Integrated Intelligent Energy

Research and application of heat pump technology in integrated energy systems

SUN Jian, WANG Yinwu, WU Kexin, TAO Jianlong, QIN Yu

2023, 45(4): 1-11. doi:10.3969/j.issn.2097-0706.2023.04.001

Asbtract ( 262 )

HTML ( 12)

PDF (1697KB) ( 349 )

Figures and Tables | References | Related Articles | Metrics

In the context of "dual carbon"， integrated energy systems are continuously promoting the technological reforms in the fields of flexible renewable energy consumption， low-carbon heating and cooling， industrial waste heat utilization and flexible and coordinated peak shaving for the power grid. Heat pumps are widely used in integrated energy systems because of their high efficiency and low pollutant emissions. Being the energy supply or energy storage unit in an integrated energy system， heat pumps can be divided into four categories according to their energy sources， air source， water source， soil source and waste heat recovery heat pumps. Heat pumps can be heat （cold） storage and electricity storage units according to their functions. Heat pumps can facilitate the low-carbon and high-efficiency operation of the system， but arise problems from energy coupling and optimal operation. Finally， the development trend of heat pumps in integrated energy systems is prospected.

Application and development of CO₂ transcritical cycle heat pumps

LI Minxia, HOU Beiran, WANG Pai, DONG Liwei, TIAN Hua

2023, 45(4): 12-18. doi:10.3969/j.issn.2097-0706.2023.04.002

Asbtract ( 193 )

HTML ( 11)

PDF (1546KB) ( 466 )

Figures and Tables | References | Related Articles | Metrics

Under the background of carbon peaking and carbon neutrality，the application of heat pumps with natural working medium CO₂ as refrigerant is more in line with the new requirements of green development and environmental protection.Comparing the status of overseas and domestic researches on CO₂ heat pumps in different scenarios，it is found out that CO₂ emissions from a CO₂ heat pump water heater is 40% lower than that from a traditional electric water heater.The most prominent advantage of a CO₂ heat pumps is the significant temperature rise which leads to high working efficiency.In low outdoor temperatures，CO₂ heat pumps can satisfy the hot water demands of users along railways and in rural areas of northern China with high annual energy efficiency ratios. CO₂ on-board air conditioners have been developed and basically into mass production.Compared with a traditional electric dryer，a CO₂ heat pump dryer can save energy by 55% at most.CO₂ heat pump technology will be a hot spot in the future research on environmental protection and low-carbon technologies， and will play a key role in China's "dual carbon" target.

Study on the optimal temperature for flue gas waste heat recovery of the heat pump with new working fluid

SUN Jian, QIN Yu, WANG Yinwu, WU Kexin, GE Zhihua

2023, 45(4): 19-25. doi:10.3969/j.issn.2097-0706.2023.04.003

Asbtract ( 81 )

HTML ( 5)

PDF (1275KB) ( 96 )

Figures and Tables | References | Related Articles | Metrics

Since the flue gas emitted from natural gas boilers is of high temperature and contains high latent heat of steam， it is worthy to be reused. To pursuit the "dual carbon" target， the waste heat in natural gas boiler flue gas is recovered by electric heat pumps with new working fluids to rise the return water temperature. In order to improve the coefficient of performance of electric heat pumps， their performances under different working conditions are studied. Six types of mixed working fluids， R134a+R245fa， R152a+R245fa， R227ea+R245fa， R134a+R142b， R152a+R142b and R227ea+R142b， show different cycling properties. Under the actual operating condition of a boiler room，the thermodynamic properties of different mixed working fluids are compared when the inlet and outlet hot water temperatures of the condenser are 50/65 ℃，and the inlet and outlet cold water temperatures of the evaporator are 40/35 ℃ or 40/30 ℃. The conclusion is that the optimal working fluid under this working condition is the mixture of R134a and R245fa whose mole fractions are 0.41 and 0.59. The benefits of the waste heat recovery system and the costs of the heat pump with the optimized flue gas temperature and selected working fluid are analysed， and the variation law of the economy of waste flue gas recovery with flue gas temperature is obtained. The analysis is beneficial for the future design of waste heat recovery systems.

Effects of mixed working fluids on the performance of a combined power and ejector refrigeration cycle

ZHAO Dongpeng, ZHAO Li, DENG Shuai, ZHAO Ruikai, XU Weicong

2023, 45(4): 26-34. doi:10.3969/j.issn.2097-0706.2023.04.004

Asbtract ( 70 )

HTML ( 5)

PDF (1298KB) ( 151 )

Figures and Tables | References | Related Articles | Metrics

A combined power and ejector refrigeration cycle （CPERC） can simultaneously generate power and cold by coupling a power cycle with a ejector refrigeration cycle. CPERCs，driven by medium and low-temperature thermal energy，are applicable in renewable energy utilization，waste heat recovery and other fields. Different from the cycle with a single function，a CPERC needs to ensure the good temperature match between the heat source and the cycle and that between the refrigerant and the cycle simultaneously.For the power cycle，the organic flash cycle can achieve a good temperature match between the temperature-swing heat source and the cycle.For the refrigeration cycle，zeotropic working fluid can achieve a good temperature match between the cycle and the refrigerant.Therefore，the CPERC taking the organic flash cycle and zeotropic working fluid can achieve the temperature matches above simultaneously.By establishing a mathematical model， the effect of the R600a/R601a zeotropic mixture on the performance of the CPERC is studied. The results show that when the mass fraction of R600a is 0.3，the exergy efficiency of the CPERC peaks at 37.38%，which is 4.20% higher than that of the CPERC taking pure R600a and 6.30% higher than that of the CPERC taking pure R601a as its working fluid.

Experimental study on factors influencing flue gas emissions of gas engine-driven heat pumps

MO Jihang, MIAO Yanshu, CHEN Changrui, ZHANG Xiaomeng, NI Long

2023, 45(4): 35-40. doi:10.3969/j.issn.2097-0706.2023.04.005

Asbtract ( 57 )

HTML ( 2)

PDF (1184KB) ( 142 )

Figures and Tables | References | Related Articles | Metrics

With the popularization of gas engine-driven heat pumps, their emission standards are becoming more and more strict. Thus, the influences of gas consumption, excess air coefficient and engine speed on the flue gas emissions from gas engine-driven heat pumps under steady operation condition are studied in a flue gas emission experiment. The results show that the w（NO_x）and flue gas temperature show upward trends with the increase of natural gas consumption, while increasing excess air coefficient can reduce the w（NO_x）and keep the w（CO）at a low level. From the point of view of reducing pollutant emissions, the excess air coefficient should be kept at around 1.40. With the increase of engine speed, both w（NO_x） and w（CO） decrease at first and then increase with their minimum values occurring at a speed of 1 250 r/min or so, and the flue gas temperature shows a positive linear relationship with the engine speed.

Performance analysis on a double-stage resorption heat storage system

DOU Pengbo, JIA Teng, DAI Yanjun

2023, 45(4): 41-46. doi:10.3969/j.issn.2097-0706.2023.04.006

Asbtract ( 64 )

HTML ( 2)

PDF (1406KB) ( 141 )

Figures and Tables | References | Related Articles | Metrics

A heat storage system based on the double-stage resorption cycle with ammonia water as working medium was constructed and its thermodynamic performance was evaluated.The system stores energy relying on the concentration difference of its solution.The concentration of the solution at the resorption circle high-pressure absorber outlet fluctuates with the circulating operating pressure.There are lower limits for the circulating operating pressure under different solution concentrations.When the mass fraction of the concentrated side solution is as low as 0.9，the circulating operating pressure should not be lower than 4.6 kPa.However，low concentration of the solution at the absorber outlet will hamper the normal operation of the cycle.Based on the feasible concentration-temperature range of the resorption heat storage cycle，a throttling failure threshold is proposed as the criterion for effective cooling capacity of refrigerant.The difference between a resorption cycle and an absorption cycle is that the former one takes the binary solution absorption process instead of the unary refrigerant condensation process， so the heat source temperature of the resorption cycle can be effectively reduced. The conclusions are drawn on the performance analysis.When the heat source temperature is 90 ℃，the COP of a single-stage resorption cycle can be 0.614，and the COP of a double-stage resorption cycle can be 0.489.When the inlet temperature is 30 ℃，the outlet temperature of the system taking single-stage heat storage mode can reach 49.38 ℃，and that taking double-stage heat storage mode can reach 52.54 ℃.The system can meet the requirements of floor heating.

Analysis on the thermal insulation of long-distance steam heating pipes

SHANG Yongqiang, WANG Wenfeng, WANG Weishu, GUO Jiawei, ZHENG Haonan, GE Xuewen

2023, 45(4): 47-51. doi:10.3969/j.issn.2097-0706.2023.04.007

Asbtract ( 60 )

HTML ( 1)

PDF (1687KB) ( 105 )

Figures and Tables | References | Related Articles | Metrics

In order to solve the thermal insulation problem in the long-distance transportation of cogeneration steam，a pipe network project undertaken was simulated to study its heat dissipation characteristics under different laying schemes.And the steam parameters at the network's user side were calculated based on the design load.The simulation results show that laying an air layer and soil over the steam heating pipes can reduce the heat loss of the pipes to a certain extent，so as to improve the thermal insulation of the pipelines.The heat loss of the directly buried section is less than that of the overhead pipe section.Since the increase of the load will reduce the temperature drop of the pipe and increase the pressure drop，condensation will occur at some user ends when the load of the pipe network is low.This simulation facilitates the theoretical study on heating pipe allocation optimization.

Study on the solar-assisted ground-source heat pump system with seasonal heat storage in cold regions

DOU Zihui, LIU Jingxia, LI Baoli

2023, 45(4): 52-58. doi:10.3969/j.issn.2097-0706.2023.04.008

Asbtract ( 90 )

HTML ( 7)

PDF (2816KB) ( 202 )

Figures and Tables | References | Related Articles | Metrics

In view of the soil heat imbalance caused by the manifested gap between higher cooling load in summer and lower heating load in winter in cold regions，TRNSYS simulation software was selected to analyze the performance of a solar-assisted ground-source heat pump（SAGSHP）system with seasonal heat storage in a hospital in Baotou City.The analysis results show that the soil temperature has increased from 10.00 ℃ to 10.68 ℃ after 10-year operation of the seasonal heat storage system，while the soil temperature has decreased by 5.62 ℃ after 10-year operation of a solar energy coupled ground source heat pump （SGSHP）system.The COP of the SAGSHP system taking seasonal heat storage was 3.25，up 2.20% year on year，and its EER was 7.55，up 0.13% year on year.At the same time， the total power consumption of the SAGSHP system taking seasonal heat storage is reduced by 11.54% compared with that of the SGSHP system.It can be seen that SAGSHP systems taking seasonal heat storage mode can not only improve the heating performance coefficient of soil source heat pumps，but also alleviate the soil heat imbalance and save the power consumption of the whole system.

Optimization and applicability analysis on temperature measurement method for the heating system based on infrared remote sensing

GAO Lianrui, CONG Mingyang, WANG Yuan, XU Haidong, XIE Hongtao, WANG Deren, ZHOU Zhigang

2023, 45(4): 59-68. doi:10.3969/j.issn.2097-0706.2023.04.009

Asbtract ( 84 )

HTML ( 3)

PDF (1919KB) ( 165 )

Figures and Tables | References | Related Articles | Metrics

User-side room temperature acquisition is an essential tool for integrated intelligent energy systems' on-demand heat supply， and room temperature is the key performance evaluation parameter for the system. However， current acquisition approaches are of excessive cost and high uncertainty caused by sensor locations. Combining the infrared remote sensing-based temperature measurement method with the actual scenarios， the impacts of sensor locations， weather conditions， users' open window behaviors and the number of baseline rooms on the temperature measurement were analyzed. Then， the optimization and applicability of the proposed method were discussed. The analysis results show that when the number of baseline rooms goes up to two， the impacts of external interferences， such as weather conditions and window opening behaviors， can be reduced significantly，and the robustness of the system can be improved. Unaffected by diminishing marginal benefits， the approach can keep the measurement error within ±1.5 ℃. As for the installation position of sensors， the edge-top combination is taken as the better choice. Compared with the conventional method， the proposed method can significantly reduce the requirements on the coverage rate of sensors， and can provide a reference for the engineering cases in the future.

Benefit analysis on the deep geothermal energy centralized heating system based on compression heat exchangers

SUN Fangtian, ZHAO Xiaoqing, XU Wanqing, HAO Baoru, XIE Yonghua

2023, 45(4): 69-73. doi:10.3969/j.issn.2097-0706.2023.04.010

Asbtract ( 49 )

HTML ( 1)

PDF (1022KB) ( 106 )

Figures and Tables | References | Related Articles | Metrics

According to the demand for clean heating in northern China， a deep geothermal energy centralized heating system based on compression heat exchangers is proposed considering the distribution of deep geothermal energy in this area. The effect of geothermal water temperature on the performance of the proposed heating system is analyzed，and the result indicates that higher geothermal water temperature can improve the thermal performance of the system. When temperature of geothermal water goes up to 75 ℃， the compression heat exchanger can lower the return water temperature of the primary network to 15 ℃， which solves the space mismatch between geothermal fields and end-users. When heat transmission distance of the primary network is 20 km， the annual system coefficient of performance （ASCOP） of the deep geothermal energy centralized heating system based on compression heat exchangers is about 12.5， and 92.0% geothermal energy is utilized for heat-supply. Thus， the proposed heating mode is characterized by larger potential of energy-saving.

Operation performance analysis on a novel solar heat recovery quasi two-stage compression heat pump system under typical weather conditions

LIN Lianjie, FAN Yi, LI Jing, ZHAO Xudong, LI Yunhai

2023, 45(4): 74-80. doi:10.3969/j.issn.2097-0706.2023.04.011

Asbtract ( 59 )

HTML ( 2)

PDF (1695KB) ( 112 )

Figures and Tables | References | Related Articles | Metrics

To solve the problems of current energy consumption in building heating/cooling， a novel solar heat recovery quasi two-stage compression heat pump is proposed to be applied in heating/cooling systems. A system simulation model is established to analyze its operation performance under typical climatic conditions of three regions in China （Chongqing， Taiyuan and Urumqi）. The research results show that the system can provide heat and cold energy for buildings with the new heat recovery technology， solar photovoltaic and solar thermal technologies. The recovered energy of Chongqing， Taiyuan and Urumqi takes about 12% of their total loads， and solar thermal energy of the three regions makes up 30%， 20% and 15% of their total loads， and PV profits accounted for 38%， 26% and 18% of their total operating costs， respectively. It can be seen that renewable energy plays a key role in new systems by greatly improving system performance and reducing carbon emissions.

Analysis of heat transfer characteristics and thermal-permeability coupling characteristics of single U-tube borehole heat exchangers

LIU Yuanyuan, GENG Zhi, ZHANG Yuanfeng, ZHANG Liang, HAN Zhao, ZHANG Bin

2023, 45(4): 81-88. doi:10.3969/j.issn.2097-0706.2023.04.012

Asbtract ( 60 )

HTML ( 3)

PDF (3767KB) ( 196 )

Figures and Tables | References | Related Articles | Metrics

To achieve the "dual carbon" target， shallow geothermal energy heating（cooling），a new utilization form of clean energy， has been widely applied. To improve the efficiency of geothermal energy， taking the ground source heat pump of an integrated energy heating（cooling） system in northern China as the research object， a 3D unsteady-state heat transfer model of a single U-tube borehole heat exchanger （BHE）was constructed， and its heat transfer characteristics and coupling characteristics thermal conduction and groundwater seepage were analyzed by the software Fluent. Comparative analyses on the total transfer heat and transfer heat per unit length were made on the BHE with three different spacing distances（4.0，4.5 and 5.0 m） and three different tube lengths（106.0，113.0 and 120.0 m），respectively. The analysis results show that the BHE with 4.0 m spacing distance and 106.0 m tube length demonstrates the optimal performance. Comparing the temperature fields of the BHE with and without seepage flow， the results show that seepage flow exerts positive effect on the BHE heat transfer efficiency， and the faster the seepage flows， the higher the heat transfer efficiency is. The analyses above provide references for the design of practical examples of BHE projects.

Table of Content