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湿空气，空气和水蒸气的混合物。参见参考文献4
本主题的进一步讨论。
1.7传热†
在研究热传递时，我们研究通过质量运动的能量
通过传导，通过对流从固体到移动液体，或
通过辐射从一个物体到另一个物体。记得：
*另见17章。
†另见18章。
暖通空调工程基础：1部分
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8.一章
热量总是从较暖的地方转移到较冷的地方，无一例外。
传导和对流的传热与驱动温差成正比。差价加倍
以使传热速率加倍（T1T2）。
辐射传热与
温差 tem-4中的小变化（T T）。1 2
温度可以在辐射传热速率中产生相对较大的变化。
对于流体之间的传热，逆流（相反方向）是
这比平行流（同一方向）更有效。
减少热传递的隔热遵循收益递减定律，即所用隔热量的倒数，例如，
…一个绝缘层是有价值的
随后的增量较小。找到
这是一个具有成本效益的快乐中位数。
传热表面结垢对设备性能不利。
定量传热与传热表面积成正比。
尽管这不是一种典型的热“传递”，但热可以通过流体（例如管道中的空气和管道中的水）从
指向另一个。此操作更好地分类为以下组合：
流体力学和热力学（不同类型流体的混合
热力学条件）。有关这方面的进一步讨论，请参阅参考文献5
话题
1.8湿度*
湿度测量学是研究潮湿空气性质的科学，即空气
与水蒸气混合。热力学的这一子集很重要
对于暖通空调行业，因为空气是所有人的主要环境
暖通空调工程。而氧气、氮气和其他干燥组分
在HVAC温度下，空气仅在气相中表现类似
范围内，水在相同温度下会发生状态变化
或者在基于温度的相同压力范围内。在人体舒适温度范围内
人和环境质量对健康、结构和环境的影响，
以及
ABB 励磁主板 UFC762AE101 3BHE006412R0101
ABB 励磁主板 UFC762AE101 3BHE006412R0101
ics of moist air, a mixture of air and water vapor. See Ref. 4 for
further discussion of this topic.
1.7 Heat Transfer†
In studying heat transfer, we study energy in motion—through a mass
by conduction, from a solid to a moving liquid by convection, or from
one body to another through space by radiation. Remember:
*See also Chap. 17.
†See also Chap. 18.
HVAC Engineering Fundamentals: Part 1
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8 Chapter One
Heat is transferred from warmer to colder—always, without exception.
Heat transfer for conduction and for convection is directly proportional to the driving temperature differential. Double the difference
to double the heat transfer rate (T1 T2).
Heat transfer by radiation is proportional to the fourth power of the
absolute temperature difference Small changes in tem- 4 4 (T T ). 1 2
perature can create relatively large changes in radiation heat transfer rates.
For heat transfer between fluids, counterflow (opposite direction) is
much more effective than parallel flow (same direction).
Insulation to reduce heat transfer follows a law of diminishing returns, the reciprocal of the amount of insulation used, for instance,
. . The first insulation is most valuable, with every
succeeding increment less so. It is a design challenge to find the
cost-effective happy median.
Fouling of heat transfer surfaces is detrimental to equipment performance.
Quantitative heat transfer is directly proportional to the heat transfer surface area.
Although it is not a classic form of heat ‘‘transfer,’’ heat can be transported by a fluid (e.g., air in ducts and water in pipes) from one
point to another. This action is better classified as a combination of
fluid mechanics and thermodynamics (mixing of fluids of different
thermodynamic conditions). See Ref. 5 for further discussion of this
topic.
1.8 Psychrometrics*
Psychrometrics is the science of the properties of moist air, i.e., air
mixed with water vapor. This subset of thermodynamics is important
to the HVAC industry since air is the primary environment for all
HVAC work. Whereas oxygen, nitrogen, and other components of dry
air behave similarly in only a vapor phase in the HVAC temperature
range, water will undergo a change of state in the same temperature
range based on pressure, or in the same pressure range based on temperature. In the human comfort temperature range, the comfort of
people and the quality of the environment for health, for structures,
and for preservation of
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