Project
| # | Title | Team Members | TA | Documents | Sponsor |
|---|---|---|---|---|---|
| 32 | Carbon Control |
Mois Bourla Tanmay Goyal Vikram Belthur |
Daniel Ahn | design_document2.pdf final_paper1.pdf photo1.jpg photo2.jpg presentation1.pdf proposal1.pdf |
|
| # Carbon Control Team Members: Mois Bourla - bourla2 Vikram Belthur - belthur2 Tanmay Goyal - tanmayg2 # Problem Ventilation quality for indoor spaces is critically important but simultaneously very difficult to empirically gauge, especially under different occupancy conditions. A ventilation system may sufficiently ventilate a room occupied by a few people, but struggle to properly ventilate a space occupied by hundreds. Large spaces may also suffer from local hot zones, which may be locally under ventilated [1]. Poorly ventilated spaces can have negative effects on disease spread and cognition [2]. Given the importance of this problem, indoor CO2 concentrations have been used as a proxy for ventilation quality [3]. Human exhalation produces CO2 causing a rise in indoor concentration [4] [5]. Public health agencies recommend against high levels of CO2 in an indoor setting. Moreover, the indoor concentration of CO2 is also used as a diagnostic to assess the effectiveness of ventilation systems by measuring the decay rate of the concentration [3]. # Solution We propose developing a wireless CO2 sensing package that can be deployed in a scalable fashion to monitor CO2 concentrations and decay rates throughout a building. The decay rate is calculated by measuring the time constant of the concentration decay. This device will be able to monitor the concentration in real-time and report analytics. We envision two use cases this device will satisfy: 1. A real-time monitoring and alarm system that can alert occupants if the room is under-ventilated by virtue of being rich in CO2. This could be useful in a space with large gatherings, where organizers want to mitigate the risk of under ventilation. An even more novel use would be in a space that was previously occupied, but is now empty, seemingly safe, but with stale air. This system could be scaled to multiple devices in a large room to detect local spikes. We will have an audible alarm for extremely high concentrations, but also provide visual feedback by having a “traffic light” system to warn occupants (green, yellow, red) of rising concentrations. This can allow an organizer to implement mitigation measures during an event, such as opening a window or activating the HVAC system. 2. This package will also be WIFI enabled to expose a web interface that can be used by facilities management personnel to record and remotely monitor levels within a given room. The system can automatically calculate the decay rates using the CO2 produced while the room was occupied, if it knows when the room is occupied based on an occupancy sensor, obviating the need to set up a specific test. This is especially useful to track changes in ventilation in a space over time, which could occur if the HVAC system is operating under different regimes during different seasons. Moreover, the system would be able to report the decay rate, as a proxy for ventilation quality, at many different levels of CO2 build up, which is impractical to do with manual tests. This provides a thorough assessment of a space’s ventilation capabilities. # Solution Components ## Subsystem 1 - Microcontroller For this project, we will be using a microcontroller in the STM32 family. We will select the appropriate part based on power consumption and sufficient compute performance. Although we don’t believe this project requires significant computing resources, we want to ensure a responsive experience for our users. We also require sufficient GPIO for our connectivity and sensor needs. The MCU will read in sensor data through the applicable bus and perform analytics on the data including calculating the decay rate of the CO2. The MCU will manage the wifi user interface. We will also add flash storage to maintain at least 1 week's worth of data if the MCU’s built-in flash storage proves insufficient. ## Subsystem 2 - Sensor subsystem The CO2 sensors will be used to determine the concentration of CO2 in a given space. We are still deciding on what sensors to use, but they must have a reasonable response time (a time constant on the order of a few minutes) to detect transient effects and high accuracy (a sensing range between 300 ppm to at least 5000 ppm, and accuracy to within 10%). The sensing range is based on background atmospheric concentrations for the minimum and empirical results for peak concentrations in past spaces with an appropriate safety factor. The power consumption of the sensor is also key to satisfying our battery life needs. Some sensors we were considering were various models of the Sensirion SCD4x. We also plan on including an occupancy sensor in our system to detect whether the room is empty or not. This will allow us to automate our concentration decay testing, as we need to know whether a room has occupants which would invalidate the test. Sensirion SCD4x series: https://www.mouser.com/datasheet/2/682/Sensirion_CO2_Sensors_SCD42_Datasheet-2634346.pdf ## Subsystem 3 - Wireless Subsystem Our device will be WiFi-enabled and have a web-based user interface. We will have to have wireless internet connectivity for the STM32. There are many ways to approach this, but two notable ones are to (1) use a WiFi chip, such as the ESP8266 wifi, or (2) use an ESP32 as a WiFi co-processor. There are many options here, and we will require further research to arrive at a definitive solution. A possible feature we are exploring is if we can establish a mesh network between various units to cover a larger building without good connectivity. The exposed web-based UI will also allow facilities management to tag sensors that are monitoring the same room and synchronize alarms or fuse the sensor readings. ## Subsystem 4 - Power Delivery We want this device to be able to connect to either low voltage AC power (standard in thermostats) for permanent installations or receive battery power for at least 8 hours for mobile deployments, to be powered on for the entire workday. ## Subsystem 5 - Alarm and LEDs When the CO2 concentration in a space has far exceeded a safety threshold, then an alarm should sound through speakers. The device will also be equipped with red, yellow, and green LEDs to indicate safety levels based on CO2 concentration. In the event of a multi-zone configuration, the alarm should sound from all sensors to grab the occupant’s attention, but the triggering zone should blink its LEDs to indicate the problem area. # Criterion for Success - The device should be able to detect whether a room is empty and automatically collect CO2 decay data. - The device will be scaled into a multi-zone system for larger spaces, with inter-device communication. - The system should be able to connect to a wireless network and transfer data to a web-based user interface. The system will report recorded and live data, as well as analytics computed on the recorded data. - The system should be able to record CO2 concentrations and show a space’s safety level through a “traffic light” system LEDs, and if a room is very highly concentrated in CO2 an alarm should sound. - The system should be able to last for up to 8 hours on only battery power so that it is active for the entire workday. # Citations [1] https://www.sciencedirect.com/science/article/abs/pii/S0378778819305377 [2] https://www.dhs.wisconsin.gov/chemical/carbondioxide.htm [3]https://schools.forhealth.org/wp-content/uploads/sites/19/2020/08/Harvard-Healthy-Buildings-program-How-to-assess-classroom-ventilation-08-28-2020.pdf [4] https://www.airtesttechnologies.com/support/reference/paper1.pdf [5] https://www.health.state.mn.us/communities/environment/air/toxins/co2.html |
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