冰源热泵系统在设施水产养殖中的技术经济性研究

针对目前刺参养殖的水温调控系统能耗大及适用性差等问题,提出基于冰源热泵的高效清洁供热及结合跨季节蓄冷实现全年冷热管理的技术思路,采用冰源热泵系统和跨季节蓄冷型冰源热泵系统对养殖水体温度进行调控,建立模型定量对比分析系统的运行能效及技术经济性。结果表明:（1）冰源热泵系统供热和供冷时的性能系数分别为3.33和3.39,全年一次能源利用率为1.05,比燃煤锅炉+冷水机组系统高出34.6%;费用年值最低,投资回收期为3 ~ 5年,具有良好的经济效益和应用前景。（2）跨季节蓄冷型冰源热泵系统全年一次能源利用率为1.46,比冰源热泵系统高39.1%,全年运行费用最低;跨季节蓄冷技术的应用有效提升了系统能效,大幅减少供冷运行费用,具有较大发展潜力。     

Performance evaluation of a new ice preservation system for supermarkets

At present, all types of large–medium‐sized supermarkets with aquatic products adopt ice preservation to ensure freshness. The traditional method of ice preservation needs to make a large amount of thick ice and thus wastes manpower and freshwater. A new ice preservation system with cold storage (IP&CS) is designed, and its performance is tested. The use of a cold storage tank to replace the thick ice laid achieves a repeated cold storage and discharge. This experiment uses NaCl solution as the cold storage phase change material (PCM). The phase change temperature of the cold storage PCM and the optimum temperature of the secondary refrigerant during the cold storage process are determined. Results show that the center temperature of aquatic products, water loss rate, color of aquatic products, power consumption, and electricity cost of the IP&CS system are better than those of the traditional ice preservation system.     

综合能源系统运行优化设计与运行策略研究

综合能源系统能整合协调各异质能源,是提高能源利用率和降低运行费用的有效途径。提出了两种运行策略及一种基于穷举法的优化策略方法,建立了包括小型燃气轮机系统、地源热泵、电制冷机、吸收式制冷机、换热器的综合能源系统能量转换模型。在案例研究中,提出了以典型日费用最小为目标的综合能源系统优化方案,对以电定热、以热定电两种运行策略下的场景进行了优化分析,确定设备的最佳容量和运行参数,给出了运行策略对比分析结果。结果表明：以电定热策略的整体经济性优于以热定电策略约10%;与传统供能系统在经济性上的适用性进行对比发现,综合能源系统成本节省比例在5%～30%之间。     

Need for thermal-storage air-conditioning in Saudi Arabia

In Saudi Arabia, the growth of demand for electrical energy in the rapidly expanding towns, cities and industries, far exceeds the growth of the power being made available. Recently the Saudi Consolidated Electric Companies (SCECO) are facing a shortage of electricity during the summer period mainly due to the high consumption of electricity in the air conditioning sector. The incorporation of thermal energy storage (TES) technologies with a conventional air conditioning system is found to be an appropriate solution for energy-demand management. In this paper an introductory overview of thermal storage air conditioning is presented, comparing phase change (e.g. ice) and sensible heat (e.g. chilled water) storage technologies. The pros and cons of each are evaluated. The suitability of TES technology for the Saudi HVAC (heating, ventilating and air conditioning) industry is explored with the benefits to the owner such as: reduced energy consumption; less operation and maintenance costs; and downsizing of the chiller plant and system for new facility; alternative to new chiller installation to cater for increased cooling load; and stored water as a fire protection source. Furthermore, an economic study has been presented to illustrate the feasibility of TES based air conditioning in Saudi Arabia.     

A review: Renewable energy with absorption chillers in Thailand

The aim of this paper is to review the energy situation, renewable energy potential and absorption chiller system in Thailand. The renewable energy which will be used in low temperature applications, under the consideration of low operating cost, high availability and non-polluted emission such as solar energy was discussed. Solar energy can be used as power sources for cooling systems, especially for the absorption chiller. Thailand is located in the area where the solar intensity is very high and thus solar energy can be used as power sources. The absorption chiller using water/lithium bromide is the most appropriate for the solar applications. This system, however, is not widely used in Thailand due to its complexity, high toxicity caused by leakage and high initial cost. The utilization of absorption chiller may increase if more researches focus on the development of this cooling system, which is driven by solar energy. This may results in a substantial decrease in electricity consumption.     

High temperature latent heat thermal energy storage using heat pipes

A thermal network model is developed and used to analyze heat transfer in a high temperature latent heat thermal energy storage unit for solar thermal electricity generation. Specifically, the benefits of inserting multiple heat pipes between a heat transfer fluid and a phase change material (PCM) are of interest. Two storage configurations are considered; one with PCM surrounding a tube that conveys the heat transfer fluid, and the second with the PCM contained within a tube over which the heat transfer fluid flows. Both melting and solidification are simulated. It is demonstrated that adding heat pipes enhances thermal performance, which is quantified in terms of dimensionless heat pipe effectiveness.     

Dynamic simulation of hydrogen-based zero energy buildings with hydrogen energy storage for various climate conditions

Solar energy systems are an effective way to meet the needs of zone heating, cooling, electricity, and domestic hot water. However, to reach sustainability, and energy storage unit should be considered for installation. In this study, two combined cooling, heating and power (CCHP) systems are simulated and studied using TRNSYS software; both using natural gas engine generators and photovoltaics as prime movers and a hydrogen fuel cell/electrolyzer storage unit, one with absorption chiller and another with compression chiller cooling. For the study, a residential building is modeled for three major populated climate zones of the United States of America, namely, Hot-humid, mixed-humid and cold using DesignBuilder and EnergyPlus software. The energy demand for its HVAC operation and domestic electricity is obtained and used for system simulation in TRNSYS software. Due to choosing actual equipment for the CCHP arrangement, precise economic and environmental models are designed to further evaluate the possibility of execution of the system. The results show that absorption chiller-equipped CCHP has better performance both environmentally and economically. In addition, the outcome shows that the suggested systems show less favorability to be utilized in hot humid climate zones.     

A thermoeconomic analysis of biomass energy for trigeneration

The principal objective of this study is to formulate a calculation process, based on the second law of exergy, for evaluating the thermoeconomic potential of a steam-turbine plant for trigeneration. The plant employs biomass, namely, waste wood as its energy source. Four different plant configurations are presented and assessed. ‘Their cost effectiveness is evaluated with varying economic and operating parameters’, because only the fuel price and electricity price are varied. In case 1, high pressure superheated steam generated is supplied to meet the demand for process heat as well as chilled water production in an absorption chiller. In cases 2 and 3, steam is extracted at appropriate stages of the turbine and supplied to meet the demand for process heat and chilled water production in an absorption chiller. Steam generated in case 2 produces sufficient power to meet internal demands while case 3 generates excess electricity for sale back to the utility. In case 4, low pressure saturated steam is generated to meet the demand for process heat and electricity is bought from the utilities, including those used to power an electric vapour-compression chiller. For all cases, it was found that exergy destruction is most extensive in the furnace, amounting to nearly 60%. Exergy destruction in the steam drum is the next most extensive ranging from 11% to 16%. It was also observed that the overall production cost decreases with steam pressure and increases with steam temperature.     

Exergetic comparison of wind energy storage with ice making cycle versus mini-hydrogen economy cycle in off-grid district cooling

For the feasible and continuous utilization of intermittent wind and solar energy sources for electricity generation in district energy systems in hot-climates, where cooling loads are dominant, ice storage may be an option. In this study, the rationality of the ice storage system for wind energy was investigated using the Rational Exergy Management Model, REMM for two options and compared with a base scenario, which comprises a wind turbine system, grid connection, conventional chillers, and the district cooling system. The main objective is to minimize exergy destructions and thus to improve the exergy performance. The first ice storage option is composed of wind turbines, deep chillers for ice making, ice storage tanks, and the district cooling system. The second option is similar to the first option but it also includes a ground-source heat pump upstream the deep chiller. These options were also compared against a mini-hydrogen economy (District size) alternative, which encompasses a hydrogen-water cycle with excess renewable energy-powered PEM electrolysis unit, hydrogen tank, fuel cell, absorption chiller, gas compression chiller, and the district cooling system. These two options and the hydrogen-water cycle alternative were compared in terms of their REMM efficiency, First and Second-law efficiencies, and the primary energy ratio. A new Sustainability Performance Index, namely SPI was also defined. SPI is the product of the REMM efficiency, First-Law Efficiency, and the load coincidence factor, CF of wind energy. In order to establish a realistic application background for the comparisons, first a nearly-net-zero exergy farmland (nZEXF) utilizing biogas, cogeneration, solar photovoltaics, heat, absorption cycle, ground-source heat pump, Organic Rankine Cycle, and wind turbines was introduced as a model. The primary objective of this study is to determine the best option with the least avoidable CO₂ emissions responsibility of the systems considered in terms of the REMM efficiency in thermal or hydrogen storage systems. Results have been compared in terms of SPI with the base scenario and it has been concluded that the second option (SPI = 0.88) is better than the first option (SPI = 0.38). However, hydrogen storage is an even better alternative with an SPI value of 1.06. These figures according to REMM with the coincidence factor being considered, mean that the avoidable CO₂ emissions may be reduced by up to 54% compared to the base case. Hydrogen cycle option may also be used with the same effectiveness in district heating, while ice storage options are limited to district cooling only. This paper provides the relevant theory, shows the fundamental calculations about the option rankings based on a unit cooling load, makes recommendations for future district energy systems, and refers to a conceptual hydrogen economy driven city.     

Thermoeconomic analysis of a standalone solar hydrogen system with hybrid energy storage

A comprehensive thermoeconomic analysis is presented for a novel integrated solar hydrogen energy system for standalone operation. The proposed system includes a solar PVT module (photovoltaic thermal), a FC (Fuel cell) and a battery to meet the electrical load demand and domestic hot water over a year. The PVT component works as a primary energy source converting solar energy into electricity and heat. The excess electrical energy and hot water produced by PVT are consumed for producing hydrogen, which can be stored. The generated hydrogen is fed to the fuel cell to produce electricity and water to satisfy the demand. The proposed system is convenient for different seasons of the year because in all time, produced power satisfy the demand. The first and second laws of thermodynamics are used to evaluate the performance of each component and the overall system. Economic assessment of this system is also conducted considering the net present cost, and the system performance is optimized based on this parameter. The overall electrical efficiency of the system is obtained as 9% and the levelized cost of electricity is determined as $ 0.286/kWh. For a steady operation of system, integrating a battery system is convenient when solar energy is not available for a short term. When there is a longer-term shortage of solar radiation, up to 8 days, the electricity can be supplied by utilizing the hydrogen storage system.     

A new zero energy cool chamber with a solar-driven adsorption refrigerator

A new zero energy cool chamber (ZECC) consisting of two cooling systems, a solar-driven adsorption refrigerator and an evaporative cooling system, was developed and then evaluated as low-cost and eco-friendly cooling storage for storing fruit with moderate respiration rates. The solar-driven adsorption refrigerator, consisting of a solar collector containing activated carbon as an adsorbent, a condenser and an evaporator, cools water based by evaporating methanol and adsorbing it on activated carbon, and then makes ice. The methanol adsorbed on the activated carbon is desorbed by applying solar heat. The ice is then used to cool the storage space, which can be done for a long time without the need for electricity. The evaporative cooling system also cools the storage space by evaporating water from the wet walls containing wet filler. The combined use of two cooling systems reduced the average inside temperature of the new ZECC to 12.07 °C compared with an average outside temperature of 31.5 °C and extended the shelf life of tomatoes from 7 to 23 days. These results suggest that the new ZECC proposed here is low-cost and energy-saving and is useful for storing fruit and vegetables in areas where electricity is unavailable.     

Experimental study on liquid/solid phase change for cold energy storage of Liquefied Natural Gas (LNG) refrigerated vehicle

The present paper addresses an experimental investigation of the cold storage with liquid/solid phase change of water based on the cold energy recovery of Liquefied Natural Gas (LNG) refrigerated vehicles. Water as phase change material (PCM) was solidified outside the heat transfer tubes that were internally cooled by cryogenic nitrogen gas substituting cryogenic natural gas. The ice layer profiles were recorded in different cross-sections observed by digital cameras. The temperatures of cryogenic gas, tube wall and bulk region were measured by embedded thermocouples continuously. The results of the smooth tube experiments and the thermal resistance analysis prove that the main thermal resistance occurs in the gaseous heat transfer fluid (HTF) inner the tube. The enhancement of the inner heat transfer is achieved by adding wave-like internal fins. Besides, the results show that the ice layer not only increases in radial direction but also propagates in axial direction. It distributes in parabolic shape along the tube length due to the parabolic axial distribution of the tube wall temperatures. This investigation provides valuable references for the design and optimization of the cold energy storage unit of LNG refrigerated vehicles and for the numerical study on the unsteady two-dimensional conjugated heat transfer with phase change.     

Experimental study on latent heat storage characteristics of W/O emulsion -Supercooling rate of dispersed water drops by direct contact heat exchange-

Recently, much attention has been paid to investigate the latent heat storage system. Using of ice heat storage system brings an equalization of electric power demand, because it will solved the electric -power-demand-concentration on day-time of summer by the air conditioning. The flowable latent heat storage material, Oil/Water type emulsion, microencapsulated latent heat material-water mixture or ice slurry, etc., is enable to transport the latent heat in a pipe. The flowable latent heat storage material can realize the pipe size reduction and system efficiency improvement. Supercooling phenomenon of the dispersed latent heat storage material in continuous phase brings the obstruction of latent heat storage. The latent heat storage rates of dispersed water drops in W/O (Water/Oil) emulsion are investigated experimentally in this study. The water drops in emulsion has the diameter within 3 ～ 25μm, the averaged water drop diameter is 7.3μm and the standard deviation is 2.9μm. The direct contact heat exchange method is chosen as the phase change rate evaluation of water drops in W/O emulsion. The supercooled temperature and the cooling rate are set as parameters of this study. The evaluation is performed by comparison between the results of this study and the past research. The obtained experimental result is shown that the 35K or more degree from melting point brings 100% latent heat storage rate of W/O emulsion. It was clarified that the supercooling rate of dispersed water particles in emulsion shows the larger value than that of the bulk water.     

Heat pumps and energy storage - The challenges of implementation

The wider implementation of variable renewable energy sources such as wind across the UK and Ireland will demand interconnection, energy storage and more dynamic energy systems to maintain a stable energy system that makes full use of one of our best renewable energy resources. However large scale energy storage e.g. pumped storage may be economically challenging. Therefore can thermal energy storage deployed domestically fulfil an element of such an energy storage role? Current electricity pricing is based on a ½ hourly timeframe which will be demonstrated to have some benefits for hot water heating from electrical water heaters in the first instance. However heat pumps linked to energy storage can displace fossil fuel heating systems and therefore the question is whether a renewable tariff based on “excess” wind for example is sufficient to operate heat pumps. An initial analysis of this scenario will be presented and its potential role in challenging aspects of fuel poverty.     

A comprehensive energy supply model in an office building based on the reference energy system

In the last decade, technological innovations have resulted in considering distributed generation with heat recovery capability in addition to centralised generation. This work aims to develop a comprehensive model analysing techno-economic parameters of energy supply in an office building. The energy model is developed on the basis of the reference energy system with the linear programming technique. The objective function is the annual value of total costs of the energy supply system. The results of the model for the building of Sharif Energy Research Institute indicate that the most appropriate generation technology is an internal combustion engine of 461 kW and a water boiler of 152 kW. In addition to supplying the final service demand, hot water feeds an absorption chiller of 507 kW to produce cold water. Furthermore, storage systems of hot and cold water are required in order to achieve high load factors in the system.     

热管蓄冰过程的数值模拟研究．

通过建立热管的简化热阻模型,采用数值计算的方法模拟了热管的动态蓄冰。模拟结果与实验结果吻合。同时,对热管冷凝段和蒸发段的长度比为1：2和1：4两种形式进行了数值模拟比较。结果表明,1：4的布置形式更优。     

New technology and possible advances in energy storage

Energy storage technologies may be electrical or thermal. Electrical energy stores have an electrical input and output to connect them to the system of which they form part, while thermal stores have a thermal input and output. The principal electrical energy storage technologies described are electrochemical systems (batteries and flow cells), kinetic energy storage (flywheels) and potential energy storage, in the form of pumped hydro and compressed air. Complementary thermal storage technologies include those based on the sensible and latent heat capacity of materials, which include bulk and smaller-capacity hot and cold water storage systems, ice storage, phase change materials and specific bespoke thermal storage media.     

Optimal flow control of a forced circulation solar water heating system with energy storage units and connecting pipes

This paper focuses on pump flow rate optimization for forced circulation solar water heating systems with pipes. The system consists of: an array of flat plate solar collectors, two storage tanks for the circulation fluid and water, a heat exchanger, two pumps, and connecting pipes. The storage tanks operate in the fully mixed regime to avoid thermal stratification. The pipes are considered as separated components in the system so as to account for their thermal effects. The objective is to determine optimal flow rates in the primary and secondary loops in order to maximize energy transfer to the circulation fluid storage tank, while reaching user defined temperatures in the water storage tank to increase thermal comfort. A model is developed using mainly the first and second laws of thermodynamics. The model is used to maximize the difference between the energy extracted from the solar collector and the combined sum of the energy extracted by the heat exchanger and corresponding energies used by the pumps in the primary and secondary loops. The objective function maximizes the overall system energy gain whilst minimizing the sum of the energy extracted by the heat exchanger and corresponding pump energy in the secondary loop to conserve stored energy and meet the user requirement of water tank temperatures. A case study is shown to illustrate the effects of the model. When compared to other flow control techniques, in particular the most suitable energy efficient control strategy, the results of this study show a 7.82% increase in the amount of energy extracted. The results also show system thermal losses ranging between 5.54% and 7.34% for the different control strategies due to connecting pipe losses.     

Parametric analysis of space cooling systems based on night ceiling cooling with PCM‐embedded piping

A parametric analysis is conducted for space cooling systems based on cold water flowing, during the night, within regularly arranged pipes embedded in a layer of phase change material (PCM), located among the structural layers of the ceiling. The introduced PCM layer in conjunction with night cooling add to the usual ceiling cooling systems offers the advantages of low energy consumption, high cool storage capacity, operation under reduced night electricity price, smoothing of electricity consumption by eliminating daily peak loads, improved thermal comfort and elimination of ceiling dripping. Our parametric analysis is based on a transient three‐dimensional finite‐difference solution of the related heat‐transfer problem for various values of all the main system parameters. PCM phase change process is simulated by using the effective thermal capacity function, which is determined experimentally for PCM suitable for air‐conditioning applications. Our tests showed that the main parameters of the system are pipe spacing, PCM layer thickness, pipe depth within the ceiling, cooling water inlet temperature, night cooling duration and PCM properties (thermal conductivity, phase change heat and ends of phase change temperature range). The effect of all the above parameters is analysed and suggestions are made for selecting the proper combinations of their values in order to obtain the lowest energy consumption in conjunction with the highest level of thermal comfort. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhancement of latent heat energy storage using embedded heat pipes

Latent heat thermal energy storage (LHTES) utilizing heat pipes or fins is investigated experimentally. Photographic observations, melting and solidification rates, and PCM energy storage quantities are reported. Heat pipe effectiveness is defined and used to quantify the relative performance of heat pipe-assisted and fin-assisted configurations to situations involving neither heat pipes nor fins. For the experimental conditions of this study, inclusion of heat pipes increases PCM melting rates by approximately 60%, while the fins are not as effective. During solidification, the heat pipe-assisted configuration transfers approximately twice the energy between a heat transfer fluid and the PCM, relative to both the fin-assisted LHTES and the non-heat pipe, non-fin configurations.