Measurement of indoor climate using acoustic travel-time tomography

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The two main criteria determining thermal comfort of occupants are the air temperature and the airflow velocity. To monitor these parameters, in-situ sensors are usually mounted in the indoor environment. One of the drawbacks of this conventional method is the measurement at a certain location instead of the distribution of target parameters in the whole room including the occupant zone. Moreover, mounting multiple sensors directly in the measurement environment (e.g., airflow sensors) is problematic due to their interference effect on the measured parameters itself. Acoustic travel-time tomography (ATOM) technique as a remote sensing method is a solution to overcome the mentioned shortcoming of traditional sensors. ATOM utilizes the dependency of the sound velocity on the air temperature and flow velocity in the medium. The average sound velocity, along propagation paths, is determined by travel-time estimation of a defined acoustic signal between transducers. This detected sound velocity can be converted into spatially distributed air temperature and airflow velocity by using a proper tomographic algorithm. The primary goal of the project is to develop a measurement system for calculating both room air temperature and airflow velocity distribution based on the ATOM method. Over the course of studies conducted in the climate chamber of the BUW, a three-dimensional representation of the air temperature distribution was successfully measured by placing a transmitter and a receiver at optimal positions. The extension of the method to include the airflow velocity measurement in parallel to the air temperature is one of the tasks of this project. Furthermore, the measuring system will be developed for an occupied room condition considering an actual workplace. With the aim of resolution enhancement, several tasks are defined in terms of numerical methods and practical measurements. To draw conclusions about the measurement accuracy, required comparative measurements will be conducted under different climatic conditions.