Mathematical model of absorption and hybrid heat pump

Recovering waste heat from industrial processes is bene ficial in order to reduce the primary energy demands and heat pumps can be used to this purpose.Absorption heat pumps are energy-saving and environment-friendly because use working fluids that do not cause ozone depletion and can reduce the global warming emissions.The hybrid heat pump processes combine the conventional vapor-compression and the absorption heat pump cycles.Studies about the simulations and modeling of hybrid heat pumps are few in literature.In this research a mathematical model for single effect absorption and hybrid heat pump is carried out with Chem Cad? 6.0.1.LiBr–H_2O is used as working fluid while electrolytic NRTL and electrolytes latent heat are used as thermodynamic model due to the better results.Binary parameters of activity coef ficients are regressed from experimental vapor pressure data while default constants are used for the solubility expressions.A design of heat pumps is developed and a new modeling of generator is analyzed.The coef ficient of performance of absorption heat pump and hybrid heat pump is equal to 0.7 and 0.83 respectively.For absorption heat pump a sensitivity analysis is carried out to evaluate the effect of temperature and pressure generator,the concentration of Li–Br solution on coef ficient of performance,cooling capacity and working fluid temperature.For hybrid heat pump,the different coef ficients of performance,the primary energy ratio,the generator heat,and the compressor power are analyzed for different values of compressor proportion.Results show that comparing the two systems the hybrid pump allows to save more primary energy,costs and carbon dioxide emissions with respect to absorption heat pump with the increasing of compressor proportion parameter.Future researches should focus on the construction of this heat pumps integrated in chemical processes as a biogas plant or trigeneration systems.

PERFORMANCE SIMULATION AND ANALYSIS OF AQUA AMMONIA ABSORPTION－RESORPTION HEAT PUMP

An investigation of an aqua ammonia atherption-resorption heat pump(ARHP) is made on the basis of experimental analysis and research. The results ofcomputer simulation are compared with the experimental data , and the relations be-tween the coefficient of performance (COP) of an aqua ammonia ARHP and its mainoperatins parameters, such as temperature and pressure,are obtained by means ofcomputer simulation.

Dynamic Model and Performance of Absorption Heat Pump in Shut-down Process

The dynamic model of LiBr absorption heat pump in shut-down process is established. The simulation results show good agreement with the experiments. The dynamic performance of high-pressure generator, low-pressure generator and heat exchanger are analyzed in detail. The proper shut-down mode of the heat pump is presented,which, in consideration of solution parameters, has a great effect on the possibility of crystallization of some components.

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.

Optimization Potentials for the Waste Heat Recovery of a Gas-Steam Combined Cycle Power Plant Based on Absorption Heat Pump

A new waste heat recovery system is presented to recover exhausted steam waste heat from the steam turbine by absorption heat pump(AHP) in a gas-steam combined cycle(GSCC) power plant. The system can decrease energy consumption and further improve the energy utilization. The performance evaluation criteria are calculated, and exergy analysis for key components are implemented in terms of the energy and exergy analysis theory. Besides, the change of these criteria is also revealed before and after modification. The net power output approximately increases by 21738 kW, and equivalent coal consumption decreases by 5.58 g/kWh. A 1.81% and 1.92% increase in the thermal and exergy efficiency is respectively obtained in the new integrated system as the heating load is 401095 kJ at 100% condition. Meanwhile, the appropriate extraction parameters for heating have been also analyzed in the two systems. The proposed scheme can not only save energy consumption but also reduce emission and gain great economic benefit, which is proven to be a huge potential for practical application.

Absorption heat pump for waste heat reuse： current states and future development

Absorption heat pump attracts increasing attention due to its advantages in low grade thermal energy utilization. It can be applied for waste heat reuse to save energy consumption, reduce environment pollution, and bring considerable economic benefit. In this paper, three important aspects for absorption heat pump for waste heat reuse are reviewed. In the first part, different absorption heat pump cycles are classified and introduced. Absorption heat pumps for heat amplification and absorp- tion heat transformer for temperature upgrading are included. Both basic single effect cycles and advanced cycles for better performance are introduced. In the second part, different working pairs, including the water based working pairs, ammonia based working pairs, alcohol based working pairs, and halogenated hydrocarbon based working pairs, for absorption heat pump are classified based on the refrigerant. In the third part, the applications of the absorption heat pump and absorption heat transformer for waste heat reuse in different industries are introduced. Based on the reviews in the three aspects, essential summary and future perspective are presented at last.

Lean and interpretable digital twins for building energy monitoring - A case study with smart thermostatic radiator valves and gas absorption heat pumps

The transition to low carbon energy systems poses challenges in terms of energy efficiency.In building refur-bishment projects,efficient technologies such as smart controls and heat pumps are increasingly being used as a substitute for conventional technologies with the aim of reducing carbon emissions and determining operational energy and cost savings,together with other benefits.Measured building performance,however,often reveals a significant gap between the predicted energy use(design stage)and actual energy use(operation stage).For this reason,lean and interpretable digital twins are needed for building energy monitoring aimed at persistence of savings and continuous performance improvement.In this research,interpretable regression models are built with data at multiple temporal resolutions(monthly,daily and hourly)and seamlessly integrated with the goal of verifying the performance improvements due to Smart thermostatic radiator valves(TRVs)and gas absorption heat pumps(GAHPs)as well as giving insights on the performance of the building as a whole.Further,as part of modelling research,time of week and temperature(TOWT)approach is reformulated and benchmarked against its original implementation.The case study chosen is Hale Court sheltered housing,located in the city of Portsmouth(UK).This building has been used for the field-testing of innovative technologies such as TRVs and GAHPs within the EU Horizon 2020 project THERMOSS.The results obtained are used to illustrate possible extensions of the use of energy signature modelling,highlighting implications for energy management and innovative building technologies development.

Numerical study of a hybrid absorption-compression high temperature heat pump for industrial waste heat recovery

The present paper aims at exploring a hybrid absorption-compression heat pump （HAC-HP） to upgrade and recover the industrial waste heat in the temperature range of 60℃-120℃. The new HAC-HP system proposed has a condenser, an evaporator, and one more solution pump, compared to the conventional HAC-HP system, to allow flexible utilization of energy sources of electricity and waste heat. In the system proposed, the pressure of ammonia-water vapor desorbed in the generator can be elevated by two routes; one is via the compression of compressor while the other is via the condenser, the solution pump, and the evaporator. The results show that more ammonia-water vapor flowing through the compres- sor leads to a substantial higher energy efficiency due to the higher quality of electricity, however, only a slight change on the system exergy efficiency is noticed. The temperature lift increases with the increasing system recirculation flow ratio, however, the system energy and exergy efficiencies drop towards zero. The suitable operation ranges of HAC-HP are recommended for the waste heat at 60℃, 80℃, 100℃, and 120℃. The recirculation flow ratio should be lower than 9, 6, 5, and 4 respectively for these waste heat, while the temperature lifts are in the range of 9.8℃-27.7 ℃, 14.9℃~4.1 ℃, 24.4℃-64.1 ℃, and 40.7℃-85.7℃, respectively, and the system energy efficiency are 0.35-0.93, 0.32-0.90, 0.25- 0.85, and 0.14-0.76.

Heat and mass transfer through spiral tubes in absorber of absorption heat pump system for waste heat recovery

Heat and mass transfer of a LiBr/water absorption heat pump system(AHP)was experimentally studied during working a heating-up mode.The examination was performed for a single spiral tube,which was simulated for heat transfer tubes in an absorber.The inside and outside of the tube were subjected to a film flow of the absorption liquid and exposed to the atmosphere,respectively.The maximum temperature of the absorption liquid was observed not at the entrance but in the region a little downward from the entrance in the tube.The steam absorption convective heat transfer coefficient between the liquid film flowing down and the inside wall of the temperature and the film temperature at the maximum temperature location and the bottom.The film heat and mass transfer coefficients rose with increasing Reynolds number of the liquid film stream.The coefficients showed opposite trend to the empirical correlation reported for laminar film flow on a straight smooth tube in a refrigeration mode in the past work.The fact can be caused due to a turbulent promotion effect of the liquid in a spiral tube.

配置吸收式热泵的热电联产机组厂级智能运行优化

为提高配置吸收式热泵的热电联产机组的全厂运行经济性,基于案例电厂的运行历史数据,使用滑动窗口法进行数据预处理并提取稳态工况,建立配置吸收式热泵的热电联产机组煤耗预测数学模型。以全厂热电联产机组总煤耗最小为适应度函数,利用粒子群优化算法求解得出配置吸收式热泵的热电机组最佳背压和各台热电机组最佳抽汽量。基于以上研究设计了供热系统智能优化软件,实现供热系统在线监测与优化调节,对各供热单元分别提出优化指导,使机组运行经济性最佳,进而降低整体煤耗。计算结果表明:实行供热系统智能优化策略可为案例电厂供热系统平均每小时节省标准煤约1.81 t,节能效果显著。

吸收式热泵-太阳能联合供热系统性能影响因素研究

为提高供热系统的供热能力,以吸收式热泵-太阳能联合供热系统为研究对象,通过分析联合供热系统原理并建立供热系统热力模型,对供热系统性能影响因素进行了分析。仿真结果表明,吸收式热泵-太阳能联合供热系统性能受多种干扰因素影响,包括聚光型集热器面积和流量、吸收式热泵容量和蓄热水箱容积。其中,增加聚光型集热面积和吸收式热泵容量,减小聚光型集热器流量和蓄热水箱容积,可有效降低平板集热器进口温度,提高平板集热器集热效率,使供热系统供热温度和供热量增加,进而提高供热系统供热能力。

驱动源及低温热源双向梯级利用热泵工艺研究

为提高一次能源利用效率,针对大庆油田吸收式热泵余热提取工艺进行了改进,采用驱动源和低温热源双向梯级利用热泵工艺,提高了能源利用效率。传统热泵工艺COP为1.7,采用双效梯级利用工艺COP达到2.7。双向梯级利用热泵工艺为耦合蒸汽直拖离心式热泵和蒸汽驱动吸收式热泵对余热余压梯级利用的工艺流程,利用中温中压蒸汽梯级驱动两级热泵,充分发挥了蒸汽的做功能力;同时梯级提取含油污水低温余热,使含油污水温度从35℃降至21℃,传统热泵工艺从35℃降至25℃。综合能源利用效率较传统热泵工艺提高了50%。

基于热泵技术的余热回收供热系统

传统热电厂的循环冷却水中含有大量的低品位余热,利用热泵技术对其进行回收,能够显著提升供热系统的能源利用效率,有利于实现节能减排和“碳中和”目标。设计基于单、双吸收式热泵机组的余热回收供热系统,旨在有效利用循环冷却水中的余热,增加供热能力并分析系统性能。结果表明,与传统供热系统相比,两种余热回收供热系统均可显著回收循环冷却水的热量,提高系统供热量并大幅减少能源消耗,带来可观的经济收益;双吸收式热泵机组系统展现出更优异的热力性能,具备显著的节能减排优势。分析循环冷却水入口温度和一次网回水温度对双吸收式热泵机组性能的影响,发现循环冷却水温度对系统性能影响较大,随着循环冷却水温度的升高,系统的供热量增加比例、节约标煤量和新增供热面积均增加,而一次网回水温度对系统性能的影响较小,随一次网回水温度的升高,系统的供热量增加比例、节约标准煤量和新增供热面积几乎不变。

地热驱动的双温热力站系统及其变工况性能

高温地热能是宝贵的可再生能源供热资源,降低地热水回水温度是发挥地热供热潜力、扩大供热面积的重要途径。鉴于既有建筑普遍采用散热器等高温供热末端,而新建建筑多采用地暖等低温供热末端,二者的需求供水温度不同,对此提出了单吸收式热泵+双换热器的地热能驱动双温热力站系统,以制取高、低温末端用双温热水,并尽可能降低地热水回灌温度。模拟分析表明:在地热出水为100℃,二次网高、低温末端供热量相同且供水温度分别为50℃和35℃条件下设计的双温热力站,可将地热水回水温度降至20.1℃,相比于采用2个换热器串联的热力站,其地热水的回水温度可降低14.9℃、流量可降低18.6%,系统的COP提升11%,具有显著的节能优势。变工况分析表明:低温供热末端的应用有利于进一步降低地热水回灌水温,增加向末端用户的供热量,并提高双温热力站系统的COP。

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。

基于压缩式热泵的CO_(2)-MDEA/PZ碳捕集工艺优化

当前化学法CO_(2)捕集系统的高投资、高吸收液再生能耗和高运行费用成为限制其大规模应用的主要障碍。为了回收解吸塔塔顶蒸汽中的潜热与显热,促进解吸反应的进行,利用Aspen plus软件建立基于压缩式热泵技术的有机胺法捕集CO_(2)流程模拟模型,主要探究了解吸塔塔底压力、进解吸塔富液温度、有机工质气化率以及工艺流程对CO_(2)再生过程的影响。结果表明:有机工质R123制热系数较R141b和R245fa高,其性能系数(COP)高达2.35,而排气温度较R141b和R245fa更低。压缩式热泵采用R123为循环工艺介质,热泵回收的热量用于加热贫富液换热器后的热富液以降低吸收液再生能耗。综合考虑解吸系统的再生能耗、工质循环量和解吸效果,通过12级位置注入15%的富液比合适。热泵回收余热工艺的投资回收期为0.82 a,具有较高的经济价值。

热泵技术在化工生产低位热能回收中的研究应用

针对蒸汽冷凝液中未被溴化锂冰机利用完的废热(70℃左右)回收利用的难题,研究了吸收式热泵技术在低位热能回收中的应用、冷凝液余热回收利用、闪蒸等废热回收利用等,热泵技术在化工生产低位热能回收中的研究及应用方面将几者相结合,不仅回收了大量的低温能源热量,而且解决了闪蒸冒白烟的问题,同时减少了新鲜蒸汽和循环水的消耗,通过实际应用达到了综合利用的效果,节能和环保效果显著,具有较高的推广价值。

燃煤机组排烟温度调控及水分回收研究

基于厂级尺度燃煤机组模型,对烟气加热、烟气冷凝、烟气冷凝再热等多种排烟温度调控技术方案进行评价,定量阐述冷凝法在烟气余热利用、污染物控制及水分回收的协同效果。定量对比地表水、冷却塔和吸收式热泵多种冷源方案的能耗及水分回收效果。研究表明:当脱硫塔出口烟气温度为50.5℃时,要保证不出现湿烟羽,环境温度需要37℃以上,需要烟气调温技术才能满足。冷凝法冷源温度越低,冷凝效果越好,其中冬季地表水冷源冷却效果最好,可回收36443.32 t/h烟气水分。考虑全年运行情况,冷凝法最优冷源方式为吸收式热泵蒸发器的冷却循环水,可回收34309.14 kg/h的凝结水。

河北省某高校地源热泵系统地温场监测与分析

为了掌握地源热泵地埋侧土壤的吸热放热特性,以某高校地源热泵供暖供冷为例对地埋侧土壤的吸热放热特性进行了研究,对6口地埋井在纵向按照每10米一个测点进行了温度监测,经过1a的监测数据分析得出,热泵系统一年内向地下的净排热量为10560.1GJ,热不平衡率为61.8%,存在热累积现象。分析了岩土体在供暖季、过渡季、制冷季的温度变化情况,换热区域地层平均温度升幅在1.65-2.24℃之间,平均累计上升1.89℃,为该地区同类项目的开发具有一定的借鉴作用。

基于余热回收的吸收式热泵系统在热电厂的节能环保效益

以某热电厂为调研对象,根据厂区的余热资源和冷热负荷需求,提出了一套基于余热回收的蒸汽型吸收式热泵系统。该系统在冬季回收脱硫塔循环水中的余热用于厂区内的建筑供暖和加热锅炉补水,并在夏季利用20℃的锅炉除盐水作为冷却剂,回收建筑得热。采用EnergyPlus软件构建了原有空调系统和余热回收系统的能耗模型,以一个模拟周期为例,对比分析了两者在能耗、运行费用、环保效益等方面的差异。结果表明,该系统每年可回收热量2656GJ、节省标煤3.79t、减少CO_(2)排放18.53t,节能环保效果显著。