A novel low pressure technique for measuring the air tightness of buildings.

近年来，英国通过《可持续住宅规范》和《建筑法规》的实质性改进，承认了建筑能效的重要性。由于英国的标准多年来一直相对较差，建筑物的外来渗漏受到了特别关注。现在，大多数新建筑都必须表现出令人满意的气密性，才能符合规定。建筑围护结构的密封性与空间空调的效率直接相关，而空间空调通常是主要的能源使用。因此，减少外泄可以显著降低能耗。目前用于确定是否符合规定的方法称为稳定加压技术。这项技术已经在全球使用多年，但也有一些不足之处，即测试大型建筑的难度和费用，风和浮力因素造成的不确定性，实验和测量误差造成的不确定性，以及无法在自然产生的压差范围内获得结果。诺丁汉大学正在开发一种新技术，它准确地关联了已知的体积脉冲在渗透压力下流过建筑围护结构，从而显著改进了当前的稳定技术。该技术的基本原理是使建筑围护结构在短时间内经历已知的体积变化(即1.5S)。这会产生流过不确定开口的流量，进而在内部压力中产生脉冲，这是建筑渗漏的特征。基本的脉搏概念以前曾被其他人尝试过，但以前从未被应用过。这一次取得成功的原因有三个关键的新奇特征。第一种是在脉冲之前和之后的短时间内测量建筑围护结构的压力差，从而在很大程度上消除风和浮力的影响。第二种方法是产生压力脉冲，以获得准稳定流动的周期，从而消除与非稳定流动相关的惯性效应。第三是尽量减少准稳定期间的压差变化，这样建筑围护结构的弯曲就不是问题了。准稳态期直接给出了低压下的泄漏特性，经过对静止空气条件的调整和对空气可压缩性产生的有效流量的微小修正后，它可以用与稳态法相同的方法来绘制。到目前为止，工作主要集中在使用活塞和气缸来产生体积脉冲。这很有效，但初步测试表明，使用喷嘴的更简单、更便携的设计也是可能的。拟议项目的第一个目标将是进一步研究活塞技术，因为仍需要对具体因素进行测试和分析，以消除不确定性。第二个目标是探索喷嘴脉冲技术的概念。这是最有潜力作为低压泄漏测试仪进行市场推广的，因为它将使系统更加紧凑和便携，从而节省运输成本和空间。然而，到目前为止，还不可能准确地测量音量的变化。它的目的是对如何做到这一点进行理论研究，然后，如果理论表明这是可能的，则进行实验测试。对泄漏测量的需求增加，加上传统方法的缺陷，意味着确实需要所描述的技术。这项技术将比传统的方法更快、更便宜、更便携、更准确。因此，潜在的受益者将是监管机构、建筑商/开发商和渗漏检测公司。

The importance of energy efficiency of buildings has been acknowledged in the UK in recent years by the Code for Sustainable Homes and substantial improvements to the Building Regulations. The adventitious leakage of buildings has received particular attention as standards in the UK have for many years been relatively poor. Most new buildings now have to show satisfactory levels of airtightness to comply with the Regulations. The airtightness of a building envelope is allied directly to the efficiency of the space conditioning, which is typically the main energy use. Therefore, reducing adventitious leakage can make a significant reduction in energy consumption. The method used presently to ascertain compliance with the Regulations is called the steady pressurisation technique. This technique has been used globally for many years, but does have a number of deficiencies; namely the difficulty and expense of testing large buildings, uncertainties due to wind and buoyancy factors, uncertainties due to experimental and measurement errors, and its inability to obtain results in the range of naturally occurring pressure differences.A novel technique is being developed at the University of Nottingham which accurately relates a known volume pulse to flow through the building envelope at pressures typically found in infiltration, hence significantly improving on the current steady technique. The underlying principle of the technique is to subject the building envelope to a known volume change in a short period of time (i.e. 1.5 s). This generates a flow rate through the adventitious openings that in turn creates a pulse in the internal pressure, characteristic of the building's leakage. The basic pulse concept has been tried previously by others, but has never before been made to work. There are three key novel features that have led to its success this time. The first is to measure the pressure difference across the building envelope a short time before and after the pulse, thereby allowing wind and buoyancy effects to be largely eliminated. The second is to generate a pressure pulse in such a way that a period of quasi-steady flow is obtained, thereby eliminating inertia effects associated with unsteady flow. The third is to minimise the variation of the pressure difference during the quasi-steady period such that flexing of the building envelope is not a problem. The quasi-steady period gives directly the leakage characteristic at low pressure and after adjustment to still air conditions and a small correction for the effective flow rate arising from compressibility of the air it can be plotted in the same way as the steady technique. Work to date has focused primarily on using a piston and cylinder to generate the volume pulse. This has worked well but preliminary tests have shown that a simpler, more portable design using a nozzle may also be possible. The first aim of the proposed project will be to research the piston technique further, as testing and analysis of specific factors is still needed to remove uncertainties. The second aim will be to explore the concept of a nozzle pulse technique. This has the most potential for marketing as a low pressure leakage tester, as it would make the system even more compact and portable, hence saving transport costs and space. To date, however, it has not been possible to measure the volume change accurately. It is intended to conduct a theoretical investigation of how this may be done and then, if the theory suggests it is possible, test it experimentally. The increased demand for leakage measurement coupled with the deficiencies of the conventional method means there is a genuine need for the described technique. The technique will be quicker, cheaper, more portable and more accurate than the conventional method. As such, the potential beneficiaries will be regulators, builders/developers, and leakage testing companies.