Variable Speed Pumps Research Articles

Data informed physical models for district heating grids with distributed heat sources to understand thermal and hydraulic aspects

The aim of the study was to develop data informed physical models for simulation of district heating (DH) grids for better presentation of hydraulic and thermal aspects in the DH grids integrating heat prosumers. A DH grid organized as a ring and integrating a heat prosumer from a data center was analyzed. In this study, an extensive analysis for thermal and hydraulic aspects of theDH grid considering different configurations of distributed sources was performed. Different configurations for the prosumer connection, the return to return and the return to supply, together with the pressure and temperature control, were investigated. The results showed that increasing the share of renewable heat from the prosumer to the DH grid caused a pressure imbalance in substations close to it. Variable speed pump control was the solution for these issues and it gave up to 34% electricity savings. Lowering temperature levels in the DH network led to a decrease in DH heat losses of up to 14%. The return to supply configuration showed advantages in integrating the prosumer, as regards lower return temperatures and better waste heat utilization. The results indicated the main hydraulic and thermal features of integrating the prosumer in the DH grid.

Pump scheduling in drinking water distribution networks with an LP/NLP-based branch and bound

This paper offers a novel approach for computing globally optimal solutions to the pump scheduling problem in drinking water distribution networks. A tailored integer linear relaxation of the original non-convex formulation is devised and solved by branch and bound where integer nodes are investigated through non-linear programming to check the satisfaction of the non-convex constraints and compute the actual cost. This generic method can tackle a large variety of networks, e.g. with variable-speed pumps. We also propose to specialize it for a common subclass of networks with several improving techniques, including a new primal heuristic to repair near-feasible integer relaxed solutions. Our approach is numerically assessed on various case studies of the literature and compared with recently reported results.

Energy Efficiency Optimized in the Dynamic Process of a Variable-speed Variable-displacement Pump Unit

Energy Efficiency Optimized in the Dynamic Process of a Variable-speed Variable-displacement Pump Unit

Energy Consumption Comparison of a Single Variable-Speed Pump and a System of Two Pumps: Variable-Speed and Fixed-Speed

The energy efficiency of a multi-pump system consisting of two low-power (0.75 kW) pumps operating in parallel mode and a single-pump mechanism (1.5 kW) is compared in this study. For this purpose, mathematical models, experimental data, and data retrieved from the manuals provided by the pump manufacturers are used. The single-pump system is fed by a single variable speed drive. A multi-pump system running in parallel mode consists of two pumps. One of them is driven by an induction motor connected directly to the electrical grid and equipped with a throttle. Another pump is actuated by an induction motor fed by a variable speed drive. The flowrate of the liquid in the multi-pump is controlled with the help of speed variation and throttling. In the case of the single-pump system the conventional speed control method is applied during the analysis. For both pump system topologies, the daily and annual energy consumption is obtained. As a result of conducted calculations, it was shown that the multi-pump provides 29.8% savings in comparison to the single-pump system in the case of a typical flowrate profile.

Automated laboratory load-based testing and performance rating of residential cooling equipment

In the U.S., with about 64% of primary occupied homes having unitary air conditioners, a small improvement in the energy efficiency of residential cooling equipment can lead to significant energy savings. Currently, standardized equipment energy efficiency rating is based on standard AHRI 210/240, that provides a metric for comparing the performance of different equipment. However, it is generally recognized that this approach fails to appropriately rate and credit equipment with advanced controls and variable-speed components. Contrarily, a load-based testing and rating approach is presented in this paper that can capture equipment performance with its integrated controls that is more representative of the field. In this approach, representative building sensible and latent loads are emulated in a psychrometric test facility at different indoor and outdoor test conditions utilizing a virtual building model. The indoor test room conditions are continuously adjusted to emulate the dynamic response of the virtual building to the test equipment sensible and latent cooling rates and the equipment dynamic response is measured. Moreover, an automated testing procedure is presented along with convergence criteria for measuring equipment steady-periodic performance. Climate-specific cooling seasonal performance ratings can be determined by propagating the coefficient of performance (COP) from load-based testing results through a temperature-bin method to estimate a seasonal COP (SCOP). In this work, the proposed approach was implemented to test and rate a variable-speed residential heat pump. Furthermore, the sensitivity of load-based testing results to virtual building parameters was investigated. Finally, repeatability results from the load-based testing approach are presented.

Selection optimization of variable speed pump as turbine (PAT) for energy recovery and pressure management

Renewable energy technologies around the world have become a priority today and among them, hydropower plants have the largest share. The most significant problem with small hydropower plants is the high cost of commercial turbines. The most economical way to generate small-scale energy is to use a pump as turbine (PAT) due to the cheapness and availability of the pump. In water distribution networks (WDNs), the PATs can be used instead of pressure reducing valves (PRVs) for both pressure reduction and energy production. The installed PAT must be capable of operating under different discharges due to fluctuations in rate of water consumption, which makes it challenging to select the appropriate pump. In this study, the process of PATs selection for PRVs replacement is optimized using particle swarm optimization (PSO) algorithm. Three different scenarios are performed for the optimization process, considering constant and variable speed PATs. It is worth mentioning that the wasted energy in the selected case study is about 494 kWh/day using PRVs. The results show, in scenario no. 3 (variable speed PATs), the total amount of produced energy is 182.15 kWh/day. Also, the penalty function is decreased by about 62% in comparison to other scenarios and as a result, the pressure of the critical nodes has better agreement to those values of PRVs utilization.

Study The advantage of variable speed pumps Economically in pumping water lines using genetic algorithms

This study includes a comparison between the use of fixed and variable speed VSP pumps, in terms of investment cost, through finding the operating schedule of pumps, for three pumping stations, using the method of genetic algorithms. The use of VSP pumps will reduce the investment costs of the Water project by more than 15%, in relation to the use of fixed speed pumps (FSP) with the same speed, pressure, discharge and engine speed . The FSP has been modified to become a VSP, using a Variable Frequency drive

Exploratory Research to Improve Energy-Efficiency of a Ground-Coupled Heat Pump Utilizing an Automatic Control Device of Circulation Pump Speed

Ground-coupled heat pumps (GCHPs) are an efficient thermal energy production system that can satisfy the gap between heating and air-conditioning. Be that as it may, exploratory research on GCHPs is still lacking. The first objective of this article is to describe a utilitarian energy-efficiency improvement device for a vertical GCHP system that includes a buffer tank (BT) between the heat pump unit and the fan coil units and user supply, utilizing the quantitative regulation of water flow rate with a variable-speed circulation pump. At that point, the investigative estimations are utilized to test the performances of the GCHP system in various operating modes. Fundamental efficiency parameters (coefficient of performance (COP) and CO2 emission) are achieved for one month of running utilizing two control strategies of the GCHP—standard and optimized regulation of the water pump speed—and a benchmarking of these parameters is achieved. Exploratory research has indicated higher efficiency of the system for the flow regulation solution utilizing a BT and programmed control equipment for the circulation pump speed compared with the standard regulation solution (COPsys with 7–8% higher and CO2 emission level 7.5–8% lower). The second objective is to elaborate a simulation model of the necessary heat/cold in heating and air-conditioning periods, utilizing the Transient Systems Simulation (TRNSYS) program. Finally, the simulation, acquired utilizing the TRNSYS program, is analyzed and compared with experimental information, leading to a good agreement and, along these lines, the simulation model is approved.

Development of a hardware-in-the-loop simulator for small-scale concentrated solar combined heat and power system

• A HiL framework of a novel integrated solar mCHP plant is developed. • The HiL simulator is designed in Matlab/Simulink and coupled with the real controller of the plant. • The HiL simulator is used for control algorithms optimization and control strategy definition. • Optimal proportional and integral gains of the PI-based control are assessed for all the diverters. • The best control strategy to assure constant inlet temperature at the ORC consists in acting on the aperture of a diverter. In this work a hardware-in-the-loop (HiL) simulator of a novel micro combined heat and power system is presented and its use for control algorithm optimization is demonstrated and discussed. The plant under investigation consists of a concentrated Linear Fresnel Reflectors solar field, a 2 kWe/18 kWt Organic Rankine Cycle unit and an advanced latent heat thermal energy storage tank equipped with reversible heat pipes as developed by a consortium of universities and companies within the EU funded project Innova Microsolar. A smart control unit manages their integration and monitors the operation of each subsystem. In order to support the optimization of the control algorithms and the definition of the best control strategy of the micro-CHP plant at different working conditions, a simulation framework based on Matlab/Simulink has been developed by the authors and connected to the real control unit according to a HiL approach. Ad-hoc models of the different subsystems together with those of the components (i.e. valves and variable speed pumps) regulating the plant operation have been included. The use of the HiL simulator has permitted to optimize the control logic of the integrated plant prior to its future commissioning, thus helping to overcome some of the technical and reliability issues occurring during the setup of the real system. In particular, the HiL has allowed: (i) to define the proportional and integral gains of the diverters in order to assure a robust and fast response of the plant during the switch among the different operation modes; (ii) to prove the limits of acting on the oil pump flow rate in assuring the nominal oil temperature at the inlet of the ORC unit, due to the inherent fluctuations caused by this control strategy; and (iii) to assess the best control strategy which is obtained by acting on the aperture of the diverter which controls the oil mass flow rate to the ORC unit. Hence, the scientific approach here proposed can be extended also to many other complex energy conversion systems in order to significantly reduce the potential critical issues during their commissioning.

Smoothing control of solar photovoltaic generation using building thermal loads

Distributed energy resources such as solar photovoltaic (PV) systems are seeing significant expansion in power grids worldwide. However, serious system integration issues have arisen including voltage fluctuations and accelerated aging of voltage regulation devices, when adopting mass amounts of volatile energy resources onto legacy distribution networks originally designed for unidirectional power flow. Building heating, ventilation and air-conditioning (HVAC) systems, collocated with the distributed generation, can be considered as flexible loads due to the inherent building thermal inertia. HVAC systems can be proactively controlled to improve voltage regulation of distribution networks with high PV penetrations. This paper presents a smoothing solution that modulates HVAC power in response to volatile PV generation as a means to mitigate fluctuations in the net demand and generation. To demonstrate the effectiveness and evaluate performance gains, hardware-in-the-loop (HIL) tests were carried out using a 3-ton variable-speed heat pump. The HIL tests leveraged a building thermal dynamic model and a steady-state power flow model for a 33-bus distribution network to capture realistic indoor thermal responses and distribution voltage variations during PV smoothing control. Test results showed that the developed strategy was effective in reducing variations of net demand and generation with negligible impact on indoor comfort. More than 55% reductions of voltage fluctuation were achieved and tap operations of voltage regulators could be fully or partially eliminated with proactive PV smoothing.

Dynamic Analysis of Sensorless Controlled Industrial Pump Drive

Industrial pumps operating with variable speed provides numerous benefits including valve elimination, wide range of flow rate, single stage higher head and energy saving. The realization of variable speed pump operation is carried out using an induction motor, power electronic switches, current sensors and controller without speed feedback is known as sensorless variable speed control. This paper implements a field-oriented control based sensorless scheme on 150 kW induction motor drive system, which is integrated to centrifugal pump load in Matlab/Simulink environment. The centrifugal pump is modelled mathematically in the same environment for obtaining the identical torque speed characteristics.

Optimal rule-based control for the management of thermal energy storage in a Canadian solar district heating system

Solar district heating systems are a promising solution to facilitate the adoption of large-scale, solar energy-based technologies. Thermal energy storage devices could also play an instrumental role to manage the mismatch between solar energy resources and community heating loads; however, controlling such systems is no easy task. In this paper, a novel heuristic reactive control strategy is developed to properly manage the thermal energy storage capacity, at both the short-term and the long-term, in a Canadian solar district heating system (the Drake Landing Solar Community). This strategy targets the optimization of: (a) the temperature difference across solar collectors and (b) the flow rate modulation of the variable speed pump linking the short-term and the seasonal thermal energy storage devices. A simulation is used to compare this new control approach with the conventional control strategy currently in place. Results are assessed for the year 2017–18 in terms of energy, cost and greenhouse gas emissions. Despite a 10% increase in natural gas consumption, electricity use was decreased by 43%; reductions of 34% and 29% were respectively achieved in terms of energy cost and GHG emissions.

Influence of Fill Point in Multiple-Heat-Sources Looped District Heating System with Distributed Variable-Speed Pumps

When regulating a pipe network according to user demand, hydraulic balance and power consumption are crucial factors for a multi-source looped-pipe network applying distributed variable-speed pumps compared to the conventional central circulating pump system. In this paper, the influence of the fill point on power consumption and hydraulic balance of the multi-source looped-pipe network was studied. A mathematical model for electricity energy consumption analysis was built and calculated for a large sized looped-pipe network with multiple heat sources and distributed variable-speed pumps. The hydraulic calculation models of each single element, such as pipe, distribution pump, valve, replenishment pump, heat source and substation, were built. A case located in Dezhou city, China was analyzed. The results showed that: the maximum power saving (39.2%) could be achieved when each heat source had its own fill point, but the heat sources would not meet their design flows; to meet the design flows of all the heat sources, only one fill point should be necessarily located near the heat source with the lowest flow rate to get the expected hydraulic stability and energy saving.

Optimal Coordinated Operation of Interdependent Power and Water Distribution Systems

With the rising electricity demand for freshwater production, power and water sectors are becoming increasingly interdependent. This vital link could create new opportunities for power and water distribution system operators to coordinate the operation of their systems and achieve operational cost and energy efficiency benefits. This paper proposes the flexible power-water flow (FlexPWF) model for co-optimizing the operation of flexible energy-intensive components in water systems with the operation of both power and water distribution systems. The FlexPWF model leverages the energy flexibility provided by water treatment and desalination plants in conjunction with variable speed pumps and water storage tanks to minimize the operating costs of interdependent power and water distribution systems. The proposed model takes into account the operational constraints of both power and water distribution systems, thus coordinating their operation without endangering the reliable supply of power and water to customers. The paper highlights the merits of integrating water treatment and desalination plants, where a detailed model is proposed to capture their dynamic operation for producing variable amounts of freshwater and providing energy flexibility. Simulations, conducted on the 33-bus test distribution system and a 15-node test water distribution system, show that the FlexPWF model effectively coordinates the operation, reduces the operating costs and improves the operational metrics of both power and water systems.

Model test of pumping operation of Sanhekou hydro-junction project

Aiming at the pumping operation of Sanhekou Hydropower Station’s pump-turbines, based on model tests, data measurements were performed on the rated speed and variable speed pumping operations. In addition, the efficiency test and hump margin test were implemented, and the corresponding performance curves were obtained. The results meet the engineering design requirements and can provide technical guidance for the speed control of the power station.

Optimal Regulation of Pumping Station in Water Distribution Networks Using Constant and Variable Speed Pumps: A Technical and Economical Comparison

Greenhouse gas emission is one of the main environmental issues of today, and energy savings in all industries contribute to reducing energy demand, implying, in turn, less carbon emissions into the atmosphere. In this framework, water pumping systems are one of the most energy-consuming activities. The optimal regulation of pumping systems with the use of variable speed drives is gaining the attention of designers and managing authorities. However, optimal management and operation of pumping systems is often performed, employing variable speed drives without considering if the energy savings are enough to justify their purchasing and installation costs. In this paper, the authors compare two optimal pump scheduling techniques, optimal regulation of constant speed pumps by an optimal ON/OFF sequence and optimal regulation with a variable speed pump. Much of the attention is devoted to the analysis of the costs involved in a hypothetical managing authority for the water distribution system in order to determine whether the savings in operating costs is enough to justify the employment of variable speed drives.

Annual Energy Consumption Cut-Off with Cooling System Design Parameter Changes in Large Office Buildings

A variety of greenhouse gas reduction scenarios have been proposed around the world to ensure sustainable developments and strengthen the global response to the climate change. To cope with this, it is urgently needed to reduce the amount of energy used for the heating, ventilating, air conditioning, and refrigerating (HVAC&R) systems in large buildings. This study discusses the reduction of cooling energy in large office buildings through the minimization of changes in components and equipment, such as heat source equipment and pumps, changes in the layout and operating methods of chilled water circulation pumps, and changes in the temperatures of chilled and condenser water. To do this, this study targeted an entire cooling system consisting of a hydronic system, a chiller, and a cooling tower, and conducted a quantitative analysis of the energy consumption and of the reduction achieved through a change in the pumping system type in the cooling system and a change in the Korean standard design and temperature of chiller and cooling tower via EnergyPlus simulations. The simulation results showed a cooling energy reduction of 103.2 MWh/yr, around 15.7%, where the primary constant-speed system (Case A) was changed to a primary variable-speed pump (Case B) in the configuration with a chilled water circulation pump. To reduce the cooling energy further, annually 142.3 MWh, around 21.7%, Case C in this study changed the outlet temperature of the chiller and temperature difference from 7 °C, 5 K to 9 °C, 9 K. Finally, when applying a change in the condenser water production temperature from 32 to 23.9 °C in accordance with ASHRAE Standard 90.1 for Case D, a cooling energy saving of 182.4 MWh/yr was observed, which is about 27.8%.

Experimental study on the dynamics, quality and impacts of using variable-speed pumps in buildings for frequency regulation of smart power grids

The increased generation of renewable power is challenging in terms of the power balance and reliability of power grids due to the intermittent nature of renewable sources. Heating, ventilation, and air-conditioning (HVAC) systems in buildings, at demand side, are promising candidates for providing frequency regulation. In this study, we systematically assessed the use of variable-speed pumps in HVAC systems for frequency regulation. The dynamic characteristics of the pump were investigated. The results show that the power of the pump can response to the frequency change rapidly (returning stable within 1s), while the response of flow rate is slightly slower. A frequency regulation control strategy is proposed and implemented on a test rig. From the viewpoint of power grids, the experimental results show that the pump can provide high-quality frequency regulation (performance scores of 0.989 and 0.968). From the viewpoint of buildings, the experimental results indicate that the fluctuation magnitude of the air-handling unit outlet air temperature increases (from 3.3 K to 7.1 K) with increasing automatic generation control (AGC) signal frequency, whereas the fluctuation magnitude of the indoor air temperature increases to some extent and then decreases when the frequency of the AGC signal is above a certain level.

EVASOR, an Integrated Model to Manage Complex Irrigation Systems Energized by Photovoltaic Generators

The carbon footprint and energy cost of irrigation are increasing due to the modernization of irrigation systems, which also necessitates highly efficient use of water resources. Alternatives to conventional energy sources to power irrigation systems are renewable sources, primarily photovoltaic energy. Photovoltaic energy has the main disadvantage of producing a highly variable amount of energy, which affects the irrigation uniformity. Modeling irrigation systems in an integrated manner generates useful information about system performance for technicians that helps in the decision-making process. The EVASOR (EVAluation of SOlar iRrigation systems) model integrates different modules to simulate the whole solar irrigation system using a holistic approach: (1) I-Solar, which simulates the instantaneous power generated by the photovoltaic system, (2) AS-Solar, which simulates the variable speed pumping system, (3) Solar-Net, which simulates the hydraulic performance of the water distribution network, and (4) PRESUD-Irregular, which determines the discharge and pressure of all the emitters of the subunits together with irrigation quality parameters (coefficient of uniformity (CU), emission uniformity (EU), and coefficient of variation of the emitter discharge in the subunit (CVq) for any pressure at the subunit inlet. The integrated model EVASOR determines the irrigation quality parameters of complex irrigation systems with information on irradiance, air temperature, wind speed, and water table level for any combination of open subunits. To validate the model, results are presented regarding a case study located in southeast Spain.

Feasibility study of collector-distributor district heating system

One of the ways to improve efficiency of district heating systems is to use thermohydraulic dispatchers (THD) along with distributed variable speed pumps (DVSP) for reducing electricity consumption. First part of this paper deals with the application of THD at consumers to evaluate its technical and economic advantages. Although the result of the analysis shows that savings are quite small for Moscow conditions, the solution still might be applicable due to low additional capital expenditures. The second part of the paper uses the obtained result and summarizes previous works in this field to introduce collector-distributor district heating system which extensively incorporates THD and DVSP. Feasibility study of the proposed system was performed in comparison with a conventional district heating system. Electricity saving potential of collector-distributor district heating system is estimated to be 42-129 MW*hr/yr, while discounted payback period of additional capital expenditures is less than 2 years.