Title
The Market available Solar Thermal assisted vapor compression air conditioning system. Is it energy efficient in its recent design?
Abstract
Keywords
Energy Efficiency, solar cooling, Residential Cooling, Solar Thermal assisted-air conditioning systems, Vapor compression air conditioning.

Introductions
Continuing increase in the global Energy consumption, fossil fuel depletion, the increasing cost of the electricity and the Global warming are the main reasons to search for and development of renewable and sustainable solutions. Conventional Air conditioning is significantly contributing to the peak electricity demand in the cooling season especially in countries located in a hot area. So that most research in academia and industry focuses to find alternative Reliable Energy sources, of which solar energy represent a very promising Solution as it is abundantly present and environmentally sustainable. Solar cooling Technology has attractive features as the cooling load profile within the buildings matches the incident solar radiation during the cooling season 6.

Solar cooling technology offers a significant contribution to both economic and ecological energy supply. Solar thermal assisted air conditioning systems are utilizing low-level energy, that providing cold energy through solar energy. This technology is more than ever representing a huge potential for improvement of solar energy 6. Bouraba et al. 10 cited that the solar cooling is among the Energy conservation strategies that represented from 30% up to 80% Energy saving with high-cost ranking compared to Operational management, Reduction of cooling loads, Buildings envelop modifications and Equipment modifications Methodologies. Egypt Residential Sector is the dominant energy consumption, it consumed approximately 47.2% of the total electricity consumption in comparison to industry and other purposes, and Most of this percentage is consuming in the air conditioners appliances 12.

Bellos et al. 4 cited that the most usual systems for using solar energy for refrigeration are adsorption chillers, absorption chillers, ejectors, desiccant wheels and hybrid systems. Ha and Vakiloroaya 5 cited that with current researches that focus into solar cooling technology it’s estimated of around 35–45% reduction in the total system cost by 2030.

Haw et al. 9 provided a technical overview and economic feasibility of a solar assisted air conditioning system under Malaysian climatic conditions. They investigated the Performance and operation parameter of the solar assisted air conditioning system adsorption and absorption chillers, market challenges, performance efficiency. They concluded that the Solar assisted air conditioning system is still at its beginning stage, there are still no standardized design procedures that exist and still, shortage of operational experiences and Solar assisted air conditioning system has a high capital investment but with a payback period of 8 years.

Baniyounes et al. 10 presented a technical review and recent developments in solar assisted air conditioning technologies in subtropical regions, Australia. They concluded that the solar assisted air conditioning can play a major role in Energy savings, reducing greenhouse gas emissions and will enhance indoor air quality. Solar assisted air conditioning is fast growing technology, compared to other fields of solar energy application. Designers, developers and business owners do not need to think only about the economic aspects of these technologies, they must focus on that these technologies contribute towards zero emissions buildings and their energy independence. Prices Reduction in manufacturing techniques of solar cooling equipment in addition to increasing solar collectors’ performance will improve the system feasibility and performance.

Ali 6 evaluated through experimental data the performance, energy efficiency, cost competitiveness and global warming assessments of residential-scale solar thermal, adsorption chiller air-conditioning system versus a conventional system in hot, arid areas, also presented a comparison both between previous systems with an off-grid PV driven air conditioning system And determine the suitable system for a hot, ride area, through a comparison parameters, Performance, cost and global warming assessments. Results showed that the off-grid PV driven DC air conditioning system can be recommended for use in residential sector application compared to conventional and Adsorption chiller air conditioning systems.

Anjali et al. 7 Evaluated and investigated through experimental data the performance of a Solar Thermal assisted vapor compression air conditioning system and presented an introduction about general features advantages and disadvantages of this system. In this system, the refrigerant gas goes to the water storage tank at high temperature and pressure from the compressor through the COPPER COIL for heat exchange, to reach the sufficient superheat temperature in order to reduce the uses of electrical energy. Results showed that the coefficient of performance (COP) of the examined system reach approx. 5.

Bellos et al. 4 Cited that the conventional vapor compression air conditioning system operates with a coefficient of performance close to 3.

Bellos et al. 4 presented and examined theoretically and through simulation tools, a Solar Thermal assisted vapor compression air conditioning system. In this system The compression process of the refrigerant is carryout through two stages, first one through a conventional way with the compressor and the second is accomplished inside Mutable a CLOSED VESSELS operating alternatively through an isochoric Heating process accomplished in an evacuated tube Solar collectors delivers the required heat to the refrigerant in order to increase its pressure To the desired levels. Results showed that the energy saving of this system range from 15% to 25%, the specific solar collector area compared to other Conventional systems is relatively low, close to 2 m2/kW for the best cases and the new design leads to energy savings in all the studied cases and especially with higher evaporating temperature.

Assadi et al. 2 presented Theoretical design through Thermodynamics analysis and simulation tools a Solar Thermal assisted vapor compression air conditioning system, to decrease Energy consumption by up to 45%. They Selected five conventional air conditioner models with different capacity ranging for investigation, ANSYS-FLUENT software used to sizing the solar collector which simulate to heat up the refrigerant temperature up to 160°C based on solar radiation data at in University Technology Petronas in Malaysia. Then, redesign the condenser to be able to cool down the refrigerant to 40°C. Compared the simulation results with theoretical calculations Also Verify the results from an experiment of additional investigators using the actual air conditioner and the solar collector to determine the energy saving. Results showed that the highest maximum achieved energy saving of 44.4% for One of the studied modules, Energy saving came from Additional thermal compression due to the solar collector which provides the compression pressure by heating the refrigerant under CONSTANT VOLUME, More Increasing refrigerant temperature due to solar collect will lead to more system energy saving, Maximum energy saving reach when the refrigerant temperature reached 160°C at the outlet of solar collector this is for R22 Refrigerant and The condenser need to be 45% longer whatever the model.

Bouraba et al. 11 investigated theoretically the performance of Solar thermal assisted a vapor compression air conditioning system, presented a Comparisons between the conventional vapor compression air conditioner system and the Solar assisted air conditioner system, Comprised the performance of three types of refrigerants R-1234ze, R-134a and R-410A. The refrigerant leaving the compressor, as superheated vapor, goes through IMMERSED COIL inside the storage tank. A portion of the Heat received from the solar collector is used to heat the superheated vapor at CONSTANT VOLUME until the condensation Pressure of the conventional system is achieved. As the refrigerant temperature leaving the storage tank increases by increasing solar collector temperature, the compressor discharge temperature and its corresponding pressure decreased which lead to increase compressor lifetime and decrease power consumption. Results showed that the solar assisted vapor compression air conditioner system has the higher coefficient of performance than the conventional vapor compression air conditioner system, R-1234ze (E) would be a suitable alternative for both conventional vapor compression and solar assisted vapor compression air conditioner systems.

Ha and Vakiloroaya 1 presented experimentally an effective method to improve the performance of a solar thermal assisted vapor compression air conditioning system. This method focused on Control refrigerant flow rate to the optimum value according to the desired temperature after the condenser, by Using a by-pass line combined with a three-way proportional control valve after the compressor to regulator the refrigerant flow rate. The refrigerant flow rate is controlled as a function of the refrigerant temperature leaving the compressor, the refrigerant temperature leaving the solar storage tank and the ambient dry-bulb temperature. Results showed that the efficiency of the new design is more than the conventional systems, the average COP by using the optimal set-point values is around 6.7% and the new design leads to decrease refrigerant temperature entering and leaving the condenser.

Ha and Vakiloroaya 5 Modified and improved experimentally the performance of a solar thermal assisted vapor compression air conditioning system. A new discharge bypass line together with solenoid valve, installed after the compressor for regulating the mass flow rate of the refrigerant that passes through a water storage tank, In order to increase the refrigerant’s subcooling process at partial loads. During partial loads, when the condensing temperature is low, the refrigerant leaving the compressor is normally enough for heat rejection process through the condenser and so the valve opens, allowing the refrigerant to go through the new by-pass line directly to the condenser inlet. During a high cooling demand when the condensing temperature is high, the solenoid valve is closed, directing the refrigerant from the compressor into the COPPER COIL inside the storage tank, where it acquires an amount of additional heat from the hot water. Experimental Results showed that the power consumption for the suggested control system showed 14% energy savings, The temperatures of refrigerant leaving both the storage tank and condenser decrease under the proposed control scheme and The comparison study using simulation results indicated that the enthalpy of refrigerant entering the expansion valve with and without the new configuration is found to reduce about 8.5%.

References
1 Ha Q. and Vakiloroaya V. 2012, A novel solar assisted air-conditioner system for energy savings with performance enhancement, Procedia Engineering 49 (2012) 116 – 123
2 Assadi M., Gilani S. and Yen T. 2016, DESIGN a solar hybrid air conditioning compressor system, MATEC Web of Conferences 38, 02001 (2016), EDP Sciences
4 Bellos E., Vrachopoulos M., Tzivanidis C. 2017, Energetic and exergetic investigation of a novel solar assisted mechanical compression refrigeration system, Energy Conversion and Management 147 (2017) 1–18
5 Ha Q. and Vakiloroaya V. 2014, Modelling and optimal control of an energy-efficient hybrid solar air conditioning system, Automation in Construction 49 (2015) 262–270
6 A.H.H. Ali. 2017, performance-cost and global warming assessments of two residential scale solar cooling systems versus a conventional one in hot arid areas, Sustainable Energy Technologies and Assessments 20 (2017) 1–8
7 Anjali, Buddhi D., Kumar N. and Singh K., 2016, Performance Analysis of a Solar Hybrid Air Conditioner with Waste Heat Recovery and Re-Use Using Evacuated Tube Collector, International Journal of Science, Engineering and Technology, Volume 4 Issue 2: 2016, pp. 436- 440.

9 Haw L., Sopian K. and Sulaiman Y. 2009, An Overview of Solar Assisted Air-Conditioning System Application in Small Office Buildings in Malaysia, the 4th IASME / WSEAS International Conference on ENERGY ; ENVIRONMENT (EE’09)
10 Baniyoun A., Ghadi Y., Rasul M. and Khan M. 2013, An overview of solar assisted air conditioning in Queensland’s subtropical regions, Australia, Renewable and Sustainable Energy Reviews 26 (2013) 781–804
11 Bouraba A., Saighi M., Saidani-Scott H and Hamidat A. 2017, Cooling mechanism of a solar assisted air conditioner: An investigation based on the pressure-enthalpy chart, International Journal of Refrigeration 80 (2017) 274 – 291
2 Egyptian Electricity Holding Company, Annual Report 2015 / 2016

Air conditioning utilization has been increased since the last decade as a result of the effect of climate change and global warming.

Increasing energy consumption with its impact on environmental issues has led to more focus in the use of renewable energies driven cooling systems in the last years with a concentration on solar energy as an energy driven source.

Increasing energy cost, decreasing fossil fuel resources and rising environmental pollution, are the key factors to utilize low-level renewable energy sources as solar energy in refrigeration systems in order to address these problems.

Conventional air-conditioning systems require high-level energy, electricity that generated from primary energy resources.

Most of the buildings’ cooling demands in cooling season are associated with the high availability of solar radiation, especially in a hot area which can represent an opportunity for additional solar energy exploiting for cooling.

Conventional air conditioner systems are not economical in the long run, due to High fuel price and electricity tariff. Moreover, generating electricity from fossil fuel produces a great number of greenhouse gases and deteriorate the global warming.