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中央空调是大厦里的耗电大户,每年的电费中空调耗电占60%左右,因此中央空调的节能改造显得尤为重要。 由于设计时,中央空调系统必须按天气最热、负荷最大时设计,并且留10-20%设计余量。但实际上绝大部分时间空调是不会运行在满负荷状态下的,存在较大的富余。中央空调系统冷冻主机可以根据负载变化随之加载或减载,冷冻水泵和冷却水泵却不能随负载变化做出相应调节,存在很大的浪费。所以节能的潜力就较大。

节能方案

中央空调系统通常分为冷冻(媒)水和冷却水两个系统(左半部分为冷冻(媒)水系统,右半部分为冷却水系统)。根据国内外最新资料介绍,并多处通过对在中央空调水泵系统进行闭环控制改造的成功范例进行考察,现在水泵系统节能改造的方案大都采用变频器来实现。

水泵系统的流量与压差是靠阀门和旁通调节来完成,因此,不可避免地存在较大截流损失和大流量、高压力、低温差的现象,不仅大量浪费电能,而且还造成中央空调最末端达不到合理效果的情况。为了解决这些问题需使水泵随着负载的变化调节水流量并关闭旁通。

再因水泵采用的是Y—△起动方式,电机的起动电流均为其额定心流的3~4倍, 一台90KW的电动机其起动电流将达到500A,在如此大的电流冲击下,接触器、电机的使用寿命大大下降,同时,起动时的机械冲及和停泵时水垂现象,容易对机械散件、轴承、阀门、管道等造成破坏,增加维修工作量和备品、备件费用。

综上,为了节约能源和费用,需对水泵系统进行改造,采用风机、泵类专用变频器,以便达到节能和延长电机、接触器及机械散件、轴承、阀门、管道的使用寿命。这是因为变频器能根据冷冻水泵和冷却水泵负载变化随之调整水泵电机的转速,在满足中央空调系统正常工作的情况下使冷冻水泵和冷却水泵做出相应调节,以达到节能目的。水泵电机转速下降,电机从电网吸收的电能就会大大减少。

减少的功耗△P=PO(1—(N1/N0)^3) (1)式

减少的流量△Q=Q0(1-(N1/N0)) (2)式

其中N1为改变后的转速,N0为电机原来的转速,P0为原电机转速下的电机消耗功率,Q0为原电机转速下所产生的水泵流量。由上式可以看出流量的减少与转速减少的一次方成正比,但功耗的减少却与转速减少的三次方成正比。如:假设原流量为100个单位,耗能也为100个单位,如果转速降低10个单位,由(2)式△Q=Q0〔1-(N1/N0)〕=100*〔1—(90/100)〕=10可得出流量改变了10个单位,但功耗由(1)式△P=P0[1-(N1/N0)^3]=100×(1—(90/100)^3)=27.1可以得出,功率将减少27.1个单位,即比原来减少27.1%。再因变频器是软启动方式,采用变频器控制电机后,电机在起动时及运转

过程中均无冲击电流,而冲击电流是影响接触器、电机使用寿命最主要、最直接的因素,同时采用变频器控制电机后还可避免水垂现象,因此可大大延长电机、接触器及机械散件,轴承、阀门、管道的使用寿命。

空调系统的变频节电原理:

·风机、冷却水泵、冷冻泵电机消耗的电功率与频率的三次方成正例

·在能保证负荷驱动的情况下, 降低电机的工作频率, 可有效节能

·节能效果约为1 - fr3/503 (fr为电机实际工作频率), 在45Hz时, 节能效果可达到 27.1%.

·压缩机的变频节能改造有一定的技术难度, 通常不对其进行变频调速改造

·在保证机房设备运行温度范围内, 可降低或提高空调的设定温度(如冬季设定温度为19度, 夏季设定为24度), 节能10~15%/2度温度差, 最好自动控制, 以达最佳节能效果

·室外温度与室内温度平衡时, 停止压缩机, 降低空调系统的功率消耗, 平均节能可达到20%左右.

空调系统变频控温系统原理:冷却泵、冷冻泵及塔顶风机系统原理特点:

·节能效果取决于环境温度与设定温度之差, 电机工作在最佳节能状态

·输入输出具有滤波装置, 可有效抑制对电网的传导干扰

·整套控制装置放置在屏蔽机柜或机箱中, 电磁辐射干扰小

·安装施工简单, 改造周期短, 维护方便

·具有故障状态自动切换回原控制系统功能, 不影响正常使用

·零力矩启动, 减少能耗, 降低对电网的冲击和干扰

·不需频繁启动, 有利于延长设备寿命

·可根据室外、室内温度, 自动调节压缩机组的温度设定, 使之处于最大节能状态

·能远程监控

一拖N变频方案

若干台冷冻泵由一台变频器控制,若干台冷却泵由另外一台变频器控制.各台泵间的切换方法如下:

(1)先激活1号泵,进行恒温度(差)控制;

(2)当1号泵的工作频率上升至50Hz时,将它切换至工频电源;同时将变频器的给定频率迅速降到0Hz,使2号泵与变频器相接,并开始激活,进行恒温度(差)控制;

(3)以下类似.当N号泵的工作频率下降至设定的下限切换频率时,则将1号泵停机;当N号泵的工作频率再次下降至设定的下限切换频率时,则再次将2号泵停机;以此类推.这是只有N号泵处于变频调速状态. 这种方案的主要优点是只用一台变频器,设备投资较少;缺点是节能效果稍差.

一拖一全变频方案

所有的冷冻泵和冷却泵都采用变频调速.其切换方法如下:

(1)先激活1号泵,进行恒温度(差)控制;

(2)当工作频率上升至设定的切换频率上限值(通常可以小于50Hz)时,激活2号泵,1号泵和2号泵同时进行变频调速.实现恒温度(差)控制;

(3)当工作频率又上升至切换频率时,激活3号泵,三台泵同时进行变频调速,实现恒温度(差)控制;

(4)当三台泵同时运行,而工作频率下降至设定的下限切换频率时,可关闭1号泵,系统进入同时控制两台的状态;

(5)当两台泵同时运行,而工作频率再次下降至设定的下限切换频率时,再关闭2号泵,系统进入单台运行的状态; 全变频调速系统由于每台都要配置变频器,故设备投资较高,但节能效果却要好得多.

两种方案的比较

假设某单位有两台水泵供水,每台泵的电动机容量是Pn=100Kw,每台泵全速时的供水流量为Qn,所需供水压力为Pa, 每天的平均流量为Qa=150%Qn. 每台泵的空载损耗约为Po=15%Pn=0.15*100Kw=15Kw.在低频低速时,空载损耗因铁损和机械损耗有所减少而减少,由于所占的比例较小,可粗略的认为Po=const.所以全速时实际的用于水泵的功率为Pp=Pn-Po=85Kw.

(1) 一拖N变频方案:

1号泵由变频启动, 接近50Hz时, 转由工频电源供电, 处于全速运行状态,提供流量为Qn; 2号泵由变频器供电,只需提供50%Qn的流量;

P=(85+15)Kw+(85*0.53+15)Kw=126Kw

(2)全变频方案 1号泵和2号泵都由变频器供电, 各提供75%Qn的流量, 两台电动机的转速都按0.75Nn(Fx=37.5Hz)计.

P=(85*0.75*0.75*0.75+15)Kw*2=102Kw

空调系统的节电投资回收分析:

·4万门交换局交换机房及办公楼, 每套100kW中央空调系统年耗电费(半年有效使用) 26 万元计算

·节能达20%, 每年节约电费 5.2 万元

·改造一套空调系统投资 8 万元

·收回投资的时间约为 1.5 年

·按空调使用寿命10年计,总节约电费 5.2 x 10 = 52 万元。


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KoldaktFG 新手上路 发表于 2019-1-3 05:28:16 | 显示全部楼层
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