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uch比平行流（相同方向）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
液体饱和空气的冷却会导致露水、雾、雨或雪。
暖空气比冷空气能保持更多的水分。
相对湿度百分比测量空气中有多少水蒸气
与空气饱和时的空气量相比
在相同的温度下。形容词“相对”是合适的，因为空气所能容纳的水的量是相对的
温度和大气压。与海拔或天气条件相关的气压变化会影响
空气的保湿能力。
湿色调
ABB 全新PC接口板 UFC760BE142 3BHE004573R0142
ABB 全新PC接口板 UFC760BE142 3BHE004573R0142
uch 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 saturated air results in dew, fog, rain, or snow.
Warm air can hold more moisture than cold air.
Percent relative humidity measures how much water vapor is in the
air compared to how much there would be if the air were saturated
at the same temperature. The adjective relative is appropriate because the absolute amount of water that air can hold is relative
to both temperature and barometric pressure. Changes in barometric pressure related to altitude or to weather conditions affect the
moisture-holding capacity of air.
A psychrome
ABB 全新PC接口板 UFC760BE142 3BHE004573R0142
