Variable Speed Pumps Research Articles

Empirical Study of the Effect of Thermal Loading on the Heating Efficiency of Variable-Speed Air Source Heat Pumps

Heating buildings with air source heat pumps (ASHPs) has the potential to save energy compared to utilizing conventional heat sources. Accurate understanding of the efficiency of ASHPs is important to maximize the energy savings. While it is well understood that, in general, ASHP efficiency decreases with decreasing outdoor temperature, it is not well understood how the ASHP efficiency changes with different levels of thermal loading, even though it is an important consideration for sizing and controlling ASHPs. The goal of this study was to create an empirical model of the ASHP efficiency as a function of two independent variables–outside temperature and level of thermal loading. Four ductless mini-split ASHPs were evaluated in a cold chamber where the temperature (representing the outdoor temperature) was varied over a wide range. For each temperature, the ASHP performance data were collected at several levels of thermal loading. The data for all four ASHPs were combined and approximated with an analytical function that can be used as a general model for the ASHP steady-state efficiency as a function of the outside temperature and level of thermal loading. To the knowledge of the authors, no such empirical model that is solely based on third-party test data has been published before. While limitations exist, the model can be used to help guide future selection and operation of ASHPs.

Dynamic analysis of the heat theft issue for residential buildings

European Union is facing a dramatic energy crisis, due to the huge increase of the natural gas cost, due to the Russian-Ukrainian war. In this framework, the fair allocation of natural gas costs, used for space heating purposes in residential centralized heating systems, is becoming a crucial issue. These systems suffer for the heat theft phenomenon, where an unheated apartment may benefit of the heat transfer from the surrounding heated apartments. Unfortunately, there is no consensus regarding a suitable heat accounting method, implemented in order to limit heat thefts. In this work, two novel billing strategies are proposed. In the first one, the heating cost includes both a variable fee and a constant fee. The second one also considers a penalty for the unheated apartments. A case study is analyzed. It consists of a multifamily building including 4 floors and located in Naples. This building is equipped with a centralized heating system, coupled with radiators, variable speed pumps, thermostatic valves, and heat metering devices. A suitable dynamic simulation model is developed in TRNSYS 18 environment to analyze the energy and economic performance of the system. The comfort parameters of unheated users are also analyzed and discussed. The proposed billing strategies are able to smooth the heating bill increase for the heated apartments adjacent to the unheated user. The novel billing strategy proposed by this research can significantly mitigate the heat theft issue. In particular, results show that the penalty should be almost 2.5 times the constant fee for preventing the unheated user issue. Simulations also show that installing a suitable thermal insulation for the walls among adjacent apartments may dramatically limit the heat thefts. However, insulating such walls may result often unfeasible for the owners of the apartments, due to reduction of the floor area and to the major refurbishment required.

The pricing method for abandoned wind power contract between wind power enterprises and desalination plants in bilateral transactions

In Northeast China’s electric power auxiliary service market, guiding interruptible load users to participate in bilateral transactions is an effective measure to ease the difficulty of grid peak regulation and improve the utilization rate of wind power. Aiming at the lack of theoretical guidance in the current bilateral transactions, this paper proposes a two-stage pricing (TSP) method. Firstly, the freshwater supply and demand balance model of the desalination plant is constructed. The upper-level optimization model of bilateral transaction for profit maximization of the desalination plant is constructed. Then, considering the profit distribution among transaction parties and constraints on wind power utilization, a low-level calculation model of wind power pricing is constructed. Finally, the TSP method is applied to the numerical analysis of bilateral transaction between a desalination plant and a wind power company. The TSP method jointly optimizes the dispatching scheme between the variable speed pump and the water storage tank of the desalination plant. Under the constraints of reasonable profit distribution and wind power utilization, the transaction price finally converges to a range acceptable to both parties. The TSP method can effectively improve the utilization rate of wind power and optimize the flexibility of energy utilization. • A detailed mixed-integer linear programming (MILP) model is developed for desalination plants. • A model for seawater desalination plants to participate in bilateral trading markets is proposed. • A TSP method for calculating the price of bilateral transactions is proposed. • The TSP method can effectively optimize the flexibility of energy utilization.

A Water-Energy Nexus Approach for the Co-Optimization of Electric and Water Systems

The staggering increase in water production, driven by population and economic growth, has consequently led to a massive increase in energy demand, particularly in countries that rely on desalination. Hence, the concept of the water-energy nexus has emerged as the best option to alleviate the gap between the demand and production of both water and power. This paper proposes a new approach for co-optimizing water and electric power systems by incorporating the energy-intensive equipment involved in water desalination and distribution. The proposed procedure leverages the energy flexibility of reverse osmosis (RO) desalination tracks that can operate alternatively in conjunction with water network storage tanks and variable-speed pumps to satisfy water demand while minimizing energy and operating costs. The developed model takes into consideration the essential constraints of both the power and water systems to meet consumer demands. Further, a mixed-integer nonlinear programming model is proposed for the day-ahead operation of the two integrated systems. The simulation findings show that the suggested technique is successful in scheduling the energy-intensive equipment in the two systems to achieve a $26,993 per day savings compared to a 4.6% decrease in overall operating costs when compared to optimizing each system independently.

A hybrid energy storage system with a modified MMCC‐TSBC converter comprised of VSPS, BESS and supercapacitor storage

IET Power ElectronicsAccepted Articles ORIGINAL RESEARCHOpen Access A hybrid energy storage system with a modified MMCC-TSBC converter comprised of VSPS, BESS and supercapacitor storage First published: 05 December 2022 https://doi.org/10.1049/pel2.12296AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Due to a technical error, the following article was published in error on Wiley Online Library as an Accepted Article on 5 December 2022. The article has been temporarily removed. Wiley would like to apologize to the authors and the academic community for this error. Kasari, P.R. and Bhattacharjee, S. (2022), A hybrid energy storage system with a modified modular multilevel cascaded converter based on a triple star bridge cell converter comprised of variable speed pump storage, battery energy storage system, and supercapacitor storage. IET Power Electronics. Accepted Author Manuscript. https://doi.org/10.1049/pel2.12296 Accepted ArticlesAccepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future. RelatedInformation

Operation optimization of existing industrial circulating water system considering variable frequency drive

The traditional circulating cooling water system regulates the flow rate through parallel pumps and valves. Due to fluctuations in operation, there will be lots of energy waste, resulting in inefficient operation of the circulating cooling water system. This research proposed a mixed-integer nonlinear programming (MINLP) method. By installing variable frequency drives (VFDs) on the pumps, changing constant-speed pumps (CSPs) into variable speed pumps (VSPs), we can regulate flow rate with valves and VSPs simultaneously. Optimizing the system using Genetical algorithm (GA) to obtain precise operating parameters, including the configuration of VFDs, the number of CSPs and VSPs and the resistance coefficients of valve in the branch and main pipe. Sensitivity analysis of the model is carried out, and the energy-saving effect of VFD under different temperature differences, pump types and electricity prices, the operating status of the pump and the status of the pipeline are compared. The results indicate that the MINLP genetic algorithm optimization model for industrial circulating water considering variable frequency drive proposed in this paper has a wide range of applicability. It can save an average of 23 % of the total cost under different conditions, and has a promising energy saving effect.

Development of an accumulator liquid-level estimator to enable zero-superheat control and active charge management in vapor-compression systems

Vapor-compression system efficiency increases with reduced superheat but excessively low superheat settings may cause wet compression and jeopardize reliable system operations. Accumulators are commonly used to intercept liquid refrigerant before it reaches the compressor and can also be used as a refrigerant reservoir to assist active charge management. For zero-superheat and active charge control, accurate measurement or estimation of the accumulator liquid level is required. This paper presents an accumulator liquid level estimation approach based on a nonlinear state observer combined with a gray-box dynamic model of the evaporator and accumulator. This approach affords virtual detection of the liquid level in real-time from refrigerant pressure and temperature measurements, which are readily available in modern vapor-compression systems, and supports zero-superheat and dynamic charge control to maximize system efficiency. Both numerical and experimental tests of the proposed liquid level estimation and charge control strategies were carried out with a 3-ton variable-speed heat pump. The tests have demonstrated the accuracy of the accumulator liquid level estimator and shown that the zero-superheat and active charge control strategy could improve the system efficiency by up to 10.5%.

Improved Operation Strategy of the Pumping System Implemented in Timisoara Municipal Water Treatment Station

Water treatment stations (WTSs) provide drinking water to the community and are critical infrastructures of any village or city. The main energy consumption of WTSs is associated with the operation of the pumping units installed in the water supply stations (WSSs). The parameters of the pumping units installed in the WSSs are continuously adjusted during service to meet the requirements of the customers. Therefore, variable-speed pumping units (VSPUs) are feasible technical solutions implemented in WSSs. Several strategies combining VSPUs and constant-speed pumping units (CSPUs) have been developed to operate in WSSs. A technical solution with four pumping units (two VSPUs and two CSPUs) is implemented in Timisoara pumping station No. 1 (TPS1) in the Bega municipal water treatment station (MWTS). The layout of TPS1 is detailed, and its energy consumption from the budget of the Bega MWTS is quantified. The operation strategy with four pumping units selected in TPS1 is investigated. The number of hours in service of each pumping unit and the total operating time of all pumping units in the last six years are examined. The specific power consumption associated with the operation of the pumping units installed in TSP1 is detailed. The failure incidents of the pumping units counted in service are enumerated and correlated with the operating conditions of the pumping units. A new strategy developed for the operation of the pumping units installed in TPS1 is proposed to better adapt to the operating conditions, improving the specific power consumption as well as diminishing the failure incidents. The new operation strategy is presented and assessed based on the data acquired from TPS1 over one year. The conclusions and the lessons learned in this case study are drawn in the last section.

Integrated optimization of multi-carrier energy systems: Water-energy nexus case

This paper focuses on the optimal operation of integrated electrical and water energy networks at the distribution level considering the demand response program. In this manner, the water network with various components including reservoirs, tanks, fixed and variable speed pumps, and control valves is modeled. Newton-Raphson method is adopted to solve the water flow problem. This technique, unlike existing methods, can be applied to any network with any type of topology, whether radial, circular or hybrid. The electrical network is also modeled with the relevant constraints and coupled with the water network to supply the required electrical power. The optimization problem in a practical energy system, including a standard IEEE 33-bus electrical network, and the North Marin water network has been solved by a teaching learning-based optimization algorithm as a parameter-free method. The objective is to minimize the total operation cost. With the participation of the water network in a demand response program, the optimal charging and discharging of tanks, and pumps scheduling has been carried out, which consequently has led to operation cost reduction. In addition, numerical results have proved that the utilization of variable speed pumps can reduce about 7% of the total costs.

AI Energy Optimal Strategy on Variable Speed Drives for Multi-Parallel Aqua Pumping System

In the industrial world, parallel pump systems are frequently employed. Due to various reasons, the pumps are frequently operated outside their intended parameters, which reduces their efficiency and performance. To operate the pump system with optimum efficiency, the pumps and their speed selection are mandatory. This research presents an optimum switching technique for variable speed pumping stations with multi-parallel pump combinations to enhance energy savings. The proposed optimal control system is designed in such a way as to decrease overall losses in the pump system. The effectiveness of the proposed method is investigated on a real scale of a multi-parallel pump drive system in a Matlab Simulink environment, and experimental validation is performed in a laboratory prototype. The suggested approach enhances power savings and shall be adapted for various pumping applications.

Coordinated operation of pumped-storage hydropower with power and water distribution systems

Small pumped-storage hydropower (PSH) units have gained popularity as distributed energy storage options that can provide flexibility to the operation of power distribution systems. Optimal operation of small PSH units is not only dependent on the energy storage provided to power distribution system, but also on the inflow and outflow of water from and to the water distribution system. In this context, this paper develops an optimization model for coordinated operation of PSH units with power and water distribution systems. The proposed model optimizes the operation of water tanks, variable-speed pumps and PSH in pumping and generating modes to minimize the operation cost of power distribution system, while respecting the power flow constraints of power distribution and hydraulic constraints of water distribution system. Appropriate electricity tariffs are implemented to avoid additional expenses in water distribution system that can be enforced by its coordinated operation in favor of power distribution system. The proposed model is implemented on a 33-bus and a 123-bus test power distribution system connected to a 16-node test water distribution system. Results demonstrate the effectiveness of proposed model in tapping PSH flexibility to reduce the operation cost of power and water distribution systems, while meeting the power and water demands.

Assessment of operational carbon emission reduction of energy conservation measures for commercial buildings: Model development

Using energy conservation measures (ECMs) for building retrofit can significantly reduce building operational carbon emissions (BOCEs) and contribute to Chinese carbon neutrality by 2060. This paper involves 11 feasible ECMs for commercial buildings in hot-summer and cold-winter zone, China, and proposes a quick assessment approach to BOCEs reduction. Prototypical models are simulated for ECMs using EnergyPlus and the emission intensity is corrected by the building shape factor and window-to-wall ratio. Based on pre-simulated results, effects on reducing emissions of individual measures and packages of them are studied to develop regression models in SPSS. The results show that decreasing the U-factor of external walls, lighting power density (LPD), or shading coefficient can reduce BOCEs linearly. BOCEs are most sensitive to LPD and using daylighting control can reduce emissions by 5–15%. In addition, increasing the boilers’ efficiency reduces emissions linearly, while performance improvement of chillers or heat pumps reduces emissions logarithmically. Furthermore, utilizing variable speed pumps, heat recovery ventilation, and air-side economizers can reduce emissions by 3.8%, 6.6%, and 15.2%, respectively. Finally, significant interactions exist among measures of enhancing glazing U-factor, adding external shading, using energy-saving lamps, and improving cooling/heating system efficiencies. The developed regression models are validated in a retrofit case in Shanghai. Through assessment, the case can reduce BOCEs by 15.9 kgCO2/m2, with a reduction rate of 20.8%. Compared with recorded data, the relative error of assessing emission reduction is −13.0% and that of assessing reduction rate is 0.5%, which are acceptable in the decision-making stage of retrofit strategies.

Economic feasibility analysis of variable-speed pumps by simulating 15 multiple water distribution systems

Abstract The UN Sustainability Goals address measures to reduce environmental pollution. Water distribution systems (WDSs) use electric energy, which pollutes the atmosphere through, at least partly, the burning of coal. This study simulates, through modeling, variable-speed pumps (VSPs) on 15 different real WDSs on the network solver EPANET and analyzes the payback period. An algorithm is introduced here to select the optimal pump speed pattern to save the most energy while satisfying the constrain of sufficient pressure at all times and all locations. It was found that five of the 15 systems operated unsuccessfully using a VSP, due to the VSP operating at lower speeds causing a lower pressure than normal, thereby causing the pressure to become negative. Additionally, a new chart that compares the payback period, project life, and energy costs between the base case and the VSP case was developed and different regions on the chart reflect different decision criteria.

Investigation of the influence of hydraulic oil temperature on the variable-speed pump performance

This paper describes investigation on the influence of hydraulic oil temperature on the performance of a hydraulic pump. The aim of the research is to determine changes in volumetric efficiency of the pump in the form of maps of operation at different temperatures of the hydraulic oil, in conditions of variable speed and pressure. The described tests were carried out on an experimental stand with a hydraulic fixed-displacement gear pump controlled by a servo motor. Based on the signals from the sensors processed with the LabVIEW program, maps of the hydraulic pump operation were drown in a wide range of speeds and temperatures. The paper presents the results of the research and based on this the conclusions regarding the main aim of the research and others that were observed during the measurements were presented. The most important conclusion from the study shows that the temperature-dependent characteristics provide users with a significant amount of information such as operating conditions that will ensure a high level of efficiency.

Experimental analysis of artificial intelligence-based model predictive control for thermal energy storage under different cooling load conditions

As the global community seeks to reduce fossil fuel dependence, improving energy efficiency and developing an optimal operational strategy are high priorities in the building sector. Integrating thermal energy storage (TES) into building energy systems is desirable for improving energy flexibility and cost efficiency. However, an optimal control strategy for TES system operation is required to maximize its advantages of balancing energy supply and demand. This study proposed a model predictive control (MPC) scheme using artificial intelligence (AI) to control the TES system and validated it by the experimental analysis. To construct a reliable and computationally manageable MPC controller, an artificial neural network was utilized as a prediction model, and a metaheuristic algorithm of εDE-RJ was employed as an optimization solver. The AI-based MPC for cooling operation was examined using a reduced-scale experimental system consisting of a chiller, sensible TES tank, heat exchangers, and variable-speed pumps. AI-based MPC optimized the charging and discharging rates of the TES system to minimize the operating cost. Three cooling load profiles were tested for both MPC and rule-based control methods. The results showed that AI-based MPC was highly feasible by flexibly managing the different load levels and reducing the operating cost by 9.1–14.6%.

Numerical Study of Constant Pressure Systems with Variable Speed Electric Pumps

This work focuses on the modeling and simulation of constant pressure systems based on variable speed pumps, with the aim of studying and evaluating their performance from a multidisciplinary approach. Using the physical models of the Simscape library, from MATLAB/Simulink R2019b, two study cases are assembled consisting of: piping system, a hydropneumatic tank, centrifugal pumps with an induction motor, variable speed drives, and a control system. Case one is comprised of one pump at a fixed speed and another at variable speed, and case two with both pumps at variable speed. For the parameterization of the models, data from manufacturers and process requirements are used. The different stages of the control system are integrated and configured; these are constant V/f control, slip compensation, space vector modulation (SVM,) and pressure controller. The dynamic response of the system, power saving, transient current at startup, and harmonic distortion are evaluated. The results showed that both cases kept the pressure constant in the face of variable flow demand and smoothed out the current during startup. Case two saved more energy (between 28 and 49%) but generated more harmonic distortion. In addition, both cases have better performance compared with traditional fixed-speed technologies.

Control Strategy Design of a Microblood Pump Based on Heart-Rate Feedback.

Based on the nonlinear relationship between heart rate and stroke volume, a flow model of left ventricular circulation was improved, and a variable-speed blood-pump control strategy based on heart-rate feedback was proposed. The control strategy was implemented on a system combining the rotary blood pump and blood circulation models of heart failure. The aortic flow of a healthy heart at different heart rates was the desired control goal. Changes in heart rate were monitored and pump speed was adjusted so that the output flow and aortic pressure of the system would match a normal heart in real time to achieve the best auxiliary state. After simulation with MATLAB, the cardiac output satisfied the ideal perfusion requirements at different heart rates, and aortic pressure demonstrated lifting and had good pulsatile performance when a variable-speed blood pump was used. The coupled model reflected the relationship between hemodynamic parameters at different heart rates with the use of the variable-speed blood pump, providing a theoretical basis for the blood-pump-assisted treatment of heart failure and the design of physiological control strategies.

Optimal day-to-day scheduling of multiple energy assets in residential buildings equipped with variable-speed heat pumps

The largest parts of energy demand within the residential sector are used for space heating (SH), domestic hot water (DHW) and space cooling (SC). The thermal and electrical needs can be mainly covered by energy systems that consist of Photovoltaics (PVs), solar thermal collectors (STCs), heat pumps (HPs) and flexibility sources, e.g. battery energy storage (BES) and thermal energy storage (TES). In this paper, various control strategies for the optimal day-to-day operation of residential energy systems that consist of a variable-speed HP, STCs, PVs, as well as BES and TES units are examined. The proposed strategies are based on the concepts of self-consumption maximization (SCM) and time-of-use arbitrage (ToUA) considering priorities on BES and TES charging. A typical Greek single-family building is assumed examining multiple criteria for the assessment of the rule-based approaches. The results demonstrate that priority on TES charging can lead to higher system performance than on BES charging. Regardless of the number of ToU tariff zones, during off/mid-peak periods the upper energy needs of the SH/SC trajectory should be fulfilled only in case of excess PV power, otherwise the cost of imported energy increases significantly. Both SCM and ToUA strategies can lead to rates of self-consumption and self-sufficiency that deviate in average per about 4% from the optimal values. Moreover, the ToUA-based strategies can approach the minimum cost of imported energy with a relative increase of 22% compared to the optimum. However, the minimum thermal discomfort due to space temperature cannot be achieved without the prediction of the daily SH/SC demand. Furthermore, the proposed strategies can reach the minimum thermal discomfort due to DHW losses, while leading to lower BES degradation rates than the optimization. Finally, from the multi-objective optimization for the first year of system operation, it is verified that the optimal dimensioning of PV, BES and TES is considerably affected by the type of rule-based strategy selected.

Evaluation of variable speed pumps in pressurized water distribution systems

In pressurized water distribution systems, a constant speed pump is often used because of its simplicity. However, constant speed pumps are not easily able to deal with changing demands in water flows. When the demand for the discharge differs from the design discharge, the required demand (discharge and head) could be met by changing the pump speed without making any special changes in the system. Using an electronic drive circuit, the electrical frequency can be changed, and the rotation speed of the pump motor can thus be modified. In this study, the application of variable speed pumps in pressurized irrigation systems is investigated. Two pumping station scenarios including a fixed speed pump and a variable speed pump are considered. The selected pump station includes a real sprinkler irrigation system near Tabriz city, Iran, with 3 lateral pipes and 600 m length of main pipe. The diameter of the main pipes is 8 and 6 inches. The results show that using a variable speed pump increases the average pump efficiency by 18.7%. In addition, the variable speed pump system reduces the electrical consumption 57.6% compared to a fixed speed pump. Therefore, the use of variable speed pumps in pressurized systems is recommended. Step-by-step calculations for a sprinkler irrigation system design are the contribution of this study. This information helps engineers who are not familiar with commutation process.

Reliability analysis of complex water distribution systems: the role of the network connectivity and tanks

Abstract A reliable water distribution network (WDN) can provide an adequate supply service to customers under both normal and abnormal working conditions. The WDN reliability analysis, therefore, is a keystone to improve the supply service efficiency. Strategies for reliability analysis are usually proved on small WDNs, which do not compare with large real complex systems in terms of number of water tanks, pressure reduction valves, variable speed pumps, controlled devices and possible alternative water supply schemes. The topological changes due to pipeline interruptions impact on emptying–filling of water tanks and network pressure status. This work proposes a two-level procedure for mechanical reliability assessment, suited for large real WDNs. It leverages a path/connectivity-based approach to set up reliability indicators for global-level analysis and local screening of the most critical scenarios. The employed advanced hydraulic model includes the automatic detection of topological changes and the robust modelling of water level in tanks using the generalized global gradient algorithm. The extended period simulation enables the reliability assessment of alternative water supply schemes and the sensitivity of tanks and controlled devices to single failure events. The procedure is demonstrated on a real complex network, being consistent with the ongoing digital transition in the WDN management sector.