Heat pumps and renewable energies

As a mean to mitigate global humanlinked environmental pollution and to achieve sustainability, renewable energies must become not just a part but THE primary energy source for the world. Heat pumps, as a process recirculating environmental heat back into useful heat production, fit the environmental requirements of this global policy. They are very useful tools to reduce the need of fossil fuels combustion in building as well in industrial sectors. As such they have a role to play in the renewable energy panel.The paper will emphasize this role and give last trends in their technology.     

Performance of ejector heat pumps

An ejector-compression heat pump can use low-grade thermal energy in the neighbourhood of 93.3°C (200°F) to provide space cooling and heating. This paper applies the existing ejector theory to estimate the performance of an ejector heat pump system at various operating conditions. The study includes parametric, sensitivity and off-design analyses of the heat pump performance. The performance enhancement options and desired ejector geometry are also examined. Refrigerants 11, 113 and 114 are three of the halocarbons most suitable for the ejector heat pump system. The estimated coefficients of performance for a simple ejector heat pump are 0.3 for the cooling mode and 1.3 for the heating mode at a sample operating condition in which the refrigerant (R-11) boiling temperature is 93.3°C (200°F), condensing temperature 43.3°C (110°F) and evaporating temperature 10°C (50°F). A 24 per cent performance improvement is predicted for a heat pump with two-stage ejectors and regenerative heat exchangers. The off-design performance is relatively insensitive to the evaporator temperature variations.     

Studies of a heat pump using water and air heat sources in parallel

The mechanism of heat pumps for hot water supply using dual heat sources of the ambient air and water and the operating conditions of selecting either one or both heat sources were discussed. Then, the performance of a heat pump which used water and the ambient air as the heat sources to heat water was examined experimentally. When the temperature of the water heat source was decreased, the heat from the water as well as the heat from the air was used for the heat pump efficiently until its temperature became approximately that of the evaporation temperature of the heat pump using the ambient air alone as the heat source. When the temperature of the water dropped further, only the heat from the air was absorbed by the evaporators like an ordinary heat pump which used only the evaporator of the air heat source at the same ambient air temperature. A theoretical analysis was made on the performance of a heat pump with dual heat sources. The results agreed well with the experimental results. © 2000 Scripta Technica, Heat Trans Asian Res, 29(6): 473–490, 2000     

绿色建筑中可再生能源利用方案的设计

通过对《绿色建筑评价标准》(GB/T 50378-2006)中关于可再生能源利用条文的分析解读,总结了在绿色建筑中可再生能源利用方案评价的主要内容和评价方法。结合实际工作经验,就不同的可再生能源利用方式在不同建筑类型中的应用方案选择进行了分析与探讨,并提出了绿色建筑中可再生能源利用的发展方向。     

Performance and economic feasibility of ground source heat pumps in cold climate

Ground source heat pumps (GSHP) are attractive alternatives to conventional heating and cooling systems owing to their higher energy utilization efficiency. In this paper, the effect of various system parameters on GSHP performance is studied using a computer model. Also, a comparative economic evaluation is carried out to assess the feasibility of using a GSHP in place of conventional heating/cooling systems and an air source heat pump. The results indicate that system parameters can have a significant effect on performance, and that GSHP is economically preferable to conventional systems. © 1997 John Wiley & Sons, Ltd.     

A new type of district heating system based on distributed absorption heat pumps

Large district heating (DH) system accounts for 70% of urban building heating in China. In North China, this proportion is even higher (The North China is the north of the Huai River and Qinling Mountains). Many cities in North China can exploit various kinds of low-grade renewable energy. This paper presents a new heating method to realize renewable energy recovery by absorption heat pumps associated with municipal network. In the DH substations, absorption heat pumps are driven by the exergy-difference originated from the larger temperature difference of heat exchange between primary and secondary heat network. There are two configurations—type I and type II substations based on the temperature of renewable energy. A reasonable parameter setting of system is suggested. The equipment operational performance was optimized based on a practical example. The low-grade renewable energy can be recovered effectively in this method. As a result, both heating capacity and energy efficiency of the DH system can be improved. Furthermore, operating costs may be reduced remarkably, due to the reduction in both the coal consumption of heat production unit and the power consumption of delivery pump. Therefore, the system is superior in energy conservation and has a promising application prospect.     

The performance of heat pumps in service—A simulation study

A computer model is developed to simulate the performance of air-to-water heat pumps heating a house via a radiator system. The performance characteristics of the heat pumps are derived from laboratory measurements. Hourly weather observations are used to calculate the heat demand of the house and the performance of the heat pump. The effects of changes in heat pump characteristics, changes of radiator size, and changes in heat demand of the house due to insulation, are compared in terms of their effects on annual energy consumption.     

化工节能中的热泵精馏工艺流程分析

介绍了几种典型的精馏热泵流程 ,分析了它们的特点、应用条件及节能效果 ,供进行热泵精馏可行性设计时参考。     

Efficiency of closed loop geothermal heat pumps: A sensitivity analysis

Geothermal heat pumps are becoming more and more popular as the price of fossil fuels is increasing and a strong reduction of anthropogenic CO₂ emissions is needed. The energy performances of these plants are closely related to the thermal and hydrogeological properties of the soil, but a proper design and installation also plays a crucial role. A set of flow and heat transport simulations has been run to evaluate the impact of different parameters on the operation of a GSHP. It is demonstrated that the BHE length is the most influential factor, that the heat carrier fluid also plays a fundamental role, and that further improvements can be obtained by using pipe spacers and highly conductive grouts. On the other hand, if the physical properties of the soil are not surveyed properly, they represent a strong factor of uncertainty when modelling the operation of these plants. The thermal conductivity of the soil has a prevailing importance and should be determined with in-situ tests (TRT), rather than assigning values from literature. When groundwater flow is present, the advection should also be considered, due to its positive effect on the performances of BHEs; by contrast, as little is currently known about thermal dispersion, relying on this transport mechanism can lead to an excessively optimistic design.     

The potential for heat pumps in drying and dehumidification systems I: Theoretical considerations

Drying is one of the most energy intensive unit operations. In many applications the drying temperatures required are low enough to make the inclusion of a heat pump in the system worthy of consideration. Five drying/dehumidification systems, including three with heat pumps, have been compared theoretically on the basis of specific power consumption (SPC), (i.e. the energy supplied per unit of moisture condensed) and primary energy consumption (PEC) which is (SPC) divided by the efficiency of primary energy conversion. The efficiency of each system is improved as the relative humidity of the air leaving the dryer is increased. The optimum is, however, very flat and a heat pump should be advantageous when a minimum relative humidity of 30 per cent is acceptable within the drying chamber. A closed cycle dryer is shown to be the most advantageous but requires careful matching.     

Private sector investment in renewable energy utilisation: strategic analysis of stakeholder perspectives in developing countries

Private sector encouragement in the development programmes of renewable energy (RE) utilisation is one of the important subjects and challenges for governments of developing countries. While profit in short-term and market-based orientation are the dominant approach of private sector to start an investment, governments and policymakers are paying special attention to participation of private investments to achieve their long-term development plans. In contrast, academic researchers notice to private investments in a structure that is sometimes in conflict with private investors and policymakers perspectives. Therefore, each group of stakeholders has its own priorities that negatively affect promotion and adoption plans of renewable alternatives utilisation. This article reviews and analyses different perspectives of RE stakeholders (beneficiaries) to encourage participation of private investments Differences in priorities, concerns, and interests in each group of stakeholders are the subjects that are discussed in the article. To close the attitudes and perspectives, a recommendations package is also presented in two levels of operational and strategic     

一种多用途热泵的分析

通过对现有热泵循环过程的全面分析,提出了一种新型的多用途热泵.该热泵有蒸汽释放出气态显热的高温换热器、工质释放出液化潜热的中温换热器(冷凝器)和工质释放出液态显热的低温换热器.计算表明,与采用相同循环工质的现有热泵相比,该新型热泵具有更高的制热系数.它可以应用于家庭、学校以及企事业等单位的采暖/空调、沐浴以及开水供应等.     

The performance of heat pumps in service-comparison of a computer model with a real installation

A comparison is made between a computer model which was developed in an earlier paper and experimental results in which a heat pump was used to heat a house during the heating season 1978–1979. The heat pump used was an air-to-water machine, and it is found that the radiator temperature in the experiment varies according to the heat demand of the house because of the effect of thermal inertia of the water and other thermal masses in the heat transfer system. The computer model simulates this effect, using hourly weather data to calculate the heat demand of the house and assuming that the radiators run at the temperature necessary to supply the heat demand during each hour. The model also calculates the coefficient of performance of the heat pump, and hence calculates the running cost in kilowatt-hours for each hour. The calculated running cost is compared with daily readings of kilowatt-hour meters. It is found that the comparison is very accurate during normal operation of the heat pump, with an accuracy of better than 1 per cent over a period of four months of the heating season, although the accuracy is not always quite so good. A comparison is also made between hourly calculated radiator temperatures and continuous recordings of flow and return temperatures. The comparison in this case is satisfactory, but there is a time lag due to the effect of thermal inertia of the building fabric which the computer model is not intended to simulate.     

Diffusion of innovation model of consumer behaviour - Ideas to accelerate adoption of renewable energy sources by consumer communities in India

Renewable Energy (RE) sources form a minuscule portion of India’s overall Energy consumption today. India continues to rely on fast depleting fossil fuel and expensive Oil imports to satisfy the energy demands of the economy. But this is hardly sustainable and India has to quickly get RE sources to play a major role in servicing the energy needs of its population. Despite the best efforts the adoption of RE sources by consumer communities in India is patchy. This article will focus on what needs to be done to create a pull from the market for RE sources, by looking at Consumer Behaviour literature available in the area of Diffusion of Innovation[1]. Demand for RE sources from consumer communities must reach a tipping point[4] quickly; for the sector to take-off on its own and become a self-sustaining business.     

Optimum arrangement and use of heat pumps in recovering waste heat

Relations are derived for the coefficient of performance of heat pump systems used to transfer heat from a low temperature heat source stream to a high temperature heat sink stream. The manner of use and operation of a number of heat pumps in such a system has been determined for the thermodynamic optimum for reversible and irreversible heat pumps.     

The potential for heat pumps in drying and dehumidification systems II: An experimental assessment of the heat pump characteristics of a heat pump dehumidification system using R114

An experimental heat pump dehumidifier is described. Actual coefficients of performance (COP)_A are plotted against the gross temperature lift (T_CO - T_EV) for various bypass ratios and air velocities. Interpolated values of (COP)_A for a specified temperature lift were obtained by fitting each set for various dry bulb temperatures of air leaving the humidifier using a linear equation. These values of (COP)_A are plotted against the linear velocity of the air stream approaching the evaporator at different dry bulb temperatures. The curves show a maximum of (COP)_A at approach velocities in the region of 1·6 ms^?1.     

海水热泵的冬季运行特性分析

海水容量巨大，冬季温度高于空气温度，可作为热泵的良好热源。介绍了海水热泵的工作原理，分析了恶劣条件下海水热泵的连续运行和间歇运行两种模式，计算了两种模式下的运行特性数据，为海水热泵的设计和应用提供了较好的参考。     

地源热泵在南方城市的应用分析

阐述了地源热泵的优势，并结合实例论证了地源热泵的优点，为该技术的推广应用提供了工程上参考。测试了实际工程的运行状态参数，为今后的设计运行提供参考。     

Experimental investigation of thermal performance of a solar assisted heat pump system with an energy storage

An experimental solar assisted heat pump space heating system with a daily energy storage tank is designed and constructed, and its thermal performance is investigated. The heating system basically consists of flat plate solar collectors, a heat pump, a cylindrical storage tank, measuring units, and a heating room located in Gaziantep, Turkey (37.1°N). All measurements are automatically collected as a function of time by means of a measurement chain feeding to a data logger in combination with a PC. Hourly and daily variations of solar radiation, collector performance, coefficient of performance of the heat pump (COP_HP), and that of the overall system (COP_S) are calculated to evaluate the system performance. The effects of climatic conditions and certain operating parameters on the system performance parameters are investigated. COP_HP is about 2.5 for a lower storage temperature at the end of a cloudy day and it is about 3.5 for a higher storage temperature at the end of a sunny day, and it fluctuates between these values in other times. Also, COP_S turns out to be about 15–20% lower than COP_HP. Copyright © 2004 John Wiley & Sons, Ltd.