thermography

The acquisition of temperatures and velocities is a permanent recurrent task for the investigation of air flow in ventilated rooms. On the one hand it is important to measure the temperature and velocity field with a high spatial resolution. On the other hand, in general, varying outdoor conditions prevent from reaching a steady state and an additonal demand consists in short measuring times. Sometimes, the obtained measuring results are used both to supply appropriate boundary conditions for numerical computations and to verify the CFD-codes used.

Preliminary work has indicated that thermography can be used to determine air leakage pathways from or to buildings. Accurate measurements have now been taken using temperature controllable environmental chambers.These results reinforce the potential useof thermography for this application. In conjunction with the physical measurements a simulation has been carried out using computational fluid dynamics.

It has been shown that thermal imaging can give an indication of air flow rates through small cracks. Using a finite difference analysis package it is possible to determine the surface temperature of an air transfer grille when subjected to airflow rates at higher temperatures than the grille surface. This paper will address this technique by presenting the results of the finite difference analysis package for a specific grille.

This BRE Report gives a guide to the use of infra-red thermography as a means to investigate the thermal properties and hidden constructional details of building envelopes. An introduction is given to infra-red thermography, the operation of the camera and the difference between photography and electronic thermography. The guide describes the aims and requirements for carrying out an infra-red survey and discusses thermal analysis and application of the results.

The heat loss associated with the external fabric of a building has been greatly reduced by the increased levels of modem insulation, but heating losses associated with cold external air flowing into a building via leakage points in the external facade are still a major problem. Some ventilation is necessary but a detailed knowledge of this leakage would enable the major heat loss routes to be blocked. A crack has been studied which has hot air of a known temperature and flowrate passing over it.

Modern one-family houses in Scandinavia are often ventilated by an exhaust fan. Most of the outdoor air probably enters through whatever cracks and openings there are and only a small part enters through the supply vents in many of these houses. The overall supply of outdoor air might be adequate, but some rooms often do not get enough of outdoor air. The constant concentration tracer gas technique was used to examine the supply of outdoor air. Fan pressurization combined with infrared photography were employed to characterize the air leakage of the building.