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The engineer’s early involvement in the design of any facility
can have a considerable effect on the energy consumed by the build-
ing. If designed carefully, a system keeps energy costs to a mini-
mum. In practice, however, a system is usually selected based on a
low first cost or for the performance of a particular task. In general,
single-duct systems consume less energy than dual-duct systems,
and VAV systems are more energy efficient than constant air volume
systems. Savings from a VAV system come from the savings in fan
power and because the system does not overheat or overcool spaces,
nor does it cool and heat at the same time like a reheat system.
The air distribution system for an all-air system consists of two
major subsystems: (1) air-handling units that generate conditioned
air under sufficient positive pressure to circulate it through (2) a dis-
tribution system that carries air from the air-handling unit to the
space being conditioned. The air distribution subsystem often
includes means to control the amount or temperature of the air deliv-
ered to each space.
AIR-HANDLING UNITS
The basic secondary system is an all-air, single-zone, air-condi-
tioning system consisting of an air-handling unit and an air distribu-
tion system. The air-handling unit may be designed to supply a
constant air volume or a variable air volume for low-, medium-, or
high-velocity air distribution. Normally, the equipment is located
outside the conditioned area in a basement, penthouse, or service
area. It can, however, be installed in the area if conditions permit.
The equipment can be adjacent to the primary heating and refriger-
ation equipment or at considerable distance from it by circulating
refrigerant, chilled water, hot water, or steam for energy transfer.
Figure 1 shows a typical draw-through central system that sup-
plies conditioned air to a single zone or to multiple zones. A blow-
through configuration may also be used if space or other conditions
dictate. The quantity and quality of supplied air are fixed by space
requirements and determined as indicated in Chapters 28 and 29 of
the ASHRAE Handbook—Fundamentals. Air gains and loses heat
by contacting heat transfer surfaces and by mixing with air of 建筑空气分布
一．全空气系统1.1概念
提供完整的明智的和潜在的冷却、预热和加湿空气供给能力的系统。没有额外的冷却或加湿，除了在某些工业系统。加热可能通过相同的气流,在中央系统或在一个特定的区域。在某些应用程序中,加热是通过一个单独的加热器。这个词带意着需要,单独的恒温控制,而术语空间意着一个分区的区域,可能会或可能不会需要单独的控制。基本的全空气系统概念是送风房间这样的条件下,显热增益和潜热获得的的空间,当被供应在空间里流动的空气,吸收将空气所需的空间条件。自热收益在空间会随时间改变能源的机制从空气供给的空间是必要的。有两个这样的基本机制:不同送风交付的数量的空间,通过改变流量提供空气或改变温度的空气被送到空间,通过调节温度或空气调节断断续续。论文网
1.2全空气系统分类两类:
1）单循环系统,包含主要的加热和冷却线圈在一系列空气流动路径;一个常见的管道分配系统在一个共同的空气温度提要所有终端设备。要么(不同温度或不同容量不同的机制卷)与单系统可以使用。
2）双循环系统,包含主要的加热和冷却与线圈并联或串并联流气流路径
1.一个单独的冷和热空气管分布系统混合的空气终端装置(双循环系统)
2.一个单独的每个区域的送风管道送风混合到所需温度的主要单元混合阻尼器。双循环系统通常改变送风原系统通过混合两个不同的温度,但可以在送风的体积也存在一些应用程序。这些类别可能会进一步划分如下: