ASHRAE OR-05-13-1-2005 Detecting Critical Supply Duct Pressure《供应管道压力的关键检测》.pdf
《ASHRAE OR-05-13-1-2005 Detecting Critical Supply Duct Pressure《供应管道压力的关键检测》.pdf》由会员分享,可在线阅读,更多相关《ASHRAE OR-05-13-1-2005 Detecting Critical Supply Duct Pressure《供应管道压力的关键检测》.pdf(7页珍藏版)》请在麦多课文档分享上搜索。
1、OR-05-1 3-1 Detecting Critical Supply Duct Pressure Clifford C. Federspiel, PhD Associate Member ASHRAE ABSTRACT Fan energy use in variable-air-volume (VAV) systems can be reduced by resetting the supply ductpressure. The standard way to reset ductpressure is by controlling the most open termi- nal
2、damper to a nearly open position. This strategu is rarely used because of a variety of issues including sensing limita- tions, network bandwidth, and stability This paper describes the development of a new method of determining the critical supply ductpressure for VAV systems. The method relies on a
3、 short, simple functional test and a data processing technique that is based on a simple model of the system behaviol: The method can be implemented during normal system operation, and it could be automated. Thesystem model includes the eflect of duct leakage, which ofers thepotential for dual use a
4、s a duct leakage diagnostic. Results from experiments on a laboratory- scale system demonstrate good accuracy for determining crit- ical pressure and moderate accuracy for determining duct leakage. Results from experiments on two commercial air- handling units demonstrate that the method is practica
5、l and that it ofers the potential for large energy savings. INTRODUCTION Every year the US consumes 0.75 quadrillion Btus of primary energy to move air in buildings (DOE 2000). This paper describes technology to reduce that energy consump- tion. The focus is on variable-air-volume (VAV) heating, ven
6、tilating, and air-conditioning (HVAC) systems, which condition 29% of the floor space in commercial buildings (EIA 1999). The standard way to control VAV fan systems is to regu- late the static pressure in the main supply duct. This strategy ensures that zone terminals have enough pressure to operat
7、e properly, but it is inefficient because the pressure setpoint will be higher than necessary all of the time. Considerable energy savings can be achieved if the supply duct pressure is reduced at part load. Lorenzetti and Norford (1994) showed that fan energy consumption in VAV HVAC systems could b
8、e reduced by 19% to 42% with static pressure reset (SPR). They also showed that SPR results in a 20% lower pressure at design load conditions. Federspiel (2003) found that reducing the pressure in response to reduced supply airflow could reduce fan power consumption by 26% and cooling power by 17% (
9、due to reduced leakage). This strategy is called static pressure adjust- ment from volume flow (SAV). The standard way to reset the pressure is to use a feedback loop that regulates the most open terminal damper to a nearly open position (e.g., 90% open) by adjusting the static pressure setpoint. Th
10、ere are a number of variants of this method. Static pressure reset (SPR) has been in existence for more than 15 years, and it is now required by ASHRAE Standard 90.1 when the VAV terminals have digital controls, but it is still not widely used. SPR is not widely used for the following reasons: 1. SP
11、R requires a networked digital control system. 2. SPR requires digital controls on zone terminal units. 3. Some SPR strategies require terminal damper position sensors. 4. SPR adds to the complexity of control software. 5. SPR strategies that use feedback are difficult to tune. Even today, many new
12、systems do not have digital termi- nal controls, and it is very uncommon for terminals to have position sensors on the terminal dampers. However, in legacy systems, it is much less common for systems to meet the control and sensing infrastructure requirements of standard Clifford Federspiel is princ
13、ipal at Federspiel Controls, LLC, El Cerrito, Calif. 02005 ASHRAE. 957 SPR strategies. Engineers have solved this problem by invent- ing ad hoc resetting strategies that reset static pressure based on some measurable quantity that is related to the load. For example, static pressure may be reset bas
14、ed on time, outdoor temperature, flow, or a combination of these. Ad hoc resetting has the advantage of not requiring digital terminal controls. They also cannot destabilize the static pressure loop because they do not involve feedback. However, they must still be configured, and there is no way to
15、do this today except through trial and error or good engineering judgment. This paper involved the development of a technique that can be used to configure ad hoc SPR strategies so that they yield nearly optimal performance. We developed a new method of determining the critical supply duct pressure
16、for VAV systems. The new method only requires measurement of supply duct static pressure and supply airflow rate. It relies on a short, simple functional test and a simple model of the system behavior. This functional test could be implemented during normal system operation, and it could be automate
17、d. The system model includes the effect of duct leakage, which offers the potential for dual use as a duct leakage diagnostic. This is important because duct leakage is a significant contrib- utor to inefficiency of air-handling equipment. Xu et al. (2002) found that the air leakage ratios in five l
18、arge HVAC systems were as high as one-third of the fan-supplied airflow. Results from experiments on a laboratory-scale system demonstrate 6. (“mi Skew - q2 go o3 ZJ 05 -a -J(Ji n a- good accuracy for determining critical pressure and moderate accuracy for determining duct leakage. Results from expe
19、ri- ments on two working VAV air-handling units demonstrate the potential for energy savings. The functional test and the corre- sponding analytical method for determining critical pressure and leakage are called “infer critical information about termi- nals (InCITE). InCITE can form the basis for c
20、onfiguring ad hoc SPR strategies so that they deliver nearly optimal perfor- mance. METHODS Test Stand We designed and constructed a test stand that has a vari- able-speed fan and a main duct supplying four VAV terminals. Each terminal duct terminated with a commonly used diffuser. We designed the m
21、ain supply duct so that we could introduce a pressure drop between the terminal duct branch points that emulated the frictional and minor losses in a long duct without actually requiring a long duct. The test stand included a computer-based data acquisition system, a pitot tube array to measure supp
22、ly airflow, and a supply duct pressure sensor. Figure 1 shows a schematic diagram ofthe test stand duct- work downstream of the supply fan. The fan is powered by a 3 hp (2.25 kW), three-phase motor. The motor is driven by a three-phase inverter so that the speed can be adjusted contin- I I Note: Rou
23、nd duck are located ai the veftical centerline of ihe main duct sections. I section 10. (25 4cm) sleeve 10 (25 4 Cm) VAV box x Figure 1 A schematic of the test stand ductwork downstream of the supply fan. 958 LZ cm) deve w(rn.3cm VAV bol ASHRAE Transactions: Symposia uously. The duct upstream of the
24、 supply fan is 15 by 15 in. (38.1 by 38.1 cm), and it contains the pitot tube array used to measure supply flow. We placed screens covered with strips of tape in the main supply duct between each terminal duct branch. The tape was applied to achieve pressure drops comparable to a system with a much
- 1.请仔细阅读文档,确保文档完整性,对于不预览、不比对内容而直接下载带来的问题本站不予受理。
- 2.下载的文档,不会出现我们的网址水印。
- 3、该文档所得收入(下载+内容+预览)归上传者、原创作者;如果您是本文档原作者,请点此认领!既往收益都归您。
下载文档到电脑,查找使用更方便
10000 积分 0人已下载
下载 | 加入VIP,交流精品资源 |
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- ASHRAEOR051312005DETECTINGCRITICALSUPPLYDUCTPRESSURE 供应 管道 压力 关键 检测 PDF
链接地址:http://www.mydoc123.com/p-455603.html