〔双语〕你家的炉灶好用么？

自工业革命以后，尽管科技长足发展，但人类烹饪的过程依旧惊人地低效，落后国家和富裕国家皆是如此。不论是发展中国家的简陋锅灶，还是更加便利和干净的发达国家的燃气灶及电灶，从能效的角度讲，它们都无一例外同样低效。

In fact, an electric cooking stove is only half as efficient as a well-tended open fire, while a gas hob is only half as effective as a biomass rocket stove. And even though indoor air pollution is less of an issue with modern cooking stoves, research indicates that pollution levels in western kitchens can be surprisingly high.

事实上，电灶的能效只有看管得当的明火土灶的一半，燃气灶的能效也只有烧生物燃料的火箭炉的一半。尽管普遍认为现代厨房没有严重的空气污染问题，但事实也并不支持这样的结论。

Three-stone Fire 石堆土灶

Present-day cooking methods in poorer countries are quite well documented, as they are one of the main concerns of NGOs which promote appropriate technological development. An estimated 2.5 to 3 billion people still cook their food over open fires or in rudimentary cookstoves, and these numbers keep increasing due to population growth.

非政府组织已对当今贫穷国家的烹饪方式进行了完善的整理和记录，因其致力于向这些国家推广更为适宜的烹饪方法。据计有 2.5 到 3 亿的人口依然使用早期的明火土灶进行烹饪活动，且由于人口的自然增长，这一数值始终在增长。

The most basic and widely used type of cooking device is the wood-fuelled “three-stone fire”, which is made by arranging three stones to make a stand for a cooking pot. Alongside the three-stone fire --- which dates back to Neolithic times---many types of home-made cooking stoves can be found. They are powered by burning coal or biomass, be it wood, crop residues, dung or charcoal. ^{[[#fn-1][1]]}

其中最广泛使用的是以木质为燃料的石堆土灶，通常这类炉灶使用三个石头作为炊具的支撑。这种炉灶最早见于自新石器时代，常常由家庭自制，名目繁多。它们常常以生物燃料和煤炭作为燃料，包含但不限于：木头，作物残茬，干粪和木炭。

The main concern with the use of crude biomass cooking stoves is their destructive influence on human welfare and natural resources. When used indoors, biomass cooking stoves lead to severe health issues such as chronic lung diseases, acute respiratory infections, cataracts, blindness, and adverse effects on pregnancy. The main victims are women, who do most of the housework, and young children, who are often carried on the mother's back while she is cooking.

这类炉灶最被人诟病的是其对人体健康的破坏和对自然资源的影响。当石堆土灶在室内使用时，可能引发若干健康问题，诸如慢性肺病、急性呼吸道感染、白内障、眼盲等，以及对孕妇造成损害。这些弊端的承受者通常都是做家务的女性和伴随在其身边的婴儿或小孩。

Inefficient biomass stoves also force people (again, most often women) to spend much of their time collecting fuel. The environmental degradation caused by biomass stoves is equally problematic. When wood is used as a primary fuel, inefficient cooking methods lead to large-scale deforestation, soil erosion, desertification and emissions of greenhouse gases. For coal-fuelled stoves, the main issue is indoor air pollution.

而低效的生物燃料炉则灶迫使人（依然主要是女性）牺牲大把时间收集燃料，同样也会引发环境破坏。当木头被作为燃料，其低效又将导致大规模森林退化、水土流失、荒漠化和温室气体排放问题。如果是烧煤的炉灶，则又会导致室内空气污染问题。

The Thermal Efficiency of a Three-stone Fire 石堆土灶的热效率

At the heart of the problem lies the low thermal efficiency of traditional cooking methods. For three-stone fires, thermal efficiency is stated to be as low as 10 to 15%. ^{[[#fn-1][1]]} In other words: 85 to 90% of the energy content in the wood is lost as heat to the environment outside the cooking pot. Obviously, this low efficiency wastes natural resources, but it also boosts air pollution and greenhouse gas emissions because the relatively low temperature of the fire leads to incomplete combustion.

热效率低下是传统土灶的硬伤。一般石堆土灶的热效率只有 10％到 15％【1】。换言之，此时木头中所含的 85％ 到 90％的能量都以热辐射的形式溃散到了炉灶周边的环境里。如此的低效率无疑是对自然资源的巨大浪费，其低温燃烧的不充分同时又引发空气污染和温室气体排放。

 Well-constructed three-stone fires protected from wind and tended with care score between 20 and 30% thermal efficiency

 看管得当并进行了防风处理的石堆土灶，其热效率可提升至 20％到 30％间。

However, the issue is more complicated than it is usually presented. To begin with, the productivity and cleanliness of an open fire (and similar crude cooking stoves) greatly depends on the circumstances in which they are used and on the skills of the cook. In its test of 18 cooking stove designs from all over the world, the Partnership for Clean Indoor Air ( PCIA) ^{[[#fn-3][3]]} concluded that:

可是，情况也并不总是这么简单。明火土灶（及其它形式简陋的土灶）的效率和清洁程度大大取决于其使用环境和操作者的技能。 *清洁室内空气伙伴关系组织(PCIA)* 在测试了 18 款来及世界各地的炉灶后，总结道：

Due to the influence of environmental factors such as wind, an indoor three-stone fire is generally more efficient than one operated outside. However, outdoor open fires can also be made more efficient by placing them in a hole in the ground or by shielding them with the use of earthen walls, which also adds thermal mass. Furthermore, PCIA remarks that “it is important to recognize that the open hearth and resulting smoke often have considerable cultural and practical value in the home, including control of insects”.

考虑环境状况因素，室内的石堆土灶比室外的会有更好的表现。但通过将灶体置于地坑或土墙内，也可显著提高其热效率。

The Thermal Efficiency of Improved Biomass Stoves

改良的生物炉灶的热效率

Especially since the 1970s and 1980s, many international NGO's have tried to improve cooking traditions in poorer countries. This has resulted in a large number of so-called “improved cooking stoves”, which again vary in terms of design, performance and costs. Hundreds of variations exist. ^{[[#fn-1][1]]}

 上世纪 70 到 80 年代期间，非政府组织一直致力于改善落后国家的烹食传统。此番行动导致出现了大量所谓的「改良炉灶」，这些炉灶不论设计、性能还是花费，都不尽相同，且变种繁多。【1】

Some of these designs are exclusively aimed at minimising air pollution at the cost of higher fuel consumption, while other designs achieve a higher efficiency but increase air pollution. ^{[[#fn-4][4]]} In this article, we will focus exclusively on cooking stoves that address both issues simultaneously. This is not to suggest that other designs can't be preferable in certain circumstances. For example, because biomass cooking stoves do not present direct health problems when used outdoors, saving fuel would be the most important aim in that context.

其中一些不计燃料高消耗代价着眼于最大程度降低空气污染，另外一些又着力于提高燃烧效率，同时却忽视了空气污染问题【4】。本文仅聚焦于同时兼顾燃烧效率和空气污染问题的炉灶。这不是要从根本上否定其它设计方案，比如，考虑到生物燃料炉不会直接导致人体损害，其在应用于室外环境时，节省燃料就成了最重要的设计因素了。

Compared to a basic three-stone fire with 10-15% thermal efficiency, improved cooking stoves can easily halve the fuel requirements of the cooking process. This can be achieved by providing an insulated combustion chamber, improving the air supply, and other measures.

跟基本款石堆灶相比，通过给炉膛加设保温层、提高空气补给和其它改进措施，改良炉灶可以节省一半的燃料。

In a laboratory comparison of five major types of biomass cooking stoves, it was found that an improved rocket stove uses 2,470 kJ to boil one litre of water and then simmer it for 30 minutes, while a basic three-stone fire requires 6,553 kJ to fulfill the same task (see the dark blue bars in the graphic above). ^{[[#fn-5][5]]} The rocket stove thus uses 60% less fuel than the three-stone fire. Furthermore, the rocket stove boils 2.5 litres of water more than 5 minutes faster (see the light blue points in the graphic above).

专家对五种主要生物燃料炉的实验结果发现，使用火箭炉烧开 1 升的水并维持其徐沸达 30 分钟需 2,470 千焦的能量，使用石堆土灶达成同样的效果则需要 6,653 千焦的能量【5】。火箭炉比石堆灶节省了 60％的燃料。更甚，煮沸 2.5 升的水，火箭炉比石堆灶能快 5 分钟。

 A rocket stove can double the thermal efficiency of a well-tended open fire

火箭炉的热效率可两倍于看管得当的石堆灶

The values are the average of three tests and measure specific energy consumption instead of thermal efficiency. Both test methods have their shortcomings---measuring the efficiency of cooking is suprisingly complex---so by applying both methods the accuracy of an experiment increases. ^{[[#fn-6][6]]} This was done by the Partnership for Clean Indoor Air, which compared the thermal efficiency and specific energy consumption of 18 cookstove designs, including a well tended open fire with a thermal efficiency of 20-30%. ^{[[#fn-4][4]]}

上面提到的实验数据取三次实验的平均值，测量的是能量消耗而非热效率。这些实验自有其弊端，但是测量热效率又太过于复杂【6】。*清洁室内空气伙伴关系组织(PCIA)* 做过更完善的实验，该实验测试了 18 款炉灶的热效率和能源消耗，其中包括照看得当、热效率可达 20-30％的明火土灶。

In this study, one of the best performing improved biomass stoves---a 20 liter can rocket stove (image below)---convincingly beats the efficiency of the well-tended open fire. It requires 733 grams of wood (12,579 kJ) to bring five litres of water to boil and simmer for 45 minutes, only 65% of the 1,112 grams of wood (19,496 kJ) required by the well-tended open fire. The thermal efficiency of the rocket stove varies between 23 and 54%. ^{[[#fn-7][7]]}

该实验中，表现突出的是一台炉膛容量为 20L 的火箭炉（见下图），烧开 5 升的水为并维持其徐沸 45 分钟需要 12,579 千焦的能量，能耗仅有照看得当的土灶（19,496 千焦，1112 克干柴）的 65％。火箭炉的热效率达到了 23％到 54％【7】

The rocket stove also lowers air pollution: the emissions are only 26% of the carbon monoxide ( CO) and 60% of the particulate matter ( PM) produced by the well-tended open fire. Lastly, it shortens cooking time to 22 minutes for five litres of water, compared to 27 minutes for the open fire.

同时，火箭炉还能降低空气污染（ 译者注：相比土灶而言）：排放的一氧化碳占比是土灶的 26％，PM（颗粒物）占比是土灶的 60％。最后，火箭炉将土灶花费的 27 分钟煮沸时间缩短到了 22 分钟。

The top performing biomass stove in the test is a wood gas stove, with slightly more than one-third the wood consumption (459 grams of wood or 9,434 kJ) and 15-20% of the pollution levels of the three-stone fire. It has a thermal efficiency of 44-46%. However, it requires an electric fan to improve combustion efficiency, while all others are natural-draft stoves.

该试验中表现最好的是一台 *木煤气炉* ，其消耗了石堆灶三分之一多一点的能量（9,434 千焦，459 克木柴），废气排放量是石堆灶的 15-20％，在电扇的助燃效果下，热效率高达 44-46％。

Cooking in Wealthy Households

富裕家庭的烹食

There is great irony in the fact that the improved biomass stoves mentioned above are much more efficient than modern cooking stoves used in the western world and in wealthier households of developing nations. In fact, most modern cooking stoves have a thermal efficiency that is on par with that of a three-stone fire.

讽刺的是，改良后的生物燃料炉，其热效率要高于富裕国家现代厨房里的炉灶。事实上，大作数现代厨房里的炉灶，其热效率与石堆土灶互不分上下。

The western world switched from open fires to closed cookstoves from the eighteenth century. Initially, these “kitchen stoves” were used for both heating and cooking, and were powered by coal, charcoal or biomass. When central heating systems were introduced in the early twentieth century, the kitchen stove was replaced by a stand-alone cooking appliance, powered by gas or electricity.

从十八世纪开始，西方世界的烹食工具便从开放的土灶转为封闭的现代炉灶。转变的最开始，此类炉灶以煤、木炭和生物质为燃料，承担着加热和烹饪的双重功能。当二十世纪早期引入中央供热系统后，厨房炉灶独立演化出来，并以天燃气或电为能源。

 Improved biomass stoves have double or triple the thermal efficiency of modern electric or gas cooking stoves

 改良的生物质燃炉可以达到两倍，甚至三倍于现代厨房炉灶的热效率。

Conventional electric hobs use attached iron plates as their heating units, while more sophisticated models use infrared, halogen or induction units, which are positioned below glass ceramics. Of these, only induction-based cooking plates are more efficient than conventional electric hobs. The others mainly offer increased convenience, such as greater ease when cleaning. Most gas cooking stoves place burners on top of a stainless steel or ceramic surface, while others place them on top or beneath a glass ceramic surface. Again, the latter offers increased convenience, but no significant efficiency benefit. ^{[[#fn-8][8]]}

传统的电热炉以黑晶面板下布置的发热炉丝作为加热单元，更复杂的还会使用红外加热、卤素和电磁感应技术。这其中，只有电磁炉的热效率能高于传统电热炉。其它电热炉的唯一可圈之处仅在于其提供的方便性，例如极易打理的特点。此类炉灶的炉头部分常常置于不锈钢或陶瓷材质的表面上，另有一些炉头是置于平整的微晶面板之下（或之上），通常后者的方便程度较高，而热效率则较前者低【8】。

Research into the efficiency of modern cooking stoves is rather limited. According to a study by the Dutch research institute VHK, a traditional electric cooktop (with vitro-ceramic plate) has a thermal efficiency of 13%, while that of an electric induction cooker is 15%. A microwave obtains 19% thermal efficiency. Only a classical gas cooking stove (23%) reaches the thermal efficiency of a well-tended three-stone fire. ^{[[#fn-8][8]]}

对现代厨房炉灶的研究十分有限。据一家荷兰研究机构 VHK 的发现，传统的使用了微晶玻璃的电热炉，只有 13％的热效率，电磁炉稍高一些，也只有 15％，微波炉则可达 19％。但只有传统的燃气灶，其热效率可以和一个照看得当的土灶相提并论【8】。

While the study is aimed primarily at the preparation of hot drinks, it is the most complete study available and its results are applicable to cooking food with only a few small caveats. ^{[[#fn-9][9]]}

尽管这个研究针对的是加热饮品这类准备性质的活动，但这是为数不多的完整性很高的实验，只需一些提示，这个实验对食物烹饪也有很强的参考性【9】。

Now, if we compare the thermal efficiencies from modern cooking stoves with those from stoves used in poorer households, we see that the improved biomass stoves in developing countries beat our “high-tech” cooking technology with a factor of two to three (graphic below). Gas or electric ovens are not included in this comparison, but their efficiency is even lower than gas or electric hobs because water is a much better conductor of heat than air.

如此一来，把现代炉灶和贫穷国家炉灶的热效率一较高下的话，我们可以说，改良过的生物燃料炉要胜过现代炉灶一大截了（见下图）。煤气炉和电烤炉不在此比较范围内，但其实这两者的热效率比起燃气灶和电热炉更为低下，毕竟水比起空气来说，是更好的热导体。

The low efficiency of modern cooking devices may surprise people, as these are not the figures that are usually presented in sales brochures or consumer reports. For example, the Californian Consumer Energy Center gives an efficiency level of 90% for an electric induction cooker, 65% for a standard electric range, and 55% for a gas burner. ^{[[#fn-10][10]]}

现代炉灶的低效能可能会让人大跌眼镜，毕竟人们从来不会在产品手册和消费报告里看到这些比较数字。更别说，像是加州消费者能源中心给电磁炉标识的热效能是 90％，给电灶标识了 65％，煤气灶 55％【10】。

Power Conversion Losses

电力转换损失

The main discrepancy with these figures is caused when one doesn't take into account that electricity first needs to be produced in power plants which sometimes convert less than a third of the primary energy into electricity ^{[[#fn-11][11]]} This is not an issue with gas or biomass stoves, where a primary fuel is directly converted into heat for cooking. ^{[[#fn-12][12]]} But it does have a destructive effect on the thermal efficiency of any electric cooking device, be it an electric hob or a microwave. In the graphic below, power conversion losses are indicated by the dark blue bars.

疑惑本文中各种炉灶的热效率值为何如此之低的人忽略了这一事实，即：电能是在发电厂里从其它能源转化而来的，而通常仅有 1／3 的原始能源的能量能被转化为电能【11】。这个问题在燃气炉和生物质燃料炉中不存在，因为这两者的能量通过燃烧全部被释放出来了【12】。因此，任何使用电作为能源的炉灶（例如电热炉和微波炉）都先天地在热效率上具有无法磨灭的缺点。

The VHK study assumes an electric grid efficiency of 40%. This figure takes into account power generation and distribution losses, as well as fuel extraction and a projected saving on these issues over an average product life of 10-15 years. ^{[[#fn-8][8]]} It should be noted that this percentage corresponds to a global average, including the use of renewables and atomic energy. Depending on the country, grid efficiency can be higher or lower. ^{[[#fn-13][13]]}

VHk 机构估计了电网的能源转换率只有 40％。该数值考虑了发电损失和传输损失。这一数字是对全球电站的平均估算，并包括了可再生能源和原子能，因国家不同，或多或少，电力转换率皆在此数值上下浮动。

Boiling water preparation energy impact (kWh primary energy for 1,000 litre useful boiled water per year) for different cooking devices. Dark blue: power generation loss. Light blue: heat loss. Red: theoretical minimum. Pink: production, distribution, end-of-life. Pink: extra boiling time. Purple: standby. Green: over-filling. Source: ^{[[#fn-8][8]]}

If we only look at the different types of thermal power plants, we find that the thermal efficiency for a traditional coal plant (81% of all coal-based power plants in use) is only 25 to 37%, while that of a common direct-combustion biomass power plant is only 20%. ^{[[#fn-13][13]]}

就发电站本身而言，我们会发现传统煤电厂的能源转换率只有 25％到 37％，而生物质直燃发电厂的能源转换率只有 20％。【13】

At world level, the average energy efficiency of thermal power plants is 36%. ^{[[#fn-13][13]]} These percentages should be reduced with electric transmission and distribution losses, which are on average 6% in Europe, 7% in the USA, and 9% on a world level. ^{[[#fn-13][13]]}

全球电站能源转换率的平均值是 36％。【13】如果纳入传输和再分配损失因素，能源效率还要再低许多，平均而言，欧洲会低至 6％，美国会低至 7％，全球会低至 9％。【13】

This means that if your electric stove is operated by electricity from a biomass power plant--- [[http://www.notechmagazine.com/2014/04/how-biomass-energy-has-become-the-new-coal.html][a fast growing “green” trend nowadays]] --- the power conversion efficiency is three to four times lower (11-14%) than the authors of the study assume, and thermal efficiency drops to about 5%. This is similar to the thermal efficiency of a neglected open fire, and one-tenth the thermal efficiency of a rocket stove. Likewise, a cookstove which uses coal or gas directly to heat food is much more energy efficient than a cookstove that runs on electricity produced by a coal or gas power plant.

这意味着，如果你的电炉靠从生物质发电厂送来的电力运作，则能量的转换率总体还要比实验估算再低三到四倍，总的热效率大概也只有 5％，仅是火箭炉的十分之一，这就和一个疏于照看的石堆土灶没啥区别了。同理，直接烧气或煤的炉灶，其热效率要高于靠煤电厂（或燃气发电厂）送来的电力运作的炉灶。

 Essentially, any electric cooking device is an insult to the science of thermodynamics

 究其本质，任何形式的电热炉不过是某种热力学的隔热层而已

Evidently, there is something wrong with the western approach to sustainability. Converting heat into electricity which is then converted back into heat, at 20-40% efficiency, is similar to building a Rube Goldberg machine; it's a needlessly complex operation compared to simply converting the primary fuel into heat to boil water. Essentially, any electric cooking device is an insult to the science of thermodynamics.

显然，西方文明在追求永续发展的道路上遇到了某种问题。通过把热能转换成电能，回头再用电能产生热能，期间再损失掉 60％到 80％的能量，就好比建了一台 *戈德堡机械* 。和直接通过燃烧燃料获取热能相比，这未免太过迂回曲折了。究其本质，任何形式的电热炉不过是某种热力学的隔热层而已

Heat Transfer Loss

热传导损失

A second problem is that the high efficiency figures given in sales brochures and consumer reports underestimate the heat loss that occurs during the heat transfer from cooking stove to cooking pot (shown by the light blue bars in the graphic above). This heat loss is present with all cooking stoves, but is especially high in the case of gas hobs. In the graphic above, the red bar concerns the minimum energy that it takes to boil 1,000 litres of water, assuming that there is no energy loss during the heat transfer between the cooking stove and the water. This value is 105 kWh/yr for a starting cold water temperature of 10 degrees celsius.

炉灶手册的另一个问题是，炉头和炊具之间热传导损失造成的热效率下降完全被低估，甚至被忽视了。热传导损失存在于任何炉灶和炊具之间，且在燃气灶上尤为严重。

Energy losses appear because of three reasons. Firstly, some heat from the cooking fire escapes before it can reach the cooking vessel. Secondly, some heat from the cooking fire is used to heat up the cooking pot, which constantly loses heat to the environment. Lastly, heat is wasted because some of the boiling water escapes through evaporation. While the red bar is logically the same for every cooking device, the light blue bar showing the additional energy required to compensate for heat transfer loss varies from 57 kWh/yr for an electric induction stove to 255 kWh/yr for a gas hob.

这个现象的成因有三。第一，部分热量在还未抵达炊具前就消散到周围环境里去了。第二，保持炊具本身的温度需要一定热量，并且炊具也会持续向环境中释放热量。最后，如果炊具没有密闭，从容器逃逸出来的水蒸汽也会带走一部分热量。

Gas stoves have the largest heat transfer losses of all modern cooking stoves. Picture: [[https://www.flickr.com/photos/handcoding/2306148621/sizes/l/in/photolist-9fwxsE-ceme3-6fsdHT-baqyQD-4vMBD8-7qKtbt-7wgwmh-5mxmYh-7t5MRY-32Zkcr-334VPJ-32ZneV-6WNUnd-4otRwY-9YKx7X-eNvbyf-5K212X-6oy431-3i4xq-5dhzoB-6aXzBk-bcpTDp-3LarEn-5Ru5J2-3i4xp-4sXcWB-4tNCfP-7teghU-8XjEGz-4KFDC7-4nXEtC-CgUdE-4hWhcF-4jFwAw-7estzW-49Ti1-9n5zm5-5vGLzJ-5LULtt-6v5ReY-67t5UC-5FrWB8-5vCsSD-6psLwc-a2JTdv-SBfWT-8shCrM-52ndMn-4RfqYF-7jkgdz/][Ashley Bischoff @ Flickr]].

Heat transfer loss is not fully accounted for in most testing standards for cooking appliances. For example, the US standard uses a test by which the heat transfer efficiency of a cooking top is established from heating up aluminum cylinders of certain dimensions, not pots of water. ^{[[#fn-15][15]]} ^{[[#fn-16][16]]} This avoids the complex phase change from liquid to vapour and is thus better reproducible.

热传导损失并未被完全纳入炉灶和炊具的标准测试里。比如，美国标准制定的测试场景里是通过铝圆柱被熔解所消耗的能量来测算热效率的【15】【16】。这种做法规避了水从液态变为气态的复杂情况，使得实验更容易复现。

 Heat transfer loss is not fully accounted for in most testing standards for cooking appliances

 热传导损失并未被完全纳入炉灶和炊具的标准测试里。

However, as all the heat of the cylinder is counted as useful, it ignores that in real life situations some energy---notably the energy to heat up the pot or kettle itself---is wasted. Only taking into account the energy loss in heating the pot itself, energy efficiency decreases with about 10% of the figures given by standard tests, concludes VHK. ^{[[#fn-8][8]]} Furthermore, the US test is modeled after the process of boiling food on all burners or hot plates simultaneously, which is not always the case. Heat transfer losses are larger when only one or two pots are on the fire.

虽然测算熔解铝圆柱的能量是十分有用的，但这种实验忽视了真实场景里，有些能量，尤其是加热炊具自身所需的能量，是必需但又不得不浪费掉的。VHK 机构总结道，仅考虑加热炊具的能量浪费，标准实验测得的数值都要下调 10％【8】。再有就是，美国标准测试的场景里，所有炉灶是一字排开并同时一起加热测试的，真实场景里是不会有这么多炉灶同时一起工作的，单一工作的炉灶因热传导损失的热量是更多的。

Apart from power conversion losses and heat transfer losses, the remainder of the energy losses are due to production, distribution and disposal of cooking devices (embodied energy), standby losses (which are only relevant for microwaves, induction stoves and sophisticated gas stoves), and cooking habits. These factors have a relatively small influence.

Of all the energy losses involved in modern cooking appliances, only heat transfer loss applies to cooking devices in poorer households. There are no power conversion losses, fuel is mostly gathered by hand, there are no standby losses, and embodied energy is negligible as most devices are home-made.

上文提到的热能损失因素中，现代炉灶都避免不了，但是贫穷家庭的土灶只会受到热传导损失这一个因素的影响。土灶没有电力转换损失的问题存在，燃料本身也是人通过双手劳动取得，更没有待机能源耗损，其制造过程也没有太多能量消耗，因为通常其都是家庭自制的。

Indoor Air Pollution in Rich vs. Poor Households

贫穷家庭和富裕家庭的空气污染对比

While the thermal efficiency of modern cooking devices is clearly inferior to that of a well-tended three-stone fire or rocket stove, they do have an advantage when it comes to indoor air pollution. However, this is not a black-and-white issue either. Air pollution levels depend on what you're cooking, how skillful you are, and which technology you use.

在热效率表现上，现今的新式炉灶是比不过管理得当的明火土灶和火箭炉的，唯其在室内空气污染方面占据优势。然而，这也绝不是非黑即白的问题。烹制的食材和方法，以及烹饪者的技巧都可能影响到空气的污染水平。

In the worst case scenario, pollution levels in modern kitchens can be similar to those of a well-tended three-stone fire indoors. This is not to say that the problem of indoor pollution in poor households is overstated, but rather that cooking in modern kitchens is not always as clean as we assume it to be.

在最坏的情况下，新式炉灶与管理得当的石堆土灶，其二者的污染水可等量齐观。倒不是说土灶的污染弊端被夸大了，而是说新式炉灶的污染问题被广泛忽视了。

 Pollution levels in modern kitchens can be similar to those of a well tended three-stone fire inside the house

 新式炉灶与管理得当的石堆土灶，其二者的污染水平等量齐观

Particulate matter ( PM) is considered as the single best indicator of potential harm in air quality. ^{[[#fn-4][4]]} In poor households where indoor cooking happens with crude stoves or open fires, PM-levels vary from 200 to 5,000 ug/m3 over a 24-hour period, and from 300 to 20,000 ug/m3 during the actual use of stoves. ^{[[#fn-17][17]]} ^{[[#fn-19][19]]} The Partnership for Clean Indoor Air measured PM emissions for a well tended three-stone fire, which resulted in values of between 281 and 2,004 ug/m3 while cooking. ^{[[#fn-4][4]]}

唯颗粒物（PM）一项指标就可作为可靠的潜在健康威胁（空气污染）指标【4】。在贫穷国家使用简陋室内土灶的家庭里，PM 值在 24 小时内可达到 200 至 5,000 ㎍/㎥之间，在烹食期间可高达 300 至 20,000 ㎍/㎥之间【17】【19】。PCIA 测定的看管得当的室内石堆土灶的 PM 排放量在 281 至 2,004 ㎍/㎥之间。

Indoor cooking with biomass stoves. Image: [[http://www.cleancookstoves.org/][Global Alliance for Clean Cookstoves]].

Similar research undertaken in a kitchen equipped with modern technology found PM concentrations in the kitchen, living room and bedroom from below the detection limit to 3,880 ug/m3 during a variety of 32 different cooking tests with gas and electric ranges. ^{[[#fn-20][20]]} The medium and average concentrations of PM during the 32 cooking tests exceeded ambient air quality standards (which are 150 g/m3 for PM10 and 65 ug/m3 for PM2.5). These values come close to the best-case scenarios in poor households.

在 32 种不同的通电或烧气的新式炉灶上经过类似的实验测算发现，厨房、客厅和卧室的 PM 浓度可以从检测仪器的最低感应值到最高 3,880 ㎍/㎥之间【20】。不管是中位值还是平均值都超过了 *环境空气质量标准*,其中规定：PM10 不超过 150 g/㎥，PM2.5 不超过 65 ㎍/㎥。也就是说在看管得当的最好情况下，土灶是可以适用的。

Importantly, cooking pollutants are not caused by the burning of gas or fuel alone, but also in the cooking process itself. PM2.5 concentrations were over 1,000 ug/m3 during stovetop stir-frying, baking lasagna in the gas oven, and frying tortillas in oil on the range top burner. The authors conclude that:

要强调的是，烹食过程中制造的空气污染平不全然来自于炉灶，烹饪活动本身也难逃其咎。炒菜、煎炸时释放的 PM2.5 可高达 1,000 ㎍/㎥。

“Very high levels of several pollutants were measured in indoor air during different types of cooking activities. The levels measured for some cooking activities exceeded health-based standards and guidelines, and could pose a risk to home occupants, especially susceptible groups of the population such as young children and the elderly.”

Unfortunately, gas stoves---which have the highest thermal efficiency of all modern cooking stoves---produce the most air pollution in modern kitchens. ^{[[#fn-20][20]]} The average indoor PM emissions for gas stoves can amount to 25% of those of biomass cooking stoves. ^{[[#fn-19][19]]} A 2014 study estimates that 60 percent of homes in California that cook at least once a week with a gas stove can reach pollutant levels of CO, NO2 and formaldehyde that would be illegal if found outdoors. ^{[[#fn-21][21]]} The authors state that:

不幸的是，所有新式炉灶里热效率最高的燃气灶，也产生了最多的空气污染物【20】。其排放的室内 PM2.5 平均值可达生物质燃料炉的 25％。【19】2014 年的一项调查估计，加州那些每周至少使用燃气灶做一次饭的家庭里有六成都在室内检测出了一氧化碳，二氧化氮和甲醛的浓度值达到了即使在室外都已违反法规的程度。

“If these were conditions that were outdoors the EPA (Environmental Protection Agency) would be cracking down. But since it's in people's homes, there's no regulation requiring anyone to fix it. Reducing people's exposure to pollutants from gas stoves should be a public health priority.”

Air Pollution and Greenhouse Gas Emissions

大气污染和温室气体排放

Obviously, indoor cooking with an electric stove is the healthiest option, albeit not totally free from producing indoor air pollution. However, electric stoves are only “clean” because they emit most of their pollution elsewhere---at the smokestacks of the power plant. Any biomass stove design with a chimney basically achieves the same. If a chimney is added to an indoor biomass stove, indoor air pollution drops to almost zero. ^{[[#fn-4][4]]}

乍看，在室内使用电热炉是最健康的选择，尽管这也不能完全摆脱空气污染。然而，这个所谓的“健康”也只是把单个家庭的室内污染统一转嫁到了电站的大烟囱里而已。其对环境的最终影响效果和一个生物质燃烧炉并无本质区分。如果所有室内的生物质燃料炉都安装上烟囱，其产生的室内污染几乎可忽略。

A clean cookstove in India. Image: [[http://www.cleancookstoves.org/][Global Alliance for Clean Cookstoves]].

And while the burning of coal or gas emits less air pollution and greenhouse gases than the burning of biomass per unit of energy produced ^{[[#fn-22][22]]} you have to burn more fuel in order to make up for the power conversion losses. Especially if your electric stove runs on electricity from a biomass power plant, then air pollution and greenhouse gas emissions are much higher than in the case of a biomass stove.

虽然以单位能量计算，烧煤和烧气相较燃烧生物质要排放更少的大气污染和温室气体【22】，但是为了弥补电能转换损失，电站又不得不消耗超量的煤/气资源。相比直接使用生物质燃料炉，当电热炉通的电来自于生物质电站时，更会加剧大气污染和温室气体排放。

 If electricity is produced by biomass, an electric cooking stove produces much more air pollution and greenhouse gases than a biomass stove

当电热炉通的电来自于生物质发电站时，更会加剧大气污染和温室气体排放。

On the other hand, if we consider biomass to be climate neutral over time because the harvested forest gets a chance to grow back, then a biomass stove beats all other cooking methods when it comes to greenhouse gas emissions. The same goes for the cooking stove powered by electricity from biomass, although it would produce considerably more air pollution than the biomass stove, and require a much larger area of sustainably managed forest.

另一方面，当考虑到生物质燃料的可再生性（林地是有机会恢复的），其对环境的影响反而是中立的，因此，生物质燃料炉相较其它烹食炉具总体要产生更少的温室气体排放。这一结论对那些使用了从生物质发电厂送来的电的炉具也是适用的，只是比起生物质燃料炉，这种方式会排放更多大气污染物，以及需要更多的森林来提供生物质。

What's the solution?

最终方案是什么？

When the German Wuppertal Institute investigated the potential for improved energy efficiency of cooking stoves on a global scale, they concluded that energy use could be halved. ^{[[#fn-2][2]]} Although it's remarkable how the proposed solutions for this energy inefficiency differ for poor and rich countries. In the developing world, the focus is mainly on designing more efficient biomass stoves that produce fewer pollutants. While achieved savings as a result of switching to biogas would be larger, its investment would be 30 times higher compared to the distribution of improved wood cooking stoves. ^{[[#fn-2][2]]}

德国的 *伍珀塔尔气候、环境、能源研究所* 曾调查研究过，如果在全球范围内统一改善能源转换效率，全球的能源消耗可减少一半【2】。这个提案里暗含着发达国家和落后国家能源转换效率的巨大不同。落后国家致力于设计出热效率更高、污染排放更少的生物质燃料炉。而如果转而以生物气体作为能源的话，虽然能产生巨大的效益，但和推广改良的柴火炉相比，要多耗费 30 倍的投资才行。【2】

An improved biomass cookstove in India. Image: [[http://www.cleancookstoves.org/][Global Alliance for Clean Cookstoves]].

For the developed world, the Wuppertal Institute focuses on a much more costly measure: extending the use of the most efficient types of “western” stoves, such as the electric induction hob. However, as we have seen, these stoves are far less efficient than the improved biomass stoves, and they are also more expensive. The authors infer that, compared to developing countries, energy saving potentials with modern cooking stoves are far smaller and less cost-efficient. But as is apparent from the inefficiencies of western cooking technology, the energy savings potential is, in reality, larger.

从落后国家的角度看来，伍珀塔尔研究所的方式似乎有点不计成本：推广新式炉具里热效率比较高的品类，比如电磁炉，但我们已经知道，即使这类炉具，其热效率比起改良的生物质燃料炉还是差远了，更别说它们也不便宜。作者推论：发达国家推广的新式炉具，其节约出来的能源潜能即小又不符合成本效益。

One possibility for the West to improve the sustainability of its cooking stoves, not mentioned by the Wuppertal Institute, is to generate electricity by wind, solar or water energy. If electricity is generated by renewable energy, electric hobs and microwaves suddenly beat all other cooking stoves when it comes to efficiency, air pollution and greenhouse gas emissions. That being said, using renewable energy to produce electricity to create heat for cooking remains a needlessly complex and costly approach to make cooking more sustainable.

伍珀塔尔研究所没有指出的一点是，西方世界如果想要提升其炉具的能源效率和可持续性的话，应该大力推广的是再生能源（风力，太阳能和水能）发电技术。如果电力来自于可再生能源，这种情况下，电热炉和微波炉在能源效率、空气污染和温室气体排放方面将击败所有其它炉具。但说到头来，使用再生能源发电再制造热量来烹食，终归还是会引入不必要的复杂性和成本。

There are some obvious but often overlooked solutions that would make cooking close to 100% sustainable in rich and poor countries alike. See our follow-up article: “ [[https://solar.lowtechmagazine.com/2014/07/cooking-pot-insulation-key-to-sustainable-cooking.html][If we insulate our houses, why not our cooking pots?]]“.

但其实有一个显而易见却被今世之人忽视的方案————不论是发达国家还是落后国家皆可适用，且几乎百分百可持续————需要我们更多的关注。欲知详情，见本站另一篇文章：《如果房子可以保温，锅具为什么不可以呢？》。

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注脚：

<<fn-1>>

   “ [[http://www.bigee.net/media/filer_public/2014/03/17/appliance__residential_cookingstoves__user_savings__20140220__8.pdf][What users can save with energy-efficient cooking stoves and ovens]]“, Oliver Adria and Jan Bethge, October 2013. [[#fnref-1][↩]] [[#fnref2-1][↩]] [[#fnref3-1][↩]]

<<fn-2>>

   “ [[http://www.bigee.net/media/filer_public/2014/03/17/appliance__residential_cookingstoves__worldwide_potential__20140220__8.pdf][The overall worldwide saving potential from domestic cooking stoves and ovens]]“, Oliver Adria and Jan Bethge, October 2013. [[#fnref-2][↩]] [[#fnref2-2][↩]]

<<fn-3>>

   As of 2012, the [[http://www.pciaonline.org/node/2][Partnership for Clean Indoor Air]] ( PCIA) has integrated with the [[http://www.cleancookstoves.org/][Global Alliance for Clean Cookstoves]]. [[#fnref-3][↩]]

<<fn-4>>

   “ [[http://my.ewb-usa.org/theme/library/myewb-usa/project-resources/technical/TestResultsCookstovePerformance.pdf][Test Results of Cook Stove Performance]]“, Partnership for Clean Indoor Air, 2012. See Appendix C for the University of California Berkeley ( UCB) Water Boiling Test ( WBT) protocols. [[#fnref-4][↩]] [[#fnref2-4][↩]] [[#fnref3-4][↩]] [[#fnref4-4][↩]] [[#fnref5-4][↩]]

<<fn-5>>

   “A laboratory comparison of the global warming impact of five major types of biomass cooking stoves”, Nordica MacCarthy, 2008 [[#fnref-5][↩]]

<<fn-6>>

   Thermal efficiency rewards the production of excess steam, while specific consumption penalizes it. For the pros and contras of both testing approaches, see [4], page 76-77. [[#fnref-6][↩]]

<<fn-7>>

   These percentages concern the outer values of different test procedures and during different stages of the cooking process. The thermal efficiency of a rocket stove is especially high when bringing water to boil but its advantage is much smaller during simmering. [[#fnref-7][↩]]

<<fn-8>>

   “ [[http://www.vhk.nl/downloads/Energy%20analysis%20Quooker%20main%20final%20april%202010.pdf][Quooker Energy Analysis]]“, Part one, Van Holsteijn en Kemna B.V.( VHK), March 2010. [[#fnref-8][↩]] [[#fnref2-8][↩]] [[#fnref3-8][↩]] [[#fnref4-8][↩]] [[#fnref5-8][↩]]

<<fn-9>>

   The heat transfer efficiency figures chosen by [8] are based on a typical mixed use of cooking stoves, in which the energy is used both for preparing meals and for hot drinks. Since boiling smaller amounts of water for hot drinks is somewhat less efficient, this approach underestimates the heat transfer efficiency of cooking food. However, to be on the safe side, the researchers are rather conservative in their revision of heat transfer efficiencies (see chapters 2.2 & 2.4), so the difference must be small. [[#fnref-9][↩]]

<<fn-10>>

   “ [[http://www.consumerenergycenter.org/residential/appliances/ranges.html][Stoves, Ranges and Ovens]]“, Consumer Energy Center, California Energy Commission. [[#fnref-10][↩]]

<<fn-11>>

   The average efficiency of a coal plant is 35%. See: “ [[http://www.iea.org/ciab/papers/power_generation_from_coal.pdf][Power generation from coal: Measuring and Reporting Efficiency Performance and CO2 Performance]]“, OECD/ IEA, 2010. [[#fnref-11][↩]]

<<fn-12>>

   It should be noted that the [[http://www.bu.edu/cas/2012/11/20/thousands-of-natural-gas-leaks-discovered-in-boston/?inf_contact_key=4a5b801cb4423703db24845fc797708d071f3806a11653eec172adbfec6cd10a][energy losses of the natural gas distribution network can be rather large,]]and this fact does not seem to be taken into account in the study. The thermal efficiency of gas stoves may thus be overstated. The same goes for the greenhouse gas emissions, mainly due to [[http://e360.yale.edu/digest/climate_benefits_of_natural_gasare_questioned_in_a_major_new_report/4076/][methane leaks during gas production]]. [[#fnref-12][↩]]

<<fn-13>>

   “ [[http://www.abb-energyefficiency.com/assets/documents-download/ABB-Trends-in-global-energy-efficiency-2013.pdf][The state of global energy efficiency: global and sectorial energy efficiency trends]]“, Enerdata. [[#fnref-13][↩]] [[#fnref2-13][↩]] [[#fnref3-13][↩]] [[#fnref4-13][↩]]

<<fn-14>>

   “ [[http://www.centreforenergy.com/AboutEnergy/Biomass/Overview.asp?page=2][How is biomass energy used?]]“, Canadian Centre for Energy Information. [[#fnref-14][↩]]

<<fn-15>>

   “ [[http://www.gpo.gov/fdsys/pkg/CFR-2012-title10-vol3/pdf/CFR-2012-title10-vol3-part430-subpartB-appI.pdf][Test Procedure for Residential Kitchen Ranges and Ovens]]“, US Department of Energy, 1997. For related documents, see “ [[http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/57][Residential Kitchen Ranges and Ovens]]“. [[#fnref-15][↩]]

<<fn-16>>

   “ [[http://fire.nist.gov/bfrlpubs/build99/PDF/b99015.pdf][Evaluation of Kitchen Cooking Appliance Efficiency Test Procedures]]“, Steven Nabinger, US Department of Commerce, 1999 [[#fnref-16][↩]]

<<fn-17>>

   “ [[http://practicalaction.org/media/preview/7052/lng:en][Smoke, health and household energy. Volume 1]]“, Liz Bates, 2005. [[#fnref-17][↩]]

<<fn-18>>

   “ [[http://whqlibdoc.who.int/hq/2002/WHO_SDE_OEH_02.05.pdf?ua=1][The health effects of indoor air pollution exposure in developing countries]]“, WHO, 2002 [[#fnref-18][↩]]

<<fn-19>>

   “ [[https://www.academia.edu/1071891/Health_effects_of_chronic_exposure_to_smoke_from_Biomass_Fuel_burning_in_rural_areas][health effects of chronic exposure to smoke from biomass fuel burning in rural areas]]“, WHO India, 2007 [[#fnref-19][↩]] [[#fnref2-19][↩]]

<<fn-20>>

   “ [[http://www.arb.ca.gov/research/indoor/cooking/0-Cover-TOC-Exec-Summary.PDF][Indoor Air Quality: Residential Cooking Exposures]]“, R. Fortmann et al., State of California Air Resources Board, 2001 [[#fnref-20][↩]] [[#fnref2-20][↩]]

<<fn-21>>

   “ [[http://ehp.niehs.nih.gov/wp-content/uploads/122/1/ehp.1306673.pdf][Pollutant exposures from natural gas cooking burners: a simulation-based assessment for southern california]]“, Environmental Health Perspectives, January 2014. [[#fnref-21][↩]]

<<fn-22>>

   “ [[http://www.pfpi.net/wp-content/uploads/2014/04/PFPI-Biomass-is-the-New-Coal-April-2-2014.pdf][Trees, Trash, and Toxics: How Biomass Energy Has Become the New Coal]]“, Mary . Booth, Partnership for Policy Integrity, April 2014 [[#fnref-22][↩]]