《HVAC基本知识培训》PPT课件.ppt

HVAC 基本知识培训,培训人：岳 文 2005-6-2,培训内容,Day1: 空调的基本功能 空气的状态参数及焓湿图 空调系统中几种典型的空气处理过程 常用空调系统的分类 定风量空调系统和变风量空调系统 空气的热湿处理设备（空调系统的组成） 风管内的压力分布（动压和静压） 应用举例,Day2： 1、空调水系统 2、冷冻水系统控制原理 3、Honeywell 风阀和水阀介绍 4、水阀选型计算公式,培训内容,空调系统的基本功能,Ventilation 空气流通 Heating 制热 Humidification 加湿 Cooling 制冷 Dehumidification 去湿 Distribution 气流分配 Filtration 空气过滤 Air Volume Control 空气流量控制,空气的状态参数,干球温度：用温度计直接读取的温度 湿球温度：在定压绝热条件下，空气与水直接接触达到热湿平衡时的绝热饱和温度。 露点温度：当空气含湿量不变，降低温度，在饱和状态下，出现冷凝水 时的温度。 含湿量(d)：湿空气中，所含水蒸汽的质量与干空气质量之比，即每公斤干 空气所含有的水蒸汽量，其单位：kg/kg干空气 绝对湿度：每1立方湿空气中所含有的水蒸汽重量 相对湿度()：空气中水蒸汽分压力和同温度下饱和水蒸汽分压力之 比，它 反映了空气接近饱和的程度。 焓(i)：物质所具有的一种热力学性质，焓值大小取决于空气温度和含湿量两个因素。对于近似定压过程，可直接用湿空气的焓的变化来度量空气的热量变化,焓湿图,焓湿图的组成,红线：等焓线 水平的绿线：等温线（干球温度） 垂直的深蓝色线：等含湿量线 蓝色的弧线：等相对湿度线 等湿球温度线：在i-d 图上，从等温度线与100%相对湿度线的交点出发， 作= 4.19ts 的热湿比线，则可得等湿球温度线。在图上 它近似等于等焓线。 饱和温度线：空气中湿空气的含量达到饱和时的温度曲线 热湿比：=i / d , 等焓线的=0 。单位：kj/kg,热湿比有正有负，它代 表湿空气状态变化的方向。,显热和潜热,显热（ SENSIBLE HEAT） 温度改变而含湿量不变所带来的能量的变化。 潜热（LATENT HEAT） 当温度不变时，水变为蒸汽或蒸汽变为水所带来的能量变化。,How Latent and Sensible Heat affect water?,空气的状态变化过程,总热量：GTH= 潜热（TSH）显热（TLH) GTH = 1.19 x L/s x h L/s: 总的送风量， h：空气状态点A 和状态点B的焓差 总的显热： TSH= 1.20x L/s x t L/s: 总的送风量， t：空气状态点A 和状态点B的温差 总的潜热： TLH= 3.0x L/s x L/s: 总的送风量， t：空气状态点A 和状态点B的含湿量差,空气的典型状态变化过程,湿空气的加热过程 利用热水、蒸汽及电能等类热源，通过表面间接对湿空气加热，其温度增高而含湿量不变，即：空气的显热增加。 热湿比 湿空气的等湿冷却过程 利用冷水或其它冷媒通过金属表面对湿空气冷却，当冷表面温度等于或大于湿空气的露点温度时，空气中的水蒸汽不会凝结，因此其含湿量也不回变化，只是温度将降低。 热湿比,等焓加湿过程 利用定量的水通过喷洒与一定状态的空气长时间直接接触，则此种水或水滴及其表面的饱和空气层的温度即等于湿空气的湿球温度，因此，此时空气状态的变化过程就近似于等焓过程。 热湿比4.19ts 等焓减湿过程 利用固体吸湿剂干燥空气时，湿空气的部分水蒸汽在吸湿剂的微孔表面上凝结，湿空气含湿量降低，温度升高 热湿比0,空气的状态变化过程（续一）,空气的状态变化过程（续二）,练习1,What is the RH of the air at all points on the saturation temperature line ANS: RH = 100% What is the dew point at 21 C dry bulb and 50% RH Dew point = 10 C What is the Dew Point of air that has an absolute humidity (moisture content) of 10 g/kg Dew point = 14 oC What is the RH of the air at 30 C dry bulb and a dew point temperature of 5 C RH = 20.3%,练习1 （续一）,What is the moisture content of the air at 22 C dry bulb and 50% RH Moisture content = 8.4 g/kg What is the RH at 26 c dry bulb and 17 c wet bulb Rh = 40% What is the wet bulb temperature of the air at 20 C dry bulb and 50% RH Wet bulb temperature = 14 C What is the RH at 22C dry bulb and 15C wet bulb RH = 47%,练习1 （续二）,What is the wet bulb temperature of the air at 24 C dry bulb and 40% RH Wet bulb temperature = 15.5 C Air at 24 C dry bulb and 20 C wet bulb is cooled to 8C along the saturation curve and then reheated to 21 c. What is the rh of the air at this condition RH = 42%,混合空气的处理,在空调系统中，空气的处理过程是从混风开始，因此我们需要在i-d 图上确定混风状态点。 （一）、通过计算方式确定 T3 = (T1xQ1)+(T2xQ2) / (Q1+Q2) Q1: 新风量 Q2: 回风量 （二）、通过 i-d 图确定 1. 确定新风状态点A和回风状态点B 2. 通过A/B 连线 3. 根据送风量，确定其混合比例，如：新风20%，回风 80%，则将AB线段分为5份，混风位于距回风1/5距 离处,按负担室内热湿负荷所用的介质分： 全空气系统 全水系统 空气水 制冷剂 按空气处理设备的集中程度： 集中式空调 半集中式空调系统 分散式空调系统 按热量传递方式： 对流和辐射 按被处理空气的来源： 封闭式 直流式 混合式,空调系统分类,空调系统分类,集中式空调系统分类,封闭式： 全部为循环空气，系统无新风； 它主要是给设备使用的空调，无人居留。 直流式： 全部用新风，不使用循环空气； 它主要用于：室内有有害气体，不能循环使用的空调系统。 一次回风系统： 除部分使用新风外，使用相当数量的循环空气 在AHU 前混合 普通应用最多的全空气空调系统 二次回风系统： 除部分使用新风外，使用相当数量的循环空气 在AHU 前混合，在AHU 后再混合一次 为减小送风温差而又不用再热器时的空调方式,集中式空调系统分类,另外，根据其他原则，进行分类： 根据系统风量：定风量和变风量 根据风道内空气流速：低速（V8m/s）和高速（V=2030m/s ） 系统用途：工艺性和舒适性空调系统 系统精度：一般性空调系统和恒温恒湿空调系统,一次回风和二次回风空调的特性,定风量空调系统和变风量空调系统,定风量空调系统： 定风量空调系统是指送风量恒定，通过改变送风温度来适应室内负荷的变化。平常所用的大部分空调系统都是采用定风量方式。 变风量空调系统： 是指送风温度不变，而改变送风量的方式来适应负荷的变化，而风量的变化是通过专用的变风量末端装置来实现。根据它的控制方式，可以分为两类： 定静压控制的变风量空调系统 变静压控制的变风量空调系统,定静压控制的变风量空调系统,定静压控制： 恒定送风管道静压的空调系统。当末端的VAV 根据室内温度的要 求开度变小后导致管道内的静压变高，这时，通过调节送风机的频率，减少送风量，使风机管道上的静压维持设定值。这种依赖静压传感器来控制风量的方法，称为定静压变风量空调系统。,变静压控制的变风量空调系统,变静压控制： 控制系统读取末端所有VAV 控制器风门开度信号，并综合这些VAV 阀门的开度信息并加以运算和判断来调节变频送风机的风量，使其具有最大静压值的VAV 阀门处于接近全开的状态,即尽量使风机在最低静压下运转，以节省能源同时减少噪音。例如：当系统中有一台VAV 阀门开度为100%，说明其入口静压不足，风机应增速，以增大风量，使其VAV 开度接近全开即可；当阀门开度处于80%90%之间，说明入口静压适中，风量满足要求，风机不调节；当全部风阀开度处于80%以下时，说明风量过多，此时降低风机转速，减少送风量。这种不依赖静压来控制风量的方法，称为变静压阀。,末端VAV 控制器类型,压力相关型VAV：,压力无关型,末端VAV 控制器类型,空调的基本构件,表面换热器 风阀门 加湿设备 去湿设备 加热设备 风机 空气过滤设备,加湿设备类型,等焓加湿设备： 喷水室 压缩空气喷雾 高压喷水加湿 湿帘 超声波加湿器 离心式加湿器 等温加湿设备 干蒸汽加湿 电极式加湿器 电热式加湿器 PTC 蒸汽加湿器（PTC： 热电变阻器 氧化陶瓷半导体） 红外电加湿,去湿设备,冷冻去湿 液体吸湿剂 固体吸湿器,常用风门,Dampers used in HVAC systems are typically air flow throttling devices and can be either modulating or two position. So it have two major type of damper actuator. They usually have multiple blades mounted on parallel shafts which are rotated in unison by an external actuator to change the blades from open to closed or closed to open Depending on the requirements of the system the assembly can be arranged as “normally open” or “normally closed” by means of the arrangement of the actuator device used to drive the damper,Depending on how the adjacent shafts are linked together the damper assembly is either :- A parallel blade damper An opposed blade damper Parallel blade dampers are constructed so that each blade rotates in parallel with or in the same direction as the blade next to it Opposed blade dampers are constructed so that adjacent blades rotate opposite to each other The damper rotation increases the resistance to the air flow since the air is funnelled through a smaller opening An opposed blade damper must be open further than a parallel damper to obtain the same resistance to air flow,常用风门,常用风门,The following diagram shows a basic parallel blade damper assembly together with the air flow pattern with the damper at 33% closed,常用风门,The following diagram shows a basic opposed blade damper assembly together with the air flow pattern with the damper at 33% closed,常用风门,Round or butterfly dampers are typically used to control air flows in ducts that have high static pressure and high velocity characteristics,常用风门,Fire dampers are used to prevent superheated air, gases or flames from crossing a fire barrier. They can be duct mounted or installed directly in a fire barrier They are always two position devices,通风机,离心式 前曲式 后曲式 径向式 轴流式,离心风机,CENTRIFUGAL FANS Found in supply air applications and quietly move air at moderate pressures Utilise VSD drives for capacity control Older installations may have fans with inlet guide vanes to vary air flow Almost always belt driven and not normally rated to operate in smoke extract applications CENTRIFUGAL FANS CAN HAVE EITHER :- Forward inclined blades Backward inclined blades,Centrifugal fans with forward inclined blades Used in the majority of HVAC installations as supply air fans Used from small domestic applications to large commercial applications in multi story buildings Centrifugal fans with backward inclined blades Generally larger and quieter in operation than forward inclined bladed fans Should always be used in variable volume systems More expensive to manufacture than forward inclined bladed fans and therefore contractors are reluctant to use them,离心风机,典型离心风机,A TYPICAL CENTRIFUGAL FAN WITH BACKWARD INCLINED BLADES IS DETAILED BELOW :-,AXIAL FANS Generally used for moving large volumes of air at low pressures Usually directly driven and may use vsd drives for capacity contriol Used in extract, return air, cooling tower and smoke control applications where high noise levels are not an issue THE MOST COMMON TYPE OF AXIAL FANS USED IN THE HVAC INDUSTRY ARE :- Propeller fan Tube axial fan Vane axial fan,轴流风机,Propeller Fans are low pressure high air flow units which work up to a maximum static pressure of 19 pa. Tube axial fans are heavy duty units arranged for installation in ducts. It work up to maximum static pressure of 750 pa. Vane axial fans are basically tube axial fans with straightening vanes and are quieter in operation than tube axial fans,轴流风机,CHARACTERISTICS OF AIR FLOW IN DUCTS A pressure difference (PD) must exist within the duct work to enable air flow to be transferred from the air handling unit fan to the field registers The PD required must be sufficient to overcome the frictional losses within the duct work and to accelerate the air flow to the required outlet operational velocity DUCT SYSTEMS HAVE A CERTAIN AMOUNT OF RESISTANCE TO THE FLOW OF AIR This is known as frictional loss and results from shear forces in the fluid near the duct wall Frictional loss causes a measurable loss of static pressure in the duct Frictional loss is proportional to velocity squared Double the flow rate and four times the pressure loss will occur,风管中气流的特性参数,The following fan affinity laws describe what happens to the flow rate, pressure and motor power when one parameter of a fan system changes,风管中气流的特性参数,A typical curve of air flow rate against static pressure in a duct is detailed below :-,风管中气流的特性参数,In HVAC systems the air supplied by the fan includes two types of pressure Velocity pressure Static pressure Velocity Pressure This is the pressure exerted by a moving fluid on an fluid on an object in the path and is kinetic energy. It is proportional to the flow or velocity squar