Chilled Water Flow Rate Research Articles

Adaptive control algorithm with a retraining technique to predict the optimal amount of chilled water in a data center cooling system

We developed control algorithms based on one of three artificial-intelligence-based retraining techniques (sliding window, vector adaptation, and vector augmentation) to provide the optimal indoor temperature and save on the energy expenditure for cooling in data centers. The artificial neural network prediction model predicts the computer room air handler supply air temperature of a central chilled water system and is added to the control algorithm. The proposed algorithm can determine the optimal chilled water flow rate required to cool the server to the set temperature by using the predicted computer room air handler supply air temperature. We developed a control algorithm embedded in an artificial neural network predictive model that includes three retraining techniques. Afterward, we compared the control performance and verified its adaptability by using computer simulation. When using the algorithm with sliding window control, the root mean-squared error between the set temperature and the control temperature was 0.08 °C, the maximum error was 0.81 °C, and the cooling load was 21,026.27 kWh. The accuracy, stability, and energy-saving ability of the sliding window control algorithm were higher those of the other two algorithms, and its superior adaptability and scalability under changing environmental conditions were demonstrated.

SOIL TEMPERATURE CONTROL FOR GROWING OF HIGH-VALUE TEMPERATE CROPS ON TROPICAL LOWLAND

Low soil temperature (14℃–20℃) favours growing of high-value temperate crops that are known to have higher return per hectare of land than other widely cultivated crops, thereby presenting increased income to farmer. However, due to high soil cooling load, growing these crops on tropical lowland area is a challenge except through greenhouse farming or on few cool higher altitudes with resemblance of temperate climate. Greenhouse farming involves cooling the entire volume of planting zone and is energy intensive, while few cool highlands are not sufficient to achieve food security in this direction. This study aims at application of chilled water for direct cooling of soil, to create favorable soil conditions for optimal performance of planted temperate crops. However, soil cooling using vapour compression refrigeration system may not be economically viable. Solar thermal chilled water production system is presented in this study to supply the cooling. The system consists of absorption refrigeration system and dimensioned size of soil bed with chilled water pipe network. The study includes modeling of soil cooling load to determine the refrigeration power required to overcome such load. The modeled system matched well with the experiment; having standard deviation of 1.75 and percentage error of 12.24%. Parametric analysis of the soil cooling showed that temperatures of cooled soil were significantly affected by chilled water flow rates. The regression equation developed from the Analysis of Variance (ANOVA) is suitable for predicting cooled soil temperature. The cooling process is technically feasible, with potential for greenhouse gas emission reduction.

Parameter selection in data-driven fault detection and diagnosis of the air conditioning system

Data-driven fault detection and diagnosis system (FDD) has been proven as simple yet powerful to identify soft and abrupt faults in the air conditioning system, leading to energy saving. However, the challenge is to obtain reliable operation data from the actual building. Therefore, a lab-scaled centralized chilled water air conditioning system was successfully developed in this paper. All necessary sensors were installed to generate reliable operation data for the data-driven FDD. Nevertheless, if a practical system is considered, the number of sensors required would be extensive as it depends on the number of rooms in the building. Hence, parameters impact in the dataset were also investigated to identify critical parameters for fault classifications. The analysis results had identified four critical parameters for data-driven FDD: the rooms' temperature (TTCx), supplied chilled water temperature (TCHWS), supplied chilled water flow rate (VCHWS) and supplied cooled water temperature (TCWS). Results showed that the data-driven FDD successfully diagnosed all six conditions correctly with the proposed parameters for more than 92.3% accuracy; only 0.6-3.4% differed from the original dataset's accuracy. Therefore, the proposed parameters can reduce the number of sensors used for practical buildings, thus reducing installation costs without compromising the FDD accuracy.

Analysis of operation and construction parameters for adsorption chiller performance with MATLAB/Simulink simulation

The study focuses on improving operation and construction parameters that affect cooling performance novel adsorption chiller with a unified condenser-adsorbent bed. The effect of the variables on novel adsorption chiller is taken into consideration. The cooling performance of the chiller is analyzed using the central composite design and response surface methodology simulations. The effects of cooling/heating water flowrates of the adsorber, chilled water flow rates in the evaporator, evaporator heat exchangers areas, and construction material of adsorption chiller on cooling performance are analyzed by a developed dynamics-based model using MATLAB/Simulink. R-square of 0.9531 showed good agreement between experimental and Simulink results. The chiller cooling performance is estimated with the developed correlation with an R-square of 0.9995 using central composite design simulations. The best cooling performance value is found as 0.9013 with an aluminum material design where water flow rates dominate the performance.

Application of energy-saving control strategy in air conditioning terminal equipment based on constant temperature difference of chilled water

Effectively reducing the energy consumption of central air conditioning systems is an important aspect of building energy efficiency. The energy consumption of terminal equipment accounts for over 25% of that of air conditioning systems. Although the heat and moisture exchange mechanism of the terminal unit has been extensively studied, studies on control strategies for terminal unit operation are lacking. This study proposes an energy-saving optimization control strategy for terminal units based on the constant temperature difference of chilled water in an engineering application study. A fan coil unit (FCU) controller was designed and manufactured, and a Local Area Network (LAN) control system was constructed and compared to determine the optimal control strategy. When adopting the energy-saving optimization control strategy for the terminal unit based on a constant chilled water temperature difference, the energy consumption of the terminal equipment was significantly decreased by 7.2%. The flow rate of chilled water was reduced by 26.94% when the indoor air temperature requirements were met, effectively reducing the energy consumption of the central air-conditioning system. The adjustment time required to reach a stable indoor temperature was reduced and environmental comfort was improved. These results demonstrate the potential of this control strategy for use in engineering practices to replace traditional control modes.

Chilled Coil Control and Field Performance for Turbine Inlet Air Chilling

Ambient conditions greatly affect the combustion turbine performance. The Absorption Refrigeration Cycle Turbine Inlet Chilling (ARCTIC) system can chill the inlet air of the turbine to maintain optimum performance at all ambient temperatures. However, turbine characteristics, bell-mouth icing concerns, economics and performance guarantees require maintaining the inlet air temperature within a narrow range throughout the year. These considerations require strict control of the Turbine Inlet Air Chilling (TIAC) coil performance over a wide range of operating conditions. This paper describes the field performance and control of the chilling coil for a Mars 100 turbine. The controls logic had been developed from previously published empirical model of the chilling coil and model of the chilling loop performance at the various ambient conditions. Since commissioning at the end of summer 2020, the ARCTIC has provided inlet air chilling over a range of ambient conditions. Typically, the inlet air is maintained at 7.2∘C (45∘F) by controlling the TIAC chilled water flow rate and temperature. On cooler days, if the inlet air temperature drops to 5.6∘C (42∘F) the chilled water pump turns OFF automatically to prevent bell-mouth icing. Thus, the chiller accommodates chilling load variations down to zero load. On colder days, the ARCTIC continues operating till the ambient temperature drops below 1.7∘C (35∘F) and then turns OFF. The chiller turns back ON when the 8 h average inlet air temperature exceeds 10∘C (50∘F). These parameters can be adjusted remotely by the operator and help maintain performance guarantees while minimizing chiller cycling. Quasi-steady state data were analyzed to quantify the chilling load and coil performance over a range of operating conditions.

Experimental investigation on the control performance of an active chilled beam system under dynamic cooling loads

Abstract In this study, the control performance of an active chilled beam (ACB) system was investigated, in order to find the suitable control parameter for controlling room air temperature and preventing surface condensation when the cooling load suddenly increases. For this purpose, the impact of ACB control parameters on the cooling capacity was evaluated with mock-up experiments. Compared to the baseline condition in this study, the adjustment of the chilled water temperature and primary air flow rate raised the cooling capacity by 47% and 98%, respectively, while the adjustment of the chilled water flow rate and primary air temperature led to a relatively small increase in cooling capacity. In addition, the control performance of room air temperature was evaluated with the room air temperature drop for one hour after a step change in cooling load. It was observed that the room air temperature dropped 0.2 °C with chilled water temperature control and 0.7 °C with primary air flow rate control, whereas it dropped 1.0 °C with the simultaneous control of the chilled water temperature and primary air flow rate. The test results further showed that simultaneous control of the chilled water temperature and primary air flow rate is effective for preventing the surface condensation while providing the sufficient cooling capacity. The findings of this study can provide the information on the thermal behavior of ACB system, which is necessary for establishing control strategies for ACB systems.

Chiller system optimization using k nearest neighbour regression

This study applies the k nearest neighbour (kNN) regression to ascertain optimal operating strategies for a chiller system, hence lowering its carbon emissions. First, 19 operating variables were identified for the regression of the coefficient of performance (COP)—the total cooling capacity divided by the total power of system components. Cross validation involved splitting ten partitions of test samples from a set of operating data with 14537 time points. The optimal k = 3 is evaluated with the lowest mean square error of 0.00148. Using the random kNN, the most significant variables are found to be the temperature and flow rate of return chilled water, the load of individual chillers is the next, followed by the condenser water leaving temperature in system optimization. Based on the existing building cooling load profile with ambient conditions, the optimal variables with the maximum COP are identified from neighbour conditions at the 99th percentile of the distance distribution. The optimal schedule of switching chillers and temperature settings improve the seasonal COP from 3.27 to 3.90, reducing the carbon emissions by 178160 kg CO2e. The novelty of this study is the application of the kNN regression with enhanced distance selection criterion to identify specific optimization strategies which fulfil the existing design and operating constraints of engineering systems.

Variable importance for chiller system optimization and sustainability

Very few studies have considered modelling the statuses of loading and component combinations (LC) in chiller systems. This study uses a decision tree (DT) and a neural network (NN) to model accurately six output levels of LC in terms of 11 predictor variables. The NN model gave a higher correct prediction of 89.52% than 84.44% in the DT model. A variable dropout analysis from the DT and NN models generalizes the top five significant variables: the statuses of cooling towers and primary chilled water pumps, and the supply temperature, return temperature and flow rate of chilled water. The system coefficient of performance (SCOP) modelled by NN has an improved R 2 of 84.18% versus 74.62% when the significant variables are included as inputs. The SCOP maximization brings three optimal strategies—implementing chiller sequencing, operating components in pairs and optimizing chilled water supply temperature—which reduce CO2 emissions by 99,815–346,987 kg.

Modified Chilled Coil Model Development and Application to Turbine Inlet Air Cooling

A Turbine Inlet Air Conditioning (TIAC) system can chill the inlet air of the turbine to maintain maximum turbine performance at all ambient temperatures. However, turbine characteristics, performance guarantees and bell-mouth icing considerations require accurate prediction of the chilling coil performance over a wide range of operating conditions. A modified wet-surface model (MWSM) is developed to more accurately predict the chilling coil performance. The higher accuracy of the model is demonstrated by applying the model to simulate performance data of two different coils. The data covered a wide range of operating conditions with ambient temperature vary from [Formula: see text]C to [Formula: see text]C dry bulb and [Formula: see text]C to [Formula: see text]C wet bulb. The turbine flow rate varies from 100% to 43% with chilled air temperature in the range of 3.3–[Formula: see text]C and chilling load variation of 100% to 5%. The chilled water flow rate varies from 100% to 32% with supply glycol-water temperature in the range of [Formula: see text]2.2–[Formula: see text]C. The MWSM uses 11 empirical parameters evaluated from the coil performance data and is able to correlate the data with an adjusted coefficient of determination ([Formula: see text]) of over 99%. The higher accuracy of the modified model enables the development of a more robust controls strategy required to maintain the inlet air temperature at the set point with varying ambient temperatures and chilling load conditions. The model can also be applied to other chilling and dehumidification applications especially those experiencing wide variations in operating conditions and load or those requiring close control of the chilling and dehumidification process.

A model-based multi-objective optimization of energy consumption and thermal comfort for active chilled beam systems

Active chilled beam (ACB) systems provide two highly-coupled cooling capacities due to its unique structure through combining primary air nozzle and cooling coil, whose energy consumption is difficult to be estimated and balanced against thermal comfort. This study considered the trade-off between energy consumption and thermal comfort as a multi-objective optimization problem and proposed a novel and practical solution by utilizing empirical energy models of the ACB system and an evolutional non-dominated sorting genetic algorithm II. The energy models are established for components of fans, pumps, and chillers based on fundamental equations which are validated by experimental data. The thermal comfort of each room is quantified by the predicted percentage dissatisfied (PPD) model. Chilled water flow rate, primary airflow rate, and room temperature in ACB systems are specifically chosen as control variables due to the control convenience. Besides, a parameterless selection strategy that considers both thermal comfort and energy consumption is proposed to select the most appropriate solution among Pareto optimal solutions. Three steady-state experiments with different heat load conditions are conducted. Compared to experienced operation, the proposed strategy demonstrates a maximum of 39.32% of energy saving and 12.21% of PPD reduction by increasing the water flow rate and room temperature, and reducing the primary airflow rate. Furthermore, this study investigates the distribution of capacities in ACB systems and suggests to assign more capacity to the cooling coil based on energy efficiency considerations. A good trade-off is achieved between energy consumption and thermal comfort through the proposed multi-objective optimization strategy.

Experimental and numerical optimization on chilled water configuration for improving temperature performance and economic viability of a centralized chiller plant

This research aimed to simulate and optimize chilled water circuit system of a central air conditioning plant applied for a five-star hotel in Bali Island, Indonesia. This optimization was performed because temperature of chilled water distributed to the loading system could not satisfy room temperature requirement. Detailed measurements have been taken on the AC system included refrigeration system of the chillers, chilled water and cooling water distribution, cooling load, heat rejection and pumping systems. Thermodynamic analyses on the system energy performance were carried out. Numerical simulations were also established to evaluate chilled water flow rate in the primary and secondary circuits. The measurement and simulation results showed there was unbalanced chilled water flow rate between primary and secondary circuits and the chilled water flow rate did not comply with rule of flow ‘primary flow must always be equal to or greater than secondary flow’ resulted in the cooling load coils lost their cooling capability. Optimization on the chilled water flow rate between primary and secondary circuits by implementing variable speed pumping system incorporated balancing valve was estimated to be potentially improve temperature performance and economic viability of the chiller plant operation.

Experımental investigation of heat pump driven humidification-dehumidification desalination system for water desalination and space conditioning

This work presents an experimental investigation of the performance of a HDH system operated by heat pump. The novel heat pump system provides the necessary heating for the humidifier and cooling for the dehumidifier of the HDH system. The proposed integrated unit is capable of producing freshwater as well as cooling effect for space conditioning through water heated or cooled heat exchange units. Influence of various operating parameters such as feed water flowrate, feed water temperature and chilled water flowrate on the general assessment metrics, including gain output ratio (GOR), recovery ratio (RR), coefficient of performance (COP), energy utilization factor (EUF), Specific electrical energy consumption (SEEC) and productivity are evaluated. The cost of freshwater production from the proposed desalination unit is estimated. Results showed that the integrated system is capable of attaining maximum GOR of 4.07, RR of 4.86%, COP of 4.85, EUF of 3.04, and productivity of 287.8 L/day. The minimum SEEC of the system was found to be 160.16 kWhr per cubic meter of freshwater. The system is also capable of providing cooling load of 3.07 kW while producing the needed desalinated water. The estimated price of freshwater production varied from 10.68 US$ to 20.39 US$ per cubic meter.

Experimental Study of a Gas Engine-driven Heat Pump System for Space Heating and Cooling

In this paper, the performance of a gas engine-driven heat pump (GEHP) was experimentally studied for space heating and cooling. An experimental test facility was developed for this purpose. The effect of key parameters on system performance was investigated under both cooling and heating modes. The results showed that as the engine speed increased from 1400 to 2000 rpm, the cooling and heating capacities increased by 23% and 28.5%, respectively while the GEHP system Primary Energy Ratio (PER) decreased by 13.5% and 11.7% in the cooling and heating modes, respectively. The system PER in the cooling mode was found lower than that in the heating mode. This indicated that heat recovery from the engine cylinder and exhaust gas was very important for improving the GEHP system performance. In the heating mode, the ambient temperature and condenser water flow rate had a large effect on the system heating capacity and PER, and insignificant effect on the gas energy input. In the cooling mode, the chilled water inlet temperature showed a large effect on both cooling capacity and gas energy input while the chilled water flow rate had a large effect on cooling capacity and insignificant effect on the gas energy input.

A theoretical and experimental study of a TBAB salt hydrate based cold thermal energy storage in an air conditioning system

Various phase change materials (PCMs) have been studied in the past decade for cold thermal energy storage (CTES), among which semi-clathrate hydrates of quaternary ammonium salts have aroused great interests. Tetrabutylammonium bromide (TBAB) hydrates can form at temperatures applicable for air conditioning applications. Based on the results of former studies on a TBAB hydrate based PCMs, this paper investigates the influencing factors of a lab-scale CTES tank based on this self-developed PCM in an emulated air conditioning system. The effect of chilled water temperature and flowrate on charge, and the effect of return water flowrate and cooling load on discharge are experimentally studied. A model of the CTES was developed using ε-NTU method, through which its performance are evaluated in terms of charging/discharging rate, charging/discharging capacity and efficiency. In addition, influencing factors such as return water temperature and flowrate, initial PCM liquid fraction, and the number and material of the heat transfer coils are analysed using TRNSYS simulation employing the developed CTES model. According to the results, it is suggested in the actual use of TBAB hydrate based CTES to apply 2.0 °C chilled water for charge with initial solids and 4.0 °C chilled water for charge without initial solids. The optimal chilled water flowrate, 12 g s−1 for charge with initial solids and 18 g s−1 for charge without initial solids, can also be employed. In addition, in the design of a CTES the heat transfer coils are suggested to have a thermal conductivity close to 16 W m–1 K−1 but no need to exceed this value.

Experimental study on characteristics of a dual temperature control valve in the chilled water system of an air-conditioning unit

The excess flow of water increases the energy consumption of water pumps in the chilled water systems of air-conditioning units. This paper proposes a strategy to control the chilled water flow rate of a fan coil unit (FCU) using a control valve. A physical simulation test bench was built to verify valve control and energy-saving effects. Results showed that the control valve could effectively regulate the flow rate of chilled water, improve the temperature difference (delta-T) between supply and return water, and reduce the energy consumption of the chilled water pump. With a supply water temperature of 7 C and low (325 m3⋅h−1), medium (500 m3⋅h−1), and high (600 m3⋅h−1) FCU air velocity levels, the average delta-T values were 4.79 °C, 4.39 °C, and 4.97 °C, respectively, and the energy consumption of the chilled water pump decreased by 12.20%, 11.31%, and 10.66%, respectively. With medium air velocity and supply water temperatures of 7 °C, 8 °C, and 9 °C, the average delta-T between supply and return water was 4.39 °C, 3.56 °C, and 3.33 °C, respectively, and the energy consumption of the chilled water pump decreased by 11.31%, 5.10%, and 7.80%, respectively. These research results provide useful insights in relation to the problem of excess chilled water flow identified above.

Experimental analysis on the decoupling of temperature and humidity by using a double circuit cooling coil

Double circuit cooling coil (DCCC) can be used to control the indoor air conditions in built environments. The working principle of DCCC is to adjust the chilled water flow rate and chilled water temperature in a cooling coil independently. The objective of this work is to obtain the quantitative influence of the variation of the chilled water flow rate and chilled water temperature on the outlet process air conditions, and the relationship between moisture removal capacity (MRC) and sensible heat ratio (SHR). A test air conditioning system is built to analyze the performance of the DCCC and case studies are carried out under various operating conditions. The response surface methodology coupled with a Box–Behnken design is conducted to fit the empirical regression models that are used to predict the outlet air process temperature and humidity in the DCCC system. The results show that independent control of outlet process air can be achieved if the outlet air temperature is controlled by the chilled water flow rate and the outlet air humidity is controlled by the chilled water temperature. The increase of MRC is inversely proportional to the increase of SHR.

Theoretical Prediction of Optimum Chilled Water Distribution Configuration in Air Conditioning Terminal Unit

The distribution of chilled water flow rate in terminal unit is a major factor used to evaluate the performance of central air conditioning unit. In this work, a theoretical chilled water distribution in the terminal units has been studied to predict the optimum heat performance of terminal unit. The central Air-conditioning unit model consists of cooling/ heating coil (three units), chilled water source (chiller), three-way and two-way valve with bypass, piping network, and pump. The term of optimization in terminal unit ingredient has two categories, the first is the uniform of the water flow rate representing in statically permanents standard deviation (minimum value) and the second category is the maximum heat transfer rate from all terminal units. The hydraulic and energy equations governing the performance of unit solved with the aid of FORTRAN code with considering the following parameters: total water flow rate, chilled water supply temperature, and variable valve opening. It was found that the optimum solution of three-way valve case at 8°C water supply temperature, 0.12 kg/s total water flow rate and valve opening order (valve 1: 100%, valve 2: 100% and valve 3: 75%) with total heat rate (987.92 Watt) and standard deviation (1.181E-3). Also, for the two-way valve case the results showed that the optimum condition at 8°C water supply temperature, 0.12 kg/s total water flow rate and valve opening order (valve 1: 75%, valve 2: 75% and valve 3: 50%) with total heat rate and standard deviation (717Watt) and (5.69E-4) respectively.

Optimal Operation Strategies for a Large Multi-Chiller System Based on Cooling Load Forecast

In semiconductor and electronics factories, large multi-chiller systems are needed to satisfy strict cooling load requirements. In order to save energy, it is worthwhile to design the chilled water system operation. In this paper, an optimal flexible operation scheme is developed based on a two-dimensional time-series model to forecast the cooling load of multi-chiller systems with chiller units of different cooling capacities running in parallel. The optimal integrity scheme can be obtained using the Mixed Integer Nonlinear Programming method, which minimizes the energy consumption of the system within a future time period. In order to better adapt the change of cooling load, the operation strategy of regulating the chilled water flowrates is employed. The chilled water flowrates are set as a design variable. When the chillers are running, their chilled water flowrates can vary within limits, whereas the flowrates are zero when the chillers are unloaded. This forecasting method provides integral optimization within a future time period and offers the operating reference for operators. The power and advantages of the proposed method are presented using an industrial case to help readers delve into this matter.

An optimization of the components and operating conditions of a pre-cooling system for tubular ice making machines

The mathematical models were developed to optimize the components and the operating conditions of a pre-cooling system for the conventional tubular ice production. The system can be simultaneously used with up to three ice making machines. The water used to feed into the machines is pre-cooled by circulating through a heat exchanger to transfer its heat to the chilled water circulating from a water chiller. Four ice machine capacities, 40, 50, 60 and 90 ton/day, were investigated. It was found that NTU=3 was the optimum heat exchanger capacity, the feed water flow rate to chilled water flow rate ratio of 0.5 and the feed water flow rate of 0.12 m3/min are the optimum operating conditions. The ice productivity was increased by the system. It increased with the machine capacity and the number of machines operating with the system. The increases in the productivity were in the range of 7,398-18,851 kg/day.