Chiller Size Research Articles

Comprehensive and quantitative evaluation for selecting a suitable scheme of central air-conditioning during the design phase

As for routinely selecting the number and size of chillers in central air-conditioning system, the conventional scheme in which the total cooling capacity is allocated in an equal or empirical way is generally suboptimal. A few factors are brought into consideration, and the time domain of evaluation is too short. The low suitability between the cooling load of building and the scheme selected results in an inefficient state of system during the most of operation time. Some novel methods provide long-term evaluations for selecting an efficient scheme by simulating the cooling loads then calculating the cost and performance of the scheme. However, the schemes are formed without correlating actual plants which is difficult to be applied to an actual project, and the long-term environmental impact is rarely considered. The evaluation method with a high engineering value is required. But the more complicated the method is, the more work is required. The relationship between the benefits and the costs is unknown. Therefore, this study proposes three evaluation methods at different levels. From simple to complex, the three methods are corresponding the cooling load curve of building calculated through EnergyPlus to the performance curves of chillers, system simulation using TRNSYS and co-simulation based on BCVTB respectively. A case study using a hospital building located in Zhejiang province, China combined with equipment list was conducted to demonstrate the evaluation process. The results calculated by different methods and the various indexes of different schemes were compared to illustrate how to optimize the scheme selection during the design phase in order to select a suitable scheme for a certain building reducing the energy consumption and carbon emission.

Performance Evaluation and Optimal Design Analysis of Continuous-Operation Solar-Driven Cooling Absorption Systems With Thermal Energy Storage

Abstract A solar absorption cooling system consisting of a flat plate collector, thermal energy storage tank, and absorption chiller is analyzed in this work. A dimensionless model is developed from the energy balance on each component and the chiller’s characteristic performance curves. The model is used to determine the interaction and influence of different parameters such as tank size, solar collector area, chiller size, cooling load, cooling temperature, heat loss, and mass flow rates on the performance. From the analysis, smaller solar collector areas are required for lower cooling loads and smaller tank volumes. A specific cooling load of 1 × 10−5 will require a specific solar collector area between two and six times larger, depending on the initial tank temperature, than the area required for a baseline system that considers typical commercial design and operation parameters. A similar behavior was observed for the specific tank volume. For the baseline system, the minimum specific area of the collector of 9.57 is achieved for an initial tank temperature of 1.19. For a cooling load of 1 × 10−5, the optimum initial tank temperature will be 1.11 that results in a minimum specific solar collector area of 25.26. A specific tank volume of 4 × 10−4 will also have an optimum initial tank temperature of 1.11 that minimizes the specific solar collector area to a value of 28.18. The approach and analysis in this work can be used to determine design parameters for solar absorption cooling systems based on a proper relation among system’s dimensions to achieve optimum operation.

A quantitative approach and simplified generic transient motor startup power models for microgrids security assessment

• A quantitative approach is proposed for microgrid security assessment; • A method is proposed for microgrid blackout risk and wear potential assessment; • Simplified transient startup power models of motors and chillers are developed; • A reliable capacity ratio is recommended, considering inrush current; • The impact of chiller/motor inrush current on microgrid security is analyzed. Microgrid security can be significantly influenced by the design and operation of large electrical equipment (e.g., motors and chillers). During the startup period of large motors, the peak inrush current poses a substantial risk to microgrid security. Increasing the microgrid capacity is the common method to decrease the surge impact on microgrid security, which leads to huge investment. Quantification of motor startup performance is very valuable for assessing the security of microgrids. In this study, a quantitative approach is proposed to assess the security of microgrids dynamic load of power consumers. Two simplified generic transient models are developed based on the ANOVA (analysis of variance) method to quantify chiller motor startup performance including inrush current and startup time. The microgrid blackout risk and system wear potential can be effectively quantified using the proposed quantitative approach and models. The quantitative approach and the utilization of the simplified generic transient startup power models are tested and verified using a hotel microgrid on a remote island. Results show that the approach and models can be used to assess microgrid security. The systematic analysis recommends that the capacity of a single motor/chiller should be limited to 8% of microgrid capacity. The outputs of this work can effectively quantify the system security and system wear potential in the real application of the microgrid design and chiller size determination.

Modeling and total cost optimization of battery thermal management system in a hybrid electric vehicle

In the present study, the battery thermal management of a series hybrid electric vehicle is modeled and optimized for different standard driving conditions. The heat generation of the battery is comprehensively studied in previous works for the steady-state charge or discharge of the battery. Despite the previous investigations, the heat generation of the battery in the present study is modeled for the real driving conditions in terms of battery state of charge and power consumption. The model is validated with the experimental data. The validated model is implemented to minimize the total cost of ownership of the battery thermal management system. In this way, the battery thermal management system is optimized for three different standard driving cycles. The independent variables are the compressor speed, fan speed, chiller size, radiator size, and condenser size. The results reveal that the total cost of optimization is converged to 200 US dollars for all driving cycles. The optimum configuration of the battery thermal management system does not considerably vary for different driving cycles. Therefore, one of the optimum configurations can be considered the overall optimum for battery thermal management.

An innovative green multi-generation system centering around concentrating PVTs and biomass heaters, design and multi-objective optimization

This article introduces an innovative off-grid biomass/solar-based building cooling/power system equipped with concentrated photovoltaic thermal (CPVT) panels, a specific biomass heater design, an absorption chiller, and thermal energy storage tanks. The hourly variation of performance, economic, and environmental metrics is evaluated to investigate the proposed system's feasibility for a case study building in India. The effect of significant operational parameters on the system's performance is assessed by observing their influence on levelized cost of energy, biomass effectiveness, solar and biomass heat load ratios, and levelized carbon dioxide emission. The optimum design and operating conditions are ascertained through a genetic algorithm-based multi-objective optimization approach contemplating techno-economic-environmental facets to be satisfied simultaneously. According to the results, the highest monthly heat and electricity produced by the CPVT system are 521.8 kWh and 593.4 kWh in May. The results further reveal that sugarcane baggas is an excellent option compared to the most commonly used biomass in India because of the lowest price sensitivity. The parametric study results show that increasing the generator temperature leads to a favorable techno-environmental condition. Besides, the results reveal that the increase in solar panels is not economically suitable due to a higher levelized cost of energy. The optimization outcomes demonstrate that the optimum values of levelized cost of energy, biomass effectiveness, and levelized carbon dioxide emission are 58.1 USD/MWh, 3342.3 MWh, and 233.6 kg/MWh, respectively. Eventually, it can be observed that the chiller size and mass flow rate entering the CPVT panels are sensitive parameters and the optimum range of the generator temperature is between 91 °C and 95 °C.

Energy saving and environmental impact of optimizing the number of condenser fans in centrifugal chillers under partial load operation

In this paper, an optimization model is extended to optimize the coefficient of performance of refrigeration systems at partial load operation, based on optimal number of condenser fans. The sizes of vapor compression chillers are 703, 1266 and 1758 kW, and the number of fans varies from 1 to 6 while the ambient temperature ranges from 30 to 50 °C and partial load ranges from 0.25 to 1. Results show that the partial load where the optimized COP reaches its maximum value, ranges from 0.68 to 0.76 and decreases by increasing the size of chiller A correlation is proposed for partial load at which COP reaches its maximum value, as a function of nominal cooling capacity and outdoor ambient temperature. Finally, it is found that the average amount of 5.6 GWh/year electric energy saving and 5.1 ton/year CO2 emission reduction can be achieved by optimization of number of condenser fans.

Experimental and numerical analyses of a cooling energy storage system using spherical capsules

Cold energy storage during the off-peak hours to supply the cooling demand during the peak hours leads to reduction of the chiller size and energy expenses. In this paper, the performance of an ice bank system based on spherical capsules is experimentally analyzed and the effects of different parameters are investigated using a numerical model. The numerical simulation is performed for optimum design of the energy storage system and the results of numerical simulation are validated against the experimental data. Moreover, temperature distribution inside the ice bank is evaluated, experimentally and numerically, and heat transfer rate from the spherical capsules wall and the liquid fraction inside these spherical capsules are determined using numerical simulations during the charge and discharge processes. The results indicate that utilization of two inlets for heat transfer fluid (HTF) leads to decrease of charging time by 11 min and increase of the efficiency by 37%. Moreover, the best efficiency during the charge and discharge modes are 77% and 51% using 0.04 kg/s mass flow rate, respectively. Furthermore, the results showed that when the capacity of the system increases by increase of spherical capsules from 60 to 120, the system efficiency during the charge and discharge processes increase by 26% and 23%, respectively.

Optimal configuration of multiple-chiller plants under cooling load uncertainty for different climate effects and building types

Configuring the number and size of chillers in a multiple-chiller plant properly is an efficient way to improve the plant energy efficiency. At the design stage, the optimal configuration can be achieved through matching the capacity to load as closely as possible across the full-load profile. However, in spite of the fact that current literature offers practical recommendations, a systematic method to optimize the configuration of multiple-chiller plants is lacking. Due to the lack of accurate information at the design stage and only limited knowledge of the eventual realization it is hard to predict the building’s cooling load. Moreover, there is no operational data to predict the system performance. Both explain the existence of uncertainty in the HVAC plant design process. This paper, therefore, proposes a strategy to optimize the configuration of multiple-chiller plants, which takes account of the load side uncertainty as well as the COP uncertainty and selects the optimal configuration through a life-cycle analysis. Both the load side uncertainty and the COP uncertainty are quantified using statistical distributions. To facilitate applications, the distributions of the cooling load profile of different types of buildings under different weather conditions are investigated and are classified into four categories, and the optimal configuration schemes under each type of cooling load distribution are analyzed and summarized in a tabulated form.

Feasibility Study of Turbine Inlet Air Cooling using Mechanical Chillers in Malaysia Climate

The performance of a gas turbine is dependent on the ambient air temperature. The gas turbine’s power output is reduced and heat rate is increased as a result of higher air temperature. The warm and humid climate in Malaysia, with its high ambient air temperature, has an adverse effect on the performance of gas turbine generators. Turbine Inlet Air Cooling is a power augmentation technology for gas turbines, which reduces the turbine inlet air temperature thereby improving the power output and heat rate of the machine. In this paper the effect of Turbine Inlet Air Cooling using electric chillers, on the performance of the LM6000PD Gas Turbine Generator (43.5MW ISO rating) is evaluated in the context of the Malaysian climate. GT Pro software is used to evaluate the performance of the gas turbine generator with ambient air temperature cooled to 12°C. The ambient design points used for the sizing of the chillers are the 0.4% Evaporative (Design Point A) and the 0.4% Cooling (Design Point B) design points for Sitiawan, Perak as published by ASHRAE. It is observed that Design Point A results in a chiller capacity of 1950RT which is sufficient to satisfy the cooling demand of the Turbine Inlet Air Cooling system for approximately 98% of the operating hours in a year, while Design Point B yields a smaller chiller size of 1700RT which is capable of meeting the Turbine Inlet Air Cooling requirement for approximately 72% of the annual operating hours. In terms of Gas Turbine performance, the net power output is increased by 27.5% and 32.11% while the net heat rate is reduced by 2.8% and 3.74% for Design Points A and B respectively. The substantial improvement in gas turbine net power output and heat rate as predicted by the GT Pro demonstrate that Turbine Inlet Air Cooling using electric chillers is effective as a power augmentation technology in Malaysia.

Design optimization and sensitivity analysis of a biomass-fired combined cooling, heating and power system with thermal energy storage systems

In this work, an operation strategy for a biomass-fired combined cooling, heating and power system, composed of a cogeneration unit, an absorption chiller, and a thermal energy storage system, is formulated in order to satisfy time-varying energy demands of an Italian cluster of residential multi-apartment buildings. This operation strategy is adopted for performing the economical optimization of the design of two of the devices composing the combined cooling, heating and power system, namely the absorption chiller and the storage system. A sensitivity analysis is carried out in order to evaluate the impact of the incentive for the electricity generation on the optimized results, and also to evaluate, separately, the effects of the variation of the absorption chiller size, and the effects of the variation of the thermal energy storage system size on the system performance. In addition, the inclusion into the system of a cold thermal energy storage system is analyzed, as well, assuming different possible values for the cold storage system cost. The results of the sensitivity analysis indicate that the most influencing factors from the economical point of view are represented by the incentive for the electricity generation and the absorption chiller power. Results also show that the combined use of a thermal energy storage and of a cold thermal energy storage during the hot season could represent a viable solution from the economical point of view.

Study on the performance of compact adsorption chiller with vapor valves

Adsorption refrigeration is considered a green refrigeration technology that can be driven by a low-grade heat source to generate cooling power. However, the large bulk of adsorption chillers can limit its use especially automobiles. The size of the adsorption chiller is a very important consideration for applying in the automobile. The new type of compact adsorption chiller applied in the automobile was proposed corresponding with the specification of the automobile installation, and was about 40L by volume in this paper. A vacuum valve was used to increase the adsorption chiller size considerably. Thus, the new adsorption chiller has four pieces of vapor valves instead of vacuum valves, as well as two pieces of adsorbers, an evaporator, and a condenser. The vapor valve was controlled by the pressure difference at both sides. The prototype adsorption chiller was manufactured and evaluated for its cooling power and coefficient of performance by testing the inlet and outlet temperatures of the evaporator, flow rate of chilled water, and cycled time. The maximum cooling power was approximately 1.5kW at a driving temperature of 368K and a cycle time of 90s.

Effects of scenario uncertainty on chiller sizing method

Opportunities to save energy in the design and operation of Heating, ventilation and air conditioning (HVAC) systems have come into sharp focus. Lighting intensity, electric equipment load and occupant density have great impact on the peak cooling load of building, which is the basis of the chiller sizing. There is inevitable uncertainty in the determination of the values of these three scenario parameters at the detailed HVAC design stage and thus these uncertainties can considerably impact chiller sizing choice. However, the conventional chiller sizing method does not deal well with these uncertainties. A new chiller sizing method is proposed in this paper taking into account the scenario parameter uncertainty, the discrete spectrum of nominal cooling capacity of available chillers, the difference of chiller cooling capacity under nominal condition and peak cooling load condition. The new approach quantifies the impacts of scenario uncertainty on peak cooling load, chiller life cycle cost (LCC), and also on annual set point unmet hours based on the Monte Carlo method and dynamic simulation. For the case study, compared with conventional sizing method, the new sizing method can greatly reduce chiller nominal cooling capacity and the minimum reduction is 22.51%. The new method can help the HVAC designer to determine the optimal chiller size with the consideration of scenario uncertainty and the balance of chiller LCC and indoor thermal comfort of HVAC system.

Transient simulation and parametric study of solar-assisted heating and cooling absorption systems: An energetic, economic and environmental (3E) assessment

This paper presents energetic, economic, and environmental (3E) analyses of four configurations of solar heating and cooling (SHC) systems based on coupling evacuated tube collectors with a single-effect LiBr–H2O absorption chiller. In the first configuration (SHC1), a gas-fired heater is used as the back-up system, while a mechanical compression chiller is employed as the auxiliary cooling system in the second configuration (SHC2). The capacity of the absorption chiller is designed based on the maximum building cooling load in these configurations. The third and fourth configurations (SHC3 and SHC4) are similar to SHC2, but the absorption chiller size is reduced to 50% and 20%, respectively. The results show that the highest primary energy saving is achieved by SHC2, leading to a solar fraction of 71.8% and saving 54.51% primary energy as compared to a reference conventional HVAC system. The economic performance of all configurations is still unsatisfactory (without subsidies) due to their high capital costs. However, if a government subsidy of 50% is considered, the results suggest that SHC4 can be economically feasible, achieving a payback period of 4.1 years, net present value of 568,700 AUD and solar fraction of 43%, contributing to 27.16% decrease in the plant primary energy consumption.

Study on Energy Materials with the Impact of Using Chilled Water Storage Systems on the Performance of Air Cooled Chillers

In the air conditioning (AC) industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. It is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending up on the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

Optimization criteria for cogeneration systems: Multi-objective approach and application in an hospital facility

Cogeneration is commonly recognized as one of the most effective solutions to achieve the increasingly stringent requirements in primary energy consumption reduction and greenhouse emissions reduction. The potential of cogeneration led to the adoption of specific directives promoting this technique. In addition, distributed generation plays a strategic role in power reliability. The study and prototyping of cogeneration plants has thus involved many research centers. Similar activities were carried out by DiME (University of Naples). These activities highlighted the need to study the cogeneration system-user interaction to estimate the real energetic and economic benefits.The paper develops a specific methodology that is used to conduct an analysis on the loads of a specific hospital facility. The energetic and economic benefits generated by CHP plants depend on plant and user characteristics, plant layout, management strategies, and economic variables. Therefore, the potential benefits that have attracted the attention of the scientific community are not always granted. For this reason, a predictive analysis is needed to find the optimum configuration of the plant (i.e., engine size, plant configuration, management strategies, absorption chiller size, engine number) that approaches the best energetic solution while ensuring a reasonable profit. Therefore, this study attempts to determine the optimal configuration through a multi-objective approach.

The Impact of Using Mathematics Principles on the Performance of Chillers

In AC industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. Since the chiller in an air cooled AC system represent more than 75% of the total electrical power consumed by an AC system during the peak demand period, the impact of using CWS systems with alternative operating strategies including partial(load leveling ),partial (demand limiting) and full load has been investigated. In our conclusions we estimate that approximately 45% of the total annual exported electrical energy is consumed solely by AC systems as a result of the very high ambient temperatures. Furthermore, it is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending up on the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

Optimal controls of building storage systems using both ice storage and thermal mass – Part II: Parametric analysis

This paper presents the results of a series of parametric analysis to investigate the factors that affect the effectiveness of using simultaneously building thermal capacitance and ice storage system to reduce total operating costs (including energy and demand costs) while maintaining adequate occupant comfort conditions in buildings. The analysis is based on a validated model-based simulation environment and includes several parameters including the optimization cost function, base chiller size, and ice storage tank capacity, and weather conditions. It found that the combined use of building thermal mass and active thermal energy storage system can save up to 40% of the total energy costs when integrated optimal control are considered to operate commercial buildings.

An integrated model for the design of air-cooled chiller plants for commercial buildings

Cooling load calculation is the first step in designing the air-conditioning system of a building. The calculated cooling capacity with appropriate buffer is then used to select the number and size of chillers in the system. N + 1 is a common formula used by designers to size the chiller plants in Hong Kong buildings, where N is the actual number of chillers required and 1 is a redundant chiller provided to ensure reliability. This paper reviews the problem of excess capacity and discusses the risk exposure of chiller systems without redundant chillers. The cooling load profiles of the chiller plants of four medium-sized commercial buildings in Hong Kong are reviewed. The risk exposure of chiller systems without redundant chillers can be minimized by applying risk-based preventive maintenance. The just-in-demand design reduces capital cost of the building and frees up funds for continuous energy measurement and improving the energy efficiency of chiller plant systems. This paper presents a model for designing chiller plants that improves the energy efficiency of the plant in a cost effective and thoughtful manner. It is designed with consideration of the life cycle of the plant and real-time continuous commissioning, monitoring, measurement, comparison and execution for better energy management.

A low carbon cooling system using renewable energy resources and technologies

A simulation study to assess the performance of a renewable energy (solar–biomass) based single effect LiBr–water absorption chiller suitable for residential applications was conducted. The model took into account the characteristics of all the components of the system. Using Bangkok meteorological data and component specifications from manufacturers and other sources, the performances of solar collector, storage tank, biomass gasifier and boiler, and the absorption cooling system, as well as the overall system performance on a daily and monthly basis has been evaluated. The chiller and overall system coefficient of performances was found to be 0.7 and 0.55 respectively and the biomass (charcoal) consumption for 24 h operation was 24.44 kg/day. To validate the model formulation and its predictions, experimental observations of a similar system (same chiller size) were compared with the model results. The results of the study indicate that solar–biomass hybrid air conditioning for tropical locations for residential applications is feasible, and can replace conventional vapor compression systems, thus reducing the need for fossil fuel based energy systems for cooling purposes.

A Novel Free-Cooling Scheme for Combustion Turbine Inlet Air Cooling

Free cooling is a well-known concept in the HVAC industry in which the cold water produced by a cooling tower is used directly to satisfy the requirement of the cooling load without assistance by the chiller; this concept, however, is not reported in the turbine inlet air-cooling applications. Free cooling works well as long as the ambient wet bulb temperature (WBT) is sufficiently low to produce cold water at the required temperature, but once WBT reaches its threshold value (hence, free-cooling mode is ceased) and the chiller kicks off working under its normal mode of operation, i.e., free cooling is either enabled or disabled. The proposed system in this paper provides, in addition to the above modes of operation, a novel mode that utilizes the cooling tower as a primary source of cooling simultaneously with the chiller that serves as a secondary source at elevated WBT. This new feature significantly reduces the yearly operating hours of the chiller and possibly its size, depending on the desired inlet air temperature, actual weather conditions, and design WBT. Chiller size can vary between 0% and 100% as compared to a similar classical chiller system with significant reduction in the operating hours. The proposed system consists basically of chiller, cooling tower, cooling coils, interconnecting piping, and controls. The arrangement of the system equipment changes with the operation modes in two configurations: dual water circulation loops and single water circulation loop. In the dual-loop configuration, the system has two separate loops such that the evaporator and the cooling coils are tied in one loop, while the cooling tower and condenser in the other loop; whereas in the single-loop configuration, all equipment is connected in series in one water circulation loop. This paper presents the major equipment and characteristics of the novel chiller scheme. In addition, the study outlines the potential reduction in the chiller load, size, and operating hours under a generalized weather envelope. The paper portrays the feasibility of using the proposed cooling scheme for turbine inlet air cooling.