外文翻译---太阳能热水系统研究背景

附录

SOLAR WATER HEATING BACKGROUND Using the sun’s energy to heat water is not a new idea. More than one hundred years ago, black painted water tanks were used as simple solar water heaters in a number of countries. Solar water heating (SWH) technology has greatly improved during the past century. Today there are more than 30 million m2 of solar collectors installed around the globe. Hundreds of thousands of modern solar water heaters, such as the one shown in Figure 1, are in use in countries such as China, India, Germany, Japan, Australia and Greece. In fact, in some countries the law actually requires that solar water heaters be installed with any new residential construction project (Israel for example).

Figure1: Evacuated Tube Solar Collector in Tibet, China In addition to the energy cost savings on water heating, there are several other benefits derived from using the sun’s energy to heat water. Most solar water heaters come with an additional water tank, which feeds the conventional hot water tank. Users benefit from the larger hot water storage capacity and the reduced likelihood of running out of hot water. Some solar water heaters do not require electricity to operate. For these systems, hot water supply is secure from power outages, as long as there is sufficient sunlight to operate the system. Solar water heating systems can also be used to directly heat swimming pool water, with the added benefit of extending the swimming season for outdoor pool applications.

◆Solar Water Heating Application Markets

Solar water heating markets can be classified based upon the end-use application of the technology. The most common solar water heating application markets are service hot water and swimming pools.

◆Service hot water

There are a number of service hot water applications. The most common application is the use of domestic hot water systems (DHWS), generally sold as “off-the-shelf” or standard kits as depicted in Figure 2.

Figure2: Solar Domestic Hot Water System in Australia

Swimming pools

The water temperature in swimming pools can also be regulated using solar water heating systems, extending the swimming pool season and saving on the conventional energy costs. The basic principle of these systems is the same as with solar service hot water systems, with the difference that the pool itself acts as the thermal storage. For outdoor pools, a properly sized solar water heater can replace a conventional heater; the pool water is directly pumped through the solar collectors by the existing filtration system.

Swimming pool applications can range in size from small summer only outdoor pools, such as the one shown at a home in Figure 3, to large Olympic size indoor swimming pools that operate 12 months a year.

Figure 3: Unglazed Solar Collector Pool Heating System in Canada

◆Description of Solar Water Heating Systems

Solar water heating systems use solar collectors and a liquid handling unit to transfer heat to the load, generally via a storage tank. The liquid handling unit includes the pump (used to circulate the working fluid from the collectors to the storage tank) and control and safety equipment. When properly designed, solar water heaters can work when the outside temperature is well below freezing and they are also protected from overheating on hot, sunny days. Many systems also have a back-up heater to ensure that all of a consumer’s hot water needs are met even when there is insufficient sunshine. Solar water heaters perform three basic operations as shown in Figure 4:

Collection: Solar radiation is “captured” by a solar collector

Transfer: Circulating liquid transfer this energy to a storage tank;

circulation can be natural (thermo siphon systems) or forced, using a circulator (low-head pump); and

Storage: Hot water is stored until it is needed at a later time in a mechanical room, or on the roof in the case of a thermo siphon system.

Figure 4: System Schematic for Typical Solar Domestic Water Heater

◆Solar collectors

Solar energy (solar radiation) is coll ected by the solar collector’s absorber plates. Selective coatings are often applied to the absorber plates to improve the overall collection efficiency. A thermal fluid absorbs the energy collected.

There are several types of solar collectors to heat liquids. Selection of a solar collector type will depend on the temperature of the application being considered and the intended season of use (or climate). The most common solar collector types are:

unglazed liquid flat-plate collectors; glazed liquid flat-plate collectors; and evacuated tube solar collectors.

◆Unglazed liquid lat-plate collectors

Unglazed liquid flat-plate collectors, as depicted in Figure 5, are usually made of a black polymer. They do not normally have a selective coating and do not include a frame and insulation at the back; they are usually simply laid on a roof or on a wooden support. These low-cost collectors are good at capturing the energy from the sun, but thermal losses to the environment increase rapidly with water temperature particularly in windy locations. As a result, unglazed collectors are commonly used for applications requiring energy delivery at low temperatures (pool heating, make-up water in fish farms, process heating applications, etc.); in colder climates they are typically only operated in the summer season due to the high thermal losses of the collector.

Figure 5: System Schematic for Unglazed Flat-Plate Solar Collector

◆Balance of systems

In addition to the solar collector, a solar water heating system typically includes the following “balance of system components”

1. Solar collector array support structure, as depicted in the Figure 6;

Figure 6: Solar Array Support Structure

2. Hot water storage tank (not required in swimming pool applications and in some large commercial or industrial applications when there is a continuous service hot water low).

3. Liquid handling unit, which includes a pump required to transfer the fluid from the solar collector to the hot water storage tank (except in thermo siphon systems where circulation is natural, and outdoor swimming pool applications where the existing filtration system pump is generally used) .it also includes valves, strainers, and a thermal expansion tank.

4. Controller, which activates the circulator only when usable heat is available from the solar collectors (not required for thermo siphon systems or if a photovoltaic-Powered circulator is used).

5. Freeze protection, required for use during cold weather operation, typically through the use in the solar loop of a special antifreeze heat transfer fluid with a low-toxicity. The solar collector fluid is separated from the hot water in the storage tank by a heat exchanger; and.

6. Other features, mainly relating to safety, such as overheating protection, seasonal systems freeze protection or prevention against restart of a large system after a stagnation period. Typically, an existing conventional water heating system is used for back-up to the solar water heating system, with the exception that a back-up system is normally not required for most outdoor swimming pool applications.

太阳能热水系统研究背景

利用太阳能来加热水的并不是一个新的想法。一百多年前，喷有黑色涂层的水箱被作为最简单的热水器在许多国家使用。在过去的一个世纪太阳能热水(SWH)技术已经大大提高了。今天，全世界已经累计安装有超过3000万平方米的太阳能集热器。成千上万的现代太阳能热水器,也应用于中国、印度、德国、日本、澳大利亚和希腊等国家，如图1所示,。事实上,在某些国家中法律明确要求太阳能热水器安装在任何新住宅建设项目(例如以色列)。

图1中国西藏的真空太阳能集热管

除了节约能源, 利用太阳能源来加热水还有其他的优点。大部分的太阳能热水器带有一个额外的水箱,这是传统的热水箱，它能给用户带来更大的热水存储容量和降低热水流失的可能性。一些太阳能热水器不需要用电，这些热水系统可以不会因为停电而停止供应热水,只要有足够的阳光就能工作。太阳能热水系统也可以用于直接加热游泳池的水,一个好处就是可以延长室外游泳池的使用季节。

⑴太阳能热水器的应用市场

太阳能热水市场可基于该技术的最终用途来分类。最常见的太阳能热水系统的应用场合是提供热水和游泳池。

提供热水

太阳能热水系统的应用形式很多，最常见的是用于户用型热水系统(DHWS),通常是卖“现成的”或标准的结构，如图2所示。

图2澳大利亚国内的热水系统

游泳池

太阳能热水系统也可以调节游泳池中水的温度、延长游泳池季节和节省常规能源成本。这些系统的基本原理与太阳能提供热水的原理是一样的,不同之处在于游泳池本身充当储热水箱。对于室外泳池,一个适当大小的太阳能热水器可以取代传统的加热器,泳池里的水由现有的过滤系统直接泵入太阳能集热器。

这种游泳池的应用范围可以从只在夏天开放的室外泳池，如图3所示的家庭用的泳池,到大型的一年12个月都能使用的奥运规模的室内游泳池。

图3加拿大的太阳能集热器游泳池加热系统

⑵太阳能热水系统概述

太阳能热水系统使用太阳能集热器和液体处理单元转移热负荷,一般通过储热水箱。液体处理单元包括泵(用来使热水在集热器和储热水箱之间循环)、控制和安全设备。设计合理时,太阳能热水器可以在外界温度为零度以下时工作,也能防止热天热水器内部过热。许多系统也有一个后备加热器，以确保即使没有充足的阳光的情况下满足所有消费者需求。太阳能热水器执行三个基本操作,如图4所示：

集热:太阳辐射被太阳能集热器收集

传输:循环水将热量到储热水箱,循环可以是自然（热虹吸系统）或强制的，用循环装置（低扬程泵）

储热:热水储存在机械室，或者在屋顶的热虹吸系统中，知道后面需要时使用。

图4典型的太阳能家用热水器系统示意图

太阳能集热器

太阳能(太阳辐射)由太阳能集热器的吸收板收集，选择性涂层常常被运用到吸收板上来效率改善整体的收集效率。一个热液吸收被收集的能量。

有几种类型的太阳能集热器可用来加热水。太阳能集热器的选型取决于应用环境的温度和预期的季节(或气候)温度。最常见的太阳能集热器类型有:无釉液体平板集热器、釉面液体平板集热器和真空管太阳能集热器。

◆无釉液体平板集热器

无釉液体平板集热器,如图5所示,通常由一个黑色的聚合物制成。它们通常不会有选择性的涂层和一个绝缘框架在后面;通常是简单地铺设在屋顶上或在一个木制的支持上。这些低成本的集热器善于捕捉来自太阳的能量,但热损失随着水温的增加而迅速增加，尤其是在多风的地方。因此, 无釉集热器通常用于要求在低温下输送能源的场合(游泳池加热、补给水鱼养殖场、加热过程应用等)。在气候较冷的地区,因高热损失集热器只用在夏天工作。

图5无釉平板太阳能集热器系统示意图

◆系统的平衡

除了太阳能集热器,太阳能热水系统通常包括以下“平衡系统”组件:

1、太阳能集热器阵列支撑结构,如图6所示。

图6 太阳能阵列支撑结构

2、贮热水箱(在持续提供低温热水的游泳池和一些大型商业或工业应用场合，这个是不需要的）。

3、液体处理单元,其中包括一个用来在集热器和贮热水箱之间传输液体的泵(除了在热虹吸系统中循环是自然的,在现有的过滤系统中泵一般用于室外游泳池)，它还包括阀门、过滤器、和热膨胀水箱;

4、控制器,只有当可用热量是从太阳能集热器得到时用于激活循环(热虹吸系统或光伏动力循环时不需要);

5、冷冻的保护,在寒冷天气下的操作,通常是通过在一个特殊的加有无毒液体防冻剂来传热的太阳能循环。太阳能集热器中的热水在贮热水箱中由热交换器分开。

6、其他特征,主要涉及到安全的地方,比如过热保护、季节性系统冻结保护或预防重启大型系统停滞时期之后。通常,现有的传统的水加热系统是用于备份到太阳能热水系统,只是一个备份系统通常不用于大部分的户外游泳池。