Variable Water Volume Research Articles

Coupling field-scale and watershed models for regulatory modeling of pesticide aquatic exposures in streams.

Estimating exposure in receiving waterbodies is a key step in the regulatory process to evaluate potential ecological risks posed by the use of agricultural pesticides. The United States Environmental Protection Agency (USEPA) currently uses the Variable Volume Water Model (VVWM) to predict environmental concentrations of pesticides in static waterbodies (ponds) that receive edge-of-field runoff inputs from the Pesticide Root Zone Model (PRZM). This regulatory model, however, does not adequately characterize potential pesticide concentrations in flowing water systems (streams and rivers) drained from watershed areas. This study aims at addressing this gap by coupling the regulatory PRZM model with a watershed-level hydrological model, the Soil and Water Assessment Tool (SWAT), to predict pesticide concentrations in flowing water habitats for aquatic organisms. This coupled PRZM-SWAT model was applied in a test watershed (~HUC12), a headwater watershed of Goodwater Creek in Missouri, and simulation results at the outlet of this watershed were compared to daily and near-daily measured streamflow and atrazine concentration data from a decade-long sampling campaign. Overall, the PRZM-SWAT model captured (1) the general magnitude and temporal trend of daily atrazine concentrations, (2) the observed high-end of exposure levels (>3 ppb) of atrazine concentrations, and (3) the 90th centile annual maximum for various exposure durations (1-, 4-, 7-, 21-, and 60-day rolling average), which are important exposure metrics used in assessing the potential ecological risks posed by the application of pesticides. The PRZM-SWAT model is expected to expand the utility of the field-scale regulatory model to include pesticide exposure prediction capability in flowing waterbodies from agricultural watersheds. Integr Environ Assess Manag 2022;18:1678-1693. © 2022 SETAC.

Numerical Analysis of Variable Water Volume Control Method without Using Differential Pressure for Heat Supply to Buildings

Numerical Analysis of Variable Water Volume Control Method without Using Differential Pressure for Heat Supply to Buildings

A study on the optimal air, load and source side temperature combination for a variable air and water volume ground source heat pump system

In this paper, mathematical models on the energy and exergy performance of a variable air and water volume (VAWV) ground source heat pump (GSHP) system serving an office building in Wuhan, China, were developed. The study aims at investigating the optimal combination of supply air temperature, load side and source side supply and return water temperature to maximize the energy and exergy performance of the whole system. To find the optimal control solution for the system, Latin Hypercube Sampling Method (LHSM) was used to create data sets for training the Back Propagation Neural Network (BPNN) models to predict the energy and exergy performance and couple with Genetic Algorithm (GA). It was found that the system coefficients of performance (COPs) for the original system under constant air and water volume (CAWV) in summer and winter were 2.17 and 1.46, respectively. The associated exergy efficiencies were 7.60% and 3.93%, respectively. The coefficients of performance (COPs) for the variable air and water volume (VAWV) system under normal operation in summer and winter were 3.70 and 3.48, respectively, while their associated exergy efficiencies were improved to 11.43% and 4.12%, respectively. The coefficients of performance (COPs) under optimal control, however, can reach 4.46 in summer and 3.99 in winter and the exergy efficiencies could reach 13.87% and 7.27%, respectively.

Study on Aeration Optimization and Sewage Treatment Efficiency of a Novel Micro-Pressure Swirl Reactor (MPSR)

This study developed a new type of micro-pressure swirl reactor (MPSR) for treating rural domestic sewage with variable water volume in northern China. The transformation of a traditional aeration tank to MPSR was mainly divided into three steps. Firstly, the aeration device was installed on one side of the aeration tank. Secondly, most of the top cover plate was sealed. Finally, the liquid level-lifting zone was set to achieve micro-pressure. The study measured the flow velocity and dissolved oxygen (DO) distribution in the main reaction zone of MPSR, studied the effects of MPSR sewage treatment in continuous operation mode and sequential batch operation mode, and analyzed the main microbial species. The experimental results showed that a stable circular circle flow and a spatial DO gradient in MPSR were formed when the aeration rate of MPSR was 0.2 m3/h. Through the MPSR sewage treatment experiment in two operation modes, it could meet the current requirements of rural environmental pollution controlled in China. Analysis of the types of microorganisms showed that microorganisms with different functions gathered in different zones of the MPSR due to the different dissolved oxygen environment and water flow environment, which further improved the ability of MPSR to simultaneously remove nitrogen and phosphorus.

Comparison of pesticide concentrations observed in community water systems to predictions from U.S. regulatory aquatic exposure models.

The Variable Volume Water Model (VVWM), the receiving water body model for the USEPA regulatory assessment of aquatic pesticide exposures, is composed of a set of static and quasistatic receiving water body conceptual models, but research comparing performance of these models to observations is limited. The water body models included are the constant volume (CVol), constant volume with overflow (CVO), and varying volume with overflow (VVO) models. This work quantified the performance of these three VVWM conceptual models compared with atrazine observations in 50 community water systems (CWSs), and the effect of alternative conceptual models on estimated environmental concentrations of pesticides in regulatory screening assessments. The 50 selected CWSs most relevant to the static and quasistatic VVWM concepts were small in size, with estimated time to peak flow of <1.5d for consistency with the daily runoff assumption in USEPA landscape Pesticide Root Zone Model (PRZM). The CVO and VVO conceptual models resulted in similar distributions of bias across CWSs with the median result being close to no bias, but the CVol model resulted in overestimation in the majority of CWSs with median model bias near three times the observed values. At present, the CVol conceptual model parameterized with conservative input assumptions has been the regulatory standard invoked in VVWM, yet our results showed that a more physically correct conceptual model (CVO or VVO) could be invoked in regulatory exposure modeling for ecological risk assessment, reducing structural model bias while still allowing users to introduce conservative model inputs for screening purposes.

SALTS CONCENTRATION AND DEPOSITION IN POWER PLANT COOLING SYSTEMS

The operation of circulated cooling systems (CCS), the conditions of solid deposits formation and their influence on the head transfer coefficient of heat exchangers are analyzed. Attention is drawn to the danger of jelly-like (mainly organic) deposits with thermal conductivity factor of less than 1 W/(m∙K). Deposits of such kind with the thickness of (1.0-1.5)mm reduce thermal conductivity of the walls of piping systems more than ten-fold though outside they seem to look quite secure. Deposits begin their formation mainly as calcium carbonate where microorganisms are fixed at. The example of turbine condensers shows how deposits reduce the efficiency of steam turbine units. Intensity of deposits formation and their growth are determined by the quality of cooling water and water mode of circulated cooling systems operation. Nowadays, while developing suggestions for deposits minimization, stationary mode of CCS operation is considered. However, the mode of CCS operation is changeable in time due to scarce water resources. The mode of CCS operation with variable water volume is considered in the work. It is shown that at V= var – CCS filling two variants of dependence of salts concentration on time are possible – their increase and decrease. In general, the operating mode of CCS (with respect to water flows) is described by three different dimensionless parameters that are interconnected. Regulatory documentation (SBC B.2.5-74:2013), on the requirements to quality of cooling water and water exchange mode uses models based on assumptions about stationarity of the process and the constant CCS water volume which is not always true. Therefore, the predictive reliability of such documentation is questionable.

A Modelling and Control Approach for a Type of Mixed Logical Dynamical System Using in Chilled Water System of Refrigeration System

The chilled water system of central air conditioning is a typical hybrid system. The dynamic adjustment of cooling capacity based on hybrid system can achieve accurate temperature control and real-time energy saving. Mixed logical dynamical (MLD) systems have advantage for solving constrained optimization problems of this type of case by numerical methods. This paper proposes a novel modified type of MLD system, which enhances the model applicability and improves the switching flexibility and control effect for the framework. In order to meet the needs of cooling capacity and energy saving, the optimal control problem is transformed as MIQP problem by defined performance index. As a numeral example of application, the model and control method is used in pumps group control for variable water volume in chilled water system of central air conditioning. At last, the dynamic and energy-saving effects of the system are simulated, which shows the ideal control results.

Experimental Study on Variable Water Volume Control Methods without Using Differential Pressure for Heat Supply to Buildings

Experimental Study on Variable Water Volume Control Methods without Using Differential Pressure for Heat Supply to Buildings

An Optimal Hybrid Control Method for Energy-Saving of Chilled Water System in Central Air Conditioning

Chilled water system of central air conditioning is a typical hybrid system; variable frequency behavior with amplitude limited of pumps reflects continuous and discrete dynamic characteristics. The way of energy-saving is variable water volume, via variable frequency behavior of pumps to gain adjustment of power consumption. Facing the situation of the variable frequency pumps with parallel operation, single continuous or discrete modeling cannot reflect the hybrid features. Thus, the control method will have some questions, such as bad energy-saving effect, difficult accurate adjustment of cold capacity, and low running energy efficiency. However, hybrid system modeling can reflect hybrid dynamic behavior of pumps, which is combining continuous and discrete features. The questions of nonlinear and multiparameters can be solved by control method based on hybrid system. Here, an optimum control method is proposed with the principle of the minimum, by setting the minimum power consumption as the performance function in fixed time, which realizes variable control of pumps and accurate adjustment of temperature inside room. At last, it shows the system characteristics and energy-saving affection by hybrid system modeling and the optimum control method.

Regulatory Modeling of Pesticide Aquatic Exposures in California's Agricultural Receiving Waters.

For the aquatic exposure assessment of pesticides, the USEPA uses the Variable Volume Water Model (VVWM) to predict the estimated environmental concentrations (EECs) of a pesticide in a water body that receives runoff inputs from the Pesticide Root Zone Model (PRZM). The standard farm pond and additional generalized static and flowing water bodies used in endangered species assessment (aquatic bins) are used by USEPA to model the worst-case aquatic exposure for the nationwide exposure assessment. However, whether or not model results are relevant to state-specific conditions has not been validated. In this study, the USEPA water body scenarios are examined for their capability of providing a conservatively realistic estimate of pesticide aquatic exposures in California's agricultural settings. The sensitivity of modeled EECs to key water body parameters (dimensions, flow, and mass transfer) was explored with a one-at-a-time approach by using the standard farm pond as a baseline. The EECs generated from different USEPA water bodies for the worst-case loading were compared with the monitoring data observed in California's agriculturally influencing water bodies. Results showed that the farm pond EECs well captured the worst-case monitoring data, whereas the aquatic bins EECs, especially the flowing bins, tended to overestimate data. The conceptual model of the standard farm pond was also found to be relevant to the highly vulnerable water bodies in California's agricultural areas. The study confirms that VVWM with the standard farm pond scenario is appropriate for the screening-level regulatory exposure assessment in California's agricultural settings.

The Analysis for Energy Consumption of Marine Air Conditioning System Based on VAV and VWV

For ocean-going vessels sailing in different areas on the sea, the change of external environment factors will cause frequent changes in load, traditional ship air-conditioning system is usually designed with a fixed cooling capacity, this design method causes serious waste of resources. A new type of sea-based air conditioning system is proposed in this paper, which uses the sea-based source heat pump system, combined with variable air volume, variable water technology. The multifunctional cabins’ dynamic loads for a ship navigating in a typical Eurasian route were calculated based on Simulink. The model can predict changes in full voyage load. Based on the simulation model, the effects of variable air volume and variable water volume on the energy consumption of the air-conditioning system are analyzed. The results show that: When the VAV is coupled with the VWV, the energy saving rate is 23.2%. Therefore, the application of variable air volume and variable water technology to marine air conditioning systems can achieve economical and energy saving advantages.

Development of Design and Performance Prediction Tool for Ground Source Heat Pump System with Variable Water Volume and Variable Refrigerant Flow

Development of Design and Performance Prediction Tool for Ground Source Heat Pump System with Variable Water Volume and Variable Refrigerant Flow

A refined ecological risk assessment for California red-legged frog, Delta smelt, and California tiger salamander exposed to malathion.

The California red-legged frog (CRLF), Delta smelt (DS), and California tiger salamander (CTS) are 3 species listed under the United States Federal Endangered Species Act (ESA), all of which inhabit aquatic ecosystems in California. The US Environmental Protection Agency (USEPA) has conducted deterministic screening-level risk assessments for these species potentially exposed to malathion, an organophosphorus insecticide and acaricide. Results from our screening-level analyses identified potential risk of direct effects to DS as well as indirect effects to all 3 species via reduction in prey. Accordingly, for those species and scenarios in which risk was identified at the screening level, we conducted a refined probabilistic risk assessment for CRLF, DS, and CTS. The refined ecological risk assessment (ERA) was conducted using best available data and approaches, as recommended by the 2013 National Research Council (NRC) report "Assessing Risks to Endangered and Threatened Species from Pesticides." Refined aquatic exposure models including the Pesticide Root Zone Model (PRZM), the Vegetative Filter Strip Modeling System (VFSMOD), the Variable Volume Water Model (VVWM), the Exposure Analysis Modeling System (EXAMS), and the Soil and Water Assessment Tool (SWAT) were used to generate estimated exposure concentrations (EECs) for malathion based on worst-case scenarios in California. Refined effects analyses involved developing concentration-response curves for fish and species sensitivity distributions (SSDs) for fish and aquatic invertebrates. Quantitative risk curves, field and mesocosm studies, surface-water monitoring data, and incident reports were considered in a weight-of-evidence approach. Currently, labeled uses of malathion are not expected to result in direct effects to CRLF, DS or CTS, or indirect effects due to effects on fish and invertebrate prey. Integr Environ Assess Manag 2018;14:224-239. © 2017 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Investigation of annual energy performance of a VWV air source heat pump system

This work studies the annual energy performance of a Variable Water Volume (VWV) air source heat pump (ASHP) system by means of experiment and simulation. An advanced R410A ASHP system, integrated with independent normal fan coil unit, small temperature difference fan coil unit and floor radiation heating coil unit indoor terminals, is constructed. Multi-groups of field tests show that system COP varies from 2.0~4.0 for the different operating load under corresponding conditions. Moreover, in order to predict the long term energy performance of the ASHP system, several quasi-steady models are constructed and validated with experimental data. Then the annual energy performances of investigated system are simulated under different climate zones in China. Both experimental and simulation results show that VWV ASHP system can achieve high competitive seasonal energy efficiency for the buildings, which shows the SPF could be more than 3.0. At last, several recommendations based on the simulation results are proposed to the existed heat pump system.

循環ループ水配管網におけるポンプによる流量制御に関する研究 : 第1報-搬送動力低減の効果

循環ループ水配管網におけるポンプによる流量制御に関する研究 : 第1報-搬送動力低減の効果

B-6 制御弁監視による冷温水ポンプ揚程最適化VWV制御の実測結果

B-6 制御弁監視による冷温水ポンプ揚程最適化VWV制御の実測結果

B-12 単式ポンプ方式配管設備のためのポンプ運転制御に関する検討 : (第2報)外乱に対する安定性改善方法

B-12 単式ポンプ方式配管設備のためのポンプ運転制御に関する検討 : (第2報)外乱に対する安定性改善方法

Experimental study of hydraulic stability for variable water volume air conditioning System

The hydraulic stability of the variable water volume air conditioning system has a significant impact on the thermodynamic stability, service life of the pipe network and energy consumption. The hydraulic stability of variable water volume air conditioning system was investigated by means of experiments. An air conditioning system with variable water volume is served as the platform, and then the changes of the passive branches’ hydraulic characteristics are studied in valve action cycle of the active branch under the following three conditions: without pump control, constant differential pressure (DP) control or variable differential pressure set-point control. The results show that the branch with the small flow and high-pressure drop has the good hydraulic stability. Under the pressure difference control, the hydraulic stability of the system is improved obviously, the energy-saving effect of the pump is better, and the energy saving of the chilled water pump at least 20.8% when closed any branch valve. This study provides a reference for the design of variable water volume air conditioning systems with good hydraulic stability.

Evaluation of AGRO-2014 for Predicting Hydrophobic Organic Chemical Concentrations in Ponds.

Highly hydrophobic organic chemicals (HOCs), like pyrethroids, adsorb strongly to eroded soil and suspended sediment. Therefore, total suspended solids (TSS) concentration in the water column of receiving waters is important for determining the proportion of chemical in the sediment-sorbed vs. the dissolved (bioavailable) state. However, most current regulatory exposure models, such as the Exposure Analysis Modeling System (EXAMS) and Variable Volume Water Model (VVWM), do not include dynamic modeling of TSS. The objective of this study is to compare the performance of those models for simulating observed pesticide concentrations in small water bodies with an updated version of the AGRO model, called AGRO-2014, which includes dynamic sediment processes. The paper also evaluates the importance of explicitly modeling sediment dynamics for HOCs. We calibrated AGRO-2014 for small, static, water bodies using published pyrethroid mesocosm data. To improve the basis for intermodel comparison, AGRO-2014 includes the same algorithm for temperature-dependent degradation found in EXAMS and VVWM, direct acceptance of organic C partition coefficient () inputs, and acceptance of user-defined pesticide loading durations. Differences in sediment processes in AGRO-2014, EXAMS, and VVWM significantly affected predicted concentrations of high- compounds for standardized loading scenarios, whereas differences between the models were less evident for compounds with lower sorption to sediments. AGRO-2014 simulations of drift and slurry pyrethroid applications to ponds closely matched observed concentrations, while EXAMS and VVWM simulations underestimated the observations. The publicly available AGRO-2014 model offers improvements over other models for predicting concentrations of HOC compounds in small water bodies.

A direct optimal control strategy of variable speed pumps in heat exchanger networks and experimental validations

Energy conservation of HENs (heat exchanger networks) has been attaching more and more attentions with all kinds of methods for operation optimization. Several methods optimize the temperature and/or pressure differential set points for HENs, but cannot control the components directly, which has to seek the help of some control strategies. This paper introduces a direct optimal control strategy of VSPs (variable speed pumps) based on the newly proposed thermal resistance-based optimization method together with the physical models of each component in HENs, which can directly calculate the optimal rotation frequencies of each VSP for optimal operation. To illustrate this method, a series of experiments are performed with a VWV (variable water volume) HEN, including a group of experiments to determine the characteristic parameters in the physical models of each component, and the others to test the HEN performances with the optimal operating parameters and other alternative ones. The results show that the newly proposed direct control strategy can directly get the optimal rotation frequencies of each VSP with the least total power consumption under specific system requirements and constraints. On this basis, for different system requirements, different operating frequencies of VSPs are optimized to demonstrate the universality of the direct optimal control strategy.