Silica Gel Water Adsorption Research Articles

Performance-cost and global warming assessments of two residential scale solar cooling systems versus a conventional one in hot arid areas

In this study, performance evaluation, energy efficiency, cost competitiveness and global warming assessments of residential scale solar thermal, a silica gel-water adsorption chiller, air-conditioning system versus a conventional system in hot, arid areas is carried out. This has been done throughout an applied research project with site measurements in which the two cooling systems were designed, build and operated at Assiut, Egypt with both systems has a nominal cooling capacity of 8kW. In addition, a comparison with an off-grid PV driven direct current (DC) with 8kW air cooling conditioning system is made with the above two systems. The comparison is based on the lifespan of 20years and 18h’ daily operation during the cooling session. The experimental results show that the indoor thermal comfort conditions are achieved in the hottest days of the year for an area of an 80-meter square with 14 occupants and lab equipment. From the results, clearly, the solar thermal driven cooling system has an energy consumption of 10.94%, with Total Equivalent Warming Impact (TEWI) of 9.96% and total cost per kW cooling of 295.96% compared with the conventional vapor AC driven air-conditioning system. While, the off-grid PV driven air conditioning system has 0% energy consumption from the grid with TEWI value of 0.648% and total cost per kW cooling of 54.88%, respectively. Therefore, the off-grid PV driven DC air conditioning system can be recommending for use in residential sector application in hot, arid areas based on its low cost per kW cooling, zero grid energy consumption, and very low Total Equivalent Warming Impact value.

Performance of a small-scale solar-powered adsorption cooling system

ABSTRACTIn this study, an experimental investigation on the performance of a small-scale residential-size solar-driven adsorption (silica gel-water) cooling system that was constructed at Assiut University campus, Egypt is carried out. As Assiut area is considered as hot, arid climate, field tests for performance assessment of the system operation during the summer season are performed under different environmental operating conditions. The system consists of an evacuated tube with a reflective concentration parabolic surface solar-collector field with a total area of 36 m2, a silica gel-water adsorption chiller of 8 kW nominal cooling capacity, and hot and cold water thermal storage tanks of 1.8 and 1.2 m3 in volume, respectively. The results of summer season field test show that under daily solar insolation varying from 21 to 27 MJ/m2, the solar collectors employed in the system had high and almost constant thermal efficiency. The daily solar-collector efficiency during the period of system operation ranged from about 50% to 78%. The adsorption chiller performance shows that the chiller average daily coefficient of performance (COP) was 0.41 with the average cooling capacity of 4.4 kW when the cooling-water and chilled-water temperatures were about 31°C and 19°C, respectively. As the chiller cooling water is cooled by the cooling tower in the hot arid area, the cooling water is at a higher temperature than the design point of the chiller. Therefore, an experiment was carried out using the city water for cooling. The results show that an enhancement in the chiller COP by 40% and the chilling power by 17% has been achieved when the city water was 27.7°C.

Design optimization of a residential scale solar driven adsorption cooling system in upper Egypt based

This study provides a decision support approach for selecting the best size of the main components of a small scale solar assisted, silica gel-water, adsorption cooling system in arid areas located in Assiut, Egypt. To achieve the objective of this work, an optimization based on a computer simulation has been performed on the design variables, which are: solar collector area, the volume of the hot storage tank, the volume of the cold storage tank, and thermostat set point of the auxiliary heating element. Economic and environmental evaluations of the proposed systems have been performed as well. A validation of the model results is performed with the experimental results of solar driven silica gel-water adsorption cooling system at Assiut University Campus which has worked since 2012. The results show that the tilt angle of 5° for the surface of the solar collectors achieved the best absorbed solar radiation by the collector filed. For all proposed systems, the solar fraction did not affect the volume of the cold water storage tank while it has a significant effect on the area of the solar collector field and as well as the volume of the hot water storage tank. The initial cost of the proposed systems ranges from 2897€/kWc to 4808€/kWc and this can be considered as a hindrance to spreading at the commercial level. Meanwhile, the running cost over a year achieves low values, and it ranges from 13.9€/kWc to 99.11€/kWc.The proposed systems of lower solar fraction give lower carbon dioxide emissions. The carbon dioxide emissions range from193kg of CO2eq./kWc per year for the fully solar driven cooling system to 1062kg of CO2eq./kWc per year for the cooling system fully driven by natural gas. Based on the solar saving approach the proposed system of 24m2 solar collector area, 0.6m3 hot storage tank, and 1m3 cold storage tank with 94°C auxiliary heater set-point temperature can be considered as the most economically feasible solution.

Study of sorption based energy storage system with silica gel for heating application

In this paper, a thermal analysis of the closed silica gel-water adsorption heat storage system is presented. Such systems have the advantage of high energy density and can be used repetitively without the heat loss to the surroundings, contrary to the sensible and latent heat storage systems. The system is designed to store 18kWh of heat and to deliver it at 3kW for 6h at an average temperature lift of 25K at any later time. Analyses are done to determine the required mass of the silica gel and heat transfer parameters to achieve the desired heating capacity. It is found that 350kg of silica gel with a heat exchanger capacity of 400W/K is needed for the above performance, at a condenser and evaporator temperatures of 30 and 25°C respectively. Under these conditions an energy density of 42kWh/m3 is obtained with an exergetic efficiency of 73%.

Study of a two-bed silica gel–water adsorption chiller: performance analysis

ABSTRACTIn this study, a lumped parameter simulation model has been developed for analysis of the thermal performance of a single-stage two-bed adsorption chiller. Since silica gel has low regeneration temperature and water has high latent heat of vaporisation, silica gel–water pair has been chosen as the working pair of the adsorption chiller. Low-grade waste heat or solar heat at around 70–80°C can be used to run this adsorption chiller. In this model, the effects of operating parameters on the performance of the chiller have been studied. The simulated results show that the cooling capacity of the chiller has an optimum value of 5.95 kW for a cycle time of 1600 s with the hot, cooling, and chilled water inlet temperatures at 85°C, 25°C, and 14°C, respectively. The present model can be utilised to investigate and optimise adsorption chillers.

Design and experimental study of a silica gel-water adsorption chiller with modular adsorbers

A silica gel-water adsorption chiller driven by low-grade heat is developed. System configuration without any vacuum valves includes two sorption chambers, a 4-valve hot/cooling water coupled circuit and a 4-valve chilled water circuit. Each sorption chamber is composed of one adsorber, one condenser and one evaporator. The design of this chiller, especially the design of modular adsorber, is suitable for low-cost industrial production. Efficient and reliable heat and mass recovery processes are also adopted. This chiller is tested under different conditions and it features the periodic variations of temperatures and cooling power. Through the experimental study, the optimal cooling time, mass recovery time and heat recovery time are 720 s, 40 s and 24 s, respectively. Besides, the obtained cooling power, COP and SCP are 42.8 kW, 0.51 and 125.0 W kg−1, respectively, under typical conditions of 86/30/11 °C hot water inlet/cooling water inlet/chilled water outlet temperatures, respectively.

A study of a wind catcher assisted adsorption cooling channel for natural cooling of a 2-storey building

This study proposes a new system composing of a wind catcher and a solar driven two-bed silica gel–water adsorption chiller in order to provide natural cooling of a two-story building. The wind catcher provides the required ventilation, and the air flowing though the wind catcher is cooled by the cooling plates fed by the adsorption chiller. The performance of the system is studied theoretically under different ambient conditions such as wind velocity, solar radiation, air temperature and relative humidity. In addition, the influence of geometric parameters such as size of the apertures, wind catcher's height and dimensions of the cooling plates and the number of them are studied. Furthermore, the system's capability to provide thermal comfort in the living space is investigated. It is found that at lower ACH (air change per hour) values, inlet air's temperature and absolute humidity reduce more. In addition, with the rise of the cooling plates' length, the cooling effect increases. The results indicated that with the increase of ACH values, thermal comfort condition is achieved for larger cooling demands. Furthermore, the system was found to be able to cool the air between 10 and 20 °C under different ambient conditions.

Solar driven air conditioning and refrigeration systems corresponding to various heating source temperatures

Solar driven air conditioning systems can cope with solar collectors working in a wide range of temperatures. Sorption systems, including absorption and adsorption refrigeration systems, are among the best choices for solar cooling. Five systems including modular silica gel–water adsorption chiller, single/double effect LiBr–water absorption chiller, 1.n effect LiBr–water absorption chiller, CaCl2/AC (activated carbon)–ammonia adsorption refrigerator, and the water–ammonia absorption ice maker with better internal heat recovery were presented. The above five sorption chillers/refrigerators work under various driven temperatures and fulfill different refrigeration demands. The thermodynamic design and system development of the systems were shown. All these systems have improvements in comparison with existing systems and may offer good options for high efficient solar cooling in the near future.

Cycle Optimization on Reheat Adsorption Cycle Applying Fixed Chilled Water Outlet Temperature

This study investigated the cycle optimization of four-bed, silica gel–water adsorption with reheat cycle, where the desorber (upper bed) and adsorber (lower bed) always interact with the condenser and evaporator, to exploit a low heat-source temperature. In a previous study, the performance of a reheat cycle with chilled water outlet temperature fixed at 9°C was observed without considering the cycle optimization. Maintaining a constant chilled water outlet temperature is also of equal importance to improve the conversion efficiency so that maximum cooling capacity can be derived. In this paper, a simulation model of reheat adsorption cycles is developed to analyze the optimization of the cycle time, including adsorption/desorption time, mass recovery time, and preheating/precooling time, with chilled water outlet temperature fixed. The reheat working principle is also introduced. The proposed cycle is compared with the four-bed versison without reheat cycle in terms of coefficient of performance (COP) and cooling capacity. The result shows that the performance of a reheat cycle is superior to that of four-bed version without reheat, especially for low heat-source temperature. For low heat-source temperature (55–65°C) both COP and cooling capacity of the reheat cycle with optimization were raised significantly compared to the high heat-source temperature (70–80°C).

Performance Study of a Four-Bed Silica Gel-Water Adsorption Chiller with the Passive Heat Recovery Scheme

Adsorption chiller technology is one of the effective means to convert waste thermal energy into effective cooling, which substantially improves energy efficiency and lowers environmental pollution. This paper uses an improved lump-parameter design model to theoretically and experimentally evaluate the efficacy of the passive heat recovery scheme as applied to a four-bed adsorption chiller. Results show that the model can accurately track the experimental temporal system outlet temperatures. The performance predictions from this model compare favourably with experimental results. At rated temperature conditions and over a wide range of cycle times, both the cooling capacity and COP can be predicted to within 12.5%. The analyses indicate that the model can be used confidently as a design tool for a four-bed adsorption chiller and the passive heat recovery scheme can effectively improve the system performance.

Performance simulation of multi-bed silica gel-water adsorption chillers

Adsorption chiller technology is one of effective means to convert waste thermal energy into cooling, which substantially improves energy efficiency and lowers environmental pollution. This article develops an improved lumped-parameter model for multi-bed silica gel-water adsorption chillers. It is validated by experimental results stemming from a four-bed silica gel-water adsorption chiller at various operating conditions. It is found that the performance predictions from this model compare favourably with experimental results. At all tested conditions and over a wide range of cycle times, the cooling capacity and COP can be predicted to within 10% and 12%, respectively.

Experimental performance investigation of small solar air-conditioning systems with different kinds of collectors and chillers

Different types of solar collectors should be integrated with different sorption chillers. Traditional evacuated tube U pipe solar collector, high efficient CPC (Compound Parabolic Concentrating) solar collector and PTC (Parabolic Trough Collector) solar collector can provide 60–85°C, 85–125°C and 125–150°C of hot water. So, they can drive silica gel–water adsorption chillers, single-effect LiBr absorption chillers and double-effect LiBr absorption chillers, respectively. This paper will present the experimental performance investigation and economic analysis of three small solar cooling systems with these different kinds of collectors and chillers. The test results show that the solar COP (Coefficient of Performance) of the solar cooling system with adsorption chiller and U pipe solar collectors is about 0.15 and the silica gel–water adsorption chiller can be driven by 55°C of hot water. The solar COP of the system with CPC solar collector and single effect absorption chiller can reach 0.24 in the sunny weather condition. The solar COP of the solar cooling system with PTC solar collectors is about 0.5 and the double-effect LiBr absorption chiller is more attractive because of its higher solar COP (Coefficient of Performance) and better economy.

Study on a solar heat driven dual-mode adsorption chiller

Environmental concerns and the rising energy cost necessitate looking for renewable energy driven environmentally benign adsorption cooling systems. Solar powered adsorption chillers with non-concentrating flat plate or evacuated tube collectors face the problem of not getting adequate driving source temperature during some months of the year. Multi-staging of the adsorption cycle is then needed to exploit the low driving source temperature. A simulation study of a solar thermal driven dual-mode, four-bed silica gel–water adsorption chiller is undertaken in this work. The solar thermal collector data of Durgapur (23.48 °N, 87.32 °E), India has been used as the heat source for the dual-mode chiller. For a driving source temperature above 60 °C, the chiller works as a single stage four-bed adsorption chiller; while the chiller functions as a two stage adsorption chiller when the driving source temperature falls below 60 °C. With a cooling water temperature of 30 °C, this two stage chiller has been found to produce cooling effect with a driving source temperature as low as 40 °C. Results indicate that the dual-mode chiller is capable of providing cooling throughout the year under the climatic condition of Durgapur, India.

Progress in silica gel–water adsorption refrigeration technology

Abstract The silica gel–water adsorption refrigeration has attracted much attention especially in the last two decades, due to its environmentally friendly refrigeration that can be powered by low grade heat source. In this paper, we reviewed the research about silica gel–water adsorption technology, cooling systems as well as heat pumps. The technological developments of silica gel–water adsorption refrigeration, including working pairs, heat and mass transfer, cycle and system design, simulation work, prototypes and applications, were discussed. The advantages of silica gel–water adsorption refrigeration technology as well as its disadvantages were elucidated. Finally, the prospect of this refrigeration method was analyzed. The weak heat and mass transfer performance of the adsorbent material was the main bottleneck of the silica gel–water adsorption refrigeration technology and resulting in large size, low performance and high cost.

Study of adsorption characteristics in silica gel–water adsorption refrigeration

As one of environmentally friendly refrigeration methods, solid adsorption refrigeration has tracked much interest over the world. Silica gel is popularly used in adsorption refrigeration systems as the adsorbent. Like a compressor in a compression refrigeration system, the adsorbent is vital to the performance of adsorption refrigeration systems. In this work, many different silica gel samples were prepared according to their application surroundings in silica gel–water adsorption refrigeration systems. The adsorption characteristics including variations, deterioration, and improvements of the adsorption property were detected. The specific surface area, silanol content, adsorption capacity, and pore size distributions of those samples were tested. The corresponding adsorption isotherms were achieved. The experimental results indicated that the adsorption capacity of the silica gel was influenced by many factors. But pollution by solid particulates was the primary factor to decline the adsorption capacity.

Investigation of adsorption performance deterioration in silica gel–water adsorption refrigeration

Silica gel acts as a key role in adsorption refrigeration systems. The adsorption deterioration must greatly impact the performance of the silica gel–water adsorption refrigeration system. In order to investigate the adsorption deterioration of silica gel, many different silica gel samples were prepared according to the application surroundings of silica gel in adsorption refrigeration systems after the likely factors to cause such deterioration were analyzed. The specific surface area, silanol content, adsorption capacity and pore size distribution of those samples were tested and the corresponding adsorption isotherms were achieved. In terms of the experimental data comparisons, it could be found that there are many factors to affect the adsorption performance of silica gel, but the pollution was the primary one to decline the adsorption capacity. In addition, the adsorption performance of the deteriorated samples after being processed by acid solution was explored in order to find the possible methods to restore its adsorption performance.

Adsorption cooling driven by solar collector: A case study for Tokyo solar data

An analytical investigation has been performed to study the possibility of application of solar cooling for the climatic condition of Tokyo, Japan. Silica gel–water adsorption cooling system has been taken into consideration for the present study and lumped parameter model is used to investigate the performance of the system. Based on the solar radiation data it is found that at least 15 collector (each of 2.415m2) is required to achieve the required heat source temperature (around 85°C) to run the cooling unit. It is also observed that the solar powered adsorption cooling unit provides cooling capacity around 10kW at noon with base run conditions, while the system provides solar COP around 0.3, however, the solar collector size can be reduced by optimizing the cycle time.

Simulation of operating characteristics of the silica gel–water adsorption chiller powered by solar energy

Abstract A lumped parameter model of a silica gel–water adsorption chiller driven by solar energy was introduced for the operating characteristics investigation. Matlab–Simulink, as a high-performance computing and programming tool, was used to simulate the operating characteristics of the chiller. Effects of the hot water tank capacity, the cycle time and the initial hot water temperature on the performance of the chiller were analyzed when the chiller was driven by a stable heat source and solar energy respectively. The simulation results indicated that when the chiller was driven by solar energy, the open circulation of the hot water with a short cycle time and the closed circulation of hot water with a longer cycle time were better. A proposal was also provided for the chiller driven by solar energy to work under the optimum working conditions, such as hot water circulation mode, cycle time and initial temperature.

Resorption system with simultaneous heat and cold production

A resorption system with simultaneous cold and heat production was studied. The heat produced could be used for sanitary or process purposes, or to drive another heat-powered machine. The resorption reactors had MnCl 2 and NH 4Cl as reactant (which are impregnated in expanded graphite) and NH 3 as refrigerant. The combined coefficient of performance and amplification (COPA) of this system reached 1.3 when the cooling effect was produced at 0 °C and heating effect at 75 °C with the regeneration temperature of 140 °C. Its COP was 0.35 with a specific cooling power (SCP) of 1.12 MJ kg −1 day −1, and the heat sink in this case remained below the cooling temperature for more than 5 h. Because of the heat production at certain temperature level (from 70 °C to 80 °C) in this study, the released heat could be used to power a silica gel-water adsorption chiller and the overall COP of the combined system would increase dramatically.

Performance research of a micro-CCHP system with adsorption chiller

This paper describes a new micro-combined cooling, heating and power (CCHP) system, which is especially suitable for domestic and light commercial applications. It mainly consists of a natural gas-fired internal combustion engine, a silica gel-water adsorption chiller and other heat recovery units. In order to study the energy efficiency and economic feasibility, an experimental investigation has been carried out. The experimental system has a rated electricity power of 12 kW, a rated cooling capacity of 9 kW and a rated heating capacity of 28 kW. Evaluation and analysis of the system are discussed in detail. The testing results show that the energy efficiency of the overall system depends on different modes. The overall thermal and electrical efficiency is over 70%. Higher heat load supplied causes higher efficiency of the system. Economic evaluation shows that the micro-CCHP system enjoys a small capital cost and short payback period, which is easily accepted by customers. At current natural gas price of 1.9 RMB/m3 (nominal condition) and electric price of 0.754 RMB/(kW·h), the total capital cost is only 90 000 RMB with a payback period of 3.21 years.