Comparison of two schemes for district cooling system utilizing cold energy of liquefied natural gas

Two schemes（scheme Ⅰ and scheme Ⅱ）for designing a district cooling system（DCS）utilizing cold energy of liquefied natural gas（LNG）are presented.In scheme Ⅰ,LNG cold energy is used to produce ice,and then ice is transported to the central cooling plant of the DCS.In scheme Ⅱ,return water from the DCS is directly chilled by LNG cold energy,and the chilled water is then sent back to the central plant.The heat transportation loss is the main negative impact in the DCS and is emphatically analyzed when evaluating the efficiency of each scheme.The results show that the DCS utilizing LNG cold energy is feasible and valuable.The cooling supply distance of scheme Ⅱ is limited within 13 km while scheme Ⅰ has no distance limit.When the distance is between 6 and 13 km,scheme Ⅱ is more practical and effective.Contrarily,scheme Ⅰ has a better economic performance when the distance is shorter than 6 km or longer than 13 km.

Possibilities of Using Solar Energy in District Cooling Systems in the Mediterranean Region

Use of district heating and cooling systems has many environmental advantages compared to individual heating and cooling. Recent advances in solar energy technologies for heat and power generation have reduced their cost and promoted their use instead of fossil fuels. Solar-PV energy for electricity generation and solar thermal energy for hot water production are broadly used today. Solar energy resources in the Mediterranean region are abundant while space cooling in buildings is required when solar irradiance is high. The possibility of using solar energy for fuelling water chillers providing cold water in district cooling systems in the Mediterranean basin has been investigated. Existing literature and studies concerning the use of district cooling systems globally as well as the energy sources used in them have been examined. Solar-PV energy combined with compression chillers and solar thermal energy combined with thermally driven chillers can be used for cold water production. Their overall efficiencies, converting solar energy to cold water, vary between 22% and 56% compared with 45% for compression chillers using grid electricity. It is concluded that various solar energy technologies could be used with different types of water chillers for fuelling district cooling networks in the future in the Mediterranean region.

Simulation of District Cooling Plant and Efficient Energy Air Cooled Condensers (Part I)

In hot arid countries with severe weather, the summer air conditioning systems consume much electrical power at peak period. Shifting the loads peak to off-peak period with thermal storage is recommended. Model A of residential buildings and Model B of schools and hospitals were used to estimate the daily cooling load profile in Makkah, Saudi Arabia at latitude of 21.42°N and longitude of 39.83°E. Model A was constructed from common materials, but Model B as Model A with 5 - 8 cm thermal insulation and double layers glass windows. The average data of Makkah weather through 2010, 2011 and 2012 were used to calculate the cooling load profile and performance of air conditioning systems. The maximum cooling load was calculated at 15:00 o’clock for a main floor building to a 40-floor of residential building and to 5 floors of schools. A district cooling plant of 180,000 Refrigeration Ton was suggested to serve the Gabal Al Sharashf area in the central zone of Makkah. A thermal storage system to store the excess cooling capacity was used. Air cooled condensers were used in the analysis of chiller refrigeration cycle. The operating cost was mainly a function of electrical energy consumption. Fixed electricity tariff was 0.04 $/kWh for electromechanical counter, and 0.027, 0.04, 0.069 $/kWh for shifting loads peak for the smart digital counter. The results showed that the daily savings in consumed power are 8.27% in spring, 6.86% in summer, 8.81% in autumn, and 14.55% in winter. Also, the daily savings in electricity bills are 12.26% in spring, 16.66% in summer, 12.84% in autumn, and 14.55% in winter. The obtained maximum saving in consumed power is 14.5% and the daily saving in electricity bills is 43% in summer when the loads peak is completely shifted to off-peak period.

The Optical Properties of Black Coatings and Their Estimated Cooling Effect and Cooling Energy Savings Potential

The optical properties of coatings pigmented with different black colorants were systematically investigated and their surface temperatures and cooling energy savings were estimated. The black coatings pigmented with chromite iron nickel black and manganese ferrite black spinel colorants are not cool enough to be energy efficient cool black coatings. The cool black coatings pigmented with NIR-transmitting perylene black and dioxazine purple colorants possess a green shade and a violet shade, respectively. The estimated surface temperature reduction values and annual cooling energy savings in Beijing range from 3.0°C and 1.21 kWhm-2yr-1 for the black coating pigmented with chromite iron nickel colorant to 13.8°C and 5.52 kWhm-2yr-1 for the black coating pigmented with dioxazine purple colorant, respectively.

Improvements in energy saving and thermal comfort for electric vehicles in summer through coupled electrochromic and radiative cooling smart windows

In hot climates,the large amount of cooling load in electric vehicle(EV)results in a lot of battery energy consumption,leading the decrease of driving range.With the widespread application of windows in EV,the electrochromic glass(EC)shows great prospect in lowering the cooling load.However,researches on the application of EC in EV lack the consideration of both passive cooling measures and passenger comfort,which limits the further application of EC.In this paper,we proposed an idea combining the novel techniques of both electrochromism and radiative cooling.Computational fluid dynamics(CFD)is modeled to simulate the application of electrochromic and radiative cooling coupled smart windows in hot parking conditions,exploring the improvement effect of the window on the thermal environment,comfort and energy saving of the EV.The results indicate that,under the intense sunlight with an outdoor temperature of 33℃,activating the air conditioning to maintain an average interior temperature of 26℃,the coupled windows reduced the cooling capacity of the air conditioning by 762 W compared to regular windows,which can further increase the range of EV.Meanwhile,compared to simple electrochromic fully colored glass,the integration of radiative cooling technology can lower the window surface temperature by up to 10.7℃.Moreover,compared to regular windows,the coupled windows lowered the standard effective temperature(SET*)for passengers by approximately 7℃,significantly improving comfort.These research findings are expected to provide guidance for optimizing window design and enhancing the performance of EV.

Electrochromism-induced adaptive fresh air pre-handling system for building energy saving

Building fresh air supply needs to meet certain regulations and fit people’s ever-growing indoor air quality de-mand.However,fresh air handling requires huge energy consumption that goes against the goal of net-zero energy buildings.Thus,in this work,an adaptive fresh air pre-handling system is designed to reduce the cool-ing and heating loads of HVAC system.The sky-facing surface of the system uses electrochromic mechanism to manipulate the optical properties and thus make full use of solar energy(solar heating)and deep space cold source(radiative cooling)by switching between heating and cooling modes.In the cooling mode,the sky-facing surface shows a transmittance of down to zero,while the reflectance is high at 0.89 on average.In the heating mode,the electrochromic glass is highly transparent,allowing the sunlight to reach the solar heat absorber.To obtain the energy-saving potential under different climates,six cities were selected from various climate regions in China.Results show that the adaptive fresh air pre-handling system can be effective in up to 55.4%time of a year.The maximum energy-saving ratios for medium office,warehouse,and single-family house can reach up to 11.52%,26.62%,and 18.29%,respectively.In addition,the system shows multi-climate adaptability and broad application scenarios,making it a potential solution to building energy saving.

The Preliminary Research of Sea Water District Heating and Cooling for Tallinn Coastal Area

This paper describes possibilities to utilize sea water for district heating and cooling purposes in Tallinn costal area. The sea water temperature profiles and suitability of heating and cooling generation are studied for continental climatic conditions. The district network study bases on 21 buildings located near to the Gulf of Finland. Industrial reversible heat pump technology is selected to cover heating and cooling loads for the new buildings. Combination of existing district heating and heat pump technology is considered for existing buildings. The results show possibilities, threats and need for further research of the sea water based heat pump district network implementation.

Impact of radiative cooling on the energy performance of courtyards in Mediterranean climate

Radiative cooling has proven to be a useful tool to address the problems of lack of comfort and excessive energy consumption in situations of high temperatures,overheating and heat waves.Likewise,incorporating courtyards in warm climate zones has been found to be highly beneficial in addressing similar challenges.Hence,there is interest in analyzing the combined effects of both:radiative cooling and courtyards.This paper presents an analysis of the impact of the application of radiative cooling on a courtyard using a comprehensive simulation approach that includes a CFD model for the thermodynamic airflow in the adjacent roofs and inside the courtyard,equations for the transient heat conduction through roofs,walls and courtyard slabs,and a hybrid raytracing-radiosity model for the evaluation of the solar radiation reaching the building surfaces and its reflections,both of specular and diffuse origin,and for the calculation of the thermal radiation exchange,especially with the sky.The results show that in the hot season,the courtyard with radiative cooling always provides lower temperatures than the initial courtyard does,with a temperature range of 18.33℃to 33.78℃,compared to a range of 19.32℃to 38.00℃in the initial courtyard,and producing a greater difference with outdoor temperatures that can reach 12℃versus 8℃for the reference case.In addition,it was found that the courtyard with radiative cooling is able to significantly reduce the observed nighttime overheating by providing lower temperatures than the outdoor temperatures in the 50%of the nights studied.It was also found that the thermal loads to achieve indoor thermal comfort in the spaces adjacent to the courtyard were reduced by 63.46%to 69.85%.

Free cooling系统在制冷系统经济运行中的研究与应用

卷烟制造工厂在过渡季节需开启制冷机组,为组合式空调机组提供低温冷冻水以确保工房温湿度指标合格,导致制冷机开启周期增长,使整个制冷系统包括制冷机、冷却塔、冷却水泵、冷冻水泵等设备的电耗增加。某卷烟厂在动力中心制冷系统中研究并引进Free cooling(自然冷却)系统。通过系统设计与改造,在过渡季节通过利用冷却塔供冷的方式降温,不仅达到控制工房温湿度指标的目的,同时减少了大功率制冷机组的开启时间,节省了运行费用,提高了设备使用寿命,达到节能降耗的经济运行目的。开展Free cooling系统在制冷系统经济运行中的研究与应用十分必要。

Optimal Operation Strategies for a Large Multi-Chiller System Based on Cooling Load Forecast

In semiconductor and electronics factories, large multi-chiller systems are needed to satisfy strict cooling load requirements. In order to save energy, it is worthwhile to design the chilled water system operation. In this paper, an optimal flexible operation scheme is developed based on a two-dimensional time-series model to forecast the cooling load of multi-chiller systems with chiller units of different cooling capacities running in parallel. The optimal integrity scheme can be obtained using the Mixed Integer Nonlinear Programming method, which minimizes the energy consumption of the system within a future time period. In order to better adapt the change of cooling load, the operation strategy of regulating the chilled water flowrates is employed. The chilled water flowrates are set as a design variable. When the chillers are running, their chilled water flowrates can vary within limits, whereas the flowrates are zero when the chillers are unloaded. This forecasting method provides integral optimization within a future time period and offers the operating reference for operators. The power and advantages of the proposed method are presented using an industrial case to help readers delve into this matter.

基于室内非均匀环境营造的新型通风模式下人员热舒适性及系统节能潜力

为解决现有通风空调系统无法根据占用区域实现按需供冷造成的热不舒适及能源浪费问题,本研究根据人员占用区域需求实时切换气流模式组合及冷量供给,提出了一种新型通风模式,旨在利用多种气流模式的最优组合控制特定需求场景。采用数值模拟的方法探究了不同占用区域情况下新型通风模式的人员热舒适性和系统的节能潜力,并与混合通风模式和层式通风模式进行了对比。结果表明:新型通风模式在气流组织上具有明显优势;新型通风模式较混合通风模式和层式通风模式具有更高的热舒适性,空气分布特性指数最大;新型通风模式局部冷量利用系数最小,冷量有效利用率最高,所需供冷量最小,因此新型通风模式的节能潜力最大。

热湿气候下蒸发冷却式冷凝器系统的节能特性对比研究

为评估和提高蒸发冷却式冷凝器系统(MVC-EC)在热湿气候条件下的应用潜力,提出了一种结构优化的两级蒸发冷却式双冷凝器系统(MVC-TSEC),并基于详细的能耗分析模型进行了性能对比研究。首先,建立了各系统中所有组件的分布式参数模型,并进行了实验数据验证。其次,分析了室外空气温度和相对湿度及房间显冷负荷对2种系统COP和节能率的影响。最后,评估了2种系统在典型热湿城市的节能潜力。结果显示:相较于MVC-EC系统,MVC-TSEC系统在高温、中高湿度和高负荷工况下具有更好的节能优势,节能率约提高4.3%~10.9%,并且可提高制冷剂系统适应温度约0.8~1.9℃;在广州市和长沙市夏季6—8月,MVC-TSEC系统的节能率分别为12.7%和21.1%,高于MVC-EC系统(8.5%和14.9%)。

专科医院手术室双冷源全生命周期节能性探讨与实践——以中山大学中山眼科中心手术室为例

专科医院可根据其特殊的负荷特性,选择最优的手术室冷源对全生命周期进行节能。文章从理论分析论证了专科手术室采用水冷与风冷双冷源的系统形式的节能性,并以中山大学中山眼科中心手术室为例,以眼科手术室双冷源的实际改造建设情况及不同季节与不同水温运维能耗数据给出分析,提出在过渡季或冬季时,针对改造过的双冷源系统,采用集中冷源供冷未必比利用风冷式机组更加节能,并提出双机组出水应考虑垂直温升冷损,为国内专科手术室双冷源提供参考。

水能风机在循环水冷却系统的应用

介绍了循环水冷却系统中采用水能风机代替大功率电动机实现节能降耗的实施措施,分析了改造后带来的经济效益。

浅谈TIE-固定篦床的优化升级

TIE-固定篦床采用中心分区供风、微调风阀、水滴型高效篦板等技术,用水平出风的高速气流快速急冷熟料,不仅系统可获得温度较高且稳定的二次风,还能均布熟料,减少粗细熟料的离析分布,从源头上控制“红河”的产生;在稳定较高的二次风温下,还可将料层厚度总体降低至650mm左右,大幅减小后续所有冷却风机的总体负载阻力,进一步有利于熟料的冷却和降低冷却电耗。实践表明,使用TIE-固定篦床局部替换旧的固定篦床,能有效地提高二次风温,降低烧成系统的能耗,还可显著提高熟料的质量。

自然通风湿式冷却塔节水方案的数值研究

为降低自然通风湿式冷却塔的耗水量,本文采用一种可用于回收其蒸发损失的空气冷凝器结构,并通过数值模拟方法对其节水特性展开研究。首先基于空气运动控制方程和水蒸气冷凝模型,建立了用于分析空气冷凝器节水特性的数学模型,其次分析了冷却空气流速、空气冷凝器的结构尺寸和材质等因素对该冷凝器节水特性的影响。研究结果表明:空气冷凝器的单位面积节水量随着冷却空气流速以及冷凝器宽度的增大而增大,但随着冷凝器长度和高度的增大而减小;空气冷凝器的材质和壁厚对其单位面积节水量没有显著影响,空气冷凝器可采用重量轻和成本低的薄壁PVC来加工制造。

数据中心间接蒸发冷却复合空调系统的节能运行分析

结合上海地区的气候条件,采用TRNSYS软件,通过设定数据中心机房条件模拟出全年所需冷负荷随时间的变化规律,确定设备选型,并基于间接蒸发冷却复合空调系统主要设备的数学模型搭建了仿真平台。通过对空调系统运行模式的切换,模拟得到3种运行模式下的送风状态图及运行特性。结果表明,冬季应采用能耗更低的干模式,过渡季采用湿模式,夏季采用混合模式。对比常规机械制冷系统,复合空调系统的全年耗电量为352.6万kW·h,节能率高达34.8%。

厂区级冷却供水系统智能控制设计实现

某厂区冷却供水系统只能以手动模式运行,无法实现自动恒压供水,能耗高、设备损耗大,对管网流量波动适应性差;通过重新设计系统PLC程序,进行加减泵逻辑控制和管网压力设置,实现了基于变频器的管网恒压控制;通过水泵轮巡逻辑控制和冗余配置,实现了水泵的自动轮换运行;通过水泵使能功能和管网压力手动设置功能,提高了系统控制的灵活性;通过优化水泵加载条件和触摸屏功能,消除了设备故障对系统自动运行的干扰;经过10个月运行验证,系统一直稳定工作,水泵运行数量减少三分之一,管网运行压力降低12.8%,可设置参数由3个增加到15个,冷却供水泵组节能23%以上。

考虑节能节水协同的循环水系统优化及应用

作为过程工业中高能耗辅助系统的代表,循环水系统表现出用户多、系统复杂、能耗高等特性,决定了工业循环冷却水的研究重点集中在系统节能和降低总体水量这两个方面。本文提出了工业循环冷却水系统的多尺度整体协同优化策略,从系统与设备层面进行循环冷却水系统的多尺度优化,以降低整体水耗和能耗。以国内某炼油厂的单个循环水系统优化为例,节能节水协同优化与改造前相比,系统节水25.6%,考虑长周期运行情况,节水23.6%,系统节能25.6%。

Energy saving potential of a fresh air pre-cooling system using radiative sky cooling

To achieve required indoor air quality,fresh air supply in buildings should meet relevant standards and regulations.However,the handling of fresh air introduced a cooling load that takes up a large portion of building energy consumption,especially in tropical and subtropical areas.A proper way should be employed to reduce the cooling load of fresh air.Radiative sky cooling,which is the process that an object cools itself by emitting thermal radiation to outer space without any energy input,is a cost-effective and eco-friendly technology.In this work,a fresh air pre-cooling system using radiative sky cooling is proposed to reduce fresh air cooling load.The system,consisting of filters,a radiative air-cooling system,an air handling unit(AHU),fans,etc.,is installed on the rooftop of the modeled building.Six cities in low-latitude areas are selected and investigated.Results show that with the radiative air-cooling system installed,annual cooling energy consumption of the modeled building can be reduced by around 10%in most cities.For arid areas,e.g.,Abu Dhabi,the system has even better performance with 19.34%annual cooling energy saving.