Novel Infiltration Diagnostics based on Laser-line Scanning and Infrared Temperature Field Imaging
This project targets the building energy efficiency problems induced by building infiltration/leaks. The current infiltration inspection techniques often require extensive visual inspection and/or whole building pressure test. These current techniques cannot meet more than three of the below five criteria of ideal infiltration diagnostics: 1. location and extent diagnostics, 2. building-level application, 3. least surface preparation, 4. weather-proof, and 5. non-disruption to building occupants. These techniques are either too expensive or time consuming, and often lack accuracy and repeatability. They are hardly applicable to facades/facades section. The goal of the project was to develop a novel infiltration diagnostics technology based on laser line-scanning and simultaneous infrared temperature imaging. A laboratory scale experimental setup was designed to mimic a model house of well-defined pressure difference below or above the outside pressure. Algorithms and Matlab-based programs had been developed for recognition of the hole location in infrared images. Our experiment based on laser wavelengths of 450 and 1550 nm and laser beam diameters of 4-25 mm showed that the location of the holes could be identified using laser heating; the diagnostic approach however could not readily distinguish between infiltration and non-infiltration points. To significantly improve the scanning throughput and recognition accuracy, a second approach was explored, developed, and extensively tested. It incorporates a liquid spray on the surface to induce extra phase change cooling effect. In this spray method, we termed it as PECIT (Phase-change Enhanced Cooling Infrared Thermography), phase-change enhanced cooling was used, which significantly amplifies the effect of air flow (infiltration and exfiltration). This heat transfer method worked extremely well to identify infiltration and exfiltration locations with high accuracy and increased throughput. The PECIT technique was systematically developed and tested for through holes with diameters 1 mm to 2 mm, and diagonal lines of 0.5 mm width at different camera-wall distances of 46 cm to 200 cm, under different pressure differences from 5 Pa to 20 Pa, and under different wind conditions. The PECIT technique had either met or exceeded the goals proposed in the project. For exfiltration, we achieved 100% accuracy under a much lower pressure difference of 10 Pa (proposed one: 50 Pa with stretch goal of 15 Pa). For infiltration, we achieved >90% accuracy under a much lower pressure difference of 10 Pa (proposed one: 50 Pa with stretch goal of 15Pa). For exfiltration, we achieved 100% accuracy under a much lower pressure difference of 10 Pa. For infiltration, we achieved 100% accuracy under a much lower pressure difference of 10 Pa. The PECIT technique can reach a throughput of 120 m2/h, which is 4 times the proposed goal for the laser line-scanning and simultaneous infrared temperature imaging approach. For commercialization and market penetration, we had meetings with two companies for feedback collection and further improvement for practical use. Also, we have interacted with Office of Intellectual Property and Technology Transfer of Iowa State University for idea disclosure and patent application.