Assessment of Low Global Warming Potential Refrigerants for Waste Heat Recovery in Data Center with On-Chip Two-Phase Cooling Loop

Data centers(DCs)are highly energy-intensive facilities,where about 30%–50%of the power consumed is attributable to the cooling of information technology equipment.This makes liquid cooling,especially in twophase mode,as an alternative to air cooling for the microprocessors in servers of interest.The need to meet the increased power density of server racks in high-performance DCs,along with the push towards lower global warming potential(GWP)refrigerants due to environmental concerns,has motivated research on the selection of two-phase heat transfer fluids for cooling servers while simultaneously recovering waste heat.With this regard,a heat pump-assisted absorption chiller(HPAAC)system for recovering waste heat in DCs with an on-chip twophase cooling loop driven by the compressor is proposed in the present paper and the low GWP hydrofluoroolefin refrigerants,including R1224yd(Z),R1233zd(E),R1234yf,R1234ze(E),R1234ze(Z),R1243zf and R1336mzz(Z),are evaluated and compared against R245fa as server coolant.For theHPAAC system,beginning with the development of energy and economic models,the performance is analyzed through both a parametric study and optimization using the coefficient of performance(COP),energy saving ratio(ESR),payback period(PBP)and net present value(NPV)as thermo-economic indicators.Using a standard vapor compression cooling system as a benchmark,the results indicate that with the evaporation temperature between 50℃and 70℃and the subcooling degree ranging from5℃to 15°C,R1233zd(E)with moderate compressor suction pressure and pressure ratio is the best refrigerant for the HPAAC systemwhile R1234yf performs the worst.More importantly,R1233zd(E)is also superior to R245fa based on thermo-economic performance,especially under work conditions with relatively lower evaporation temperature as well as subcooling degree.Under the given working conditions,the overall COP,ESR,NPV,and PBP of R1233zd(E)HPAAC with optimum subcooling degree range from4.99 to 11.27,25.53 to 64.59,1.13 to 4.10×10^(7) CNY and 5.77 to 2.22 years,respectively.Besides,the thermo-economic performance of R1233zd(E)HPAAC under optimum working conditions in terms of subcooling degree varying with the evaporation temperature is also investigated.

Exploring heating performance of gas engine heat pump with heat recovery

In order to evaluate the heating performance of gas engine heat pump（GEHP） for air-conditioning and hot water supply, a test facility was developed and experiments were performed over a wide range of engine speed（1400-2600 r/min）, ambient air temperature（2.4-17.8 ℃） and condenser water inlet temperature（30-50℃）. The results show that as engine speed increases from 1400 r/min to 2600 r/min, the total heating capacity and energy consumption increase by about 30% and 89%, respectively; while the heat pump coefficient of performance（COP） and system primary energy ratio（PER） decrease by 44% and 31%, respectively. With the increase of ambient air temperature from 2.4 ℃ to 17.8 ℃, the heat pump COP and system PER increase by 32% and 19%, respectively. Moreover, the heat pump COP and system PER decrease by 27% and 15%, respectively, when the condenser water inlet temperature changes from 30 ℃ to 50 ℃. So, it is obvious that the effect of engine speed on the performance is more significant than the effects of ambient air temperature and condenser water inlet temperature.

Analysis on Several Heat Pump Applications in Large Public Buildings

The consumption of cooling and heating energy and the methods of heating and cooling used in large public buildings are analyzed in this paper. A comparison between initial investment and operation costs of heat pump and traditional heating modes used in large public buildings is also introduced. A life cycle cost (LCC) mathematical model is established to analyze the main factors that affect the LCC including the advantages and disadvantages of heat pumps currently in use. Some suggestions about heating and cooling modes applied in large buildings in different geographical areas are given in this paper.

The Efficiency Analysis of the Exhaust Air Heat Pump System

This paper is based on long term parameter measurements of the exhaust air heat pumps (EAHP) system in a new built apartment building. The building was equipped with an exhaust air ventilation system and exhaust air heat pump for ventilation heat recover. The results of the measurements show that the COP of the EAHP is mainly related to the temperature graph of the heating system and the supply temperature of domestic hot water (DWH). During the measurement period some other impact factors, such as the quality of maintenance, the nighttime temperature graph of the heating system, the reduction of the exhaust air flows in case of low temperatures, mistakes in designing and low building quality, have also played a role. An analysis of energy consumption shows that in winter conditions the COP is about 3.0 and in the transition period about 3.3. The energy recovery value of the EAHP is 0.5.

Economic Model Predictive Control for Hot Water Based Heating Systems in Smart Buildings

This paper presents a study to optimize the heating energy costs in a residential building with varying electricity price signals based on an Economic Model Predictive Controller (EMPC). The investigated heating system consists of an air source heat pump (ASHP) incorporated with a hot water tank as active Thermal Energy Storage (TES), where two optimization problems are integrated together to optimize both the ASHP electricity consumption and the building heating consumption utilizing a heat dynamic model of the building. The results show that the proposed EMPC can save the energy cost by load shifting compared with some reference cases.

Efficiency of Combined Solar Thermal Heat Pump Systems

In this project, different combinations of solar energy and heat pump systems for preparation of DHW （domestic hot water） and space heating of buildings are analyzed through dynamic system simulations in TRNSYS （Transient System Simulation Program）. In such systems, solar thermal energy can be used, on one hand, directly to charge the buffer storage and, on the other hand, as heat source for the evaporator oftbe HP （heat pump）. In this work systems, in which solar heat is only used directly （parallel operation of solar and HP）, systems using the collectors also as a heat source for the HP are analyzed and compared to conventional air HP systems. With a combined parallel solar thermal HP system, the system performance compared to a conventional HP system can be significantly increased. Unglazed selectively coated collectors as source for the HP have the advantage that the collector can be used as an air heat exchanger. If solar radiation is available and the collector is used as source for the HP, higher temperatures at the evaporator of the HP can be achieved than with a conventional air HP system.

Heat flow balance and control strategies for a large GSHP

The possibility of underground imbalance between heat emission and absorption has a negative impact on the performance of ground-source heat pump systems （GSHPs）. Numerical and experimental researches were made in a residential building, which is supplied with a GSHP system and a ceiling radiation system combined with a replacement fresh air system. EnergyPlus simulations were used to estimate heating and cooling loads, and to assess the heat generated from the water pump, the fan and the heat pump unit. Then, Fluent simulations were used to compare three different control strategies of handling the underground heat exchange. These simulations were strongly based on an experimentally verified model. It is obtained that a ratio between cooling and heating loads is 5.08 ： 1 in a case study in Nanjing. Moreover, the control strategy based on the starting time is more efficient and reliable than the temperature and temperature difference strategies to control the underground heat exchange.

Comprehensive evaluation and analysis of a nearly zero-energy building heating system using a multi-source heat pump in severe cold region

The integrated application of multi-energy coupled technology in nearly zero-energy building(NZEB)is promising from the perspective of low-carbon development to achieve the goal of net zero energy.PVT(photovoltaic/thermal),air,and ground sources were combined organically to establish an experimental platform of a multi-source heat pump(MSHP)system,which can realize flexible switching of multi-energy sources.The paper presents the analytical hierarchy process and fuzzy comprehensive evaluation method to comprehensively evaluate the five modes of the MSHP system with regard to energy,economic and environmental benefits.The results indicate that the waste heat of the PVT cavity can improve the coefficient of performance of the heat pump unit(COP)by approximately 8.0%.The initial investment in air source heat pump(ASHP)modes is lower than that of a coal-powered system.The ground source heat pump(GSHP)modes have high stability and their payback period is 8.81–10.66 years.The photovoltaic/thermal-dual source heat pump(PVT-DSHP)mode presents the most appropriate system applied in the NZEB in severe cold region,followed by the DSHP,GSHP,ASHP,and PVT-ASHP mode.When compared with other modes,COP,annual saving cost,carbon dioxide emission reduction,and comprehensive value of the PVT-DSHP mode have improved by 7.07%–29.57%,2.21%–23.88%,3.38%–14.83%,and 27.91%–52.62%,respectively.The study provides important insights into the practical application and sustainable development of multi-energy coupled systems in the NZEB in severe cold region.

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.

光伏光热联合双源热泵系统运行模式研究(2):供暖季系统仿真研究

使用TRNSYS软件建立了光伏光热-双源热泵(PV/T-DSHP)系统的仿真模型。选取夏热冬冷地区某一近零能耗居住建筑作为研究对象,模拟研究了供暖季PV/T-DSHP系统在COP_(s)切换模式下的运行特性和能耗。结果表明:平均光电效率为15.08%,平均光热效率为33.05%;水源热泵运行模式下供暖季平均COP为4.55,空气源热泵运行模式下供暖季平均COP为3.19,PV/T-DSHP系统的平均COP_(s)为2.98;供暖季系统自满足率为61%。

大滑移温度CO_(2)非共沸工质余热回收热泵热水系统实验研究

通过热泵技术将生产/生活中的低品位余热提质增效具有广泛的应用潜力。其中,非共沸工质能够实现热泵循环换热过程中的温度匹配,实现余热资源的深度利用。基于水源热泵热水实验台对基于大滑移温度的CO_(2)/R1234yf、CO_(2)/R290、CO_(2)/R600a和CO_(2)/R32非共沸工质进行实验分析,并以R290工质作为对照,研究蒸发器与冷凝器同时满足大温差情况下的热泵性能表现。结果表明:非共沸工质充注量主要影响循环过冷度,进而影响系统COP,当CO_(2)/R1234yf的质量分数为15%/85%时,循环存在最优充注量,在实验工况(热源进水温度25℃,出水温度5℃;热汇进水温度15℃,出水温度45℃)下最优充注量对应的COP为7.66。同时,在实验工况下,相较于R290单工质,CO_(2)/R290工质对最优COP提升了75.2%,对应q v(单位容积制热量)提升了107.7%;CO_(2)/R1234yf工质对最优COP提升了27.7%,对应q v提升了92.0%;CO_(2)/R32工质对最优COP提升了15.0%;而CO_(2)/R600a工质对最优COP仅提升1.7%,应用潜力较低。

考虑空气源热泵负荷聚合参与的需求响应

基于“电网-聚合商-负荷”三级架构,提出空气源热泵负荷聚合参与需求响应的控制策略。供暖运营商作为热泵负荷的聚合商,在保证用户热舒适度的基础上,利用建筑本身的蓄能能力,结合分时电价最小化供热成本,并对负荷可调节潜力进行评估。当电网调度部门下发调控指令后,考虑用户舒适度和电网调节需求,基于多目标遗传算法分配各负荷调节量,在满足调控目标的同时可改善调控带来的聚合功率振荡、反弹负荷大等问题。最后,仿真验证所提策略的有效性。

水环热泵系统辅助热源容量设计与调控策略

提出采用工况分析法设计水环热泵系统辅助热源容量,利用循环水能量变化量逆推建立辅助热源容量模型,并以天津地区某办公建筑群为实例,设计3种辅助热源容量方案,采用负荷与水温2种热量调控方案分析辅助热源对系统运行的影响,并采用负荷能耗分析法分析控制方案。测试结果表明:3种辅助热源容量方案均能够保证系统正常运行,按55%负荷率选取设计容量时,系统能效最高;优化中低负荷的供热量、实现机组与辅助热源能量平衡是提升系统能效的关键技术;相比负荷控制,水温调节更适宜水环热泵系统。

利用数据中心余热供热的系统设计与分析

数据中心余热供热是提高数据中心能源利用效率和实现冬季清洁供暖的重要途径。本文提出了一种适用于数据中心的长距离供热系统,在热源和热汇处设置多级热泵以增大供热管网供回水温差,并使用储热装置保障数据中心和供热系统的安全性,提高数据中心余热利用率。以张家口某数据中心为例进行了分析,该系统初投资为50.21元/m^(2),运行费用为26.37元/GJ,投资回收期约为5.31 a,具有较好的经济性和节能减排效果。

某调度通信楼空调系统节能减碳改造设计实践

重点介绍了某调度通信楼空调系统的节能减碳改造设计,通过综合运用余热回收、可再生能源、固体蓄热、高效制冷机房等多项技术,构建了安全可靠、绿色低碳、高效节能的空调系统。采用HDY-SMAD空调负荷计算及分析软件模拟了建筑物全年的空调能耗,并对优化前后空调系统的运行能耗和碳排放进行了测算。结果显示,优化方案空调系统全年节约电量100万kW·h,全年碳减排573 t,节能减碳效果显著。

制热工况下跨临界CO_(2)热泵最优排气压力的影响因素研究

最优排气压力是影响跨临界CO_(2)热泵性能最重要的因素。为研究最优排气压力存在原因及其影响参数,并揭示各参数对最优排气压力的影响机理,基于传热夹点理论对最优排气压力进行了理论分析。利用AMESim软件搭建了考虑气体冷却器内部传热夹点的跨临界CO_(2)热泵模型进行仿真计算,在进水温度为10~40℃、出水温度为60~90℃、环境温度为-30~25℃的宽工况内定量研究了进水温度、出水温度、环境温度及回热率对热泵系统最优排气压力的影响。研究结果表明:进水温度越低、出水温度越低、环境温度越低,均会导致传热夹点向气体冷却器出口移动,从而使系统的最优排气压力减小;同时,采用回热方式也能够将传热夹点进一步向气体冷却器出口推移,从而减小最优排气压力。研究结果证实传热夹点的位置对于系统最优排气压力的取值具有重要影响,因此基于传热夹点的分析与设计方法具有更强的适用性,可为热泵供暖、车辆热管理等用途中CO_(2)热泵系统的设计和性能优化提供理论与工程基础。

电动工程机械双热源热泵空调系统的仿真和试验

热泵空调系统是电动汽车新型加热取暖方式之一,具有制热制冷效率高、控制方便等优势,其在电动工程机械领域也有良好的应用前景。但热泵空调系统最大的应用难题是其利用的冷媒R134a在低温环境温度下,由于制冷剂本身性质的限制及室外侧换热器结霜现象,导致系统的制热性能严重下降,进而影响热泵空调系统的综合性能。据此,提出了基于双热源热泵空调的纯电工程机械整车热管理系统的解决办法,引入工程机械的电驱系统余热作为电驱源,与传统热泵空调的空气源组成双热源热泵空调系统,通过系统中余热的合理运用,提高能量利用率。AMESim仿真和热管理试验平台不同模式下的试验结果表明,电驱源热泵系统的制热性能明显优于传统空气热源热泵,有效提高制热能效系数。

吸收-压缩热泵回收高水分杂醇烟气余热研究

为了处理煤化工过程中产生的有害副产杂醇并回收热能,本文设计了一台以杂醇为燃料的热水锅炉,并在锅炉尾部加装了一种新型吸收-压缩复合热泵来回收烟气余热,通过Aspen Plus软件对热泵回收烟气余热流程进行模拟。结果表明杂醇烟气蕴含丰富潜热,采用该新型热泵能实现余热有效回收,额定工况下能使锅炉热效率提高11.01%。进一步研究了压缩机压比、回水温度和锅炉负荷对热泵性能的影响,并提出分别基于节能和碳减排效果的热泵性能系数COP_(a)和COP_(e)来全面分析热泵的运行性能。结果发现在压比为9.6时热泵COP_(a)和COP_(e)最高,且在压比小于9.6时,热泵性能会受回水温度升高的影响较大。随着锅炉负荷的增大,热泵系统的COP_(a)和COP_(e)先增大后减小。本文研究可为高水分烟气余热的深度回收和新型复合热泵的应用提供一些理论依据。

喷油参数对螺杆式空气源热泵系统性能的影响

针对北方寒冷地区的稠油热水驱技术面对的问题,设计一台带经济器的螺杆式低温空气源热泵加热原油机组,增加油冷热回收系统,测试分析低温环境下热泵系统的制热性能以及油冷热回收对系统性能的影响。结果表明:油冷换热器可以有效帮助螺杆式空气源热泵降低压缩机排气温度,提高热泵在低温环境下的制热量和能效比C_(op),实现环境温度-35—43℃的稳定运行。有油冷热回收时,系统能效比最高可达3.74,油冷换热器最高能回收25.8%的热量。蒸发温度-24℃时,制热量可达350 kW。喷油量的增加对系统性能的改善呈现先增加后下降的趋势,油冷热回收回路存在最佳喷油量使得系统能效比最高。随着喷油温度的增加,压缩机排气温度呈上升趋势,系统能效比呈下降趋势。

余热回收型空气源热泵烘干系统设计与能效实验

采用电能空气源热泵替代传统的木柴燃烧进行经济农作物烘干具有节能环保、降本增效等优点。针对空气源热泵烘干过程中热量随高温空气流失而降低了能源利用率的问题,设计了一款余热回收再利用的空气源热泵烘干系统,首先通过调节新风阀与回风阀开度使热风在烘干机内持续循环;然后通过热回收器与热泵将排出的高温空气余热回收,可显著提升热能的利用效率。为量化空气源热泵的电热转换与烘干加热过程能源利用率,研究了两级能效指标。一级能效指标可衡量电热转换与回收的利用效率;二级指标可直接衡量电能对产量的产出效率。研制了余热回收型空气源热泵烘干样机系统,并设计了一套远程监控系统,可在云端和手持终端实时在线监控作业过程和状态,控制烘干作业的工艺流程,并计算两级能效指标。食用菌烘干实验结果表明:该余热回收型空气源热泵烘干系统样机的一级能效指标为84.69%、二级指标为4.37 kg/(kW·h),具有能效利用率高、安全可靠等优点。