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Dedicated electronic noses for enhanced performance of medium/large size air conditioning systems ('CLEANAIR')

Objective

Objectives: The attention towards the problems connected with the management of HVAC systems either in terms of IAQ or energy consumption has become more and more pronounced. The consciousness that the highlighted problems cannot be solved with the present available approaches has brought the CLEAN-AIR consortium to propose innovative solutions and new operating concepts.
The objectives of CLEAN-AIR proposal can be summarized in:
a) the development of a number of devices miniaturized in silicon (sensors, pre-combustion unit, gas separation column), whose ultimate performances can be improved by the miniaturization and by the integration on a common micro-fluidic platform;
b) a drastic improvement of the indoor/outdoor air quality status knowledge through the development of dedicated, miniaturized, low cost electronic noses realized using state-of-the-art microsystems/sensors fabrication technologies;
c) energy consumption reduction while insuring comfortable working/living places operating the HVAC facility taking into account
ì) the indoor/outdoor air quality status and
ii) operating the HVAC under demand and not on the base of a defined duty cycle. Scientific and technological achievements.
During the project duration the major achievements obtained are:
1. Accurate definition of the system specification and identification of set of gas compounds to be monitored for keeping trace of the air quality: For the indoor and outdoor air quality, IAQ & OAQ, current standard definitions along with the minimum and maximum pollutant concentrations have been reviewed and, whenever possible, improved;
2. Sensing material development and optimisation: The definition of a standard for IAQ & OAQ has allowed to better targeting the development of the sensing material (sensitivity, selectivity, minimum detectable concentration, etc). NO2 and CO concentrations well below the target values (100 ppb and 10 ppm, respectively) are currently detected and measured having enough sensitivity, selectivity and stability to ensure sensor operation longer than 6 months. To better diversify the sensor response, different sensor-operating modes were deeply investigated. This was made possible being the sensing element integrated in a low-power consumption micro machined substrate heater elements developed within this project. This activity leads to the disclosure of optimal operating conditions for the detection of the different compounds. Several difficulties were encountered trying to keep stable the sensor response to very low VOC concentrations, which were well detected by brand new sensors. However, the drift of the VOC sensors is still too high to allow a reliable usage in open air, as those for CO and NO2. Therefore, within the CA project, it was decided that the detection of NO2 and CO would be implemented with sensors in open air with a suitable set of math algorithms for pattern recognition. In parallel, for the detection of VOC a pneumatic motherboard integrating the GCC has been designed and fabricated.
3. Accurate definition of the operating condition for the detection of NO2 and CO down to very low concentrations in a test system simulating real world. The work carried out in this field has brought to the identification of optimised operating parameters for the sensors dedicated to the detection of these pollutants. Furthermore, the extended test performed has provided a significant amount of data for the development of the mathematical algorithms necessary to evaluate the concentration of the different pollutants present in the air.
4. Definition of the operating conditions for the detection of VOC using a gas-chromatographic approach. This activity became necessary since we observed a significant degradation of the sensors developed for this class of substances, which could not be overcome simply improving the performances of the sensors. However, operating these sensors together with a gas chromatographic column miniaturized in silicon under suitable operating conditions, sub-ppm concentrations of VOC were detected.
5. Development of a packed gas chromatographic column integrated in silicon to increase the selectivity of the sensors towards certain compounds, by separating them in time. The realization of these devices has brought to extended activities aiming to identify the suitable materials for the realization of the column, the suitable fabrication process, the suitable active phase to be used all together with metal oxide semiconductor gas sensors and the suitable operating conditions. In particular, to create circular shaped structures in silicon, necessary for the fabrication of the GCC device, a modified ASE process was developed at IMSAS. The spiral shaped column allows higher packaging than it can be obtained with a meander shaped configuration. Furthermore, an ad-hoc wafer bonding technique suitable to seal with a Pyrex wafer the column realized in silicon has been developed. All these information were used for the realization of the first prototypes of columns integrated in silicon. The test performed highlighted the possibility to detect and identify very low concentrations of VOC, down to few ppb in any gas mixture.
6. Development of a miniaturized pneumatic motherboard suitable to lodge the devices realized using a micro system approach and capable to perform specific tasks needed to detect the target gas species. This activity has brought to specific investigations aiming to identify those materials compatible with the application, innovative solutions for micro fluidic and electrical interconnectivity and for the packaging.
7. Development of suitable pattern recognition math algorithms, based on PCA/PLS, Fuzzy logic and peak detection approach, to evaluate the concentration of the different pollutants in the gas mixture. In spite of the effort done to increase the discrimination capabilities of the gas sensors developed within the project, metal oxide based devices needs post-signal treatments to identify and evaluate the different compounds in the gas mixture. The tools developed within the project have shown their capability to discriminate and to evaluate the concentration of CO and NO2 in air from the signal out from thin film gas sensors operated under suitable conditions. Furthermore, specific tools capable to identify and evaluate VOC out from a miniaturized gas chromatographic column detected with a thin film gas sensor were developed.
8. Development of a driving electronic prototype based on a microprocessor to control the EN. The main task of this electronics is to convert the chemical information coming from the sensors into usable output exchangeable with the air-conditioning management system. This task include the control of all the fluidic and selectivity functionality's within the EN, that is the control of the operating parameters of the sensors, the control of valves, gas chromatographic column and pre-combustion unit if needed. Finally, the µP systems perform an accurate measurement of the resistance change exhibited by the chemical sensor as well as data logging and data conversion communication toward the air-conditioning management system.
9. Development of a miniaturized analytical tool - electronic nose - to detect and monitor indoor and outdoor pollutant species (NO2, CO and VOC) realized with a micro systemic approach bringing together the different units (hardware and software) described so far. The test of the preliminary prototypes is in progress.
10. Development of the driving unit (hardware and software) for the heating venting air condition systems suitable to integrate a tool for air quality monitoring and to undertake specific actions on the basis of the information coming from the different electronic noses installed.
Results and exploitation plans:
Based on the planned activities and on the results obtained so far, several objectives of the Clean Air project were fulfilled and the proposed approach has been validated under controlled laboratory conditions. Despite those encouraging results, an important delay has been accumulated in several tasks. In particular, some devices were available only at the very last period of the project and the characterization of GCC, PCU and PMB prototypes was preliminary or it has been carried out on a subsystem of the final EN micro system, only. For these reasons, the in-field validation of the EN, the test of the final prototype together with the HVAC systems and the achievement of the objectives were not possible in the timeframe project. However, the collaboration between the partners is still ongoing because of the common interest in the exploitation of the results from both the scientific and the commercial point of view. In this view, an extension of the project duration would be necessary to fully accomplish the requirement of the project.

Call for proposal

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Coordinator

AERMEC SPA
EU contribution
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Address
Via Roma 44
37040 BEVILACQUA
Italy

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