Chiller Coefficient Of Performance Research Articles

Electrical Energy Efficiency Improvement in Chiller Operation

The need for electrical energy to meet consumers is increasing which must be addressed immediately. Along with population growth and economic growth, this energy need will continue to increase. With the use of large amounts of electrical energy, it is necessary to increase efficiency in operating equipment. Airports are one of the largest users of electricity, especially when it comes to cooling systems. Therefore, it is necessary to save energy in airport operations. Airports are one of society's activities, so airports need to save energy. By optimizing power management and calculating the chiller coefficient of performance (COP) value, an airport can be built that saves energy on the HVAC system (especially chillers). Through analysis, it was found that COP increased to 0.584, and the value before optimization was 6.181. As COP increases, chiller performance will increase. The optimized electrical energy efficiency of the cooler is 138.82 kWh / day.

Thermo-economic analysis, energy modeling and reconstructing of components of a single effect solar–absorption lithium bromide chiller for energy performance enhancement

This research includes a thermodynamic analysis of a solar absorption chiller due to design temperatures and pressures. Integration of solar energy and absorption chiller in low capacities is done by: static relations (including point-to-point system behavior variations) ruling absorption chillers, calculating the amount of required heat for the generator of the chiller and how it is supplied with, coding and determining optimal chiller coefficient of performance (COP) in Engineering Equation Solver (EES) software, evaluating the affecting factors on the COP by system analysis method. According to the system analysis of a combined solar-chiller system, the best COP is determined to be 0.77; which is a technically acceptable amount in small-size chillers. Also, the computational model for the economic evaluation of energy and energy-saving from receiving solar heat by using a suitable collector shows a 9-year payback period (considering the subsidized price: 0.01$ (2,500 Rails) per cubic meter of natural gas) and a 2-year payback period (considering FOB price equals 0.16$ per cubic meter natural gas). Therefore, it is proven that the economic feasibility of integrating absorption chillers and solar energy is affected by the price of energy carriers in real or subsidiary form and the bank interest rate.

Energy-Efficient Approaches for a Machine Tool Building in a University through Field Measurement and Energy Modelling

The heating, ventilating, and air conditioning (HVAC) system consumes nearly 50% of the building’s energy, especially in Taiwan with a hot and humid climate. Due to the challenges in obtaining energy sources and the negative impacts of excessive energy use on the environment, it is essential to employ an energy-efficient HVAC system. This study conducted the machine tools building in a university. The field measurement was carried out, and the data were used to conduct energy modelling with EnergyPlus (EP) in order to discover some improvements in energy-efficient design. The validation between field measurement and energy modelling was performed, and the error rate was less than 10%. The following strategies were proposed in this study based on several energy-efficient approaches, including room temperature settings, chilled water supply temperature settings, chiller coefficient of performance (COP), shading, and building location. Energy-efficient approaches have been evaluated and could reduce energy consumption annually. The results reveal that the proposed energy-efficient approaches of room temperature settings (3.8%), chilled water supply temperature settings (2.1%), chiller COP (5.9%), using shading (9.1%), and building location (3.0%), respectively, could reduce energy consumption. The analysis discovered that using a well-performing HVAC system and building shading were effective in lowering the amount of energy used, and the energy modelling method could be an effective and satisfactory tool in determining potential energy savings.

Development of a user-friendly regression model to evaluate carbon emissions of office buildings design in the subtropics

Purpose Design teams have difficulties in assessing building carbon emissions at an early stage, as most building energy simulation tools require a detailed input of building design for estimation. The purpose of this paper is to develop a user-friendly regression model to estimate carbon emissions of the preliminary design of office buildings in the subtropics by way of example. Five sets of building design parameters, including building configuration, building envelope, design space conditions, building system configuration and occupant behaviour, are considered in this study. Design/methodology/approach Both EnergyPlus and Monte Carlo simulation were used to predict carbon emissions for different combinations of the design parameters. A total of 100,000 simulations were conducted to ensure a full range of simulation results. Based on the simulation results, a regression model was developed to estimate carbon emissions of office buildings based on preliminary design information. Findings The results show that occupant density, annual mean occupancy rate, equipment load, lighting load and chiller coefficient of performance are the top five influential parameters affecting building carbon emissions under the subtropics. Besides, the design parameters of ten office buildings were input into this user-friendly regression model for validation. The results show that the ranking of its simulated carbon emissions for these ten buildings is consistent with the original carbon emissions ranking. Practical implications With the use of this developed regression model, design teams can not only have a simple and quick estimation of carbon emissions based on the building design information at the conceptual stage but also explore design options by understanding the level of reduction in carbon emissions if a certain building design parameter is changed. The study also provides recommendations on building design to reduce carbon emissions of office buildings. Originality/value Limited research has been conducted to date to investigate how the change of building design affects carbon emissions in the subtropics where four distinct seasons lead to significant variations of outdoor temperature and relative humidity. Previous research also did not emphasise on the impact of high-rise office building designs (e.g. small building footprint, high window-to-wall ratio) on carbon emissions. This paper adds value by identifying the influential parameters affecting carbon emissions for a high-rise office building design and allows a handy estimate of building carbon emissions under the subtropical conditions. The same approach may be used for other meteorological conditions.

Optimised dynamic control philosophy for improved performance of mine cooling systems

Mine workers require substantial cooling and ventilation to work in a safe and habitable environment. Deep level mine cooling systems were identified as significant energy-intensive consumers to supply such cooling. Mine cooling systems can make up to 25% of a mine’s total electricity consumption. Coupled with increasing electricity costs, deep level gold mines are struggling to remain competitive. Literature reveals a need for a simple and practical solution to optimise deep level mine cooling systems for improved system performance. In this paper, an optimised dynamic control strategy is presented to optimise the control of mine cooling systems. An integrated dynamic temperature set point algorithm and ambient dry-bulb (DB) temperature prediction model was formulated, implemented and verified. The optimised dynamic control model, when compared to existing control practises, attained a chiller coefficient of performance (COP) improvement and compressor power reduction of 7% and 4% respectively. Implementation results also showed a power demand reduction of 45.7% during the evening high electricity cost period. This strategy demonstrated to be simple and cost effective while showing significant performance improvements for South African mines.

Fuzzy logic approach in the analysis of heat transfer in a porous sorbent bed of the adsorption chiller

Thermal conductivity in the boundary layer of heat exchange surface is the crucial parameter of adsorption process efficiency which occurs in the adsorption bed. In order to improve heat transfer conditions in the adsorption chiller, novel constructions of adsorption beds are currently investigated. The porous structure of the sorbent layer causes low thermal conductivity in the adsorption bed. One of the methods to improve heat transfer conditions is a modification of porous media bed structure with glue which is characterized with higher thermal conductivity. The optimum parameters of sorbents and glues to build the novel coated construction, in terms of improving the chiller Coefficient of Performance (COP) were defined in (Grabowska et al. 2018a). The paper implements fuzzy logic approach for predicting thermal conductivity of modified porous media layers. The developed model allows determination of the sorbent layer thermal conductivity based on various input parameters: arithmetic average of particle distribution d, density ρ and thermal diffusivity k. The data from empirical research was used to build up the model by fuzzy logic methods.

ANALISIS WATER BALANCING PRIMARY LOOP CHILLER SYSTEM TERHADAP COP (Coefficient Of Performance)

Water is one of the major media for heat transfer process in the cooling system. The size of the flow rate of water entering the system will affect the overall cooling. Analysis of water balancing primary loop chiller system against COP (Coefficient Of Performance) is based on the observation the performance of the chiller system during operational with temperature of chilled water produced that not able to achieve the desired criteria when demand for chilled water increasing. After analysis conducted, it is known that decreasing efficiency of cooling system caused by uncontrolled water flow rate into the system. After water balancing is done, the flow rate of the water coming into the system (evaporator) can be controlled by using the balancing valve so that the flow rate increased from 16.07 x 10 -3 m 3 / s to 52.70 x 10 -3 m 3 / s, resulting in increased chiller COP value system from 2.4 to 4.1.

Parametric analysis and optimization of a cooling system with ejector-absorption chiller powered by solar parabolic trough collectors

Solar cooling is one of the most promising technologies for covering the increasing needs of our society with a clean and sustainable way. This paper examines an ejector-absorption cooling system operating with the LiBr-H2O working pair which is driven by parabolic trough solar collectors. The main objective of this investigation is to optimize the total solar cooling system and to compare it with the respective optimum system with conventional absorption chiller and parabolic trough collectors. The generator temperature and pressure, as well as the pressure drop in the ejector, are the optimization parameters, while the maximization of the system performance is the objective function. According to the final results, the system with the ejector leads to higher COP (coefficient of performance) for the majority of the examined operating scenarios. Moreover, the optimized ejector-absorption system presents performance enhancement up to 60.9% compared to the conventional absorption system for the case with 12.5 °C evaporating temperature and 30 °C condenser temperature. For this optimum case, the system COP is about 1.01, the chiller COP is 1.65 and the system exergy efficiency is 4.76%. Generally, the system COP is ranged from 0.473 to 1.01 for the system with ejector, while the demanded specific collecting area from 0.987 to 2.11 m2/kWcooling. The analysis is performed with a developed model in Engineering Equation Solver which is validated with literature results.

Optimal design, operation and analytical criteria for determining optimal operating modes of a CCHP with fired HRSG, boiler, electric chiller and absorption chiller

The configuration, design and operation strategy are the main factors that can affect the technical, economic and environmental performances of combined cooling, heating and power (CCHP) system. In this paper, the operation of a CCHP system with fired heat recovery steam generator (HRSG), electric chiller, absorption chiller and a boiler is classified into one of three scenarios which are determined by gas turbine size and magnitude of thermal and electric loads. The optimal operating strategies are presented for these scenarios. For scenario with high cooling loads, we derive analytical expressions for calculation of ratio (electricity price/natural gas price) values which delimit three optimal modes for providing cooling demand in summer, thereby enabling selection of optimal operating strategy without numerical optimization. We examine the optimal design of CCHP system in three climate zones based on the proposed strategy. Supplementary firing as well as a higher coefficient of performance (COP) of the absorption chiller increase system efficiency and enable reduction of gas turbine size. Our case studies show that supplementary firing, (for some values of price ratio, absorption chiller COP and climate zone) the electric chiller and/or the boiler are necessary components to achieve optimal system performance.

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.

A Solar Heating and Cooling System in a Nearly Zero-Energy Building: A Case Study in China

The building sector accounts for more than 40% of the global energy consumption. This consumption may be lowered by reducing building energy requirements and using renewable energy in building energy supply systems. Therefore, a nearly zero-energy building, incorporating a solar heating and cooling system, was designed and built in Beijing, China. The system included a 35.17 kW cooling (10-RT) absorption chiller, an evacuated tube solar collector with an aperture area of 320.6 m2, two hot-water storage tanks (with capacities of 10 m3 and 30 m3, respectively), two cold-water storage tanks (both with a capacity of 10 m3), and a 281 kW cooling tower. Heat pump systems were used as a backup. At a value of 25.2%, the obtained solar fraction associated with the cooling load was close to the design target of 30%. In addition, the daily solar collector efficiency and the chiller coefficient of performance (COP) varied from 0.327 to 0.507 and 0.49 to 0.70, respectively.

Performance assessment and gained operational experiences of a residential scale solar thermal driven adsorption cooling system installed in hot arid area

In this study, performance assessment of a residential scale size solar thermal driven adsorption cooling system installed in hot arid and dusty area at Upper Egypt, and, in operation since summer 2012 until now is carried out experimentally for four years in operation, moreover, the gained operational experiences are presented. The system performance is expressed in term of the solar collectors' field thermal efficiency, actual chiller chilling capacity, the temperature of cold-water outlet from the chiller, chiller coefficient of performance (COP) and cooling-water temperature outlet from the cooling tower. The system performance results show that the daily solar collector efficiency during the reported period was ranged from about 50% to 78%. While, the average chiller COP was varied from 0.4 to 0.64 in combination with average chilling power ranged from 3.6 to 6.42kW and average chiller outlet cold water temperature ranged from 19°C to 12.12°C correspondence to cooling tower outlet cooling water temperature ranged from 31.4°C to 23.4°C, respectively. In the cooling session of 2014, a 50kW cooling capacity wet cooling tower is integrated into the system, and the measurements show that the outlet water temperature from the cooling tower is about 23.4°C at ambient air dry bulb temperature of 35.7°C and wet bulb temperature of about 19°C. Consequently, under this new heat rejection condition, the chiller average cooling capacity and COP reaches were 6.42kW and 0.64 with a chilled water temperature of 15°C. Clearly from the system operation period, the heat rejection through the re-cooling sub-system has the main significant impact on the system performance in the hot arid areas. Therefore, it should be based on alternative heat sink recourses with appropriate cost performance techniques.

The Development and Full-Scale Experimental Validation of an Optimal Water Treatment Solution in Improving Chiller Performances

An optimal solution, in combining physical and chemical water treatment methods, has been developed. This method uses a high voltage capacitance based (HVCB) electrodes, coupled with biocides to form a sustainable solution in improving chiller plant performances. In this study, the industrial full-scale tests, instead of laboratory tests, have been conducted on chiller plants at the size of 5000 RT to 10,000 RT cooling capacities under commercial operation for more than two years. The experimental results indicated that the condenser approach temperatures can be maintained at below 1 °C for over two years. It has been validated that the coefficient of performance (COP) of a chiller can be improved by over 5% by implementing this solution. Every 1 °C reduction in condenser approach temperature can yield approximately 3% increase on chiller COP, which warrants its future application potential in the HVAC industry, where Ta can degrade by 1 °C every three to six months. The solution developed in this study could also reduce chemical dosages and conserve makeup water substantially and is more environment friendly.

Performance analysis of an innovative PCM-based device for cold storage in the civil air conditioning

An innovative solution to store cold energy for civil application based on phase change materials (PCM) is presented and evaluated. The storage tank is thought to be installed in a traditional chiller-fan coil system to shave the electricity peak loads required by the users, thus allowing a better management of the electricity grids (by avoiding the summer peaks for air conditioning) and a significant energy saving thanks to the improvement of the chiller Coefficient of Performance (COP).A 5kWh prototype has been tested to prove the technological feasibility and has been simulated by a physical-mathematical model based on the energy balance and heat exchanging equations. The model, once validated against experimental data, has been implemented to assess the technology behavior changing operating parameters as the filling ratio, the initial temperature of the PCM and the charging power.The optimization of the heat exchanging configuration can lead to a minimum loading time of 54min for the 5kWh storage tank (charging power of 5.7kW). Globally, the mathematical simulations confirmed the capability of the system to operate at high charging/discharging power, thus making it optimal for the integration in a chiller-fan coil system with the “peak shaving” logic.

Detailed analysis on part load ratio characteristics and cooling energy saving of chiller staging in an office building

Commercial buildings account for significant portions of the total building energy in Korea and thus a variety of research on the chiller operation was carried out thus far. However, most of the researches were carried out on the chiller itself, i.e., the part load ratio characteristics and the corresponding electricity energy consumption patterns were not analyzed in the existing studies. In this study, the part load ratio and the operating characteristics of vapor compression chiller were analyzed within an office building equipped with the conventional variable air volume system. In addition, the energy consumption among different chiller staging schemes was comparatively analyzed. As a result, significant portions of total operating hours, cooling load and energy consumption turned out to be in the part load ratio range of 0 through 50% and thus the energy consumption was significantly affected by the chiller COP (Coefficient of Performance) at low part load conditions, indicating that the chiller operation at the part load is an important factor in commercial buildings. In addition, utilizing sequential chiller staging scheme can save annual cooling energy usage by more than 10.3% compared to operating a single chiller. For further reduction in cooling energy, applying the sequential control chiller staging during the intermediate season and applying the uniform control chiller staging algorithm during the cooling season is considered to be the optimal control algorithm for maximum efficiency of chillers.

Design, construction and operation of a solar powered ammonia–water absorption refrigeration system in Saudi Arabia

This study presents an experimental investigation of a solar thermal powered ammonia–water absorption refrigeration system. The focus of this study lies on the design of the components of the absorption chiller, the ice storages and the solar collector field as well as the integration of the data acquisition and control unit. An ammonia–water (NH3/H2O) absorption chiller was developed in the laboratory of the Institute of Thermodynamics & Thermal Engineering (ITW) at the University of Stuttgart (Germany). A demonstration plant was built in the laboratory of the CoRE-RE at King Fahd University of Petroleum & Minerals (KFUPM – Saudi Arabia). The whole system was tested successfully. The results of the experiments indicated a chiller coefficient of performance (COP) of 0.69 and a cooling capacity of 10.1 kW at 114/23/−2 (°C) representing the temperatures of the generator inlet, the condenser/absorber inlet and the evaporator outlet respectively. Even at 140/45/−4 (°C), the chiller was running with a cooling capacity of 4.5 kW and a COP of 0.42.

Modelling and experimental investigation of an adsorption chiller using low-temperature heat from cogeneration

Adsorption technology enables construction of chillers that can be driven with a low temperature cogeneration, solar or waste heat source. As compared with absorption chillers, the adsorption devices have the unique advantages like the utilization of heat source characterized by lower temperature. The paper presents the thermodynamic model of a three-bed adsorption chiller of a cooling capacity equal to 90 kW. The chiller has been commissioned at Wrocław Technology Park and is instrumented in a way allowing a full identification of important thermodynamic and operational parameters like COP (coefficient of performance), switching time, temperatures and pressures of adsorption and desorption processes as well as water condensation. The chiller provides cooling power at two temperature levels of about 13 and 8 °C. Experimental results of a long-term chiller investigation are presented. The dependence of the chiller COP on the adsorption bed regeneration temperature in the range from 45 °C to 70 °C has been identified. It has been demonstrated that the chiller can be driven with a hot water of 65 °C, what is a typical cogeneration heating temperature in distributed systems. It allows the utilization of cogeneration heat in trigeneration mode, what is especially important for distributed heating systems in summer time.

A Novel Control Strategy for Air-Cooled Twin-Circuit Screw Chillers

Air-cooled chillers are generally the major electricity consumers in air-conditioned buildings in the subtropical climate. To improve the energy efficiency of the air-cooled chillers at part load conditions, two or more refrigeration circuits are designed. This paper considers how the use of optimal circuit loading sequence (CLS) enables these chillers to operate more efficiently. A thermodynamic model for the air-cooled chillers with twin refrigeration circuits was developed using TRNSYS and validated using a wide range of operating data. Based on the sophisticated chiller model, an analysis was carried out on how the chiller COP varied with different CLS and variable condensing temperature control (CTC). A chiller plant designed for a representative office building in Hong Kong was investigated to assess the potential electricity savings by use of CLS. 4.2% of the annual electricity consumption by chillers could be achieved with optimal CLS compared with the base case. Under CTC, the coefficient of performance (COP) was improved further, and CTC coupling with optimal CLS would reduce the annual total electricity consumption for cooling by 9.6%.

Energy consumption and optimization of internally cooled/heated liquid desiccant air-conditioning system: A case study in Hong Kong

LDAC (liquid desiccant air-conditioning system) is promising for reducing the energy consumption, and improving the indoor air quality. In this paper, the operation performance of LDAC with internally cooled/heated dehumidifier/regenerator was simulated and optimized. The cooling tower and solar collectors were employed as the cooling/heating source. Four nested iteration loops were developed and solved for system modeling. A typical commercial building in Hong Kong was selected as a case study, which air-conditioning load was obtained by Energy-plus. Results show that with the increase of solar collector area, the electricity consumption of AC (air-conditioning systems) system reduced by 11–35% in original system, but only a part of dehumidification demand was handled with liquid desiccant ventilation, which led to a low chiller COP (coefficient of performance). By adding a cooling coil for the solution entering dehumidifier, the electricity saving effectively increased to 22–47%, while the heat demand for regeneration also increased by 17%. So, a heat exchanger between water leaving regenerator and solution leaving dehumidifier was introduced. With the lower thermal requirement (reduced by 20%) and higher solar fraction (increased from 30 to 40%), the saving further increased to 29–49%, and the required collector area obviously reduced by 50–60% for the similar energy saving purpose.

An analysis on the energy efficiency of air-cooled chillers with water mist system

This paper presents the effect of operating water mist system to enhance the energy efficiency of air-cooled chillers under various operating conditions. A thermodynamic model for an air-cooled chiller with twin refrigeration circuits coupled with a water mist system was developed and validated by measured operating data. The validated model was used to investigate how the thermal properties of the entering condenser air and the performance of the air-cooled chiller varied under different operating schemes with water mist pre-cooling. Under the conventional head pressure control (HPC) with a designed water mist generation rate, the coefficient of performance (COP) increased by up to 21.3%. The chiller performance could be improved further under variable condensing temperature control (CTC). Under CTC, chiller COP was increased up to 51.5% with optimal water mist generation rate. The potential energy savings of these chillers serving a representative office building in subtropical climate was evaluated, and CTC coupling with optimal water mist generation rate would reduce the annual total electricity consumption for cooling by 14.1%. The water consumption of the water mist system was comparatively small, comparing with the total water losses for an open-loop cooling tower system with equivalent heat rejection capacity.