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SMART HVAC SYSTEMS
The infrastructure of the future, smart buildings, are automated buildings that have interconnected HVAC, electrical, lighting, and other components. The overarching goal being to maximize safety, comfort, and efficiency. Smart HVAC systems within the building are extremely important components that have superior temperature control, energy efficiency, humidity control, CO2 monitoring and even infection control capabilities. In tomorrow’s world, Smart HVAC systems will be essential in improving energy efficiency and public health.
BACKGROUND
There is a need to actively measure, model and predict mass (air with particulates) flow in large buildings such as Atkinson Hall at the University of California, San Diego. Such a system can aid in controlling flow that produces desired environmental conditions and/or reduces the transport of unwanted harmful particles such as viruses. There are software tools from the National Institute of Standards and Technology (NIST), such as FATIMA and CONTAM, that allow us to simulate fairly realistic models that incorporate HVAC elements including supply and return ducts, infiltration, exfiltration, particle generators and the actual geometry of the space. These tools then predict the likelihood of transmission of particulate matter through the HVAC system. It is also possible to model many of these elements with common circuit components: resistors, capacitors, inductors, etc. With an electrical analogy of each part in an HVAC system, the whole system can be modeled as a circuit. Then, if we wanted to calculate the airflow at different locations of the building, for example, we could use one of the above programs to calculate the flow at these different locations instead of having to solve the Navier-Stokes equations.
Atkinson Hall
CONTAM simulation
An example sensor array. Shown above is a microcontroller connected to various CO2 and particulate sensors which would be placed around a room. Bluetooth modules could be utilized for long distance monitoring.
PROJECT OBJECTIVE
The goal of this project is to build an HVAC modeling and measurement system for Atkinson Hall. Useful as simulations can be, their ability to track the transport of aerosols will require careful validation. For this reason, this project will focus on developing low cost, networked probe stations that can measure airflow and other environmental parameters such as temperature, CO2 levels, relative humidity and particulate counts, that are designed for monitoring HVAC systems. With the advent of networked Internet of Things (IoT) devices, it is likely that one can develop and deploy a dense array of such sensors to get a much more accurate understanding of air flow and transport of particulate material in a building. This will enable establishment of new HVAC controls and settings to not only address energy efficiency but also infection control.
FINAL DESIGN
Our final design consists of a single Arduino Mega 2560 microcontroller connected to multiple SCD30 CO2 sensors with help from an Adafruit TCA9548A I2C Multiplexer. Various rooms have various shapes, so our final design keeps modularity in mind. By adding more Microcontrollers, our sensors are able to cover separate areas of a room at the same time. By utilizing long jumper cables, each microcontroller is able to cover a larger space. With this open design, we are able to measure and collect data on critical areas in a room no matter their location.
Picture of the completed array. In this configuration, all CO2 sensors are connected to one microcontroller, this allows for higher density measurement.
EXPERIMENTATION
Our first CO2 experimental setup. This setup tested CO2 sensor displacement from a source to test the feasibility of the Sensirion SCD30 environmental sensors.
The box test was designed to test the CO2 canisters volumetric flow rate in an environment with negligible turbulence and mixing. The CO2 source on the left was attached to a reinforced cardboard box that was sealed to the ground.
Above is the gas canister valve used to regulate the flow of CO2 inside of a room. Set to .5 LPM, it mimics the breath of 2 humans.
Shown are all of the components of our experimental setup. Below our CO2 canister with connected regulator valve is the completed CO2 sensor array connected to the microcontroller and is actively running.
Shown above is our experimental setup to determine the effect of gravity on CO2 as it emanates from our canister. Unlike human breath, which tends to stick around in the air, CO2 falls quickly to the ground.
There are many unique applications of our system as exhibited above. Here we integrated a system of five CO2 sensors into a vehicle to test (1) internal CO2 generation by cabin occupants with ventilation recirculation on and off, and (2) test the quantity of CO2 that infiltrates the cabin from outside the vehicle.
Above is a different experiment testing the radial emission of our CO2 canister. CO2 sensors are placed radially to examine the dispersion angle of our CO2 sensor.
Circuit schematic of sensor array via circuitlab.com
VEHICLE ENVIRONMENTAL CONDITIONS EXPERIMENT
To measure CO2 and particulate matter at different ventilation configurations inside of a car, CO2 and PM sensors were evenly distributed while 2 participants drove on the highway.
With aid from our long jumper cables, CO2 and particulate sensors were able to be placed in a myriad of locations.
Sensors were placed at the headrest of the passenger and driver-side seats to get an accurate reading of what two passengers might be directly exhaling.
Old Town, San Diego, CA
Imperial Beach, San Diego, CA
The route taken to conduct the experiment was from Old Town, San Diego to Imperial Beach Primarily following the Interstate 5.
With Recirculation on, the results showed that CO2 concentrations reached as high as 3000 PPM within 20 minutes. This was notable in that both participants felt uneasy and experienced headaches by the end of the experiment.
With recirculation off but windows up, the concentrations did not surpass 800 PPM. This would arguably be the ideal condition for riding in a vehicle provided that the outdoor air quality is not substandard.
With windows down, you can see slight spikes in CO2 when moderate traffic was experienced. Further testing is recommended in order to document spikes in CO2 concentrations due to surrounding vehicles.
Executive Summary
Pitch Deck
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