空调用太阳能集热器适用性分析

计算了平板集热器、真空管集热器、热管真空管集热器和CPC真空管集热器的太阳能利用系数,分析了几种太阳能集热器在空调系统中的适用性。结果表明,太阳能空调(热泵)系统集热器的热性能随着气象条件、热源温度的变化而变化,具有不同热源温度要求的系统应选用不同的集热器。     

Exploitation thermique du proche sous-sol par pompe a chaleur

In the heating systems using the near underground as cold source for the heat pump, ground calories are taken out by shallow buried exchangers (less than 3 meters deep). Presently, the design of this kind of plantings is quite empirical. In order to forecast more exactly the thermal behaviour of the plant and of the surrounding ground, we built a bi-dimensionnal model of the heat transfers in a ground section perpendicular to the pipes being used as buried exchanger. The first results achieved with this model are presented here. They show the influence on the temperature field in the ground and on the heat exchanges around the pipes, of essential parameters as deepness of the tubes planting, ground thermal properties and eventual injection of calories provided by solar collectors.     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

Renewable energy for passive house heating: Model of the active solar heating system

The large windows on the south-oriented façade of a passive house strongly contribute to building space heating. These windows constitute the passive solar heating system. This paper studies the active heating system of a passive house, which includes the following sub-systems: (1) solar thermal collectors, (2) a water storage tank, (3) a secondary water circuit, (4) a domestic hot water preparation system and (5) an air ventilation and heating system. Models for all sub-systems are presented. The integrated model was implemented to Pirmasens Passive House (Rhineland Palatinate, Germany). The active solar heating system provides a smaller amount of heat than the heat provided by the passive solar heating system. Almost all the solar energy collected is not used for space heating but to domestic hot water (DHW) preparation. However, there is still a need for the classical water heater to operate all over the year. Almost all space heating thermal load is covered by using the classical air heater that operates mainly during the nights from November to April. The solar fraction lies between 0.180 in February and 0.679 in October, with a yearly average of 0.446. The study reveals that on a yearly basis it is more advantageous to use vertical south-oriented solar collectors instead of roof placed collectors.     

Economic and exergy analysis of alternative plants for a zero carbon building complex

The feasibility of zero carbon emission plants for heating, air conditioning and domestic hot water (DHW) supply, is analyzed, with respect to conventional plants, for a new residential building complex to be constructed, in Northern Italy. Two zero carbon plants are considered: the first is composed of air-to-water heat pumps for space heating and cooling, PV solar collectors, air dehumidifiers, thermal solar collectors and a wood pellet boiler for DHW supply; in the second, the air-to-water heat pumps are replaced by ground-coupled heat pumps. The conventional plant is composed of a condensing gas boiler, single-apartment air to air heat pumps, and thermal solar collectors. The economic analysis shows that both zero carbon plants are feasible, and that the air-to air heat pumps yield a shorter payback time. The exergy analysis confirms the feasibility of both plants, and shows that the ground coupled heat pumps yield a higher exergy saving.     

A comparative numerical study on natural convection in inclined wavy and flat-plate solar collectors

The present study deals with the numerical analysis of natural convection heat transfer inside the inclined solar collectors. Two collectors are compared. In the first case, the collector has wavy absorber and in the second case, it has flat absorber. The solution was performed assuming the isothermal boundary conditions of absorbers and covers of collectors. CFDRC commercial software is used to simulate the laminar flow and thermal field. Governing parameters are taken as Rayleigh number (from 1×10⁶ to 5×10⁷), inclination angle (from 20° to 60°), wave length (from 1.33 to 4) and aspect ratio (from 0 to 4). Results are presented by streamlines, isotherms and local and mean Nusselt numbers. It is observed that flow and thermal fields are affected by the shape of enclosure and heat transfer rate increases in the case of wavy enclosure than that of flat enclosure.     

平板太阳能集热器与墙体不同一体化形式分析

针对平板型太阳能集热器与建筑墙体一体化结构,在贴合式和分离式2种结合方式下,以上海地区典型气象年的典型气象日作为外扰参数,使用状态空间模型对二者的传热特性进行了研究。研究结果表明:2种形式的一体化结构的集热器以及单一集热器的出口温度和有效得热量相互差别均很小。三者出口温度最大差值为0.15℃。夏季时,分离式和贴合式一体化结构全天有效得热量分别占单一集热器的99.89%和97.22%,贴合式一体化结构集热器出口温度和有效得热量都比分离式低。而冬季则相反,且该比例为99.26%和106.65%。夏季时,分离式和贴合式一体化结构通过围护结构的传热量分别占单一墙体的90.83%和40.53%。而在冬季,该比例为96.66%和11.12%。2种一体化结构均能减弱室外气象参数波动对墙体内壁面热流的影响。尤其是贴合式,冬季内壁面热流的波动幅度仅占单一墙体的9.75%。     

A simple model for assessing the energy performance of windows

A simple model for the annual energy balance of the window taking solar radiation and heat losses into consideration has been further developed and analysed. Hourly meteorological data for the solar irradiation and the outside temperature are used together with the optical and thermal performance of the window to evaluate the net energy heat flow through a window. The model renders a very simple way to compare different advanced windows in different geographical locations, orientations and buildings using basically only the balance temperature as building input. The energy balance and the cost efficiency for several glazing combinations are evaluated for buildings with different balance temperatures in a typical mid-Swedish climate. This model has a potential to be used for energy rating of windows.     

Experimental study of a solar-assisted ground-coupled heat pump system with solar seasonal thermal storage in severe cold areas

This paper presents the experimental study of a solar-assisted ground-coupled heat pump system (SAGCHPS) with solar seasonal thermal storage installed in a detached house in Harbin. The solar seasonal thermal storage was conducted throughout the non-heating seasons. In summer, the soil was used as the heat sink to cool the building directly. In winter, the solar energy was used as a priority, and the building was heated by a ground-coupled heat pump (GCHP) and solar collectors alternately. The results show that the system can meet the heating-cooling energy needs of the building. In the heating mode, the heat directly supplied by solar collectors accounted for 49.7% of the total heating output, and the average coefficient of performance (COP) of the heat pump and the system were 4.29 and 6.55, respectively. In the cooling mode, the COP of the system reached 21.35, as the heat pump was not necessary to be started. After a year of operation, the heat extracted from the soil by the heat pump accounted for 75.5% of the heat stored by solar seasonal thermal storage. The excess heat raised the soil temperature to a higher level, which was favorable for increasing the COP of the heat pump.     

Estimation of direct solar irradiance intercepted by a solar concentrator in different modes of tracking (case study: Algeria)

While reasonably accurate knowledge of solar radiation data at the location of interest is necessary for the design of any solar energy conversion system, the use of concentrating solar collectors implies that these systems only work with the direct solar irradiance. In the present study, by using a methodology based on simple equations, the total hourly, daily, monthly and annual direct radiations incident on four different oriented solar concentrators were calculated only from the recorded data of monthly mean daily global and diffuse horizontal solar irradiance for three different Algerian sites, in order to choose the best mode of tracking for concentrating solar thermal power systems and concentrating solar photovoltaic power systems applications. The model predictions were found to be consistent with ground measurements and prior studies of Kalogirou. It was found that the greatest energy gains were achieved by using full tracking. Furthermore, the model can be included for application to other Algerian and worldwide locations for estimating direct solar irradiance intercepted by a solar concentrator in different modes of tracking.     

热管平板集热器在建筑与太阳能一体化系统中的应用

建筑能耗在各种能耗中所占的比例较大,降低建筑能耗有很多措施,太阳能就是减少常规能源消耗的有效途径之一.热管平板集热器是一种有良好发展前景的集热器型式,热管平板式集热器具有热容小,启动快,防冻防腐性能好等特点.结合热管平板集热器的特点,分析了其在太阳能系统的应用,设计良好的集热器及太阳能利用系统可以有效地实现建筑节能.     

Thermal study of school buildings in winter conditions

In this paper, a thermal study of a school building with real occupation levels in winter conditions is presented and a software that evaluates the air quality and simulates the thermal response of buildings with complex topology in steady-state and transient conditions is used. After validation, the numerical model is used, in the first phase, to evaluate the occupants’ comfort levels in several spaces, while in the second phase two solutions, to improve acceptable thermal comfort and air quality levels (1) the electric air-heating systems, with predicted mean vote control, and (2) three solar collectors, placed instead of the roof area, used to heat the air in uncomfortable spaces are studied.     

Achieving total domestic hot water production with renewable energy

Various means of producing domestic hot water (DHW) with renewable energy in zero net energy homes (ZNEH) are examined for two climates (Montréal and Los Angeles). Four alternatives are examined: (i) a regular electric hot water tank; (ii) the desuperheater of a ground-source heat pump (GSHP) with electric backup; (iii) thermal solar collectors with electric backup; and (iv) a heat pump water heater (HPWH) indirectly coupled to a space conditioning GSHP. Results show that heating DHW with thermal solar collectors with an electric backup (which is either provided by the photovoltaic (PV) panels or the grid in a ZNEH) is the best solution for a ZNEH. The second part of this paper focuses on determining what should be the respective areas of the thermal solar collectors and PV array to obtain the least expensive solution to achieve total DHW production with renewable energy.     

太阳能聚光光伏光热(CPV/T)系统研究

聚光光伏光热(CPV/T)系统将太阳电池与集热器相结合,通过聚光和跟踪太阳提高太阳辐照强度,增加太阳电池的单位面积发电量,集热器在冷却太阳电池的同时回收多余热能,获得电能和热能双重收益。本文研究聚光比、太阳电池效率、组件中电池片的有效覆盖率、热传导率等因素对系统性能的影响。     

Choice of solar collector for applications below 100°C

Non-tracking collectors are the important technology options to harness the solar thermal energy at temperatures below 100°C. Thermal energy below this level has very wide applications in the residential and industrial sectors. Also, energy at this level can be used indirectly to produce cooling, fresh water or electricity. Flat plate and evacuated tube collectors with different design, configuration and cost were considered and their energy collection capabilities were estimated under the Kuwaiti conditions for different applications identified with the temperature. Based on the manufacturers' quotations and other economic parameters, the annual amortized cost of solar collectors were estimated. These values were used to estimate the system cost per unit of energy generation. A domestic solar water heater with an unglazed collector is the only solar system having economic viability at present. Evacuated tube collectors stand a good chance of being economically viable in future with increase in fuel prices and/or reduction in system cost.     

Performance study of underground thermal storage in a solar-ground coupled heat pump system for residential buildings

This paper is performed to analyze the performance of underground thermal storage in a solar-ground coupled heat pump system (SGCHPS) for residential building. Based on the experimental results, the system performance during a longer period is simulated by the unit modeling, and its parametric effects are discussed. The results show that the performance of underground thermal storage of SGCHPS depends strongly on the intensity of solar radiation and the matching between the water tank volume and the area of solar collectors. Compared with the solar radiation, the variations of the water tank temperature and the ground temperature rise lag behind and keep several peaks during the day time. For the case of Tianjin, the efficiency of underground thermal storage based on the total solar radiation and absorbed solar energy by the collectors can reach over 40% and 70%, respectively. It is suggested that the reasonable ratio between the tank volume and the area of solar collectors should be in the range of 20–40 L/m².     

平板式太阳能安装实例及分析

开发和普及多种太阳能光热系统是我国城市化进程中建筑节能的必由之路。平板式太阳能集热器在中国市场占有率低,经过数年研发平板式太阳能的利用已取得明显成果。通过某工程平板式太阳能集热器在安装施工中出现的问题进行分析总结,以期对越来越多的平板式太阳能安装施工带来帮助。     

一种新型太阳能集热装置——太阳能多级加热系统

常规能源过度消耗与环境污染正成为我国经济与社会可持续发展的重要制约因素,急需发展环境友好型的可再生能源利用技术.分布式太阳能热利用系统可以有效解决人口非密集地区的能源供给问题.太阳能多级加热系统的研究旨在为以较小的代价提供高品位热能提供新的思路和用能模式.该系统把真空管太阳能集热器、线聚焦型太阳能集热器和点聚焦型太阳能...     

Thermoeconomic analysis and optimization of high efficiency solar heating and cooling systems for different Italian school buildings and climates

The paper investigates the energetic and economic feasibility of a solar-assisted heating and cooling system (SHC) for different types of school buildings and Italian climates. The SHC system under investigation is based on the coupling of evacuated solar collectors with a single-stage LiBr-H₂O absorption chiller; auxiliary energy for both heating and cooling is supplied by an electric-driven reversible heat pump. The SHC system was coupled with different types of school buildings located in three different Italian climatic zones. The analysis is carried out by means of a zero-dimensional transient simulation model, developed using the TRNSYS software; the analysis of the dynamic behaviour of the building was also included. An economic model is proposed, in order to assess the operating and capital costs of the systems under analysis. Furthermore, a parametric analysis and a subsequent mixed heuristic-deterministic optimization algorithm was implemented, in order to determine the set of the synthesis/design variables that maximize system profitability. The results are encouraging, as for the potential of energy saving. On the contrary, the SHC economic profitability can be achieved only in case of public funding policies (e.g. feed-in tariffs), as always happens for the great majority of renewable energy systems.     

福建省太阳辐射接受面最佳方位角及倾角的计算

本文介绍了一种计算太阳辐射接受面最佳方位角及倾角的方法和工具,并以此计算得到福建省7个县市的最佳安装角度。本研究选择天空各向异性的Reindl模型作为太阳辐射计算模型;在气象数据上,采用SWERA和CSWD两种数据源,并优先采用准确度较高的SWERA数据源。在这基础上,本研究研制出“太阳能辐射接受面角度计算器”,该软件可可以为太阳能利用的研究、标准编制,以及设计提供数据支持。最后,福建省7个县市太阳辐射接受面的最佳安装角度被计算得到,以便于实际工程应用。