Applied Sciences

Research

Jump to: Review

17 pages, 2325 KiB

Open AccessArticle

Improved Solar Operation Control for a Solar Cooling System of an IT Center

by Jan Albers

Appl. Sci. 2020, 10(10), 3354; https://doi.org/10.3390/app10103354 - 12 May 2020

Cited by 3 | Viewed by 2873

Abstract

In this contribution, a model predictive control algorithm is developed, which allows an increase of the solar operating hours of a solar cooling system without a negative impact on the auxiliary electricity demand, e.g., for heat rejection in a dry cooler. An improved [...] Read more.

In this contribution, a model predictive control algorithm is developed, which allows an increase of the solar operating hours of a solar cooling system without a negative impact on the auxiliary electricity demand, e.g., for heat rejection in a dry cooler. An improved method of the characteristic equations for single-effect

H_{2} O / LiBr

absorption chillers is used in combination with a simple dry-cooler model to describe the part load behavior of both components. The aim of the control strategy is to find a cut-in and a cut-off condition for the solar heat operation (SHO) of an absorption chiller cooling assembly (i.e., including all the supply pumps and the dry cooler) under the constraint that the specific electricity demand during SHO is lower than the electricity demand of a reference cooling technology (e.g., a compression chiller cooling assembly). Especially for the cut-in condition, the model predictive control algorithm calculates a minimum driving temperature, which has to be reached by the solar collector and storage in order to cover the cooling load with a low cooling water temperature but restricted auxiliary electricity demand. Measurements at a solar cooling system for an IT center were used for the testing and a first evaluation of the control algorithm. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

17 pages, 928 KiB

Open AccessArticle

Effect of Modified Flow Schemes of Heat Transfer Fluid on the Performance of a Solar Absorption–Cooling System for an Educational Building in Pakistan

by Iftikhar Bashir Butt, Jinwang Tan, Adeel Waqas, Majid Ali, Adeel Javed and Asfand Yar Ali

Appl. Sci. 2020, 10(9), 3327; https://doi.org/10.3390/app10093327 - 11 May 2020

Cited by 5 | Viewed by 3325

Abstract

Performance of solar absorption cooling systems (SACS) is the focus of contemporary studies for decreasing the electrical energy consumption of buildings as the conventional cooling system of buildings is the main consumer of electrical energy during the summer season in hot–humid climates. In [...] Read more.

Performance of solar absorption cooling systems (SACS) is the focus of contemporary studies for decreasing the electrical energy consumption of buildings as the conventional cooling system of buildings is the main consumer of electrical energy during the summer season in hot–humid climates. In this study, the performance analysis of SACS by manipulating different flow schemes to the heat transfer fluid between different components of the system was performed. TRNSYS model of SACS in an education building located at the city of Peshawar (34.00 N, 71.54 E), Pakistan to encounter the peak cooling load of 108 kW (during operating hours of the building i.e., 09 a.m. to 05 p.m.) is developed and all possible flow schemes of heat transfer fluid between the system’s components were compared. In Scheme-1 (S-1), a conventional flow pattern is used in which the hot water exiting from the chiller unit flows directly toward the stratified thermal storage unit. In Scheme-2 (S-2), the modified flow pattern of hot water exiting from the chiller unit will divert towards the auxiliary unit, if its temperature exceeds the temperature at the hot side outlet of the tank. Another modified flow pattern is Scheme-3 (S-3) in which the hot water leaving the chiller to keep diverting towards the auxiliary unit unless the outlet temperature from the hotter side of the tank would reach the minimum driving temperature (109 °C) of the chiller’s operation. Simulations in TRNSYS evaluates the SACS’s performance of all the schemes (conventional and modified) for the whole summer season and for each month. In general, S-3 with evacuated tube solar collector results in better primary energy saving with the smallest collector area per kilowatt for achieving 50% primary energy saving for the whole summer season. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

16 pages, 3081 KiB

Open AccessArticle

Performance of a Solar Absorption Cooling System Using Nanofluids and a Membrane-Based Microchannel Desorber

by María Venegas, Néstor García-Hernando, Alejandro Zacarías and Mercedes de Vega

Appl. Sci. 2020, 10(8), 2761; https://doi.org/10.3390/app10082761 - 16 Apr 2020

Cited by 6 | Viewed by 3782

Abstract

In this work, the performance of a single effect absorption cooling system fed by solar thermal energy is evaluated. The absorption chiller includes a membrane-based microchannel desorber using three types of nanoparticles: Al₂O₃, CuO, or carbon nanotubes (CNT). Correlations [...] Read more.

In this work, the performance of a single effect absorption cooling system fed by solar thermal energy is evaluated. The absorption chiller includes a membrane-based microchannel desorber using three types of nanoparticles: Al₂O₃, CuO, or carbon nanotubes (CNT). Correlations available in the open literature to calculate the thermal conductivity of nanofluids are reviewed. Using experimental data for the water-lithium bromide solution (H₂O-LiBr) with Al₂O₃ and CNT nanoparticles, the most appropriate correlation for thermal conductivity is selected. Nanofluid properties are evaluated using a concentration of nanoparticles of up to 5% in volume. The largest increase in the desorption rate (7.9%), with respect to using pure H₂O-LiBr solution, is obtained using CNT nanoparticles and the maximum concentration of nanoparticles simulated. The performance of the chiller is evaluated and the daily solar coefficient of performance (SCOP) for the solar cooling facility is obtained. The best improvement with respect to the conventional system (without nanoparticles) represents an increase in the cooling effect of up to 6%. The maximum number of desorber modules recommended, always lower than 50, has been identified. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

17 pages, 7051 KiB

Open AccessArticle

Potential Study of Solar Thermal Cooling in Sub-Mediterranean Climate

by Mustafa Jaradat, Mohammad Al-Addous, Aiman Albatayneh, Zakariya Dalala and Nesrine Barbana

Appl. Sci. 2020, 10(7), 2418; https://doi.org/10.3390/app10072418 - 1 Apr 2020

Cited by 9 | Viewed by 2810

Abstract

Air conditioning is becoming increasingly important in the energy supply of buildings worldwide. There has been a dramatic increase in energy requirements for cooling buildings in the Middle East and North Africa (MENA) region. This is before taking the effects of climate change [...] Read more.

Air conditioning is becoming increasingly important in the energy supply of buildings worldwide. There has been a dramatic increase in energy requirements for cooling buildings in the Middle East and North Africa (MENA) region. This is before taking the effects of climate change into account, which will also entail a sharp increase in cooling requirements. This paper presents the potential of using a solar thermal absorption cooling system in Sub-Mediterranean Climate. Four sites in Jordan are now equipped with water-lithium bromide (H₂O-LiBr) absorption chillers with a total nominal capacity of 530 kW. The focus of the paper was on the pilot system at the German Jordanian University (GJU) campus with a cooling capacity of 160 kW. The system was designed and integrated in order to support two existing conventional compression chillers with a nominal cooling capacity of 700 kW. The system was economically evaluated based on the observed cooling capacity results with a Coefficient of Performance (COP) equals 0.32, and compared with the values observed for a COP of 0.79 which is claimed by the manufacturer. Several techniques were implemented to evaluate the overall economic viability in-depth such as present worth value, internal rate of return, payback period, and levelized cost of electricity. The aforementioned economic studies showed that the absorption cooling system is deemed not feasible for the observed COP of 0.32 over a lifespan of 25 years. The net present value was equal to −137,684 JD and a payback period of 44 years which exceeds the expected lifespan of the project. Even for an optimal operation of COP = 0.79, the discounted payback period was equal to 23 years and the Levelized Cost of Electricity (LCOE) was equal to 0.65 JD/kWh. The survey shows that there are several weaknesses for applying solar thermal cooling in developing countries such as the high cost of these systems and, more significantly, the lack of experience for such systems. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

14 pages, 3077 KiB

Open AccessFeature PaperArticle

Feasibility Analysis of a Membrane Desorber Powered by Thermal Solar Energy for Absorption Cooling Systems

by Jonathan Ibarra-Bahena, Eduardo Venegas-Reyes, Yuridiana R. Galindo-Luna, Wilfrido Rivera, Rosenberg J. Romero, Antonio Rodríguez-Martínez and Ulises Dehesa-Carrasco

Appl. Sci. 2020, 10(3), 1110; https://doi.org/10.3390/app10031110 - 7 Feb 2020

Cited by 7 | Viewed by 2295

Abstract

In absorption cooling systems, the desorber is a component that separates the refrigerant fluid from the liquid working mixture, most commonly completed by boiling separation; however, the operation temperature of boiling desorbers is generally higher than the low-enthalpy energy, such as solar, geothermal, [...] Read more.

In absorption cooling systems, the desorber is a component that separates the refrigerant fluid from the liquid working mixture, most commonly completed by boiling separation; however, the operation temperature of boiling desorbers is generally higher than the low-enthalpy energy, such as solar, geothermal, or waste heat. In this study, we used a hydrophobic membrane desorber to separate water vapor from an aqueous LiBr solution. Influencing factors, such as the H₂O/LiBr solution and cooling water temperatures, were tested and analyzed. With the experimental data, a solar collector system was simulated on a larger scale, considering a 1 m² membrane. The membrane desorber evaluation shows that the desorption rate of water vapor increased as the LiBr solution temperature increased and the cooling water temperature decreased. Based on the experimental data from the membrane desorber/condenser, a theoretical heat load was calculated to size a solar system. Meteorological data from Emiliano Zapata in Mexico were considered. According to the numerical result, nine solar collectors with a total area of 37.4 m² provide a solar fraction of 0.797. The membrane desorber/condenser coupled to the solar system can provide an average of 16.8 kg/day of refrigerant fluid that can be used to produce a cooling effect in an absorption refrigerant system. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

17 pages, 3828 KiB

Open AccessArticle

Performance of Solar Absorption-Subcooled Compression Hybrid Cooling System for Different Flow Rates of Hot Water

by Jinfang Zhang, Zeyu Li, Yue Jing and Yongrui Xu

Appl. Sci. 2020, 10(3), 810; https://doi.org/10.3390/app10030810 - 23 Jan 2020

Cited by 9 | Viewed by 1676

Abstract

The solar absorption-subcooled compression hybrid cooling system (SASCHCS) is tech-economically feasible for high-rise buildings. Since such a system operates with no auxiliary heat source, the performance coupling of its absorption subsystem and solar collectors is sensitive to the variation of hot water flow [...] Read more.

The solar absorption-subcooled compression hybrid cooling system (SASCHCS) is tech-economically feasible for high-rise buildings. Since such a system operates with no auxiliary heat source, the performance coupling of its absorption subsystem and solar collectors is sensitive to the variation of hot water flow rate. In this regard, the relationship of system performance and hot water flow rate is required to be clarified exactly. Therefore, this paper aims to illustrate the effect mechanism of hot water flow rate and to propose the corresponding decision criterion. The case study is based on a typical high-rise office building in subtropical Guangzhou. The daily working process of this system with different hot water flow rates is simulated and analyzed. Subsequently, the useful heat of collectors and cooling capacity of the absorption subsystem with the hot water flow rate is discussed in detail. The results show that the SASCHCS operates with hot water temperatures ranging from 60 °C to 90 °C. The energy saving increases with the rise of hot water flow rate, but such variation tends to be flat for the excessively high flow rate. As the collector flow rate increases from 1 m³/h to 10 m³/h, the daily energy saving improves by 21% in August. Similarly, the daily energy saving increases by 37.5% as generator hot water flow rate increases from 1 m³/h to 10 m³/h. In addition, the collector flow rate of 3.6 m³/h (13.33 (kg/m² h)) and the generator flow rate of 5.2 m³/h (19.26 (kg/m² h)) are optimal for the annual operation, with considering power consumption of water pumps. This paper is helpful for the improvement of SASCHCS operating performance. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

13 pages, 1908 KiB

Open AccessFeature PaperArticle

Design of a 35 kW Solar Cooling Demonstration Facility for a Hotel in Spain

by Pedro J. Martínez, Pedro Martínez, Victor M. Soto, Luis A. Bujedo and Juan Rodriguez

Appl. Sci. 2020, 10(2), 496; https://doi.org/10.3390/app10020496 - 9 Jan 2020

Cited by 14 | Viewed by 3128

Abstract

Solar cooling systems have the advantage of the coincidence between the hours of cooling demand and the hours of solar radiation availability, and they can contribute to reduce the energy consumption in buildings. However, the high cost of thermal solar cooling facilities with [...] Read more.

Solar cooling systems have the advantage of the coincidence between the hours of cooling demand and the hours of solar radiation availability, and they can contribute to reduce the energy consumption in buildings. However, the high cost of thermal solar cooling facilities with absorption chillers, maintenance issues, legionella risk and water consumption (associated to the necessary cooling tower) have limited the use of these systems to demonstration projects. A simplified Transient System Simulation Tool (TRNSYS) model was developed to provide the owner of the demonstration facility the information he needs for design decision-making. This model was validated with experimental data registered in a solar cooling system designed and built by the authors. Different collector field surfaces, hot water storage tank volumes, and absorption machine driving temperatures were analyzed for a hotel demonstration facility. In terms of the energy delivered to the absorption chiller the optimum dimensioning corresponded to the lowest values of the driving temperature (75 °C) and specific storage volume (15 Lm²). From an economic point of view, the saving of 1515 euros per year when compared with an electric compression chiller does not compensate the investment of 3000 euros per kW of cooling capacity that cost the thermal solar cooling facility. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

27 pages, 7073 KiB

Open AccessArticle

CO₂ Transcritical Refrigeration Cycle with Dedicated Subcooling: Mechanical Compression vs. Absorption Chiller

by Evangelos Bellos and Christos Tzivanidis

Appl. Sci. 2019, 9(8), 1605; https://doi.org/10.3390/app9081605 - 18 Apr 2019

Cited by 15 | Viewed by 4530

Abstract

The objective of this paper is the comparison of two dedicated subcooling methods, after the gas cooler, in a CO₂ transcritical refrigeration system. The use of vapor compression refrigeration with R134a for subcooling is the first method, and the second is the [...] Read more.

The objective of this paper is the comparison of two dedicated subcooling methods, after the gas cooler, in a CO₂ transcritical refrigeration system. The use of vapor compression refrigeration with R134a for subcooling is the first method, and the second is the use of an absorption chiller that operates with a LiBr-H₂O working pair. The examined systems are compared energetically and exegetically with the reference transcritical CO₂ refrigeration cycle without subcooling. The analysis is conducted for different operating scenarios and in every case, the system is optimized by selecting the proper temperature and pressure levels. The analysis is performed with a developed and validated model in Engineering Equation Solver. According to the final results, the use of the absorption chiller is able to decrease the system electricity consumption by about 54% compared to the simple transcritical cycle, while the decrease with the mechanical subcooling is 41%. Both systems with dedicated subcooling are found to have an important increase in the system exergy performance compared to the simple transcritical cycle. However, the system with the mechanical subcooling is found to be the best choice exegetically, with a small difference from the system with the absorption chiller. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

Review

Jump to: Research

40 pages, 8951 KiB

Open AccessReview

New Developments and Progress in Absorption Chillers for Solar Cooling Applications

by Dereje S. Ayou and Alberto Coronas

Appl. Sci. 2020, 10(12), 4073; https://doi.org/10.3390/app10124073 - 12 Jun 2020

Cited by 25 | Viewed by 13273

Abstract

At present, novel, small-to-large capacity absorption chillers with unique technical features have emerged on the global market, and laboratory and pre-industrial prototypes have also been developed. These chillers have been designed for the efficient use of low-grade heat sources; some are air-cooled, small [...] Read more.

At present, novel, small-to-large capacity absorption chillers with unique technical features have emerged on the global market, and laboratory and pre-industrial prototypes have also been developed. These chillers have been designed for the efficient use of low-grade heat sources; some are air-cooled, small capacity systems; compact water/LiBr chillers; or solar-gas-fired single/double-effect chillers. Also, some advanced commercial absorption chillers have an extensive temperature glide in the driving heat stream (>30 K) which extracts approximately twice as much heat (~200%) as the single-effect chiller. This large temperature glide means that the chillers are well suited to solar thermal collector installations and district heating networks, and the extra driving heat increases cold production. Moreover, recent advances in R718 turbo compressor technologies have helped to solve the problems water/LiBr absorption chillers have in adapting to extreme operating conditions (e.g., high ambient temperature, >35 °C) by using a compressor-boosted absorption chiller configuration. This review paper presents and discusses the developments and progress in these absorption chiller technologies. In summary, the new absorption chillers may be useful for developing efficient, cost-effective, and robust solar cooling solutions that are needed to mitigate the unsustainable impact of the rising global demand for space cooling. Full article

(This article belongs to the Special Issue Solar Cooling Systems)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Solar Cooling Systems

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Published Papers (9 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI