Chilled Water Inlet Temperature Research Articles

Performance of a 5 kW hot water driven diffusion absorption chiller

This paper presents experimental results of a 5kW Diffusion-Absorption Chiller (DAC). The chiller has been tested at varying inlet generator temperatures, inlet cooling water temperatures and inlet chilled water temperatures. The lowest driving temperature to keep the bubble pump running was about 90°C with 3.6kW cooling capacity and chilled water inlet temperature being set at 18°C. The maximum cooling capacity and COP reached for the DAC was about 4.52kW and 0.45, respectively. The prototype has demonstrated a good potential for air-conditioning applications, while not requiring electricity internally for its operation and allowing coupling with waste heat or solar thermal collector systems.

Experimental evaluation of a triple-state sorption chiller

This paper presents the experimental testing results of a novel triple-state sorption chiller with integrated cold storage. The performance of the chiller was measured for hot water inlet temperatures between 65 °C and 95 °C, heat rejection inlet temperatures between 15 °C and 35 °C, and chilled water inlet temperatures between 10 °C and 25 °C. An empirical model was developed for implementation in the TRaNsient SYstem Simulation (TRNSYS) software. To validate the model, a five-hour experimental charge test was conducted during which the hot water and heat rejection inlet temperatures were continuously varied. The model was able to predict the total heat input and heat rejection energy to within 0.7% and 1.3% of the experimentally measured values, respectively.

Adsorption chiller using flat-tube adsorbers – Performance assessment and optimization

The performance of two-bed silica gel-water adsorption chiller using flat-tube adsorbers is modelled in wide range of operating conditions: heating water inlet temperature in the range of 50–90°C, cooling water inlet temperature in the range of 20–35°C, chilled water inlet temperatures of 10°C and 15°C, switching time 420s and silica gel grain size 0.3mm. In order to improve Coefficient of Performance (COP) and Specific Cooling Power (SCP) of the chiller optimization of fin height and spacing of the flat-tube heat exchanger is carried out. Flat-tube heat exchangers are found to be suitable for application as silica gel-water adsorbers. They are characterized by distinctive SCP (up to 750Wkg-1). Optimization of flat-tube adsorbers geometry led to improvement of COP up to 3.7% and SCP up to 6.3%.

A field investigation of a solar-powered adsorption cooling system under Guangzhou's climate with various numbers of heat exchangers in the adsorbers

In the current study, a solar-powered double-bed adsorption cooling system has been built and tested in the Guangzhou climate. The effect of the pre-heating process on the cooling performance of the adsorption cooling system powered by solar energy has been experimentally investigated. A specific cooling power of 52.2 W/kg and a coefficient of performance of 0.20 were achieved under a 2-h pre-heating process with operating conditions of 26°C cooling water inlet temperature, 16°C chilled water inlet temperature, 8 L/min hot water and cooling water flow rate, 2 L/min chilled water flow rate and 600 s adsorption/desorption phase time. The average specific cooling power and coefficient of performance were improved by 26.1% and 33.3%, respectively, as compared to the case without conducting the pre-heating process. In addition, the influence of dead volume on the specific cooling power and coefficient of performance of the adsorption cooling system has also been investigated. Using various numbers of heat exchangers in the adsorber achieved different values of adsorber dead volume. The results show that a higher specific cooling power value is obtained with a smaller dead volume. Finally, the cooling performance of the adsorption cooling system was also studied under various operating conditions and a maximum specific cooling power and coefficient of performance are 180.4 W/kg and 0.29, respectively.

Parametric Study of an Adsorption Refrigeration System Using Different Working Pairs

Adsorption refrigeration system (ARS) is regarded as one of promising clean technologies since it uses a low-grade thermal energy (solar energy, waste heat, etc.). The present paper provides a dynamic modeling of two-bed ARS with RD silica gel/water and SWS–1L/water as working pairs based on MATLAB program. The refrigeration capacity and coefficient of performance are calculated in terms of cycle time, hot water inlet temperature, cooling water inlet temperature, and chilled water inlet temperature. Simulation results indicated that the coefficient of performance increases linearly with adsorption/desorption time. Refrigeration capacity increases gradually until reaches an optimal adsorption/desorption time and then reduces. RD silica gel/water and SWS–1L/water pairs provides a refrigeration capacity of 11.7 kW and 4 kW, respectively at evaporator temperature of 10⁰c.Both working pairs are limited by the hot water inlet temperature of 95 . The half cycle times are fixed to 350⁰cand 280 s for RD silica gel/water and SWS–1L/water, respectively which selected based on optimum time which gives maximum cooling capacity, whereas the switching time for pre-cooling and pre-heating processes is set to 30 s for both working pairs.

Performance Simulation of Two-Bed Adsorption Refrigeration Chiller with Mass Recovery

The technology of adsorption chiller is an efficient way of heat conversion. It can significantly reduce environmental pollution and improve energy efficiency. This paper deals with numerical study of refrigeration systems with silica gel/water pairs with mass recovery. The model is validated with experimental results from the ENERBAT platform. Numerical results are in good agreement with those of experiment. A process of mass recovery is added to study its the effect on the performances of the system. The effect of hot water temperature, cooling water temperature, chilled water temperature and cycle time, on the coefficient of performance (COP), the specific cooling capacity (SCP), the cycled mass, the evaporator outlet temperature and efficiency system are investigated in order to extrapolate the results in the Tunisian climate and to determine their optimum values able to maximize the performance of the system under analysis. The simulation calculation indicates a COP value of 0.7 with a driving source temperature of 85°C in combination with coolant inlet and chilled water inlet temperature of 40°C and 15°C, respectively. The most optimum adsorptiondesorption cycle time is approximately 1240s based on the performance from COP and SCP, achieving a SCP of 400 W/kg.

Energy Analysis and Modeling Study of Combined Activated Carbon-Silica Gel/Methanol Adsorption Ice Production System

In this article, the transient modelling for a new construction of the Adsorption cold production was investigated. This system, named in this work the combined Adsorption Ice Production system (com-AIP system), was filled by both silica gel (SG) and activated carbon (AC) together in one adsorption reactor as the adsorbent and methanol as the adsorbate and refrigerant. A fined-tube heat exchanger was designed (named combined adsorption reactor) in order to contain two different adsorbents in the adsorption reactor and increase the heat transfer ability between the particles of adsorbents and heat exchanger fins. As a result the input energy required from the external heat source is saved and the coefficient of performance COP of the com-AIP system is improved. The mass flow rate of refrigerant increases and consequently, the refrigeration energy Qe rises too. A cycle simulation computer program of this innovative bed was developed to analyze the refrigeration energy and COP variations by varying heat transfer fluid (hot, cooling and chilled water) inlet temperatures and adsorption/desorption cycle time. The transient behavior of heat and mass transfer fluids has been also studied. Under the standard test conditions of 100 °C hot water, 24 °C cooling water, and 15 °C chilled water inlet temperatures, the simulation results showed that the amount of the ice produced per cycle of 5.34 kg and 0.73 COP can be achieved from the com-AIP system. It was found that the system performance is very much sensitive to the mass flow rate of the refrigerant. The cycle time of the system is not dependent on the amount of the adsorbents but is strongly dependent on driven temperature of heat exchange fluid and the design of the heat exchanger. The com- adsorption reactor allows using the advantages of physical properties of both adsorbents SG and AC. Consequently, this innovative com-AIP system utilizes effectively low-temperature heat sources of temperature between 65 and 100 °C, because of the inferior thermodynamic properties of methanol and the low regeneration temperature from silica gel and activated carbon as adsorbents. This strategy (com-AIP system) is completely different from the conventional adsorption reactors, which are filled with one adsorbent in one bed or in two beds.

Modeling study of two-stage, multi-bed air cooled silica gel + water adsorption cooling cum desalination system

This paper presents a transient numerical study of two-stage, air-cooled silica gel+water adsorption system producing cooling and potable water. The key aspect of the present study is an attempt to model the inter-stage pressure dynamics when two beds exchange mass in terms of vapors across the stages. This is an important improvement over prior models wherein the inter-stage pressure was assumed to be either constant or user input. Furthermore, the evaporator and condenser pressures are also allowed to vary in this study in contrast to the previous papers. The simulation results are compared with the experimental data for various cycle times and chilled water inlet temperatures in the range of 11.5–20.0°C, while having the heat source temperature fixed at 85°C and air temperature at 36°C. Depending on the chilled water inlet temperature and cycle time, the SCC is found to be between 2 and 7Rton/tonne of silica gel; SDWP ranges within 0.3–0.9m3/day/tonne of silica gel and COP varies between 0.05 and 0.26.

Theoretical Analysis of a Novel Integrated Energy System Formed by a Microturbine and an Exhaust Fired Single-Double Effect Absorption Chiller

Integrated Energy Systems (IES) combine a distributed power generation system (DG) such as a microturbine generator (MTG) or a fuel cell with thermally activated technologies (TAT) such as absorption cooling. This integration maximizes the efficiency of energy use by utilizing on-site most of the waste heat generated by DG, and reduces harmful emissions to the environment. This study investigates the energy and exergy performance of an IES. This system is comprised of an MTG with internal recuperator and a novel absorption cooling cycle. The absorption cycle is a single-double effect exhaust fired cycle, which recuperates the heat exchanged from the MTG exhaust gases using two generators at two different levels of temperature. The selection of the DG element, the TAT element and their internal configurations is based upon a real IES commercial unit that has been tested in the APEP-UCI DG testing facilities in Irvine, California. This unit has an electrical power capacity of 28 kW and a cooling capacity of 14 refrigeration tons (49.2 kW). Inputs for the thermodynamic models developed for the MTG and for the absorption cycle are derived from experimental variables that will be controlled in the testing phase. The MTG model is using empirical correlations for key model parameters (pressure ratio, turbine inlet temperature, etc.) from previous studies in order to predict the observed change in performance with part load operation. The calculated mass flow rate and temperature of the exhaust gases are inputs for the absorption cycle model, together with cooling and chilled water inlet temperatures and flow rates. Heat and mass transfer efficiencies along with heat transfer coefficients for the suite of heat exchangers comprising the single-double effect absorption cycle are determined from proprietary testing data provided by the manufacturers.

Performance of finned tubes used in low-pressure capillary-assisted evaporator of adsorption cooling system

Adsorption cooling systems (ACS) are a viable alternative to vapor compression refrigeration cycles (VCRCs) where low-grade waste heat is readily available. In an ACS, which works with water as a refrigerant, the operating pressure is quite low (∼1kPa). Under such low evaporation pressures, the height of a water column affects the water saturation pressure and, consequently, its saturation temperature, which can severely affect the performance of an ACS. This makes the design of evaporators of ACS different from those of conventional VCRCs. One practical solution in low pressure (LP) evaporators is to use capillary-assisted tubes. In this study, three enhanced tubes with different fin geometries (fin spacing and fin height), and a plain tube as a benchmark, are tested for different chilled water inlet temperatures. The results show that enhanced tubes have 9.8–21 times lower external convective heat transfer resistances compared to the plain tube. In addition, the enhanced tube with the highest fin height (Turbo Chil-26 FPI) has 33% lower external convective resistance than that with lower fin height (GEWA-KS-40 FPI). The major finding of this study is that up to 89% of the overall thermal resistance in the enhanced tubes is due to the internal convective resistance. This clearly indicates that the main bottleneck in the performance of a LP evaporator is the convective heat resistance inside the tube. Therefore, the internal heat transfer coefficient and internal surface area of enhance tubes should be increased to enhance the performance of the LP evaporator and overall specific cooling power (SCP) of ACS.

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.

Effects of capillary-assisted tubes with different fin geometries on the performance of a low-operating pressure evaporator for adsorption cooling system applications

This study investigates the performance of a low-operating pressure evaporator using capillary-assisted tubes for adsorption cooling systems (ACS). When using water as a refrigerant in an ACS, the operating pressure is low (<5kPa) and the performance of the system is severely affected when using conventional evaporators. This problem can be addressed by using capillary-assisted evaporators. A custom-built apparatus for evaluating cooling power is used to test five types of enhanced tubes with different fin geometries. Tests were performed with 10–20°C chilled water inlet temperatures and water vapor pressures of 0.5–0.8kPa. The results show that the capillary-assisted tubes provide 1.6–2.2 times greater heat transfer rate compared to a plain tube. Comparing tubes with equivalent inner surface areas (0.049m2/m) and equivalent outer surface areas (0.193m2/m), and different fin heights indicates that tubes with 1.42mm parallel continuous fins (26 fins per inch (FPI)) have a 13% higher heat transfer coefficient than those with 0.9mm fins (40 FPI). The effects of refrigerant height, dead volume inside the evaporator and chilled water mass flow rate on the performance of evaporator are studied. The heat transfer rate increases by 65% when the water height to tube diameter ratio decreased from 1.8 to less than 1. Increasing the chilled water mass flow rate from 2.5 to 15.3kg/min (6.1 times higher) increases evaporator heat transfer coefficient by 110%.

Performance analysis of a novel expansion valve and control valves designed for a waste heat-driven two-adsorber bed adsorption cooling system

Two new ideas for the expansion valve and control valves of an adsorption cooling system (ACS) for vehicle air conditioning applications are suggested to reduce its weight and parasitic power consumption, and simplify its control system. A check valve with cracking pressure of 3.5–7 kPa is proposed for the expansion valve and a combination of low cracking pressure check valves and solenoid valves with an innovative arrangement is proposed for the control valves. These new designs are installed on a two-adsorber bed silica gel/CaCl2-water ACS and tested under different operating conditions. These designs result in reducing the total mass of the ACS up to 10.5 kg and the parasitic power consumption of the control valves by 50%. The results show that the expansion valve and control valves operate effectively under the heating and cooling fluid inlet temperatures to the adsorber beds of 70–100 °C and 30–40 °C, respectively, the coolant water inlet temperature to the condenser of 30–40 °C, and the chilled water inlet temperature to the evaporator of 15–20 °C. Also, an ACS thermodynamic cycle model is developed and compared against the experimental data for prediction and further improvement of the ACS performance. The results of the numerical modeling show that by increasing the adsorber bed heat transfer coefficient and surface area, the specific cooling power of the system increases up to 6 times.

Cascaded energy plant using ammonia absorption refrigeration system for combined cooling and heating applications

A cascaded energy plant for the pharmaceutical industry has been developed and implemented to generate chilled water at 7°C and hot water at 58°C for the required applications using ammonia absorption refrigeration system making use of low-grade thermal energy, such as steam. The internal heat recovery (Qihr) of an ammonia–water absorption refrigeration system was improved with additional components. The additional components, such as a generator heat exchanger and solution cooled rectifier, significantly improved the system performance compared to the systems using only conventional components (evaporator, generator, condenser, absorber, solution heat exchanger, and economizer). In addition to the conventional components, the condensate cooler has been added to the system for condensate heat recovery. The system delivers the cooling and heating coefficients of performance of 0.6 and 1.53, respectively, for the tested conditions with a steam inlet temperature of 147°C, cooling process water inlet temperature of 30°C, and chilled water inlet temperature of 15°C. The developed system delivers 300–430 kW of cooling load and 700–1100 kW of heating load, depending on the cooling load of the plant requirement since installation.

Performance Analysis of Four Types of Adsorbent Beds in a Double-Adsorber Adsorption Refrigerator

Four advanced types of adsorbent beds were designed, investigated and compared to each other in a double-adsorber adsorption refrigerator. The four types of adsorbent beds were assembled by several vehicle radiators with two different sizes. A prototype of the adsorption refrigerator built up in our laboratory was used to test the performances of the adsorbent beds. Silica gel-water was used as the working pair. The length, width and thickness of the radiators were measured. The amount of adsorbent filled into these four types of adsorbent beds was recorded. The dead area volume was estimated. The coefficient of performance (COP) and specific cooling power (SCP) of the system were tested after utilizing the four types of adsorbent beds. The COP and SCP of the four types of adsorbent beds were estimated under the standard operating condition and optimized operating condition. A SCP and a COP of the small-radiator adsorbent beds with 198.4W/kg and 0.30 were achieved under the optimized operating condition with 480 s adsorption/desorption time, 90 s heat and mass recovery time, 9 L/min hot water and cooling water flow rate, 2 L/min chilled water flow rate, 16°C chilled water inlet temperature, 90°C hot water and 25°C cooling water. Under the standard operating condition, the result showed that smaller dead volume leads to a slightly higher SCP. The adsorbent bed with smaller size radiator had a better heat and mass transfer ability and a higher SCP and COP could be achieved.

Thermodynamic performance assessment of carbon dioxide blends with low-global warming potential (GWP) working fluids for a heat pump water heater

Blends of CO2 with ten low-global warming potential (GWP) working fluids are evaluated for use in a heat pump water heater. The effects that the discharge pressure, component ratio, hot-water outlet temperature and chilled water inlet temperature have on the coefficient of performance (COP) of heat pump are analyzed when the pinch point of the heat exchange is considered. It is found that temperature glide of zeotropic mixture has a good thermal match with the temperature change of water as two pinch points appear in the gas cooler/condenser or evaporator. The good thermal match in the heat exchangers promotes the system COP. Addition of low-GWP working fluids to pure CO2 can reduce the high-side pressure. The results show that CO2/R41 and CO2/R32 are suitable candidates for heat pump water heaters because of their high COP and low high-side pressure in comparison with those of a pure CO2 cycle.

Design and Modeling of One Refrigeration Ton Solar Assisted Adsorption Air Conditioning System

The modeling of the performance of a one refrigeration ton (RT) solar assisted adsorption air-conditioning refrigeration system using activated carbon fiber/ethanol as the adsorbent/adsorbate pair has been undertaken in this study. The effects of hot water, cooling water, chilled water inlet temperatures, and hot water and chilled water flow rates were taken into consideration in the optimization of the system and in the design of the condenser, evaporator, and hot water storage tank. The study includes analysis of the weather data and its effect on both the adsorption system and the cooling load. This is then followed by estimation of the cooling capacity and coefficient of performance (COP) of the adsorption system as a function of the input parameters. The results of the model will be compared to experimental data in a next step.

Assessment of R-438A as a retrofit refrigerant for R-22 in direct expansion water chiller

The present work aims to evaluate the performance characteristics of a vapor compression refrigeration system using R-438A as a retrofit refrigerant for R-22. In order to achieve this objective, a test facility is developed and experiments are performed over a wide range of chilled water inlet temperature (11:20 °C), condenser water inlet temperature (25:35 °C) and condenser water mass flow rate (363:543 kg h−1). Results showed that as the chilled water inlet temperature changes from 11.5 to 20.5 °C, system COP increases from 1.78 to 2.07 at constant condenser water inlet temperature of 25.5 °C. Cooling capacity and COP of the system using R-438A are lower than R-22 by 11% and 12.5%, respectively. However, compressor discharge temperature using R-438A is slightly lower than R-22 which confirms that R-438A can be used as a retrofit refrigerant for R-22 to complete the remaining life time of the existing plants.

Study of various adsorbent–refrigerant pairs for the application of solar driven adsorption cooling in tropical climates

This article presents analytical investigation results on the performance of solar powered adsorption cooling systems for Malaysia and similar tropical regions. The studied adsorbent–refrigerant pairs are silica gel-water, activated carbon fiber-ethanol and activated carbon-methanol. A computer simulation program has been developed for modeling and performance evaluation for the solar driven adsorption cooling cycle using the meteorological data of Kuala Lumpur, Malaysia The simulation is based on the experimentally confirmed adsorption isotherms, kinetics and isosteric heat of the adsorption data for the respective adsorbent–refrigerant pairs. The optimum cooling capacity and coefficient of performance (COP) of the different adsorbent–refrigerant pairs varying adsorption–desorption cycle time, regeneration temperature and chilled water inlet temperature are calculated and compared.

PERFORMANCE IMPROVEMENT OF AN ADSORPTION CHILLER USING COMPOSITE ADSORBENT, SILICA GEL IMPREGNATED WITH LITHIUM CHLORIDE, PAIRED WITH METHANOL AS THE ADSORBATE

This study aimed at analyzing different operation strategies to improve the performance of a new type adsorption chiller employing a novel composite adsorbent, silica gel impregnated with lithium chloride, paired with methanol as the adsorbate. The chiller's experimental test results showed an average Specific Cooling Power (SCP) and Coefficient of Performance (COP) of 286 W/kg and 0.48, respectively. This was when the average hot water inlet temperature, cooling water inlet temperature, and chilled water inlet temperature were 83°C, 26°C and 15°C, respectively. In addition, the corresponding mass flow rates were 0.22, 0.39 and 0.09 kg/s, respectively. Despite the fact that the average SCP and COP, were rather satisfactory, analysis of experimental results conducted with different cycle times, inlet hot water temperatures, and hot water flow rates showed that a much better performance could be achieved. Experimental results indicated the following: (1) the COP increased while the SCP decreased with increased cycle time, (2) both the COP and the SCP increased with increase in heat and mass recovery time to an optimal time then started to decrease as heat and mass recovery time increased beyond the optimal time, (3) both the cooling power and COP generally increased with increase in inlet hot water temperature at a relatively higher value from 60°C to about 90°C beyond which the incremental value started diminishing, and, (4) increase in mass flow rates produced higher cooling power with decreased COP while decrease in mass flow rates of hot water produced lower cooling power with increased COP. This paper therefore recommends an adsorption/desorption time, heat and mass recovery time, inlet hot water temperature, and hot water mass flow rate of 780 s, 60 s, 83°C, and 0.22 kg/s as appropriate to give the best chiller performance for refrigeration.