Storage Tank Size Research Articles

Dynamic modeling of stratification for chilled water storage tank

Air conditioning of buildings can be costly and energy consuming. Application of thermal energy storage (TES) reduces cost and energy consumption. The efficiency of the overall operation is affected by storage tank sizing design, which affects thermal stratification of water during charging and discharging processes in TES system. In this study, numerical simulation is used to determine the relationship between tank size and good thermal stratification. Three dimensional simulations with different tank height-to-diameter ratio (HD) and inlet Reynolds number ( Re) are investigated. The effect of the number of diffuser holes is also studied. For shallow tanks (low HD) simulations, no acceptable thermocline thickness can be seen for all Re experimented. Partial mixing is observed throughout the process. Medium HD tanks simulations show good thermocline behavior and clear distinction between warm and cold water can be seen. Finally, deep tanks (high HD) show less acceptable thermocline thickness as compared to that of medium HD tanks. From this study, doubling and halving the number of diffuser holes show no significant effect on the thermocline behavior.

Design of a Site-Built Integrated Collector Storage Solar Water Heater Under Uncertainty

A straightforward framework for identifying key design parameters and determining their values for a site-built integrated collector storage solar water heater (ICSSWH) under uncertainty is developed. The framework is then used to evaluate the design for a ICSSWH, which uses locally available materials and can be assembled by builders without spe- cialized training in solar system construction. In the framework, first the most important design parameters are identified by a sensitivity analysis using TRNSED software to predict system performance. Then a decision tree is constructed that identifies discrete outcomes of various combinations of design parameters, uncertainty quantities, and resulting system performance as predicted by the TRNSED model. For the ICSSWH that is evaluated in this project, three key design pa- rameters are identified: storage tank size, top surface area, and household daily hot water cosumption. Three different sys- tem sizes are evaluated in this manner, a 114-liter, 227-liter, and 341-liter system. Only the 341-liter system has a favor- able economic return compared to a conventional, gas heater. All systems present some risk of performing worse than a conventional system. Further research is warranted into higher surface area designs to improve the performance of the system. The expected return of the system selected by this analysis is modestly higher than the return of the option which would be selected without any consideratoin of uncertainty. This indicates that straightforward frameworks, such as this, for considering uncertainty in the design of residential solar water heaters, may offer benefits to builders and home buy- ers.

Development of an integrated simulation model for treatment and distribution of reclaimed water

Research is currently being conducted as part of the AQUAREC project, with the objective being the development and validation of design principles for water reuse systems. To achieve the project objective, simulation and optimisation software for integrated water reuse systems need to be developed. A water reuse system is likely to have many possible design options: type and degree of treatment, number and location of treatment plants, number and location of pumps/pumping stations, number, size and location of storage tanks, layout and size of distribution pipe network. These elements are all linked, to give multiple interactions and a very large number of design combinations. A hydraulic/process simulation model has been developed and is described, which will be used in combination with an integrated optimisation engine to allow a range of design possibilities to be explored. The model includes a computational module for wastewater treatment trains, a computational/optimisation module for reclaimed water distribution system, and a knowledge base. The computational modules are used to calculate the performance of userdefined reuse system alternatives, utilizing the information contained in the knowledge base that includes rules for generation of treatment trains, design, cost and evaluation criteria information.

Optimization of parabolic trough solar collector system

Process heat produced by solar collectors can contribute significantly in the conservation of conventional energy resources, reducing CO2 emission, and delaying global warming. One of the major problems associated with solar process heat application is fluctuation in system temperature during unsteady state radiation conditions which may cause significant thermal and operation problems. In this paper a transient simulation model is developed for analysing the performance of industrial water heating systems using parabolic trough solar collectors. The results showed that to prevent dramatic change and instability in process heat during transient radiation periods thermal storage tank size should not be lower than 14.5 l m−2 of collector area. Small periods of radiation instability lower than 30 min do not have significant effect on system operation. During these periods when water flow rate of collector loop is doubled the time required to restore system normal operating condition increased by a ratio of 1.5. Copyright © 2005 John Wiley & Sons, Ltd.

THE ENERGY BALANCE AND ENERGY-SAVING MEASURES IN GREENHOUSE TOMATO CULTIVATION

Reliable and quick assessment of energy conservation measures in greenhouse cultivation supports growers in their operations. Such an overview should quantify the consequences of changes in energy flows for total energy consumption, amount and quality of production, and farm economy. Using tomato as an example crop, comprehensive energy balances were developed for a reference situation in The Netherlands. Solar radiation, primary and secondary heating circuits and CO2 from the flue gasses of the heating system were quantified as energy sources. Energy use for air and leaf temperature increase, crop photosynthesis, crop transpiration, as well as energy losses through the roof, walls and ground surface were quantified. Subsequently, the effects of 11 energy conservation measures were computed. Consequences for gas consumption and production were simulated with a greenhouse and a crop growth model, respectively, consequences for quality were assessed on the basis of expert knowledge, and economic consequences were simulated with a cost-benefit model. For tomato, most energy was saved by increased insulation of the greenhouse cover (23% saving) and lowered temperature set point (16%), followed by increased set point for air relative humidity, screen gap control in steps, and temperature integration (all about 5%). Fresh tomato production fell in most cases, except in case of increased light transmission by the greenhouse cover. Energy use efficiency was defined as the amount of energy required to produce a certain quantity of fresh harvestable product. Energy-conservation aims to decrease the energy use efficiency. Greatest gains were reached through insulation (-20%), lowered temperature set point (-12%) and improved light transmission (-8%). Improved light transmission resulted in the strongest increase of the balance of yield and costs (?2.6, or 10%), followed by increase of RH set point, crop-based RH control, crop-based use of the energy screen, increased size of the thermal storage tank and reduction of crop transpiration (all less than ?0.5). Although energy conservation reduces fuel costs, its implementation depends on the effects on production an overall economic profitability of the farm. Improved roof insulation, reduced temperature set point, screen gap control in steps, increase of the RH set point, temperature integration, and crop-based RH control are first candidates for (further) implementation. Other measures require prior technological advancements or fine-tuning

Numerical simulation and performance assessment of a low capacity solar assisted absorption heat pump coupled with a sub-floor system

A prototype low capacity (10 kW) single stage Li–Br absorption heat pump (AHP), suitable for residential and small building applications has been developed as a collaborative result between various European research institutes and industries. The primary heat source for the AHP is supplied from flat plate solar collectors and the hot/chilled water from the unit is delivered to a floor heating/cooling system. In this paper we present the simulation results and an overview of the performance assessment of the complete system. The calculations were performed for two building types (high and low thermal mass), three climatic conditions, with different types of solar collectors and hot water storage tank sizes and different control systems for the operation of the installation. The simulations were performed using the thermal simulation code TRNSYS. The estimated energy savings against a conventional cooling system using a compression type heat pump was found to be in the range of 20–27%.

Modeling of a space cooling system with underground storage

An analytical and computational model for a space cooling system utilizing a chiller with an underground storage tank is presented. An analytical solution given previously for the transient heat transfer problem in earth is utilized for modeling of the cooling system. Analytical expressions for heat gain to the space and energy consumption of the chiller are acquired, which is then coupled with the solution of the problem to obtain the analytical model. An analytical–numerical iterative procedure is used to determine the annual variation of water and earth temperature for different earth type, chiller and storage tank characteristics, and coefficient of performance of the chiller (COP). The results show that water temperature remains under ambient air temperature during summer months, and thus the proposed ground coupled cooling system should yield higher COP values compared to a corresponding air source system. The higher thermal conductivity and diffusivity values for an earth gives the lower storage temperature. The lower the storage and ambient air temperature, the higher the COP of the chiller, which decreases the electrical energy consumption. Earth behaved as an additional storage medium and storage tank size have strong effect on the COP of the chiller.

Optimization of solar systems using artificial neural-networks and genetic algorithms

The objective of this work is to use artificial intelligence methods, like artificial neural-networks and genetic algorithms, to optimize a solar-energy system in order to maximize its economic benefits. The system is modeled using a TRNSYS computer program and the climatic conditions of Cyprus, included in a typical meteorological year (TMY) file. An artificial neural-network is trained using the results of a small number of TRNSYS simulations, to learn the correlation of collector area and storage-tank size on the auxiliary energy required by the system from which the life-cycle savings can be estimated. Subsequently, a genetic algorithm is employed to estimate the optimum size of these two parameters, for maximizing life-cycle savings: thus the design time is reduced substantially. As an example, the optimization of an industrial process heat-system employing flat-plate collectors is presented. The optimum solutions obtained from the present methodology give increased life-cycle savings of 4.9 and 3.1% when subsidized and non-subsidized fuel prices are used respectively, as compared to solutions obtained by the traditional trial-and-error method. The present method greatly reduces the time required by design engineers to find the optimum solution and in many cases reaches a solution that could not be easily obtained from simple modeling programs or by trial-and-error, which in most cases depends on the intuition of the engineer.

Numerical and experimental study on the design of a stratified thermal storage system

The purpose of this study is to figure out the thermal stratification mechanism of a storage tank and thereby to determine optimum design and operating conditions. To this end, a computer program is developed to investigate the fluid flow in a tank, using Patankars SIMPLE algorithm. The validation of program is made successfully by the comparison against experimental data measured with a bench scale facility. Further a systematic investigation has been made in terms of important design and operational parameters such as storage tank size (commercial-scale and bench-scale), loading time, shape of diffuser, turbulence model and inlet velocity or Fr No. Considering the thermal efficiency of storage tank is critically impaired by the effect of flow recirculation and mixing by turbulence, a novel model with minimum mixing between hot and cold water is proposed for the evaluation of the performance of storage system by the assumption of the uniform plug-type flow. This is made by solving only the following governing equation of temperature which has no convective mixing with constant axial velocity, that is, ∂(ρT) ∂t +u ∂(ρT) ∂x =∇· k c p ∇T Based on a series of parametric investigation, a number of useful results can be drawn. In general the large scale system shows better storage performance than the small system. As the increase of loading time, the degree of stratification lowered due to the increased effect of heat transfer by convection and diffusion via thermal stratification region. And the curved type diffuser shows better performance of thermal stratification compared to the diffuser of flat type. As for the case of large-scale tank, the effect of Fr No., or inlet velocity does not show any significant effect on the thermal stratification compared to the small size one. The calculated results show that the model of ideal type-plug flow can be used as a possible tool for the evaluation of performance of storage system by giving the reference condition of best thermal stratification or least mixing condition. But in the case of full scale system, the difference between ideal and actual cases not significant compared to the case of bench scale. It is considered possibly due to the relatively decreased heat transfer effect by the increased effect of water flow in the full scale system. Two turbulence models, say standard k– ε and RNG k– ε models, show no visible difference in this study.

Solar energy potential for heating and cooling systems in big cities of Turkey : Şaylan, L. et al. Energy Conversion and Management, 2002, 43, (14), 1829–1837

The thermal utilization of solar energy is usually confined to domestic hot water systems and somewhat to space heating at temperatures up to 60 °C. Industrial process heat has a considerable potential for solar energy utilization. Cyprus has a small isolated energy system, almost totally dependent on imported fuels to meet its energy demand. The abundance of solar radiation together with a good technological base, created favorable conditions for the exploitation of solar energy in the island. The number of units in operation today corresponds to one heater for every 3.7 people in the island, which is a world record. Despite this impressive record no solar industrial process heat system is in operation today. The main problem for this is the big expenditure required for such a system and the uncertainty of the benefits. The objective of this work was to investigate the viability of using parabolic trough collectors for industrial heat generation in Cyprus. The system is analyzed both thermally and economically with TRNSYS and the TMY for Nicosia, Cyprus, in order to show the magnitude of the expected benefits. The load is hot water delivered at 85 °C at a flow rate of 2000 kg/h for the first three quarters of each hour from 8:00–16:00 h, 5 days a week. The system consists of an array of parabolic trough collectors, hot water storage tank, piping and controls. The optimum collector area for the present application is 300 m2, the optimum collector flow rate is 54 kg/m2 h and the optimum storage tank size is 25 m3. The system covers 50% of the annual load of the system and gives life cycle savings of about C£6200 (€10800). This amount represent the money saved from the use of the system against paying for fuel. The savings however refer to a non-subsidized fuel price, which will be in effect from 2003. The optimum system can deliver a total of 896 GJ per year and avoids 208 tons of CO2 emissions to the atmosphere. The effect of various design changes on the system performance was investigated. The E–W tracking system (collector axis aligned in N–S direction) was found to be superior to the N–S one. The required load temperature affects the performance of the system as for higher temperatures the auxiliary energy required is bigger. Also a number of variations in the load use pattern have been investigated and presented in this paper. It was found that the bigger the load (double shift, full hour use pattern) the bigger the collector area required, the greater the first year fuel savings and the greater the life cycle savings of the installation. This means that it is more viable to apply solar industrial process heat to higher energy consumption industries.

Parabolic trough collectors for industrial process heat in Cyprus

The thermal utilization of solar energy is usually confined to domestic hot water systems and somewhat to space heating at temperatures up to 60 °C. Industrial process heat has a considerable potential for solar energy utilization. Cyprus has a small isolated energy system, almost totally dependent on imported fuels to meet its energy demand. The abundance of solar radiation together with a good technological base, created favorable conditions for the exploitation of solar energy in the island. The number of units in operation today corresponds to one heater for every 3.7 people in the island, which is a world record. Despite this impressive record no solar industrial process heat system is in operation today. The main problem for this is the big expenditure required for such a system and the uncertainty of the benefits. The objective of this work was to investigate the viability of using parabolic trough collectors for industrial heat generation in Cyprus. The system is analyzed both thermally and economically with TRNSYS and the TMY for Nicosia, Cyprus, in order to show the magnitude of the expected benefits. The load is hot water delivered at 85 °C at a flow rate of 2000 kg/h for the first three quarters of each hour from 8:00–16:00 h, 5 days a week. The system consists of an array of parabolic trough collectors, hot water storage tank, piping and controls. The optimum collector area for the present application is 300 m 2, the optimum collector flow rate is 54 kg/m 2 h and the optimum storage tank size is 25 m 3. The system covers 50% of the annual load of the system and gives life cycle savings of about C£6200 (€10800). This amount represent the money saved from the use of the system against paying for fuel. The savings however refer to a non-subsidized fuel price, which will be in effect from 2003. The optimum system can deliver a total of 896 GJ per year and avoids 208 tons of CO 2 emissions to the atmosphere. The effect of various design changes on the system performance was investigated. The E–W tracking system (collector axis aligned in N–S direction) was found to be superior to the N–S one. The required load temperature affects the performance of the system as for higher temperatures the auxiliary energy required is bigger. Also a number of variations in the load use pattern have been investigated and presented in this paper. It was found that the bigger the load (double shift, full hour use pattern) the bigger the collector area required, the greater the first year fuel savings and the greater the life cycle savings of the installation. This means that it is more viable to apply solar industrial process heat to higher energy consumption industries.

How Should We Determine Storage Tank Size?

This month's question comes from two different inquiries about how to ensure the correct storage tank size. The first thing to do is choose a reputable engineer or contractor for the job and work with him on the tank design. Things to consider about tank design include: tank capacity; effective storage; emergency capacity; and, maintenance considerations. Further sources of information are given.

Modelling and simulation of an absorption solar cooling system for Cyprus

In this paper a modelling and simulation of an absorption solar cooling system is presented. The system is modelled with the TRNSYS simulation program and the typical meteorological year file containing the weather parameters of Nicosia, Cyprus. Initially a system optimisation is carried out in order to select the appropriate type of collector, the optimum size of storage tank, the optimum collector slope and area, and the optimum thermostat setting of the auxiliary boiler. The final optimised system consists of a 15-m 2 compound parabolic collector tilted 30° from the horizontal and a 600-l hot water storage tank. The collector area is determined by performing the life cycle analysis of the system. The optimum solar system selected gives life cycle savings of C£1376 when a nonsubsidized fuel cost is considered. The system operates with maximum performance when the auxiliary boiler thermostat is set at 87°C. The system long-term integrated performance shows that 84,240 MJ required for cooling and 41,263 MJ for hot water production are supplied with solar energy.

99/03934 Comparative study of the performance of an ejector refrigeration cycle operating with various refrigerants: Sun, D.-W. Energy Convers. Manage., 1999, 40, (8), 873–884

A prototype low capacity (10 kW) single stage Li–Br absorption heat pump (AHP), suitable for residential and small building applications has been developed as a collaborative result between various European research institutes and industries. The primary heat source for the AHP is supplied from flat plate solar collectors and the hot/chilled water from the unit is delivered to a floor heating/cooling system. In this paper we present the simulation results and an overview of the performance assessment of the complete system. The calculations were performed for two building types (high and low thermal mass), three climatic conditions, with different types of solar collectors and hot water storage tank sizes and different control systems for the operation of the installation. The simulations were performed using the thermal simulation code TRNSYS. The estimated energy savings against a conventional cooling system using a compression type heat pump was found to be in the range of 20–27%.

Yearly simulation of a solar-aided R22-DEGDME absorption heat pump system

The performance of a solar-aided R22-DEGDME absorption heat pump system designed for 100 kW cooling capacity is investigated by a computer simulation using hourly data for Ankara. In summer the generator, and in winter the evaporator, receives solar energy while the remaining demands are met by auxiliary heaters. When needed, these boost the temperature of the water from the storage tank to the minimum allowable levels which are determined as 20°C in winter and over 80°C in summer. The system performance, judged by the fraction of the load supplied from solar energy, is affected mostly from the climate, source temperature limit, collector type and area but little from storage tank size, for the sizes and configuration under investigation. With 400 m 2 of high efficiency collectors, the solar energy supplied 38% of the demand in winter and 91% of the demand in summer.

Optimum design of a photovoltaic powered pumping system

Photovoltaic (PV) powered pumping systems are relatively simple and reliable, hence they are applied worldwide. Two conventional techniques are curently in use; the first is the directly coupled technique where a PV array is directly coupled to a d.c. motor-pump group, and the second is the battery buffered PV pumping system where a battery is connected across the array to feed the d.c. motor driving a pump. Recently, a third system is proposed to make use of the advantages of the previously mentioned conventional systems. It is the switched mode PV powered pumping system. The switched mode PV powered pumping system couples the pumping system to the PV array directly when the storage battery is fully charged as explained in Ref. [5]. The objective of such a system is the maximum utilization of available solar radiation to minimize the cost per pumped cubic meter from a given water depth. For a given location, four main parameters affect the design of this system; (1) d.c. motor-pump group parameters, (2) PV array size, (3) battery storage size and (4) water storage tank size. The system designer has to determine the previously mentioned four parameters so that the minimum cost per pumped cubic meter is achieved. It is found that some factors are more effective in reducing the cost than others. The PV array size is the predominant factor, while the battery storage and water tank sizes have relatively less effect. The system installation cost is considered in the detailed economic analysis discussed in this work.

Use of evaporatively cooled underground water storage for convective cooling of buildings: An analytical study

Convective cooling of a room through a heat exchanger (cooling loop) using cold water from an underground evaporatively cooled water storage tank has been studied. The water in the tank is being evaporatively cooled by a suitable aeration system (aeration loop). The performance of the system is evaluated in terms of a seasonal discomfort index of the room. The effects of size of storage tank, mass flow rates in the aeration loop and cooling loop, temperature penalties of the aeration loop and cooling loops on the performance of the system have been numerically investigated. The analysis shows that, for given system parameters (corresponding to a specific value of discomfort index), there is an optimum value of mass flow rate in the aeration loop for which the total pumping energy required to operate the aeration and cooling loops is a minimum.

Optimum design of a photovoltaic powered pumping system

Photovoltaic (PV)-powered pumping systems are relatively simple and reliable. Hence, they are applied worldwide. Two conventional techniques are currently in use: the first is the ‘directly-coupled’ system where a PV array is directly coupled to a d.c. motor-pump group; the second is the ‘battery-buffered’ system where a battery is connected across the array to feed the d.c. motor that drives the pump. Recently, a third system has been proposed, namely, the ‘switched-mode’ PV-powered pumping system. This system couples the pump to the PV array directly when the storage battery is fully charged. The objective is the maximum utilization of available solar radiation to minimize the cost per pumped cubic meter from a given water depth. For a given location, four main parameters affect the design of this system: (i) d.c. motor-pump group parameters; (ii) PV array size; (iii) battery storage size, and (iv) water storage tank size. It is found that some of the factors are more effective in reducing the cost than others. The PV array size is the predominant factor, while the battery storage and water-tank sizes have relatively less effect. A detailed economic analysis is given.

175 The design and synthesis of batch/semicontinuous processes

Until now, an evolutionary method or empirical rule has been used to improve the initial design of batch/semicontinuous processes. In this paper, the proposed approach is to make a superstructure which fully contains all possible structures. And then suing a MINLP(mixed integer nonlinear programming) model, we obtain the optimal process network. MINLP model contains methodology deciding the candidates of merging tasks and using parallel equipments. Thus, the economic savings of capital cost of batch/semicontinuous processes are possible by adding equipment in parallel for bottleneck stages or merging/splitting tasks. MINLP model is solved by using a generalized reduced gradient algorithm. The effectiveness of MINLP model in single product batch plant is demonstrated by solving example problems. Also, by inserting intermediate storage tank, we reduce the capital cost for batch/semicontinuous processes and determine the optimal size of intermediate storage tank.

The Design and Synthesis of Batch/Semicontinuous Processes

Until now, many papers discussed the formulation of sizing problem for the optimal design of batch/semicontinuous processes. In this study it shows that the solutions for the sizing problem of batch/semicontinuous processes are applicable to retrofitting problem. Then several synthesis procedures have been proposed because the economic structural design and efficient equipment utilization can reduce the overall idle time in the processing units. In this study, to improve the initial design of batch/semicontinuous processes, an mathmatical procedure is proposed. The proposed approach is to make a superstructure which fully contains all possible structures. And then using a MINLP(mixed integer nonlinear programming) model, we obtain the optimal process network. The MINLP model contains methodology deciding the candidates of merging tasks and using parallel equipments. Thus, the economic savings of capital cost of batch/semicontinuous processes are possible by adding equipment in parallel for bottleneck stages or merging/splitting tasks. The MINLP model is then solved by using a generalized reduced gradient algorithm. The effectiveness of the MINLP model in single product batch plant is demonstrated by solving example problem. Also, by inserting intermediate storage tanks, we reduce the capital cost for batch/semicontinuous processes and determine the optimal size of the intermediate storage tank.