Optical sensor for continuous monitoring of dust deposition in HVAC systems

The aim of this thesis is to study the feasibility of an optical sensor able to continuously monitor the duct conditions and to reveal the dust accumulation levels in order to require their cleaning process when needed. Traditionally three main method has been used to sample and measure dust deposition: the vacuum method, the gravimetric tape method and the optical method. All this testing procedure requires the manual sample acquisition by the operator. Some new techniques start to be proposed based on both the direct measurement of the mass deposited on the duct and a new optical method. This device has been designed starting from a mechanical structure, to the hardware design and finally the firmware development. This device has been developed using a PIC micro-controller and is based on the acquisition of the residual light produced by an IR LED that reach a photodiode when dust is deposited between them. Different tools has been used during the development, production and testing phase. Some criticalities has been found during testing operations, when thinner materials used to test the acquisition values do not perfectly fit with the base of the device producing a noisy measurement result. With the detailed testing technique it is possible to clearly distinguish deposition that varies of 0.1 mm between every acquisition, with a maximum thickness ranges between 1.5 and 2 mm. The device must be tested in a real plant environment in order to better characterize its feature and correlate the dust deposition thickness with the correspondent weight, because the Italian law require to have a maximum of 1 g/m^2 of deposited dust. The possibility of apply this device on any wall of squared ducts and the added BLE communication module allows to install and monitor different points of the duct to continuously monitor their cleanliness. Finally it is provided of an RTC module that can be programmed to wake up in precise moment the device to perform acquisitions leaving always the micro-controller in SLEEP except during the acquisition phase ensuring a low power consumption.