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热量总是毫无例外地从较暖的地方转移到较冷的地方。
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，
1, 1
⁄2, 1
⁄3 , 1
/4，…一个绝缘层有价值，每个
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，
而对于材料的保存也与水分有关
*另见19章。
暖通空调工程基础：1部分
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暖通空调工程基础：1部分9
空气。湿空气条件的控制是
暖通空调系统。记住以下几点：
当水在给定温度和大气条件下蒸发到空气中时，空气被视为水分饱和
压力被水蒸气同时凝结到
液体佐藤冷却
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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,
1, 1
⁄2, 1
⁄3 , 1
⁄4 , . . . . 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 materials are also related to the moisture in
*See also Chap. 19.
HVAC Engineering Fundamentals: Part 1
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HVAC Engineering Fundamentals: Part 1 9
the air. Control of the moist-air condition is a primary objective of the
HVAC system. Remember the following:
Air is considered to be saturated with moisture when the evaporation of water into the air at a given temperature and atmospheric
pressure is offset by a concurrent condensation of water vapor to
liquid. Cooling of satu
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