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

近年来，英国通过《可持续住宅守则》和对《建筑法规》的重大改进，认识到建筑物能源效率的重要性。由于多年来英国的标准相对较差，建筑物的偶然渗漏受到特别关注。现时，大部分新建筑物均须达到令人满意的气密程度，才能符合规例的规定。建筑围护结构的气密性直接关系到空间调节的效率，这通常是主要的能源使用。因此，减少偶然泄漏可以显著降低能耗。目前用来确定是否符合《规章》的方法称为稳定加压技术。这项技术已在全球使用多年，但确实存在一些缺陷;即测试大型建筑物的难度和费用，由于风和浮力因素引起的不确定性，由于实验和测量误差引起的不确定性，诺丁汉大学正在开发一种新的技术，该技术准确地将已知的体积脉动以在渗透中通常发现的压力下流过建筑物外壳，因此显著改进了当前的稳定技术。该技术的基本原理是使建筑物外壳在短时间内（即1.5秒）发生已知的体积变化。这产生了通过偶然开口的流速，这反过来又产生了内部压力的脉冲，这是建筑物泄漏的特征。基本的脉冲概念以前曾被其他人尝试过，但从未被付诸实践。有三个关键的新颖特征导致了它这次的成功。第一种是在脉冲前后短时间内测量建筑物围护结构的压差，从而在很大程度上消除风和浮力的影响。第二种方法是产生一个压力脉冲，以便获得一个准稳定流动周期，从而消除与非稳定流动相关的惯性效应。第三个是在准稳定期间最小化压差的变化，使得建筑物外壳的弯曲不是问题。准稳定期直接给出低压下的泄漏特性，在调整到静止空气条件和对空气压缩性引起的有效流速进行小的校正后，可以用与稳定技术相同的方式绘制准稳定期。迄今为止的工作主要集中在使用活塞和气缸来产生容积脉冲。这种方法效果很好，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。该项目的首要目标是进一步研究活塞技术，因为仍需要对特定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。这最有可能作为低压泄漏测试仪销售，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，迄今为止，还不可能准确地测量体积变化。它的目的是进行一个理论研究，如何可以做到这一点，然后，如果理论表明这是可能的，测试它的实验。对泄漏测量的增加的需求加上传统方法的缺陷意味着对所描述的技术存在真正的需求。该技术将比传统方法更快，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/开发商和泄漏测试公司。

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.