Abstract

Ductwork airtightness test protocols implicitly assume that the pressure across the leaks is identical for all leaks. In fact, the pressure difference at the leaks decreases in absolute value as the distance from the moving air increases, due to friction and dynamic losses. This paper aims to quantify the impact of these pressure losses on airtightness test results, and thereby the measurement error generated by the constant pressure assumption. To this end, we developed an analytical model and performed measurements on an experimental set-up that reproduces residential ductwork at 1:1 scale with dynamic losses that can be modified using dampers. We compared the results obtained using the analytical model and the experimental set-up. The analytical model makes it possible to calculate the maximum “test length” for which the error due to pressure drop remains below 5%. According to this model, the impact of pressure losses on the measured flow rate is very small for airtight ductwork (Class C). In this case, the model shows that a length of 260 m between the measuring device and the far end of the ductwork can be tested at one time, even if the ductwork is quite narrow (average diameter of 200 mm) and the test pressure very high (1000 Pa). However, when testing very leaky ductwork (3*Class A) with an average diameter of 400 mm and a test pressure of 200 Pa, the distance between the measuring device and the far end of the ductwork must be no more than 67 m to limit the error to less than 5%. This model can be used to produce charts giving the maximum length to be tested as a function of the pressure drop and the expected ductwork airtightness class.

摘要

管道系统气密性测试协议隐含地假设所有泄漏的泄漏压力都是相同的。事实上，由于摩擦和动力损失，泄漏处的压差随着与移动空气距离的增加而绝对值减小。本文旨在量化这些压力损失对气密性测试结果的影响，从而量化恒压假设产生的测量误差。为此，我们开发了一个分析模型并在一个实验装置上进行了测量，该装置以 1:1 的比例再现住宅管道系统，动态损失可以使用阻尼器进行修改。我们比较了使用分析模型和实验装置获得的结果。分析模型可以计算最大“测试长度”，此时压降误差保持在 5% 以下。根据该模型，对于密闭管道系统（C 级），压力损失对测量流量的影响非常小。在这种情况下，模型显示测量设备和管道系统远端之间 260 m 的长度可以一次测试，即使管道系统非常窄（平均直径为 200 毫米）并且测试压力非常大高（1000 帕）。但是，在测试平均直径为 400 mm 且测试压力为 200 Pa 的非常泄漏的管道系统（3*A 级）时，测量装置与管道系统远端之间的距离必须不超过 67 m，以限制误差小于5%。