I like to race Radio Control cars here in California in the Central Valley but I get heatstroke symptoms (headache, dizzy, nausea) on 100 degree plus days. (Heatstroke is risky). I was bummed I couldn't race all summer. I then sought a solution and came up with this. It is not a cheap as anyone would like ($410), but it is better than trying to save money by buying cheap, then the merry-go-round of stuff that doesn't work, and then buying the expensive stuff in the end anyway.
The shirt can be assembled in any order, so it isn't really step-by-step. Also, my eBay links can go stale, so I will tell you what to google.
The vest has tubing that you circulate ice water through with a pump. The hydration pack has a reservoir that you half fill with water then add ice. As the ice melts you pour out the excess water and add more ice. A 5lb bag of ice from a convenience store lasts all day.
The shirt works. I can spend all day in 100 degree plus weather and be comfortable. When you first switch the pump on, it fells like jumping into an freezing pool, but then your body acclimates and you don't even know it's working. Then you take it off, and holy crap, you see how hot it is outside.
The design is a coolshirt vest (vest with hose sewed in), a pump, a battery, a switch and a hydration pack.
Step 1: Hydration Pack and Coolshirt
You can pick any pack you want. I got one that hold 3 liters and is meant for bicycling. Less than 3 liters probably would not work. 3 liters is like 100 ounces. The military ones are the most expensive but seem the best quality. This is the one I bought, it was about $68:
Coolshirt makes the vest with hoses sewn in. I called the saleman at coolshirt for a recommendation. Here is his contact info just in case. You can buy from him so you don't get the wrong thing, or save money and do the research yourself.
I bought a large sized coolshirt vest, 2 female connectors, and a bottle of maintenance additive for total $240. I bet you can get cheaper if you shop around. I then bought 5 feet of 5/16" inner diameter tubing at home depot. I then cut the tubing in half and pushed the female connectors on one end of each piece. These will plug into the coolshirt. One tube I connect to the pump (sump, inlet at bottom), that will pump into the coolshirt, and the other piece of tubing will be the return.
Step 2: Pump, Battery and Switch
Here is the pump. It is small, like 6 inches long. Tom at coolshirt recommended it. The model is Comet Elegant. They are made in the UK for tiny RV's. I bought mine for $30. The inlet for the pump is on the bottom. I attached one end of the tubing to the top outlet. I put a zip tie on it just in case. Here is a link but it can go stale, so google "Comet Elegant pump". You just push the pump down to the bottom of the hydration pack reservoir.
It is a 12V pump, so a 3 cell Lipo battery can power it (3 cell is called 3s). I bought mine at a hobby store. I picked a large capacity (5000mAh) and cheap $62. The pump is rated at 2.8A but when I measured it, it was 1.3A. The math for how long the battery will last is:
5000 / 1300 = 3.8hrs
You will need a way to charge it. The hobby store can sell you are charger. I will buy a second battery to go all day.
I then just ran wiring from the battery to the pump and a roller on/off switch. You can buy wire and switches at these places:
Batteries (get RC car type)
I have this charger because I use all types of Lithium Polymer Batteries (Lipo) for my projects.
Step 3: Final Notes
You can save money on this project if you are creative. You have alternatives for every part. The refrigerator shirt can be improved by adding a control unit, instead of just a switch. You can PWM the pump motor speed. You could add a sensor and buzzer when the battery need charging. A more energy efficient pump could make the battery last longer. You could make this shirt for your grandparents, so the could garden in the heat. You could make a system for riding your bicycle or motorcycle or any outdoor sport. The possibilities are endless.