Solar-assisted Air-conditioning System Research Articles

Practical application of machine learning in energy and thermal management: Long-term data analysis of solar-assisted AC systems in portable cabins in Kuwait and Australia

Machine learning techniques are advancing rapidly in theoretical grounds, but their practical application and real evaluation in engineering disciplines are limited. This study investigates one-year of experimental data for indoor air conditions and energy monitoring of two identical portable cabins in Kuwait. Additionally, a 9-month period of solar photovoltaic energy production is experimentally obtained for assessing energy saving aspects of a solar assisted air conditioning system in one of the cabins. A transient system simulation tool model is developed and validated for the portable cabins. Both one-year experimental data and the validated simulation data are used for developing machine learning models for six case studies in Kuwait and Australia. In simulations, there are issues related to lack of access to real-time weather data from a locally installed weather station. In experimental works, there were issues related to disruption of data collection due to power or internet shutdowns. To resolve these issues, nineteen regression models are investigated. It was found that all models performed very well although the Matern 5/2 and Exponential gaussian process regression model performed slightly better, with all models achieving high accuracy, as indicated by R-squared values close to 1.0 in all six case studies. Overall, it was found that the photovoltaic solar-assisted air conditioning system could save annually 26.2 % and 75.7 % energy in Kuwait and Rockhampton, Australia, respectively.

Transient analysis of an efficient solar assisted air-conditioning system for subtropical climate with various solar thermal collectors

The air conditioning demand of the world is largely fulfilled by vapor compression systems; however, these systems are also responsible for depleting ozone layer due to the nature of refrigerants. Desiccant cooling systems integrated with solar thermal energy technologies could be an attractive alternative with some performance enhancement techniques. In this study, transient seasonal performance investigation is performed for an innovative solar integrated desiccant cooling system that uses regenerative evaporative cooler known as solar assisted desiccant integrated Maisotsenko cycle cooler for better cooling performance. Furthermore, transient annual performance analysis of solar system for meeting thermal energy requirement for regenerating the desiccant wheel in summer season and handling heating load of the building in winter season is also carried out with three different solar thermal collector technologies for finding out more efficient technology. The key performance indicators in this study are useful energy gain, solar source efficiency, auxiliary energy sharing, coefficient of performance, and solar fraction. The results of the key performance parameters are reported as monthly average values. The proposed integrated system resulted to be very efficient with a maximum COP value of 1.13 in April when latent cooling loads are low and 0.78 in August when latent cooling loads are higher. The system’s maximum cooling capacity is 24 kW in April corresponding to a sensible heat factor of 0.720. Furthermore, the regeneration temperature requirements ranged from 50 °C to 78 °C, respectively that makes it favorable to use low grade thermal energy through non concentrating solar thermal collectors. The regeneration thermal energy requirement for desiccant wheel fluctuates throughout the year, maximizing in August due to higher dehumidification requirements. The study also revealed that the evacuated tube collector technology is most suitable with average annual efficiency of around 36 %.

Experimental investigation of a solar-assisted air conditioning system: Energy and life cycle climate performance analysis

Among building elements, HVAC (heating, ventilation, and air conditioning) systems use the most energy. In this regard, effective solutions should be developed to reduce the energy consumption and negative environmental impacts of these systems and improve their efficiency. In addition, the relative coincidence of energy availability and cooling demand makes indoor space cooling a significant possibility for solar energy use. In this study, the effect of air conditioners (ACs) on reducing energy consumption in the case of supporting AC systems used in residential air conditioning with solar energy from renewable energy sources was experimentally studied. For this purpose, if the outdoor temperature in August was 32, 36, and 38 °C, and the indoor temperature was kept at 18, 19, and 20 °C, the performance of the solar-powered AC system was compared with a conventional AC system under the same ambient conditions. For comparison, two rooms with the same internal volume and insulation properties were built. Increasing the input temperature of the compressor saved about 8-28% of the energy. Moreover, the environmental effects of energy savings from the proposed system for the hottest summer times in residential buildings were examined by life-cycle assessment, and depending on the decrease in energy consumption, there was a decrease in emission values between 7.74-28.27%.

Development and energy analysis of a solar-assisted air conditioning system for energy saving

Development and energy analysis of a solar-assisted air conditioning system for energy saving

Performance improvement of solar-assisted air-conditioning systems by using an innovative configuration of a desiccant dehumidifier and thermal recovery unit

The present study aims to construct an innovative configuration of a desiccant air conditioner that achieves thermal comfort conditions with the lowest electrical power consumption rates. To achieve this, an innovative configuration of a desiccant dehumidifier channel with multi-stages of silica-gel pads and heat exchangers for inter-cooling (DDC-MSSGP&HEI) was incorporated with the suggested air conditioner. The DDC-MSSGP&HEI is characterized by increasing the dehumidification capacity as well as cooling the process air with cooling rates higher than the heat generated by the adsorption heat effect. The thermal recovery unit was also incorporated with the suggested air conditioner to achieve the lowest electrical power consumption rates; it was utilized as a preheating unit to heat the regeneration air before entering into the solar collectors. The results showed that the system could supply air with a temperature of 12.2 °C and a humidity ratio of 7 gw kgda−1, this is because of the positive effect of DDC-MSSGP&HEI. Also, the energy performance of the innovative configuration of a desiccant air conditioner is more efficient where TCOP and ECOP reached 1.96 and 3.14, respectively at a regeneration temperature of 90 °C. Moreover, the energy saving due to the utilization of the thermal recovery unit reached 28.7%. The economic feasibility indicates that the proposed configuration has the potential to save the life cycle cost by a rate of up to 33% compared to the conventional system with a payback period of 5.8 years.

Improving energy flexibility of a net-zero energy house using a solar-assisted air conditioning system with thermal energy storage and demand-side management

The increasing penetration of solar energy into buildings can mitigate the great challenges of energy shortage and global warming, while the inherent intermittence of solar energy could endanger power grids. This study investigated the energy flexibility of a net-zero energy (NZE) house using a solar-assisted air conditioning system with integrated thermal energy storage (TES) and demand-side management (DSM) strategies. The main contribution is to investigate and reveal the interactions among the utilisation of solar energy, thermal energy storage, and DSM strategies, to improve building energy flexibility. A simulation system of the NZE house was first developed using TRNSYS. A total of 40 alternative designs of the solar-assisted air conditioning system with TES were formulated by exhausting the combination of the photovoltaic/thermal (PV/T) collectors and a phase change material TES unit, and four DSM strategies including over-heating/cooling, pre-heating/cooling, temperature set-point relaxation, and heat pump charging TES. The results showed that heat pump solar contribution (i.e. the ratio of the energy consumption provided by PV to its total energy consumption) of 0.79 was achieved by using DSM strategies. Using TES unit could further increase solar contribution to nearly 1.0. The influence of the temperature set-point relaxation and over-heating/cooling strategies on energy flexibility was negligible when the over-heating/cooling and/or heat pump charging TES were used. The 1% peak grid import was mostly contributed by the appliances when the designs with high energy flexibility were used. The findings of this study could be used to facilitate the development of NZE buildings with increased energy flexibility.

Economic analysis of a novel solar-assisted air conditioning system with integral absorption energy storage

The application of solar cooling systems is directly linked to the availability of solar radiation. Consequently, energy storage is important to achieve extended cooling coverage. This paper presents the economic performance evaluation of a novel solar-assisted absorption air conditioning system integrated with absorption energy storage (AES). The proposed solar-assisted air conditioning system consists of a parabolic trough solar collector (PTC), parallel-flow double-effect water-lithium bromide (H2O–LiBr) absorption chiller, and AES. In this paper, the economic feasibility of the system is evaluated based on the annuity method. The results indicate a payback period of about 5 years to recover the initial investment of the proposed system for a commercial building based on the weather conditions of the Eastern region of Saudi Arabia. The existing vapour-compression air conditioning system operating alone consumes more energy compared to that when supplemented with the solar-driven absorption chiller with AES. A maximum of 58% energy-saving is achieved from the integrated solar-assisted cooling system in July and August. Furthermore, a solar fraction of 63% is obtained from the integrated solar cooling system. Finally, the annual levelized cost of energy-savings of about 137,944 USD is achieved from the proposed cooling system.

Cooling operation analysis of multienergy systems in a nearly zero energy building

A 4025 m2 office building was built in Beijing, China, in 2014 as a living laboratory and prototype to explore the technical energy systems of nearly zero energy buildings (NZEBs) in China. Not only the building itself but also the heating, ventilation and air conditioning (HVAC) systems were designed with flexibility to explore their performance. Solar-assisted air conditioning (SAAC) and ground source heat pump (GSHP) systems with different terminal units were designed as HVAC systems for either experimental, comparison, or measurement purposes.In this paper, the cooling operation of multienergy systems is discussed on the basis of actual measurement data. HVAC systems have three possible types of operation configuration types, namely, SAAC priority, GSHP only and multimode. Operation scenarios for these configurations are presented first, and the small-scale simulation was carried out to analyze the performance of SAAC priority and GSHP#1 only mode. It indicates that SAAC could save about 47% of energy than that of GSHP#1. Then, the actual operation performance in 2018 was analyzed by reference to the operation data. Through this study, it is found that 1) multienergy systems of SAAC and GSHP operated well in this NZEBs during the summer season; 2) a 10 RT absorption chiller can work well for an NZEB building of approximately 1000 m2 when outdoor enthalpy is low and the solar radiation is stronger than 400 W/m2 as a result of high building thermal performance and air tightness; 3) SAAC can save about 40 to 50% of energy compared to that of GSHP system when providing services for the same terminal system under the same outdoor weather conditions and 4) The GSHP system is a good complement to the SAAC system which works well in June, September and early July when outdoor enthalpy is low. This study indicates that a combination of GSHP and SAAC systems is highly promising for NZEBs in cold climate zones such as Beijing, where the solar radiation is sound.

Simulation of a Solar-Assisted Air-Conditioning System Applied to a Remote School

In this work, we present an absorption cooling system with 35 kW capacity driven by solar thermal energy, installed in the school of Puertecitos, Mexico, an off-grid community with a high level of social marginalization. The cooling system provides thermal comfort to the school’s classrooms through four 8.75-kW cooling coils, while a 110-m2 field of evacuated tube solar collectors delivers the thermal energy needed to activate the cooling machine. The characteristics of the equipment installed in the school were used for simulation and operative analysis of the system under the influence of typical factors of an isolated coastal community, such as the influence of climate, thermal load, and water consumption in the cooling tower, among others. The aim of this simulation study was to determine the best operating conditions prior to system start-up, to establish the requirements for external heating and cooling services, and to quantify the freshwater requirements for the proper functioning of the system. The results show that, with the simulated strategies implemented, with a maximum load operation, the system can maintain thermal comfort in the classrooms for five days of classes. This is feasible as long as weekends are dedicated to raising the water temperature in the thermal storage tank. As the total capacity of the system is distributed in the four cooling coils, it is possible to control the cooling demand in order to extend the operation periods. Utilizing 75% or less of the cooling capacity, the system can operate continuously, taking advantage of stored energy. The cooling tower requires about 750 kg of water per day, which becomes critical given the scarcity of this resource in the community.

Exergy analysis of a solar-assisted air-conditioning system: Case study in southern Spain

This work describes the exergy analysis applied to a single effect LiBr-H2O refrigeration system working together with a flat-plate-collector array. The main objective was to properly match the refrigeration cycle and the heat source. I used the experimental data collected from a solar-assisted air-conditioning system operating in the Solar Energy Research Center (Ciesol). The system employs a flat-plate-collector array, a hot-water single-effect LiBr-H2O absorption chiller, a cooling tower, two hot storage tanks, an auxiliary heater, as well as two chilled water storage tanks. The findings demonstrate that, from the exergetic point of view, I can achieve best results by supplying the absorption chiller with water within a temperature range of 70–80°C supporting it with the action of the chilled water storage tanks. As a result of this analysis, I recognized that there is great optimization potential for the control system of the studied system. At the same time I have ensured a proper balance between the refrigeration cycle and the heat source, making the solar-assisted air-conditioning system less energy intensive and safeguarding environmental protection.

Development and application of a dynamic model for a solar assisted liquid desiccant air conditioning system

The investigation showed that there were few research works about the real dynamic performance of solar-assisted liquid desiccant air conditioning systems with an unsteady term in the governing equations. Regarding the unsteady properties of the components, a novel dynamic model was developed for a solar-assisted internally cooled liquid desiccant air conditioning system. In the model, the variable t (time) was involved in the governing equations of each component to take into consideration the influence of the previous condition on the following state of the system. The accuracy of the above mathematical model was verified partly with experimental results of some key components. Then the model was applied to a real solar-assisted internally cooled liquid desiccant air conditioning system for an office building with the capacity for eight people in Hong Kong. The transient performance of the system on a summer design day in Hong Kong was investigated. The results reflected the necessity of considering the influence of the former state on the following running of the system. In conclusion, the novel model could be a reliable tool to predicate the system operation and provide useful information for better control of the system.

Performance Comparison of Solar Assisted and Inverter Air-Conditioning Systems in Malaysia

© 2017, University of Malaya. All rights reserved. Heating, ventilation, and air-conditioning (HVAC) systems account for approximately 55% o f the total energy consumption in buildings. Different types of cooling technologies that integrate solar thermal energy have been explored because of increasing worldwide energy shortage. Latest air-conditioning systems have achieved improved energy efficiency. The application o f solar energy to various types of HVAC systems proved its huge potential for reducing energy usage. However, solar radiation is highly time dependent and fails to meet building demand. In this study, the potential of a 1.5 HP solar assisted air-conditioning system was evaluated by collecting and using real data, including current, voltage, power, and temperature. The application o f the solar-assisted and inverter-type air-conditioning systems was compared for evaluating their performances. The study was conducted in the northern region of Malaysia, specifically Kedah, in a room with the same as that o f a standard office space. Results showed that the average coefficients o f performance of the solar assisted air-conditioning system ranged from 3.00 to 4.45. This range allows for the optimal consumption of electric energy without wastage. Therefore, the solar-assisted air-conditioning system can provide an environmentally friendly alternative to reducing electricity rates.

Comparison of Different Solar-Assisted Air Conditioning Systems for Australian Office Buildings

This study has investigated the feasibility of three different solar-assisted air conditioning systems for typical medium-sized office buildings in all eight Australian capital cities using the whole building energy simulation software EnergyPlus. The studied solar cooling systems include: solar desiccant-evaporative cooling (SDEC) system, hybrid solar desiccant-compression cooling (SDCC) system, and solar absorption cooling (SAC) system. A referenced conventional vapor compression variable-air-volume (VAV) system has also been investigated for comparison purpose. The technical, environmental, and economic performances of each solar cooling system have been evaluated in terms of solar fraction (SF), system coefficient of performance (COP), annual HVAC (heating, ventilation, and air conditioning) electricity consumption, annual CO2 emissions reduction, payback period (PBP), and net present value (NPV). The results demonstrate that the SDEC system consumes the least energy in Brisbane and Darwin, achieving 56.9% and 82.1% annual energy savings, respectively, compared to the conventional VAV system, while for the other six cities, the SAC system is the most energy efficient. However, from both energy and economic aspects, the SDEC system is more feasible in Adelaide, Brisbane, Darwin, Melbourne, Perth, and Sydney because of high annual SF and COP, low yearly energy consumption, short PBP and positive NPV, while for Canberra and Hobart, although the SAC system achieves considerable energy savings, it is not economically beneficial due to high initial cost. Therefore, the SDEC system is the most economically beneficial for most of Australian cities, especially in hot and humid climates. The SAC system is also energy efficient, but is not as economic as the SDEC system. However, for Canberra and Hobart, reducing initial cost is the key point to achieve economic feasibility of solar cooling applications.

PERFORMANCE OF SOLAR-ASSISTED ABSORPTION CYCLE AIR CONDITIONING SYSTEM

A study of the efficiency of the cycle of solar assisted absorption air conditioning system has been carried out. The absorption cycle system has been in operation in Malaysia, but only in large buildings such as the KL International Airport, government buildings in Putrajaya and KLCC buildings. This study focuses on a small-scale lithium-bromide (LiBr) absorption cycle air conditioning system for residential application. The important component of the system has been designed with the capacity of 3.517 kW cooling load suitable for small-capacity application. Generator, condenser, evaporator and absorber have been designed, fabricated, assembled and tested in the laboratory. A total of ninety-pieces of evacuated tube solar collectors have been installed to produce hot water to be used as a heat source to separate the absorbent and refrigerant. Lithium bromide-water pair was used in this experiment. With the concentration of lithium bromide of 33%, the average coefficient of performance (COP) obtained was 0.446, 0.438 and 0.431 for category A, category B and category C respectively. This study shows that the cycle of solar absorption air conditioning system in small scale can be used in Malaysia and tropical climate countries.

DESIGN a solar hybrid air conditioning compressor system

This thesis presents the investigation into the feasibility of solar assisted vapour compression air conditioning system in providing thermal comfort in Malaysia. Conventional vapour compression air conditioning system consumes large amount of energy which is a clear disadvantage considering the high fuel price and electric tariff. Therefore, this research was intended to develop and integrate solar hybrid system into conventional air conditioning system which provides the same cooling load with considerably less electricity demand. In addition, Microsoft Excel spreadsheet is also prepared to facilitate the calculation of refrigerant temperature and energy saving of the system. DC compressor and evacuated tube solar compressor is introduced to assist the electric compressor in compressing the refrigerant, effectively reducing the air conditioning electricity consumption by up to 45%. Meanwhile, during night time, energy saving is only contributed by the DC compressor which reduces electricity consumption by up to 25%. The development and utilization of solar energy reduces the dependency on energy generation from fossil fuel which emits greenhouse gases and worsen the global warming while also pushing Malaysia one step closer to their aim in reducing CO₂ emissions and harnessing renewable energy. Malaysia as a tropical country with average solar radiation of 4500Wh/m² per day, has endless potential in solar energy (Borhanazad, 2013). This project provides technical overview which involves the study of solar energy conversion system and viability of solar hybrid vapour compression air conditioning system under Malaysia climate.

‘Transition’ from successful solo practice to Clinic Director; MSQ'S story

Australia has a very sunny climate, with a very high demand for air conditioning. Implementing solar assisted air conditioning is an ideal option to achieve a high solar fraction which leads to a significant amount of energy and greenhouse gas emission savings. Solar assisted air conditioning systems are environmentally friendly by being constructed in a way that minimises the need for chlorofluorocarbons CFC, Hydro chlorofluorocarbons HCFC or Chlorofluorocarbons HFC refrigerants and by using a low grade thermal renewable energy, therefore, making them energy efficient and environmentally safe. They can be used either as stand-alone systems or with conventional AC, to improve the indoor air quality. Solar cooling is a new and a fast growing technology compared to other fields of solar energy applications. On the other hand most of the current solar cooling applications are demonstration projects in nature; the technologies are advancing yet still need a lot of additional design, planning, development, and research efforts. T now solar assisted air conditioning's main obstacles are the high installation costs, and the lack of knowledge and familiarity with this technology between designers, developers and architects.In this paper a feasibility study is carried out to assess a solar assisted air conditioning system for an office building under three of Queensland's subtropical climates; Rockhampton, Gladstone, and Emerald. The technical aspects of a proposed solar cooling system are investigated. Cooling load profile for a proposed reference building was obtained using TRNSYS software under the influence of these different climates. An electric vapour compression pump, with 2.5 coefficient of performance (COP) for cooling is used as a reference system to assess the primary energy consumption, assuming 80% of primary energy consumed by the reference conventional system is replaced by solar energy. The results of analysing the proposed system indicated that an 80% of the primary energy savings can be achieved by installing 50 m2 of solar collectors and 1.8 m3of hot water's storage tank under the three selected climates.

Modeling and optimal control of an energy-efficient hybrid solar air conditioning system

Abstract The paper addresses the modeling and optimal control problem of a new hybrid solar-assisted air conditioning system developed for performance enhancement and energy efficiency improvement. To regulate the mass flow rate of the refrigerant vapor passing through a water storage tank for increasing the refrigerant's sub-cooling process at partial loads, we propose a new discharge bypass line together with an inline solenoid valve, installed after the compressor. In addition, to control the air flow rate, a variable speed drive is coupled with the condenser fan. For the control purpose, a lumped parameter model is first developed to describe the system dynamics in an explicit input–output relationship; then, a linear optimal control scheme is applied for the system's multivariable control. The system has been fully-instrumented to examine its performance under different operation conditions. The system model is then validated by extensive experimental tests. Based on the obtained dynamic model, an optimal controller is designed to minimize a quadratic cost function. Numerical algorithms, implemented in a simulation tool, are then employed to predict the energy performance of the system under transient loads. The experimental results obtained from implementation with PLC demonstrate that the newly-developed system can deliver higher system efficiency owing to amelioration of the refrigeration effect in the direct expansion evaporator and adjustment of its air flow rate. The development is thus promising for improvement of energy efficiency, enhancement of the system performance while fulfilling the cooling demand.

Reducing a solar-assisted air-conditioning system’s energy consumption by applying real-time occupancy sensors and chilled water storage tanks throughout the summer: A case study

This study describes an innovative occupancy and chilled-water storage-based operation sequence implemented in a solar-assisted air-conditioning system. The core purpose of this solar-assisted air-conditioning system is to handle the cooling and heating load of the Solar Energy Research Centre (CIESOL), thus minimising its environmental impact. In this study, the cooling mode was investigated with special attention focused on the chilled-water storage circuit. The critical concern is that the solar-assisted air-conditioning system should always operate considering the actual load conditions, not using an abstract maximum load that is predetermined during the system’s design process, which can lead to energy waste during periods of low occupancy. Thus, the fundamental problem is to identify the optimum operation sequence for the solar-assisted air-conditioning system that provides the best energy performance. The significance of this work lies in the demonstration of a new operation strategy that utilises real-time occupancy monitoring and chilled-water storage tanks to improve the efficiency of solar-assisted air-conditioning systems, thereby reducing their electricity consumption. Adopting this strategy resulted in a large energy-saving potential. The results demonstrate that during one cooling period, it is possible to conserve approximately 42% of the total electrical energy consumed by the system prior to the adoption of this operation strategy.

Performance of a solar assisted air conditioning system at different locations

HVAC systems are the most energy consuming devices among building components. Therefore, to achieve the global aims in energy reduction, the efficiency of HVAC systems has to improve significantly. Thermally driven air conditioning systems are a possible way to reduce the dependency on traditional vapor compression cycles and to lower the primary energy consumption. Due to the separation of dehumidification and cooling, natural heat sources, e.g. solar thermal energy, and natural heat sinks, e.g. shallow geothermal energy, can be used or, when combined with a traditional vapor compression cycle, the temperature level of the heat sink can be increased. With the separation of cooling and ventilation the overall efficiency can be increased even more.This paper introduces a pilot installation of a solar thermal and geothermal assisted air conditioning system located in Hamburg, Germany. The combination of a desiccant assisted air conditioning system with radiant heat exchanger enables a highly efficient HVAC system. Due to the strong influence of outdoor air conditions, a system model is built to evaluate the performance of this system at different climate conditions worldwide. This paper presents an energy and economic evaluation of a highly efficient HVAC system at different geographical locations.

Technical and economic analysis of a solar-assisted air-conditioning system

This paper presents analysis aiming at assessing the feasibility and economic performance of a solar-assisted air-conditioning system for a middle class house under the climatic conditions of Tunis City. Two alternative cooling modes for the single effect water-lithium bromide absorption machine are considered, a water-cooling in association with a cooling tower and air-cooling. The numerical simulations show that for the water-cooling case, a solar system with 18 m2 of evacuated tube collector area and a thermal storage tank of 1.3 m3 maintained at a temperature of 95°C can cover 50% of the energy needs of the machine. The corresponding optimal results for the air-cooled chiller are: energy needs coverage 40%, hot water tank capacity 1 m3 at 110°C, collector area 14 m2. The annually total costs for the case of water-cooling and air-cooling are respectively 3.52 €/kWh and 2.51 €/kWh.