Portable Personal Cooling System

*Open into dramatic shot of a sweating college girl laying on her basement floor*

"I have long dreamed of a way to shed the suffocating heat of summer, and while many find refuge in nearby lakes or pools, all I have access to here in Pullman Washington is a questionable stream downtown and a small fountain by the library that is apparently “not for that use”. Well, Thomas Edison once said that genius is 99 percent perspiration and 1 percent inspiration and by god I already had the sweating part down, so all that I needed now was the idea."

*End Scene*

Melodramatic introductions aside, the idea behind this project was to create a means of cooling oneself for at least an hour. I was originally going to attempt to build a swamp cooler for my living room, but after looking at the complexity of that project I became a bit intimated. So I decided to allow my roommates to fend for themselves and take the much lower-difficulty option of making a personal cooling system.

The method involves running ice-cooled water through tubes that are held again heat-sensitive parts of the skin. The current setup includes a "Cooling Pack" that is kept pressed against the back of the wearers neck, which is automated to be sent fresh, cool water when a button mounted on the shoulder is pressed. You could also do this via a timer, but I opted for a button because depending on my exterior environment I ended up needing to cycle through the water with different frequency.

The intent is to allow for an efficient, portable, reusable cooling system. This project is still in a relatively early stage of development, but since the current setup is functional (though admittedly not the most attractive) I figured I would share and then just update as I go along!

Step 1: Gather Materials

For this project I used:

• A Camelbak (It will not be ruined in any way)

• A "gummy" phone case of any size

• Plastic rectangle (I used an old Analog Discovery case)

• 4 feet of aquarium tubing

• A plastic pen or WD40 straw

• Foam padding

• A syringe (either with a built in valve, or you will also need to purchase a valve, see the system diagram to ensure your valve is appropriate)

• A chipKIT uC32 microcontroller (and the accompanying MPIDE software) (An Arduino Uno would work as well, you would just have to open the code and copy it into the Arduino IDE)

• Two servos, or one servo and one linear actuator (I used a Tower Pro MG90S and a Tower Pro Micro Servo 9G for the pump mechanism and valve control respectively)

• 1 by .5 foot styrofoam piece

• Popsicle Sticks and small Lego pieces

• Small breadboard and wires, and one 10K resistor.

Step 2: Assemble the Cooling Pack

There are three main physical parts to this project. The Cooling Pack, the pump/valve system, and the Camelbak itself (which serves as both the skeleton for the project and a reservoir for the ice-water). Once you have built these three it is just a matter of assembly and connecting the tubing.

The first part I worked on was the Cooling Pack. This is going to be placed against the back of the wearers neck, and this contact is the way that the user obtains the "cooling" effect from the system. I built this by taking the aquarium tubing and wrapping it around a rectangular Popsicle stick skeleton I had built to keep it supported, then wedging it into the gummy phone case. I then threaded the tubing through the rectangle skeleton, attempting to keep it as exposed as possible while keeping it also all around the same "level". This was to ensure that there did not end up being "bumps" of tubing protruding from the front, because I wanted to maximize the surface area and contact between the front of the Cooling Pack and the back of the users neck. The Cooling Pack will eventually be secured with zip-ties threaded through the phone case against the foam pads. The foam pads are mounted on the back of the plastic rectangle that houses the pump and electronics, which will be detailed further in the next step.

The first photo shows the Cooling Pack pulled away from the tubing to highlight where to place the foam pads. When secured properly it should rest firmly against the users neck.

If you would prefer, you can also opt to get longer tubing and circle it around your wrists then secure it with Velcro straps. The wrists are a great place to apply cooling if you want to cool down the rest of your body, I just happen to always have very cold hands and limbs anyway, so I opted to keep contact location more centralized for my design.

Step 3: Build the Pump System

The complete tubing system is outline in the next step, but the basic idea is that the pump pulls the water from the Camelbak, then runs it through the Cooling Pack to cool you, and then exhausts it into the air through a tiny relief tube.

The tiny relief hole is simply the end of the aquarium tubing. I have cut and stuck a 1/2 inch piece of a WD40 straw into it (the tip of the tube that holds the ink in a standard cheap pen would do as well if it fits your aquarium tubing. If not you can also try using the part of the pen that houses the nib.) so that the hole is very small. The reason that the hole needs to be small is so that while water can escape the surface tension prevents it from leaking. You can choose where to place the end of the relief tubing, but I just ran it off the back of the Camelbak (or into a cup/Ziploc bag if I am indoors) so it does not get me wet. Considering this is a cooling system though, and it is dispensing a very small amount of water, it can be advantageous to think about where you could put it where you wouldn't mind a occasional spritz of water for those particularly hot days.

For the pump system itself I used a syringe and two servos to pump the water through my Cooling Pack and out the relief tube. While you could arguably just purchase a small aquarium pump to achieve this same goal, I opted to build mine because this particular design allows me a very high degree of control over the amount of water moving though my system. I am able to move water in 3 milliliter increments (the size of the syringe I am using), which is especially nice when I am using the relief tubing to cool myself, as well. I figure it may put a damper on my day if I constantly have water rushing out and soaking me with each cycle.

For the actual construction of the pump system, I first hot glued the syringe to the back of the plastic rectangle. Then I attached the arm of the servo (calibrated at 90 degrees) to so it lined up exactly with the valve that controlled the direction of the water flow. I used Lego pieces and Popsicle sticks to reinforce and provide additional support for the servo, and hot glued the body of the servo to the supports. Finally I took two small zip-ties and attached tied the servo arm to the valve arm.

Once I had a way to control the valve, I needed a method of pumping the syringe. For this part I would highly recommend just acquiring a linear actuator, but since I am impatient I opted to just make do with what I had (another servo). I built this with my second servo by mounting it behind the top of the syringe plug and then attaching a paper clip through the last hole on the servo's arm. I then took the other end of the paper clip and broke it so it extended out the same distance as the height of the syringe. I also ziptied a small Lego to the top of the plunger. I then took the broken off end (which still had a nice little hook from the breaking) and heated it with a flame, then pushed into the top of the Lego. I aligned so when the servo spun it pulled the plug up, then when it rotated the other way pushed it back down.

Lastly I mounted the chipKIT board and a small breadboard using a zUNO clip and hot glue respectively.

Step 4: The Tubing Connections

Time to connect up all the tubing!

The yellow and green drawing details the general flow of the system and which tubing connections to reinforce. I have also labelled which sizes of tubing I used for each part, but varying tubing sizes is optional. Cut up your tubing and arrange it into the manner shown in the diagram.

The two connections between the valve and the tubing (and the valve and the syringe) should not require reinforcement so long as you bought the appropriate size tubing for your valve and syringe. The other connections likely require some epoxy or strategic hot gluing, and I have highlighted those in green on my Tubing Diagram. There are three main tubing connections to reinforce in my design, first one being the connection between the Camelbak tube (with the mouthpiece removed) and the aquarium tubing. The second one is between the syringe output (through the right side of my valve) which leads to the Cooling Pack, and the last one is between the Cooling Pack and the relief tube.

I reinforced my connections with a very small zip-tie placed around the larger tubing with the smaller tubing inside to enhance the tightness of the seal, then hot glue encircling the outside.

Step 5: Circuit and Code

The circuit may look like an intimidating mess of wires, but it is luckily very simple. I just have both servos connected to dedicated ground and 5V on the breadboard, then the two data lines are connected to the board. The valve servo is attached to pin 9 and the pump servo is on pin 8 on the uC32. For the button, I simply followed the classic button circuit (shown above) and attached it to pin 2.

Code is uploaded as a zip file, open in MPIDE to upload it to your board!

Step 6: Attach to Camelbak

In order to keep the ice water from being heated by your body, place the styrofoam between the Camelbak bladder and the inner backpack. Then wedge the bottom lip of the plastic rectangle into the Camelbak. Secure with zip-ties. You may have to slice the bottom of the plastic rectangle into more of a plastic triangle to get this to fit well.

I mounted my push button on the right shoulder.

To operate, simply fill the bladder with ice and water and start pressing the button to get the water flowing through. It may take a little extra, manual assistance to get the system started (I took a second syringe and used it to fill the tubing from the relief tube when the Camelbak was open and before I added the ice-water. However once water starts flowing it should be fine!

Step 7: Optional Extension Idea - Sweat Detection

This project is currently a bit of a work in progress, however it does function as intended even if it is not the most…attractive looking aesthetic. My next steps include hiding the mechanics within the backpack so I can carry it outside without attracting judgmental looks from strangers and law enforcement, as well as adding a sweat sensor for autonomous cooling (without having to press the button each time).

This idea intends to take full advantage of the capabilities of your microcontroller and relieves you of any responsibility for your own body temperature.

You can use the concept of galvanized skin response to create the sensor, then set a threshold in the code for at what point you are "too sweaty" and need cooling. A awesome example of a project that uses similar technology comes from a 2016 finalist team in the Digilent Design Contest Europe. This team created a Wearable Wellness system using the Zybo ARM/Zynq FPGA development board, PmodOLED, PmodRF2and PmodIA that can measure changes in skin impedance. While their team focused on the stress aspect of wellness, it can also be applied as a cooling sensor so your Cooling System would be completely autonomous.

Also, if you don't feel one run through of the pumping mechanism is enough to sufficiently cool you, feel free to have it run through twice or three times by changing the loop conditions in the code. The necessity of this will likely depend on the size of your syringe, as larger ones will not have to run through as many times to refresh the system whereas smaller ones (like mine) may need to.