VAXXWAGON: An Innovative Eco-friendly, "No Ice, No Electric" Active Refrigeration System for Last-Leg Vaccine Transportation

"To handle yourself, use your head; to handle others, use your heart." - Eleanor Roosevelt

As an infant, I experienced first-hand what last-leg vaccinations can mean for the many thousands who require it.

My grandparents carried me nearly 10 miles to have me vaccinated, only to find out when they arrived that the vaccinations were no longer effective. I was fortunate. For many, that trek to be vaccinated is a matter of life and death.

My subsequent research motivated me to find a better and more reliable way to transport vaccines to remote locations in developing countries throughout the world. Last-leg vaccine transportation to remote locations has long been a logistically challenging phase of vaccine delivery to millions in dire need of vaccinations.

Because of the dependency on both ice-packs and electricity, the vaccines can arrive either too hot or too cold, rendering them completely ineffective. According to the World Health Organization, in 2013 there were approximately 1.5 million children who died as a result of not receiving the appropriate and effective vaccines.  

Taking into account the very serious limitations associated with current methodologies, I set out to design and develop a "No Ice, No Electric" vaccine transportation system which is unique and innovative. Based on intensive test results in the lab, I am now capable of successfully executing cold chain delivery in the last-leg (2-8°C) without compromising the integrity of the vaccines, ensuring intact and effective vaccinations to those urgently needing it now.


The future depends on what you do today.” - Mahatma Gandhi

Engineering, Science and World Geography have always been part of my keen interests and passion.  I placed 3rd at National Geography Bee in Maryland .  I am also an avid tennis player and play #1 singles for my school.  Applying these passions to solve real world problems from public health to biometric identification has been a source of inspiration to me the last several years.

Recently, I won the Johns Hopkins University Research Award for my design with innovative vaccine transportation.  I have been advised by Hopkins to pursue this research with their grant money.  Next, I entered a Science Contest utilizing biometric identification as a way to identify humans through footprints.  This project was judged by the Central Intelligence Agency (CIA). 

Finally, NBC’s Today Show interviewed me live, as one of the national winners of Shell’s “Make the Future” contest, among thousands of entries.

My idols include Sir Richard Branson, who sees every problem as an opportunity to make the world better for all.  I’m also a great admirer of Albert Einstein, who famously stated, “imagination is more important than knowledge.”  Currently, I’m a sophomore at Clarksburg High School in MD.  My future goals include becoming a Social Entrepreneur. 

I appreciate the fantastic opportunity that the Google Science Fair provides to communicate my invention, and I genuinely believe that this will help to get effective vaccines where they're needed most in any part of the world.


One of the areas where innovation might be most effective in the short term would be innovations in the logistics and 'cold chain system'.   - Bill and Melinda Gates Foundation

“Cold chain system” refers to maintaining vaccine temperature in the range of 2-8°C throughout the transport process: manufacturer to distributor, distributor to remote clinic, and clinic to patient.

The transport process often ends with a last-leg of typically about 15 miles, which is the most logistically challenging part of the vaccine journey. Healthcare workers might traverse rough terrain with no roads, and the destination may not have proper refrigeration to keep the vaccines at safe and effective temperatures.

The majority of last-leg vaccine transportation requires ice packs to maintain cold temperatures but using ice packs limits cold life or cause freezing of vaccines. Freezing is one of the major problems for vaccine transport and storage in developed and developing countries.

Frozen or Overheated Vaccines lead to:

  • Reduced vaccine potency and effectiveness
  • Costs exceeding thousands of dollars in wasted vaccines and re-vaccinations
  • A loss of patient confidence

Can I design, build, and test an Eco-friendly, "No Ice, No Electric" active refrigeration system powered by a human or an animal for last-leg vaccine transportation to remote locations?


"Persistence in scientific research leads to what I call instinct for truth" - Louis Pasteur

Others have noticed a need for better last-leg vaccine transport. Two examples I found are Princeton professor Winston (Wolé) Soboyejo and Rogers Feng, a student of Northwestern University in Chicago. Dr. Soboyejo proposedR1 that solar panels carried by a camel will charge a battery which in turn powers a standard electric refrigerator. This is clearly a large system that depends on a camel for transport.

Mr. Feng’s systemR2 utilizes a hand crank in order to power a generator which charges a battery. The battery powers Peltier elements which cool the inside of an insulated container. Peltier systems are typically only 10% efficient so to generate 1 w of cooling 10 w of crank power will be needed.

Both these systems are impractical; the first because of its size, the second because too much human work is required. 

Most current last-leg vaccine transportation utilizes insulated containers passively cooled with ice-packsR3, which may be water or packaged phase change material. Ice-packs pose two problems: obviously cold life is limited, and they can be supercooled below 0°C such that they can cause vaccine freezing. Both warming above 8°C and freezing below 2°C reduce vaccine potency.

“A healthy well-fed laborer over the course of an 8-hour work shift can sustain an average output of about 75 watts” R4. By only requiring 3 w to power VAXXWAGON, it is easy to provide this by human or animal.

I originally thought of using propane as a refrigerant but I chose R134a because it is non-flammable and non-toxic. Chemically it is 1,1,1,2-tetrafluoroethane, an inert gas used primarily as a "high-temperature" refrigerant for domestic refrigeration and automobile air conditioners.

VAXXWAGON is designed to supply unlimited cold life, simply by being in motion about eight hours daily. It can also be designed to never chill its cargo below 2°C, even in case of operator error, by storing thermal energy in phase change material (PCM) as well as thermostatic control. 


"Anyone who never made a mistakes has never tried anything new" - Albert Einstein

Thermodynamic Design

I calculated the heat load of a commercial one gallon water jug, assuming a temperature differential of 40°C and polyurethane foam insulation 5.6 cm thick. 0.46 watts (w) is sufficient to maintain 5°C inside.  Opening 10 times daily adds .02 w

Therefore I speculated that a simple vapor compression refrigeration system could supply sufficient cooling, even powered by a human or animal.

The system will not be powered continuously. Assuming a duty cycle of 1/3, energy storage is needed, provided by a phase change material (PCM). The PCM has two functions: preventing overcooling or overheating by releasing or absorbing heat of fusion. An additional .3 w is required to freeze the Phase 5® PCM at 5°C.

Incorporating the factors above, the power required is 2.3 w, or 3% of what a human can provide.

My vapor compression refrigeration system compresses and expands R134a refrigerant to modify entropy and enthalpy, and causes temperature changes as shown in this Pressure-Enthalpy diagram. The cycle ABCD corresponds to the indices in the following schematic diagram.


Independent variables:

  • expansion orifice size
  • low side refrigerant pressure
  • compressor speed

Dependent variables:

  • temperatures, high side pressure
  • cooling rate of the evaporator water

The independent variables were optimized for 0+/-2°C in the evaporator for all experiments. 

Phase I 

Below are views of my first prototype. A model airplane engine running backwards was the compressor (a). Insulated 1/8 inch copper tubing (b) extended from the compressor to the pressure gauge (c), the condenser water bath (d), and the expansion valve (e - a needle valve). Cooling is measured in the evaporator water (f). The tubing returns to the compressor via the Schrader valve fill port (g). This prototype was abandoned because of high torque and leaks revealed by UV tracing.

Phase II 

Phase II is shown below.  I replaced the engine with a double-acting pneumatic cylinder (H).  The condenser is simply a loop of copper tubing. For testing, I attached a motor (K) to power the compressor;  (J) is a DC power supply.  The cold chamber (L) was modified from a commercial water jug.  The evaporator, submerged in PCM, surrounds a smaller inner chamber which would contain vaccines.  The power input at 180 rpm was 35 w.

Phase III

Phase III was created by attaching Phase II to a bicycle trailer and adding a two-stage ground-driven transmission. To facilitate the data gathering, I operated VAXXWAGON on a treadmill at 8 mph for 6 hours, followed by 4.75 hours of unpowered data collection, mimicking last-leg transportation.  A vaccine simulant, 500 mL of bottled water at 5.7°C, placed in the cold chamber, remained in the 2-8°C range for 10.25 hours.  In the first photo below left, the two-stage ground-driven transmission can be seen. The second photo shows VAXXWAGON mounted on a treadmill.  The third shows VAXXWAGON in its anticipated use.


Safety Measures

Please see the list of safety measures here


Product Evolution

In Phase I, a model airplane engine was used as a compressor, which was powered by a drill motor. Water baths were used for both the evaporator and condenser to measure heat flow. The evaporator water bath temperature declined but the design was abandoned due to refrigerant leaks revealed by UV leak testing, immeasurable temperature change in the condenser water bath, and the large torque to operate the compressor. These problems prevented extended operation.

In Phase II, the compressor was changed to a double acting pneumatic air cylinder. After acquiring cooling rate from the evaporator water bath, it was replaced by building a custom cold chamber using 330 grams of PCM, coils of copper tubing (evaporator), and polyurethane foam added inside a commercial water jug. The condenser water bath was replaced by a long length of copper tubing. A DC motor powered the compressor through a single stage transmission. The heat withdrawn from the evaporator water bath at 180 rpm was 23 w.

In Phase III, the Phase II system was placed on a bicycle trailer. The DC motor was replaced with the two stage transmission linked to the ground driven wheel such that the compressor turns .36 revolution for every revolution of the wheel. The current prototype costs less than $100.

Treadmill Test Results

The treadmill test was conducted at an ambient temperature of 22°C. The high side refrigerant pressure was 117 psi and the low side pressure was 27 psi. The pulling force was 1.38 newtons which corresponds to 5 w of power. The first plot shows all the temperatures collected in the experiment; the second plot shows the temperature of the PCM to allow more detailed discussion of its phase changes. It can be seen that the temperature of the condenser immediately went up with compressor power as the temperature of the evaporator went down. These trends reversed when the treadmill stopped. Vaccine temperature is the most important variable and it remained between 2°C and 8°C for 10.25 hours.

A significant feature of this design is PCM used for energy storage. Other actively refrigerated systems utilize batteries for energy storage (although PCM might be used as a thermal buffer in other systems). The plot above shows the temperature of the PCM; its phase changes can be inferred from the temperature profile. In the first zone, liquid PCM is cooling. In the second zone, the nearly constant temperature indicates that the PCM is freezing. The third and fourth zones represent undesirable supercooling. This happened because all the PCM froze; in the future this can be prevented with more PCM. The fifth zone shows the PCM melting and absorbing heat to maintain the temperature of the vaccines. The sixth zone shows the liquid PCM warming to ambient temperature, therefore the vaccines are in jeopardy.

Here is a video of the treadmill test!


VAXXWAGON: Human Powered Demonstration

Next, I took VAXXWAGON outside and hitched it to a bike and rode around my neighborhood. Here is a video!



"Don't think what's the cheapest way to do it or what's the fastest way to do it....think what's the most amazing way to do it." - Richard Branson

There are several reasons why the VAXXWAGON concept is feasible. Only 2.3 w is required to cool a well-insulated cold chamber. Vapor compression refrigeration systems are typically more than 100% efficient. A human can generate 75 w over a course of 8 hours, so outputting 5-10 w is easily achieved.

With my Phase II system, I measured power input and output: 35 w of electrical power yielded 24 w of cooling at 180 rpm which was the minimum speed I could run the system electrically. The resultant efficiency was 65%.

I operated my Phase III system at 8 mph down geared by a factor of .36, yielding an expected 8 w of cooling at 64 rpm. The high side refrigerant pressure was 117 psi and the low side pressure was 27 psi, lower than specified by my design simulation, but still sufficient to provide cooling. The pulling power of 5 w was twice the calculated value but can be understood because transmission friction must be overcome, and from the VAXXWAGON Operating Temperature Profiles plot it is apparent that more than 2.3 w of cooling was being provided because the vaccine temperature declined.  Pulling at 5 w to produce 8 w of cooling is reasonable since vapor compression refrigeration systems can operate above 100% efficiency.

The validity of my non-electric design was supported by the VAXXWAGON Operating Temperature Profile (PCM only) plot. The PCM behaved just as expected and provided an effective method of energy storage.

The VAXXWAGON Operating Temperature Profiles plot describes the experiment which simulated real operation of last-leg vaccine transportation. VAXXWAGON was powered for 6 hours after loading a vaccine simulant. The plot shows the vaccine temperature stayed within range during that time and continued in range for 4.25 hours after the treadmill was stopped.

Therefore, I have successfully designed, built, and tested an Eco-friendly, "No Ice, No Electric" active refrigeration system which can be powered by a human or an animal for last-leg vaccine transportation to remote locations. The prototype is designed for attachment to a bicycle.

I have submitted a patent application and intend to continue developing VAXXWAGON. Future goals include improvements under different terrain conditions and ultimately perfecting my system for developed and developing countries.


  • Provides an effortless method of Eco-friendly, “No Ice, No Electric” active refrigeration system utilizing either human or animal power 
  • Is a viable and affordable alternative to current last-leg vaccine transportation
  • Can be utilized in both developing and developed countries worldwide
  • Sustains typical travel speeds of 8-10 mph while maintaining a safe and effective vaccine temperature of 2-8°C
  • 200 hours of continuous testing and 10 trials
  • Can replace the current systems and processes of last-leg vaccine transportation and revolutionize this phase, saving countless of lives


R1) Fengs, Roger. "Rogers Feng’s Human-Powered Refrigeration System Wins US James Dyson Award." Inhabitat Sustainable Design Innovation Eco Architecture Green Building Fridge Plan Comments. Inhabitat, 8 Sept. 2012. Web. 21 Jan. 2015.

R2) Emery. "Homeward Bound: Princeton Engineers Promote Science in Their Native Countries." Princeton University. Trustees of Princeton University, 2 July 2009. Web. 21 Jan. 2015.

R3) Dometic. "RCW 4." Products. Dometic, 1 Jan. 2012. Web. 27 Jan. 2015.

R4) (Eugene A. Avallone et. El, (ed), Marks' Standard Handbook for Mechanical Engineers 11th Edition , Mc-Graw Hill, New York 2007 ISBN 0-07-142867-4 page 9-4)(Eugene A. Avallone et. El, (ed), Marks' Standard Handbook for Mechanical Engineers 11th Edition , Mc-Graw Hill, New York 2007 ISBN 0-07-142867-4 page 9-4)

Ylidiz, Seyfettin. "Design and Simulation of a Vapor Compression Refrigeration Cycle for a Micro Refrigerator." Design and Simulation of a Vapor Compression Refrigeration Cycle for a Micro Refrigerator. Middle East Technical University, 1 June 2010. Web. 21 Jan. 2015.

Heydari A., "Miniature vapor compression refrigeration systems for active cooling of high performance computers," Proceedings of the Inter Society Conference on Thermal Phenomena, IEEE, 2002, pp. 371-378.


I would like to thank the following persons for their invaluable contributions to my project:

  • Dr. Lindsey Nelson of The Johns Hopkins University for providing me with excellent mentorship as part of the CTY Cogito Research Award which provided with both grant money and assistance
  • Dr. Shooshtari and Dr. Dessiatoun of the Smart and Simple Thermal Systems lab at the University of Maryland for providing me with a solid understanding of thermodynamic concepts relating to refrigeration
  • Dr. Milton Axley for his support and guidance in helping me to understand the global challenges associated with last-leg vaccine transportation
  • My Mother and Father, for their tireless support and assistance during this entire project. They provided the platform by which I could freely work on this project. Thanks Mom and Dad! :)