement with experimental results. Compared with our approach, the models with ideal treatment of evaporator and condenser overestimated COP (coefficient of performance) and SCP (specific cooling power) by as much as 16.12% and 24.64%, respectively. The models based on LPM overestimated COP and SCP by 22.82% and 11.28%, compared to our approach. Full article

(This article belongs to the Special Issue Solar Thermal Energy Conversion and Storage)

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