利用能源要讲究效率。效率是评价用能设备和用能系统是否合理的指标。指标标定得是否科学对推动节能工作有重要的作用。十八世纪发明了蒸气机,把煤燃烧时放出的热能转变为机械功,从而得到强大的动力。又经过长期的实践,才总结出热与功之间有一种等量关系。即一物体失去的能量等于另一物体得到的能量。它说明在孤立系统中,能量的“量”永远保持不变,即能量守恒和转换原理在热现象上的应用。这就是热力学第一定律。从此,对热设备在输入和输出能量之间平衡关系的考查一直就是评价的基础。之后,在研究动力机如何提高热变功百分比的过程中,发现热变为 Use energy to be efficient. Efficiency is an index to evaluate whether energy-using equipment and energy-using systems are reasonable. Whether the indicators are calibrated or not has an important role in promoting energy conservation. In the eighteenth century, steam engines were invented to convert the thermal energy released from the combustion of coal into mechanical work, thereby gaining powerful power. After a long period of practice, it was concluded that there is an equal relationship between heat and work. That is, the energy lost by one object is equal to the energy obtained by another object. It shows that in isolated systems, the “quantity” of energy is always kept constant, that is, the application of energy conservation and conversion principles in thermal phenomena. This is the first law of thermodynamics. Since then, the examination of the balance relationship between the input and output energy of thermal equipment has always been the basis for evaluation. Later, in the process of studying how the power machine increased the percentage of thermal power, it was discovered that the heat became