Environmental Concerns Force Change in Refrigerants—And Chemical Sensors


Chemical detection, like many other areas of electronic design, evolves rapidly. Not only do applications change as they run the gamut from HVAC to industrial facility safety monitoring, but the types of chemicals they measure must adapt as regulations change over time. 

Recently, NevadaNano announced its latest solution for propane detection for air conditioning, vending machines, clothes dryers, and commercial refrigeration racks. Let’s take a look at how this device and this company provide examples of how chemical sensors are changing over time.

 

NevadaNano’s R-290 sensor can be implemented in various propane applications; air conditioning, vending machines, commercial refrigeration racks, and clothes dryers. Image used courtesy of NevadaNano Systems, Inc.

 

Adapting to New Refrigerant Standards

Traditional refrigerants such as chlorofluorocarbons (CFCs) GWP or global warming potential is a measurement used by international institutions such as the US Environmental Protection Agency (EPA) to assess the impact of materials on global warming. According to the EPA, “Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs)… are sometimes called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO2.” 

Senior Director of Business Development, NevadaNano Systems, Bob Christensen stated, “Nearly 200 countries around the world have resolved to eliminate ozone-depleting hydrofluorocarbons refrigerants with high Global Warming Potential.”

As such, new alternatives with lower GWP are being pursued, including R-290 propane. R-290’s GWP is cited by NevadaNano as being 3. Compare this to the thousands or tens of thousands averaged by CFCs and other such refrigerants.  In the press release for this sensor, NevadaNano specifically called out R410, a hydro-fluorocarbon (HFC) that is competing with R-290 as a viable replacement for the R-22 refrigerant now banned per the Montreal Protocol, which has a GWP of 3,900.

The tradeoff with R-290 is that fully sealed containers of propane occasionally spring a leak, providing a potential ignition opportunity. Some leaks may not be massively dangerous, but even the smallest amount of leaking propane could reduce the levels of refrigerants, causing HVAC units to work harder. A system that works harder consumes excessive electrical power, driving up costs and also increasing impact on the environment.

NevadaNano asserts that the R-290 is a suitable alternative refrigerant and presents its most recent sensor as an accurate way to address leak detection for safer implementation.

 

Integrating Molecular Property Spectrometry into Sensors

MPS is a proprietary term that stands for molecular property spectrometer. NevadaNano describes MPS as their effort to integrate multiple complementary chemical sensors on a single silicon chip.

One of the benefits of its MEMS (microelectromechanical systems) design is that the sensor’s IC avoids the need for maintenance over its entire lifetime of 10-15 years. Over this time, NevadaNano reports that the device accurately reports 0-100% LEL (lower-explosive-limit). 

 

NevadaNano designed the sensor to offer real-time measurement that has built-in compensation for environmental factors, including temperature, pressure, and humidity. Image used courtesy of NevadaNano Systems, Inc.

 

NevadaNano’s device has a refrigerant sensor, a MEMS transducer acting as a micro-machined membrane with an embedded Joule heater and resistance thermometer. The resistive heaters allow for temperature control within the device and help the sensor clean up after each sample of air is analyzed for a leak.

The sensor aims to offer design flexibility by introducing micro-cantilevers, versatile points that allow MPS sensors to detect the smallest changes in the structural element from vibrational frequency. For larger systems, an array of MPS-based sensors can be strung out and monitored electrically thanks to the piezoelectric element that helps the system find resonance frequency as well as signs of mechanical stress. 

 

A “Flying Nose” for US Military Applications

NevadaNano’s chemical sensor applications go beyond stationary sensors embedded in HVAC systems. 

Sometimes they fly. 

The University of Utah partnered with NevadaNano in 2015 through Professor Kam K. Leang’s “DARC Lab” (where DARC stands for “Design, Automation, Robotics & Control”). The project was officially known as the “Autonomous Broad Spectrum Environmental Sentinel” program—but was unofficially dubbed the “flying nose” as it aimed to create a quadcopter capable of sniffing out the presence of chemicals in the air.

 

A 2015 iteration of the University of Utah DARC Lab’s “flying nose” quadcopter. Modified screenshot used courtesy of the University of Utah

 

The goal of the project is to enable autonomous drones to conduct real-time chemical mapping of airborne chemical plumes. The system’s data would wirelessly relay information to a central command post to provide real-time, actionable intelligence. This would add another layer of user protection by eliminating the risk of human interaction in high-risk areas.

The project was admitted to the STTR (Small Business Technology Transfer) program through the US Army DOD in 2014. Two years later, In 2016, the project was awarded federal funding and moved to STTR Phase II. This designation typically means initial Phase I research was promising enough to warrant further investigation, a distinction that generally comes with a grant of around $750,000 for use over two years of research. 

The current iteration of the program, in which NevadaNano is listed as an officially partnering investigator, has reached Phase II through US Air Force sponsorship and will conclude in December of 2022. The long-term goal as stated back in 2016 is to create autonomous drones capable of swarm movement for accurate data gathering at a massive scale. 

 


 

Have you ever built a chemical detection system? What criteria do you most often look at when selecting chemical sensors? Share your experiences and lessons learned in the comments below.



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