A thermodynamic analysis of a transcritical cycle with refrigerant mixture R32/R290 for a small heat pump water heater

In this study, a thermodynamic analysis on the performance of a transcritical cycle using azeotropic refrigerant mixtures of R32/R290 with mass fraction of 70/30 has been performed. The main purpose of this study is to theoretically verify the possibility of applying the chosen refrigerant mixture in small heat pumps for high temperature water heating applications. Performance evaluation has been carried out for a simple azeotropic mixture R32/R290 transcritical cycle by varying evaporator temperature, outlet temperature of gas cooler and compressor discharge pressure. Furthermore, the effects of an internal heat exchanger on the transcritical R32/R290 cycle have been presented at different operating conditions. The results show that high heating coefficient of performance (COP_h) and volumetric heating capacity can be achieved by using this transcritical cycle. It is desirable to apply the chosen refrigerant mixture R32/R290 in small heat pump water heater for high temperature water heating applications, which may produce hot water with temperature up to 90 °C.     

Comparison of natural gas driven heat pumps and electrically driven heat pumps with conventional systems for building heating purposes

Electrically driven heat pumps achieve good efficiencies for space heating. If heat pumps are driven directly by a combustion engine instead of an electric motor, losses attributed to the production and transport of electricity are eliminated. Additionally, the use of the combustion engine's heat leads to a reduced temperature difference across the heat pump. This article presents annual efficiencies of these systems and compares internal combustion engine and electrically driven heat pumps in terms of primary energy consumption and CO₂ emissions. Because heat pump performance depends strongly on the heating circuit's flow temperature level, the comparison is performed for air-to-water and geothermal heat pump systems in two cases of maximum flow temperatures (40 °C and 60 °C). These temperature levels represent typical modern buildings with large heating surfaces and older buildings with high-temperature radiators, respectively. In addition to the different heat pump setups, conventional space heating systems are included in the comparison. The calculations show that natural gas-driven heat pumps achieve about the same efficiency and CO₂ emissions as electrically driven heat pumps powered with electricity from the most modern natural gas-fired combined cycle power plants. The efficiency of such systems is about twice that of conventional boiler technologies.     

Energy-saving judgment of electric-driven seawater source heat pump district heating system over boiler house district heating system

As a renewable energy utilization system, the electric-driven seawater source heat pump district heating system is gaining popularity in some coastal areas. However, under what conditions can the system achieve its energy-saving effect and how to evaluate its energy-saving potential are not clear in practice. In this paper, an expression of the critical COP value of the heat pump unit for energy-saving (COP_h,c) is derived through the comparison of the system and the conventional boiler house district heating system in the energy consumption respect. On the other hand, the actual COP values of the heat pump unit (COP_h,a) are calculated by an experimental data regression model on the basis of the manufacturer's dataset. The comparison of the values of COP_h,c and COP_h,a makes the energy-saving judgment of an electric-driven seawater source heat pump district heating system and its energy-saving potential, if it has, readily available. It was found that both the heating district radius and the natural conditions of the seawater are the most important factors that determine the energy efficiency of the system. And through comparison, it was also found that the type of the fuel of the boiler has significant impact on the crucial index value of COP_h,c.     

两种工况下空气双热源热泵热水器的试验研究

对空气源热泵热水器在标准工况和低温工况下的性能进行了试验研究,并分析了进水温度对排气压力、排气温度、消耗功率、热效率的影响规律。结果表明,排气压力、排气温度和消耗功率随着进水温度的升高而增加,制热功率和性能系数随着进水温度的升高而降低;标准工况下的性能优于低温工况下的性能。     

Experimental study of a heat pump system with flash-tank coupled with scroll compressor

A heat pump system with a flash-tank coupled with a scroll compressor is compared with a system with a sub-cooler. The heat pump performance was measured experimentally. The heating capacity of the prototype decreased as the evaporation temperature decreased, but the decrease was much slower than that of a conventional air-source heat pump. The power input varied slightly with the evaporation temperature. The heat pump system with a flash-tank is more efficient than the system with a sub-cooler at low ambient temperatures, so it will be very useful as a small capacity air-source heat pump.     

空气-太阳能-电能复合热源热泵型冷热水机组

研制了一种集空气源热泵、太阳能热水器和电热水器于一体的冷热水机组,可根据地理和气象条件从11种运行方案中优选节能方案,实现空调、热水供应和供暖;介绍了机组的构成和工作原理。该机组可减少换热环节和融霜次数,利用循环水显热蓄热,太阳能集热效率和系统供热效率较高,初投资和运行费用低于分别采用空气源热泵、太阳能集热器和电热水器的费用。     

Analysis on performance of a novel frost-free air-source heat pump system

Heating capacity of an air-source heat pump (ASHP) system often decreases due to frost on the air-side heat exchanger (evaporator) when the air temperature drops in winter. If the amount of frost accumulates to a certain value, performance of the system will degrade. Therefore, defrosting mode needs to be operated periodically. In order to solve the above problems, heat transfer enhancement or advanced defrosting methods should be adopted, but all these methods cannot solve the problems mentioned in essence. A novel frost-free air-source heat pump system is proposed, the new system can realize heating which does not need defrost in winter. In this new system, extracting heat process from environment includes two steps: the first one is extracting heat from the environment and then to the solution, the second one is releasing heat to the evaporator from the solution, avoiding frosting on the evaporator surface. A theoretical model is established to analyze the performance of the system. Results indicate that the novel system can operate more efficiently than the conventional air-source heat pump in winter. In addition, the new system does not need to run in defrosting mode periodically.     

空气源热泵集中热水系统应用于学生公寓的经济性分析

空气源热泵热水系统被誉为"第四代热水系统",应用前景广阔。通过介绍空气源热泵的工作机理,并以重庆某高校8号学生公寓的热水改造系统——空气源热泵热水系统为例,对空气源热泵热水系统的经济性进行研究,并与其他能源设备运行费用进行分析比较,表明空气源热泵热水系统具有较好的节能潜力,为集中热水供应系统设计提供相关参考。     

供热方式的技术与经济性分析

对采用热电联产、区域供热锅炉房、燃气热水器、直接用电、电蓄热锅炉、燃气机热泵、电动空气源热泵、电动水源热泵等供热方式的技术及经济性进行了探讨。     

Quasi-dynamic energy-saving judgment of electric-driven seawater source heat pump district heating system over boiler house district heating system

The electric-driven seawater source heat pump district heating system is a renewable energy utilization system, but this cannot guarantee the energy-saving effect of the system. The static energy-saving judgment between this system and the conventional boiler house district heating system was provided in a former research paper. However the static method has proved to be a very rough evaluation method and may lead to misjudgment as well. So a quasi-dynamic method, taking the total energy consumption during a whole heating season into consideration, is established in this paper. The energy-saving index turns out to be the expression of the lower limit of the average COP of the seawater source heat pump unit throughout the heating season (COP_h,mc). Then a case study is presented to show how the index of COP_h,mc and the actual average COP of the heat pump unit throughout the heating season (COP_h,ma) are calculated. The calculation results show that the quasi-dynamic method improves the calculation accuracy dramatically, and thus provides a better solution to the quantitative energy-saving evaluation of the electric-driven seawater source heat pump district heating system.     

A techno-economic comparison of ground-coupled and air-coupled heat pump system for space cooling

This paper reports a techno-economic comparison between a ground-coupled heat pump (GCHP) system and an air-coupled heat pump (ACHP) system. The systems connected to a test room in Firat University, Elazig (38.41°N, 39.14°E), Turkey, were designed and constructed for space cooling. The performances of the GCHP and the ACHP system were experimentally determined. The experimental results were obtained from June to September in cooling season of 2004. The average cooling performance coefficients (_COPsys${\mathrm{COP}}_{\mathrm{sys}}$) of the GCHP system for horizontal ground heat exchanger (HGHE) in the different trenches, at 1 and 2 m depths, were obtained to be 3.85 and 4.26, respectively and the _COPsys${\mathrm{COP}}_{\mathrm{sys}}$ of the ACHP system was determined to be 3.17. The test results indicate that system parameters can have an important effect on performance, and that GCHP systems are economically preferable to ACHP systems for the purpose of space cooling.     

Low-temperature baseboard heaters with integrated air supply – An analytical and numerical investigation

The functioning of a hydronic baseboard heating system with integrated air supply was analyzed. The aim was to investigate thermal performance of the system when cold outdoor (ventilation) airflow was forced through the baseboard heater. The performance of the system was evaluated for different ventilation rates at typical outdoor temperatures during the Swedish winter season. Three different analytical models and Computational Fluid Dynamics (CFD) were used to predict the temperature rise of the airflow inside the baseboard heater. Good agreement between numerical (CFD) and analytical calculations was obtained. Calculations showed that it was fully possible to pre-heat the incoming airflow to the indoor temperature and to cover transmission losses, using 45 °C supply water flow. The analytical calculations also showed that the airflow per supply opening in the baseboard heater needed to be limited to 7.0 l/s due to pressure losses inside the channel. At this ventilation rate, the integrated system with one air supply gave about 2.1 more heat output than a conventional baseboard heating system. CFD simulations also showed that the integrated system was capable of countering downdraught created by 2.0 m high glazed areas and a cold outdoor environment. Draught discomfort in the case with the conventional system was slightly above the recommended upper limit, but heat distribution across whole analyzed office space was uniform for both heating systems. It was concluded that low-temperature baseboard heating systems with integrated air supply can meet both international comfort requirements, and lead to energy savings in cold climates.     

燃气机热泵在夏热冬冷地区应用的经济性分析

以上海地区某独立的两层结构别墅为对象,考虑了燃气机热泵、电驱动空气源热泵与电热水器及燃气热水器组合3种方案,比较了三者在夏季制冷、冬季供暖、制备生活热水时的全年能耗及运行费用。在生活热水产量相同的情况下,燃气机热泵的能耗和运行费用均低于电驱动空气源热泵与电热水器及燃气热水器组合方案,经济性显著。     

Development and experimental validation of a high-temperature heat pump for heat recovery and building heating

The performance of a high-temperature heat pump unit using geothermal water for heat recovery in buildings is experimentally evaluated. The unit consists of a twin-screw refrigeration compressor, a condenser, an evaporator and an oil cooling system. The effect of the cooled oil temperature on the performance of the heat pump unit is experimentally investigated. Results show that the unit stably produces outlet hot water at a constant temperature of 85 °C and performs well in a wide range of high-temperature conditions with a high energy efficiency ratio. The results also indicate that the key to improving the performance of a high-temperature heat pump unit often depend on the selection of proper cooled oil temperature. The optimum cooled oil temperature is 50-65 °C when the condensing temperature is above 70 °C. At these temperatures, the oil cooling system can increase the energy efficiency ratio of the heat pump by 6.3%.     

双级耦合热泵在寒冷地区高层建筑中应用的模拟分析

分析了寒冷地区高层建筑供暖空调的特点,提出了四种可供高层建筑使用的、以空气为低位热源的双级耦合热泵系统。选择一幢写字楼,以空气源热泵+热泵型水冷VRF系统为例,通过建立数学模型,模拟分析了该系统在寒冷地区代表城市的运行特性,并与传统的低温空气源热泵系统进行了经济性比较。     

废水热源热泵热水系统的探讨与性能分析

针对热水能耗和废热利用的现状,提出了以废水为热源的热泵热水系统。介绍了该系统的工作原理,进行了系统理论循环性能分析,并与空气源热泵热水系统进行了比较。对系统的应用提出了一些建议和需要考虑的问题。     

家用空气源热泵热水器节能分析

简要介绍了空气源热泵热水器的技术特点,并对其节能环保效益进行了分析,通过与其他形式热水器比较,指出空气源热泵热水器具有诸多优点,十分适合于家庭使用,值得大力推广。     

Field performance measurements of a heat pump desiccant unit in heating and humidification mode

In this study, a novel self-regenerating electric vapor compression heat pump desiccant (HPD) unit operated in the heating and humidification mode during the winter season is introduced. The HPD unit was installed in an office suite for the field test. The performance of the HPD unit and the provided indoor conditions were measured over a wide range of operating conditions. The target indoor humidity ratio was set to 4.4 g/kg, which is the minimum required indoor humidity ratio for a comfortable indoor environment indicated in the ASHRAE winter thermal comfort zone. The seasonal comparison revealed that even though 77.7% of all outdoor humidity ratio data was lower than 4.4 g/kg, 78.2% and 85.8% of all the indoor humidity ratio data of each room were found to be higher than 4.4 g/kg. In addition, due to the significant sensible capacity of the HPD unit, the indoor temperatures could be maintained within 20-25 °C. These results prove that the HPD unit not only properly humidifies the indoors without using any additional water source, like the conventional humidifier, but also helps to keep the indoor temperature at the desired temperature levels.     

Performance analysis of a solar-assisted ground-source heat pump system for greenhouse heating: an experimental study

This study investigates the performance characteristics of a solar-assisted ground-source (geothermal) heat pump system (SAGSHPS) for greenhouse heating with a 50 m vertical 32 mm nominal diameter U-bend ground heat-exchanger. This system was designed and installed in the Solar Energy Institute, Ege University, Izmir (568 degree days cooling, base: 22 °C, 1226 degree days heating, base: 18 °C), Turkey. Based upon the measurements made in the heating mode from the 20th of January till 31st of March 2004, the heat extraction rate from the soil is found to be, on average, 57.78 W/m of bore depth, while the required borehole length in metre per kW of capacity is obtained as 11.92. Design practices in Turkey normally call for U-bend depths between 11 and 13 m/kW of heating. The entering water temperature to the unit ranges from 8.2 to 16.2 °C, with an average value of 14 °C. The greenhouse air has a maximum day temperature of 31.05 °C and night temperature of 14.54 °C with a relative humidity of 40.35%. The heating coefficient of performance of the heat pump (COP_HP) is about 2.00 at the end of a cloudy day, while it is about 3.13 at the end of sunny day and fluctuates between these values in other times. The COP values for the whole system are also obtained to be 5–20% lower than COP_HP. The clearness index during experimental period is computed as average 0.56. At the same period, Cucumus sativus cv. pandora F₁ was raised, and product quality was improved with the climatic conditions in the designed SAGSHPS. However, experimental results show that monovalent central heating operation (independent of any other heating system) cannot meet the overall heat loss of the greenhouse if the ambient temperature is very low. The bivalent operation (combined with other heating system) can be suggested as the best solution in Mediterranean and Aegean regions of Turkey.     

地埋管地源热泵制热性能测试与分析

理论分析地埋管地源热泵相比空气源热泵的节能率。结合工程实例,对地埋管地源热泵地埋管换热器进出水温度、冷凝器进出水温度、热泵机组日能效比、供暖期能效比进行了实测计算。在测试期,地埋管换热器进出水温度、冷凝器进出水温度均在正常范围内波动。日能效比基本不随室外温度的变化而波动,说明热泵机组的制热性能比较稳定。供暖期能效比为3.05,说明该项目地源热泵的制热性能比较理想。