Chilled Water Research Articles

Performance optimisation of serial chilled water system under m-out-of-n: G policy

Performance optimisation of serial chilled water system under m-out-of-n: G policy

Comprehensive assessment and sustainability improvement of a natural gas power plant utilizing an environmentally friendly combined cooling heating and power-desalination arrangement

Considering the significant waste heat generated by existing natural gas power plants, it is imperative to implement eco-friendly combined process designs to ensure their long-term sustainability. The present paper introduces and investigates a novel integrated process aimed at achieving multiple generational advantages within an environmentally friendly framework, with the ultimate goal of enhancing sustainability. The new structure incorporates a natural gas power plant, high-temperature and low-temperature organic Rankine cycles, a combined cooling and power subsystem, and a water desalination unit to produce power, heating, cooling, and freshwater simultaneously. This system is simulated within the Aspen HYSYS software and examined from energy, exergy, economic, environmental, and sustainability perspectives. Furthermore, parametric studies evaluate the impact of the overall system's various environmental, economic, and operational conditions. It is found that the production capacities of power, hot water, chilled water, and freshwater are 179,265.17 kW, 387.8 kg/s, 563.6 kg/s, and 21.4 kg/s, respectively. Hence, the overall energy and exergy efficiencies improve to 66.06% and 42.95%, respectively. The financial estimation also reveals a cost of energy of 0.1084 $/kWh and a total net present value of 818.67 M$. It is also determined that the cost per unit of destroyed exergy is equal to 7.156 $/GJ.

THE SIGNIFICANCE OF PROPER COOLING TOWER WATER TREATMENT: A CASE STUDY

This paper presents the result of a study of the effect of cooling tower system in terms of performance and cost of maintenance. The study was conducted in a two-storey shopping complex building. Observation on site was held to obtain data on full load amp (FLA) and chilled water temperature (CWT) before and after servicing cooling tower unit. Energy of cooling tower were evaluated by analysis of FLA and CWT in percentage value. The condition on the system and component were also observed to differentiate the condition before and after treatment. The result obtained showed that cooling system performance after the treatment was increased.

Performance analysis of a novel two-bed adsorption humidification-dehumidification desalination system using Metal-organic framework 801

Adsorption desalination techniques have been increasingly studied over the last century as a sustainable option for meeting the rapidly growing demand for fresh water. One of the attractive factors for using adsorption desalination systems is the use of low-grade thermal energy normally wasted in the atmosphere. The current study introduces a novel adsorption desalination system integrated with a humidification dehumidification system for producing potable water. Four system configurations are presented. The main distinction between them is the source of hot water used for the humidifier. Scheme #1 utilizes the heat of condensation, Scheme #2 applies the heat of condensation plus the heat of adsorption, while Scheme # 3 adds the outlet of heating water from the desorber as a source of heat to the humidifier. Scheme #4 is a standalone adsorption desalination system that applies chilled water to cool the condenser. The novelty of this system is the application of the chilled water from the evaporator to the dehumidifier to create the highest possible temperature difference necessary for the humidification and dehumidification process. This advantage allows larger water productivity, especially in hot humid regions. In this case, it is possible to extract water vapour in the ambient humid air, water vapour gained from the humidification process and water vapour condensed in the condenser of the adsorption desalination system. Moreover, we have used a novel material Metal Organic Frameworks 801 as an adsorbent for a highly efficient process. Based on the results, Scheme #3 produced the maximum amount of fresh water, 210 kg/h while Scheme #2 obtained the maximum gained output ratio, 4.4 with a minimum cost of 0.0079 $/L. A standalone adsorption system produced the minimum amount of distillate water and the lowest gained output ratio. It is not advisable to use a standalone adsorption system to produce distillate water; as the full desalination potential is not achieved.

An environmentally friendly process design of an innovative CCHP-desalination system combined with a geothermal cycle and LNG regasification unit

The importance of geothermal energy in the urban energy supply is derived from its renewable nature, power generation capabilities, and potential for lowering air pollutants. The utilization of combined arrangements utilizing geothermal energy represents an outstanding alternative option. Hence, present investigation proposes a novel and environmentally friendly multigeneration framework for a geothermal energy resource, incorporating combined cooling, heating, power (CCHP), and desalination systems. Furthermore, the entire system includes a liquefied natural gas regasification unit. The present study simulates the system utilizing the Aspen HYSYS software, wherein a comprehensive analysis is conducted on considerations of energy, exergy, economics, and environment. The study also includes a comprehensive parametric study. According to the study's findings, the system can generate 863.8 kg/s of hot water, 22.01 kg/s of chilled water, and 59.67 kg/s of fresh water, along with a power output potential of 120,185 kW. Besides, this process yields energy, thermal, and electrical efficiencies at 25.08 %, 10.25 %, and 14.12 %, correspondingly. The exergy analysis findings demonstrate that the system's efficiency for power generation and multigeneration modes is 45.17 % and 47.79 %, respectively. From the economic aspect, the total unit cost of products is found at 2.91 $/GJ and the cost of energy at 0.0962 $/kWh.

Review of Micro- and Nanobubble Technologies: Advancements in Theory and Applications and Perspectives on Adsorption Cooling and Desalination Systems

Adsorption refrigerators are a compelling ecological alternative to compressor refrigerators; global warming forces us to constantly look for alternative sources of energy and cold. Cold production in adsorption chillers is based on the use of heat generated by other processes running in the company. Waste heat from production processes, which has, until now, been irretrievably lost, is a potential source of energy for generating cold via an adsorption unit producing chilled water. Cooling optimizes the use of the heating network in summer and can lead to increased electricity production while reducing heat supply losses. Thus far, attempts to implement adsorption refrigerators for widespread use have not been successful as a result of the low efficiency of these devices; this is directly related to the poor heat and mass transfer conditions in the beds and heat exchangers of adsorption refrigerators. The solutions used so far, such as new working pairs, glued beds or modifications to the structure or cycle length, are still not strong enough for these devices. Therefore, it is necessary to look for new solutions. Using micro- and nanobubbles as media to increase mass and heat transfer in refrigerators is an innovative and pioneering solution. Thus, this document describes the most important features of micro- and nanobubble technology applications in adsorption refrigerators. This article is an introduction and a basis for the implementation of further research, consolidating the existing literature as a review.

Parametric analysis of chiller plant energy consumption in a tropical climate

The approach that could reduce the energy consumption of water-cooled chillers in office buildings was investigated through experimental and simulation methods. The chiller was modelled in TRNSYS and validated using physical measurements from an operational water-cooled water chiller and fan coil system. The validated model was used to analyse the energy consumption of the water chiller-fan coil system under a high chilled water temperature setpoint (CWTS) in a representative commercial office building. Subsequently, indoor thermal comfort was evaluated using the PMV-PPD model. Finally, the design of experiment (DOE) was employed using a statistical two-level non-randomized factorial design in Minitab to study the effects of high CWTS, number of rows, and tube diameter on the heat and mass transfer performance of the fan coil unit. The results showed that the CWTS can be increased by various degrees from 10 up to 18 °C for energy efficiency for a commercial office building in the tropics. This increase in CWTS would result in a daily energy saving potential of about 5% of the chiller as compared to the existing operational settings without any extra cost. Conversely, the daily energy consumption by the fan coil would increase by about 5.5% by this increment in the CWTS. It was determined that the chiller system can provide comfort even when the CWTS is increased to 14 °C. The DOE analysis showed that under the condition of high CWTS (14 °C), energy consumption that is less than the current energy consumption may be expected from the fan coil system when the number of rows increased from 3 to 6 and the tube diameter increased from 7 to 9 mm.

Development and experimental study of a compact silica gel-water adsorption chiller for waste heat driven cooling in data centers

In recent years, data centers have experienced rapid construction, leading to a significant surge in energy consumption, and cooling systems have emerged as prominent energy consumers of data centers. Among the cooling technologies, liquid cooling allows higher cooling circuit temperatures and provides potential for heat recovery. As a thermally driven cooling technology, adsorption refrigeration systems offer an alternative way to compression refrigeration systems by utilizing low-grade waste heat from liquid-cooled circuits to produce chilled water for air-cooled components. In this study, a compact silica gel-water adsorption chiller is developed for a small modular data center and experimentally investigated under extremely low driving temperatures. Under the typical summer conditions with the hot/cooling/chilled water inlet temperatures of 50 °C/30 °C/23 °C, the adsorption chiller achieves the cooling power of 4.9 kW and the COP of 0.50. When the cooling water inlet temperature changes from 32 °C to 24 °C, both the cooling power and COP show significant improvements, from 3.04 kW to 10.50 kW and from 0.44 to 0.66, respectively. Moreover, the increase of the hot water inlet temperature from 48 °C to 56 °C can enhance the cooling power to some extent, while the chilled water inlet temperature has little influence on the performance. The experimental results demonstrate the feasibility and performance of the developed adsorption chiller in data center waste heat driven cooling. Besides, potential adsorbents and possible optimization strategies are presented for performance improvement based on adsorption potential method.

Techno-economic analysis of solar-powered membrane distillation system with circulated permeate gap

This study investigates a novel integration of a circulated permeate gap membrane distillation (C-PGMD) module with flat plate solar collectors. The investigation is performed through a comprehensive performance study and techno-economic analysis, revealing unique insights and findings. The development of mathematical models enables the anticipation of system production and energy efficiency, capturing the employment of single and multistage C-PGMD modules under diverse design and operational conditions. Additionally, an innovative assessment of different powering modes, including solar-only, electrical-only, and hybrid solar-electrical is performed, which offers a unique perspective on system control and unit production costs. Results showed that circulating the permeate gap has significant effects on the permeate flux and the temperature of the solar tank such that the circulation rate controls the operation of the system. The revelation that increasing solar collector numbers amplifies productivity while reducing costs stands out as a noteworthy breakthrough. Cooling the system using a water source at ambient temperature is much recommended compared to cooling with chilled water. The pinnacle of this research lies in the proposal of a well-designed pilot hybrid-power 30-stage C-PGMD system, showcasing a remarkable achievement in reducing production costs to approximately 0.03 USD/Liter for 24-hour operation, predominantly powered by renewable energy sources. These novel findings redefine the landscape of integrated solar membrane distillation and pave the way for more sustainable and economically viable water desalination solutions.

Experimental Investigation of Chilled and Hot Water Inlet Temperature, and Mass Flow Rate Influence on Energy and Exergy Efficiency in a Prismatic Adsorbent Bed Cooling Systems

Adsorption technologies offer a promising solution for managing high electricity demand in building by leveraging waste heat recovery and renewable energy sources. The prismatic adsorbent bed adsorption water cooling system investigates energy and exergy analyses for cooling application. With hot water temperature of 80 °C, cooling water inlet temperature 30 °C, and chilled water inlet temperature 14 °C, the system achieves an energy efficiency of 45.2% while demonstrating an energy storage density of ≈340 kJ kg−1. As a result, the exergy efficiency reaches 12.2%, and the mass fraction at the end of the adsorption process is a significant value of 0.13kgadsorbate/kgadsorbent. Increasing the water mass flow rate in the evaporator results in a decrease in exergy efficiency, while simultaneously causing an increase in energy efficiency. With an increase in the chilled water inlet temperature of the evaporator and the hot water inlet temperature of the adsorbent bed, there is an increase in the energy storage density, energy efficiency, and exergy destruction due to irreversibility and losses. According to this study, the impact of the chilled water inlet temperature on the energy and exergy performances of the evaporator is more significant compared to the effect of the water mass flow rate.

Model Predictive Control for Energy Optimization of HVAC Systems Using EnergyPlus and ACO Algorithm

The deployment of model-predictive control (MPC) for a building’s energy system is a challenging task due to high computational and modeling costs. In this study, an MPC controller based on EnergyPlus and MATLAB is developed, and its performance is evaluated through a case study in terms of energy savings, optimality of solutions, and computational time. The MPC determines the optimal setpoint trajectories of supply air temperature and chilled water temperature in a simulated office building. A comparison between MPC and rule-based control (RBC) strategies for three test days showed that the MPC achieved 49.7% daily peak load reduction and 17.6% building energy savings, which were doubled compared to RBC. The MPC optimization problem was solved multiple times using the Ant Colony Optimization (ACO) algorithm with different starting points. Results showed that ACO consistently delivered high-quality optimized control sequences, yielding less than a 1% difference in energy savings between the worst and best solutions across all three test days. Moreover, the computational time for solving the MPC problem and obtaining nearly optimal control sequences for a three-hour prediction horizon was observed to be around 22 min. Notably, reasonably good solutions were attained within 15 min by the ACO algorithm.

The relationship between the permeability and liquid water content of polycrystalline temperate ice

Abstract To better constrain meltwater transport and ice viscosity in temperate glaciers, particularly in ice stream shear margins, we use a custom permeameter to study the untested model relationship between the permeability of temperate ice and its liquid water content. The permeability of lab-made ice of two mean grain diameters (1.8 and 4.2 mm) is measured, and water content is controlled with the ice salinity and measured calorimetrically. Fluorescein dye is added to through-flowing, chilled water to highlight flow pathways through the ice after experiments. As predicted by a simple model, permeability increases with approximately the square of the water content and by about three orders of magnitude across water contents of 0.1–4.4%. However, permeability values are less than those of the model by average factors of 2.6 and 4.1 for the finer and coarser ice, respectively. This discrepancy is likely due to tortuous, truncated or air-clogged veins. The order-of-magnitude agreement between measured and modeled values may indicate that reduced permeability from these factors is nearly compensated by preferential flow in oversized veins that are isolated or arborescent. Both kinds of preferred flow pathways are observed but the latter only in fine-grained ice at water contents > 2%.

Ammonia heat pumps for district heating: thermo-economic optimization analysis based on evaporator geometry for either direct expansion or chilled water configurations

Electric heat pumps are recognized as a key technology for decarbonization and have received increasing policy support in several countries over the last few years. These devices offer a highly efficient form of electric heating and could make an important contribution to the transition to a low carbon future, especially in case of district heating systems. Within this context, this paper presents a thermo-economic optimization analysis of a 7.35 MW electric heat pump system employed for district heating purposes and using ammonia as working fluid. The implemented code gathers multiple sub-models calibrated ad-hoc from real data or manufacturers’ datasheets. The heat exchangers are simulated by considering phenomenological equations and well-known heat transfer coefficient and pressure drop prediction methods. The optimization analysis is performed at constant condensation temperature that guarantees in/out hot water temperatures of 30/62 °C and is focused on the matching between compressor and evaporator heat exchanger, by considering either a direct expansion system or a chilled water heat pump. Both the coefficient of performance (COP) and the set-up costs are considered as optimization performance indicators for the construction of the Pareto front.

A comprehensive thermo-economic-environmental study of an eco-friendly process incorporated with a natural gas-fed combined power plant for a novel multigeneration application

In order to achieve very efficient heat recovery, this study presents an innovative, environmentally friendly multigeneration process that is incorporated into a natural gas combined cycle system. A water electrolyzer, an enhanced absorption refrigeration cycle, a water desalination unit, and methanol production are only a few of the subsystems that must be used in this process. The simulation methods are carried out using the Aspen HYSYS program, which allows for a comprehensive study about the thermo-economic-environmental component. The feasibility analysis results show that the system can produce 111 MW of electricity, 175.6 kg/s of chilled water, 334.9 kg/s of domestic hot water, 7.54 kg/s of oxygen, 18.8 kg/s of fresh water, and 4.59 kg/s of methanol. Consequently, it is found that the energy and energy efficiencies are, respectively, 55.58% and 62.36%. It is shown that 344.3 MW is the overall irreversibility related to the suggested construction. Notably, the combustion chamber contributes the most of all the components, making up a significant 42.94% of the total. The primary cause of irreversibility among the subsystems is the natural gas combined cycle, which accounts for 76% of the total. Furthermore, from an economic standpoint, the entire product cost is 0.0566 $/kWh, but the total unit cost of the goods is 3.59 $/GJ. Additionally, 807.98 M$ is the determined number for the net present value. Furthermore, the suggested system has a carbon dioxide footprint of 0.286 kgCO2/kWh. This variable is 8.88% and 8.13% less than those of stand-alone power plants powered by natural gas and oil, respectively.

Simulation and performance research of absorption heat pump unit based on R134a-DMF working fluid pair

R134a-DMF absorption heat pump unit is an energy-saving heat pump unit that can utilize renewable energy, and has great potential in the refrigeration and heating fields of urban and rural areas. The purpose of this article is to conduct in-depth research on the dynamic characteristics of absorption heat pump units based on R134a-DMF, a new working fluid pair. A mathematical model of the thermophysical properties of the R134a-DMF working fluid pair and the mathematical models of various components of the heat pump unit are constructed. This paper constructs a simulation program, and uses the Control variates to study the change trend of the Coefficient of performance of R134a-DMF absorption heat pump unit affected by the generator outlet concentrated solution temperature, condenser air volume and temperature rise, and chilled water outlet temperature. The results indicate that the established mathematical model for thermophysical properties and the unit model are both accurate models, which can provide guidance for the actual operation and optimization of R134a-DMF absorption heat pump units. Through simulation, it can be concluded that for the three combined forms of R134a DMF (3:2), R134a DMF (1:1), and R134a DMF (2:3), the average increase in COP and refrigeration capacity is 0.85 %, 0.39 %, and 0.42 % for each 1 °C increase in the outlet concentrated solution temperature of the generator, respectively, and the growth rate is relatively slow. The larger the proportion of refrigerant in the binary solution, the greater the COP of the unit under the same operating conditions.

Tracking the contamination sources of microbial population and characterizing Listeria monocytogenes in a chicken slaughterhouse by using culture-dependent and -independent methods

Listeria monocytogenes is the etiologic agent of listeriosis, a foodborne disease that poses a threat to public health globally. Chicken meat exhibits heightened susceptibility to L. monocytogenes contamination during butchery. The persistence of this pathogen in the slaughterhouse environment enables recurring contamination of meat products. This study aimed at identifying the sources and transmission routes of L. monocytogenes contamination within an abattoir where it was consistently detected for three consecutive years (2019–2021). Furthermore, the environmental factors aiding contamination along chicken processing lines were determined by surveying the microbiome within the facility. Samples collected in 2019 to 2021 were subjected to culture-dependent analysis to assess the prevalence, serotypes, and multi-locus sequence typing (MLST) of L. monocytogenes. Additionally, the specimens collected in 2021 underwent culture-independent analysis via real-time quantitative polymerase chain reaction (qPCR) and 16S rRNA gene amplicon sequencing to identify the contamination sources and characterize the entire microbial community within the slaughterhouse. L. monocytogenes was isolated only from the clean zone, where the final slaughtering stage occurs. Most strains isolated from the final carcasses showed the same genetic cluster as the isolate in the chilling water and were assigned to MLST profile ST3. Culture-independent qPCR confirmed L. monocytogenes contamination in all samples, excluding post-scalding carcasses, prewashed post-evisceration carcasses, and the bleeding areas. Consequently, qPCR enabled more comprehensive identification of L. monocytogenes contamination points than culture-dependent approaches. Moreover, 16S rRNA gene amplicon sequencing demonstrated that psychro-tolerant and spoilage-related bacteria with L. monocytogenes-like attributes exhibited enhanced viability in the clean zone and immersion-chilling water. Metagenomics-based source tracking analysis further revealed that the shackles and chilling waters represent predominant sources of cross-contamination between different slaughterhouse zones, whereas the grading and packaging workstations and chilling water in the clean zone were deemed crucial sources affecting final carcass contamination. Collectively, these findings demonstrate through culture-dependent and -independent methods that L. monocytogenes spreads along the slaughter line, contaminating the slaughterhouse. Moreover, by investigating changes in microbial community and bacterial flow along the slaughter line within the facility, the sources influencing carcass contamination can be effectively traced.

Exploiting district cooling network and urban building energy modeling for large-scale integrated energy conservation analyses

Research effort in analyzing the energy consumption of buildings in districts or cities is increasing as new paradigms of distributed energy production and sharing are spreading. In this work, the Urban Building Energy Model of the Quad, an area of the University of California Davis campus, is presented, validated, and analyzed for possible actions to reduce the district cooling energy consumption. Energy conservation measures involve buildings' air handling units and district chilled water generation. To investigate this system, a district cooling networks module has been developed in EUReCA, the Urban Building Energy Modeling tool used for the analyses. The model has been validated with energy demand and temperature data from 2018 to 2020, resulting in a district cooling demand deviation lower than 7% for 2018 and 2019. Normalized Root Mean Square Error is lower than 35% for each building, proving the reliability at the hourly time scale. Systems energy reduction actions like heat recovery units' installation and heuristic control of the air supply cooling temperature are beneficial in reducing the cooling demand, and they allow a more efficient discharging of the chilled water storage, reducing the average electricity price by load shifting during peak demand.

Optimal supply air temperature with respect to data center operational stability and energy efficiency in a row-based cooling system under fault conditions

This is the first study of data center row-based cooling strategies under fault conditions. An optimal supply air temperature (SAT) for row-based cooling is proposed to ensure energy efficiency and operational reliability. The appropriate SAT for emergency operation is determined by evaluating how long the allowable IT equipment's inlet air temperature (IAT) can be maintained by only running the fan of the computer room air handling (CRAH) unit when the chilled water supply is interrupted. Three cases with SAT values of 20 °C, 22 °C, and 24 °C are evaluated in a numerical analysis, and the maintenance potential of the IAT is assessed by analyzing 600 s of transients from the time of cooling failure. In all cases, the IAT is almost the same as the SAT under normal cooling, but in cooling failure, the time to reach downtime beyond the allowable IAT is 246s in Case 1, 133s in Case 2, and 85s in Case 3. Response strategies to cooling failure include increasing uninterruptible power supply (UPS) capacity and applying a thermal buffer tank. The study concludes that it is reasonable to set the SAT of row-based cooling to 22 °C or lower and to install a thermal buffer tank in the chilled water system for effective downtime delay. These results are based on a rack power density of 7 kW/rack.

Performance enhancement and environmental analysis of vapor compression refrigeration system with dedicated mechanical subcooling

The primary focus of this study is on the energy, exergy, and environmental (3E) analysis of a dedicated mechanical subcooled vapor compression refrigeration (DMS-VCR) system for applications involving commercially available water chillers that employ R134a (in both subcooler and main cycle). For a cooling capacity of 100-kW water chillers, the mathematical model of the DMS-VCR system is built to determine the performance parameter of the system. The DMS-VCR system reduces electricity usage by 15.52% and increase in COP by 9.5%, which results in a significant reduction in CO2 emissions of about 15.55%. When compared to equivalent vapor compression refrigeration system (VCRS), the system’s exergetic efficiency is also increased by 8%. Since the computer simulation results will undoubtedly give design engineers a better option, the subcooling and superheating of the vapor compression refrigeration system become alluring in this study. Consequently, the DMS-VCR system performs better as per the combined 3E study.

Research on the day-ahead scheduling optimization method of medium-depth geothermal cascade heating system

The medium-depth geothermal cascade utilization technology plays a crucial role in achieving low-carbon and low-cost heat supply. However, the traditional rigid regulation method faces challenges in ensuring real-time supply-demand balance due to the district heating demand being influenced by outdoor weather and the complexity of the operating parameters of the medium-depth geothermal cascade heating system. Consequently, problems such as low utilization of geothermal water and high operating costs arise. To address these issues, this study proposes a day-ahead scheduling optimization method for the medium-depth geothermal cascade heating system, integrating the adaptive moment estimation (Adam) optimized long short-term memory (LSTM) prediction algorithm, interior point method, and particle swarm optimization (PSO) algorithm. Based on enhanced precision prediction, this study aims to optimize variables including partial load rate (PLR), flow rate, cooling water return temperature, and chilled water return temperature. The effectiveness of the proposed optimization method is verified through the establishment of a TRNSYS simulation platform in conjunction with MATLAB, focusing on a geothermal cascade heating project in Tianjin. The results demonstrate that the proposed day-ahead scheduling optimization method effectively promotes the coordinated operation among energy systems, achieving significant energy savings for the energy station (10.13 %). The novelty of this research lies in the utilization of scientific algorithms to optimize multiple variables within the system, which holds the potential to enhance the matching of supply and demand and improve the operational effectiveness of comparable systems. In summary, this study provides valuable insights and practical implications for the field of strategic optimization. However, it is essential to acknowledge that the applicability of the findings to other geographic locations, different scale projects, or varying system configurations necessitates additional investigation. The generalizability is subject to further research and exploration.