Within seconds of starting the pump you'll feel like someone dumped a glass of iced tea down your back!
Race car drivers use an expensive version of this with a heat exchanging t-shirt under their jackets to keep cool.
The parts cost less than $100. I've made these for classic cars, electric cars and for lawn chairs. They'll make you more comfortable if you don't have air conditioning and have to be in the heat.
Warning: Do not use for extended periods of time. Should not be used if you have poor blood circulation.
Step 1: Parts and tools
Ice Chest - any size, larger can hold more ice for longer cooling.
Plastic beverage bottles: At least two of any size. One to freeze and the other to use in the backcooler. I use two 1 liter pop bottles. Fill with fresh, clean water 2 inches from the top to allow for expansion. Remove the labels! The pump doesn't like label fragments!
10 feet of 1/4" od vinyl tubing: - get the drip irrigation tubing; it's tough, cheap and withstands UV
5 feet of 3/8" od, 5/32 id vinyl tubing: Usually clear, does not have to be food grade or reinforced.
3 inches of 3/4" id vinyl tubing: Clear - Size to fit your bilge pump outlet.
Two 1/4 to 3/8 reducer couplers: I used Eldon James C4-2.5NP
Two 3/8" quick release couplers: Optional
( Colder part number APC22004 and APC17004 from www.US Plastics.com)
Do not use drip irrigation fittings, they will leak when you move the tubing around!
One 12v submersible bilge pump, 350 gallons per minute for single seat, 500 gpm for a double.
One cigarette lighter plug with 2A internal fuse
3 feet of 12v 2a wire - Size to your needs
Two crimp connectors
One square yard of 1/4" nylon mesh or similar fabric, or a car seat cushion.
Two 6' nylon straps and buckles
UV resistant fabric
Heavy thread, UV resistant
3 small nylon cable ties
Drill & bits, 5/32"
Step 2: Ice Chest set up
Bilge pump: It will work in any position so I didn't mount it. Most pumps have a mounting bracket, you can try gluing it to the bottom or side of the chest. It's easier to clean the pump and chest if it's not mounted. My pump has a 3/4" OD outlet, find the tube size and adapter to fit yours. The seal does not have to be water tight on the bilge pump.
Connect the wires to the bilge pump wires outside the ice chest. The Rule model pumps are not polarized, but if yours is connect it correctly! If you want to put a switch in line, go for it. You can also wire it to your car's fuse box with a disconnect.
The supply and return tubes are interchangeable. Make the lines long enough to reposition around ice bottles if needed.
Use the nylon ties on the inside to keep the tubes and wires from being pulled out. Not too tight!
Step 3: Seat heat exchanger
The idea is to put about seven feet of tubing on the back of a seat so it contacts your upper back and can absorb heat which cools you off.
Use nylon mesh like that pictured or get a car seat cushion and fasten the tubing to it. I used UV resistant, heavy thread with an upholstery needle. My technique needs some improvement and if anyone has any suggestions on how to attach the tubing to the mesh securely and quickly, let me know. I did try threading the tubing in and out of the mesh, but it distorts the mesh and takes a long time.
The tubing must not be kinked, so any pattern that you like should work. I sized it so my back would cover the tubing and reduce condensation. Place it on your wide upper back, do not use it near your kidneys in the small of your back.
Supply and return lines are interchangeable.
I had a friend sew some UV resistant upholstery fabric into a tube, about 1" diameter to hold the vinyl tubes together, insulate them and reduce condensation. Don't sew? Use pipe insulation, taped on plastic packing material or leave them bare.
The length of the supply lines depend on where you use this. Shorter is better.
If you want two back coolers you'll need to find 3/8" Y adapters.
Step 4: Adapting, improving & FAQ
I'm open to any suggestions and am happy to answer any questions. Let me know how you use yours and if it's helped you beat the heat.
Tips: Put a teaspoon of bleach in the ice chest water to keep it fresh. Do NOT drink the ice chest water, DO drink the melted ice water from the clean pop bottles. You can put ice directly in the ice chest, but you'll have to empty the water later. Swapping melted bottles for frozen bottles is easy, no mess. Any size bottle can be used, remove any paper labels because they'll jam the pump.
Here's some questions I've heard...
How about using it as a heater? A. You'd have to have a thin layer of clothes to use it as a heater, go for it.
How about sitting on it? A. That might work, but you could pinch a hose and reduce flow.
How about a head band or a hat with some tubing? A. Sure, go for it.
How about condensation, won't it get wet like a glass of iced tea? A. Yes, a bit, but it's better than sweat and it will help transmit heat from your skin to the tubing. You want cool AND dry? Get air conditioning.
My back went numb! A. Don't use it for prolonged periods, turn it off for a while or lean forward. When your skin gets too cold the blood flow decreases and it's not as effective pulling heat from you. Do not use this if you are diabetic or have low blood flow.