Physics of Driver Cooling

By: John Creech                                     July 24, 2009

It is no secret. Racing drivers get hot. Really hot. Really, really hot. After a recent race, I heard one driver mention that he had lost nearly 6 pounds after a particularly warm stint. This is close to a gallon of sweat and water which left his body. With a loss like this, regardless of his core body temperature readings, he would likely be within the first stage of Heat Stress simply because his body may have lacked sufficient fluid to continue the sweating process. He laughed. I just shook my head.

So there is no ambiguity - the dangers and performance risks associated with Heat Stress are very clear, well documented, and most important… Are very real. Studies by NASA, Stand 21, UC Berkeley, and the French Government have detailed and proven time and again that even a slight elevation in body core temperature – as little as one half of one degree – can put a driver into the first stages of Heat Stress and can result in between 60 and 80 mistakes in judgment and performance PER HOUR! That is a lot of missed apexes and braking points not to mention the dangers inherent in handling vehicles in close proximity to others… Others who are more than likely are also suffering from Heat Stress as well.

Again, let us agree that heat stress is a very real problem and a detriment to performance. So how do we win?

Like any good word problem, in order to solve this one, we will need to know at least two things. First, what am I trying to find out… What am I solving for? And second, what formula or strategy is best to help me determine the answer.

Put simply, we want to keep our core body temperatures at its ideal. That is 98.6 degrees Fahrenheit for most of us (is the company name making more sense now?). We don’t want it to depart from this number… Not one little bit. If it drops, we become hypothermic. If it increases beyond 98.6 degrees, we are in Heat Stress (Syncope for those of you with an M.D. on your diplomas).

We want to solve the problem of keeping the body right at 98.6 degrees then. Simple enough. What are the options for keeping a driver cool? Well, they fall into some neatly designated categories which adhere very nicely to the laws of physics. Subsequently, we can also determine their likelihood of helping in our quest through some simple logic. Here’s how it plays out:

Evaporation – By sweating, we move heat and moisture to the surface of the skin where the water vapor (hot) can be evaporated into the ambient environment…taking the heat with it. Big problem: The ambient environment in the case of a racing driver is the interior of a driving suit. Due to the tight weave of modern fire suits, the interior becomes saturated with water vapor very quickly. Evaporation fails and cooling via this method ceases. Bah!

Radiation – By radiating heat into the ambient environment, heat is dissipated from our bodies and internal energy (heat) is decreased. But what happens when we’re in a hot fire suit, in a hot car, in a warm environment? Well, the environment produces more heat than the driver and the net result is that the driver absorbs more heat than he radiates. Warmer, not cooler? Blast!

Convection – By being near an object of a different temperature, the driver’s body could have its heat wicked away. But like Radiation, the ambient environment and nearby object in the car are likely to be much warmer than the driver. Again, cooling fails and the driver is, convectively, heated by the environment (seats, restraints, ambient air and fire suit). Warmer yet again? Double blast!

Conduction – By being in direct contact with an object of a different temperature, the driver’s body could have its heat wicked away… But as with Convection, this one fails also when you consider how hot the clothing and fire suit are.

Yes. We simply need to trick the laws of physics by changing the objects which are near the driver’s body. In short, we are going to put another substance in the environment which IS significantly cooler than the driver so that the heat transfer methods listed above will be effective. If there is something cold next to the driver’s skin, then Radiation, Convection, and Conduction all work. We’re still a bit stuck on that pesky Evaporation… but we will deal with him as a bi-product of another process.

Let’s explore some options for adding a cold substance next to the driver. Most of these will be easy to grasp as we are all familiar with the process and garments which use these methods. However, we will point out the pitfalls here for each as you learn more from your losses than you do your successes.

Ice – Putting ice on the human body is a shock to the system. It is TOO COLD when looked at locally. Of course, there is also the pesky habit it has of melting. Locating ice within a jacket, vest, pockets, and the like have all been tried. But the fact is, when it is a solid, it is too cold. When it melts to liquid form, it is hard to keep in contact with the body and of course, it warms and doesn’t stay cold enough. It doesn’t tend to last very long and is only at an ideal temperature for cooling for a few moments.

Air – Plumbing cool air into a fire suite may be effective at cooling some parts of the body… But it doesn’t reach a sufficient surface area to be useful as its movement across the body is restricted by the restraint system. You may end up with a cool chest at best. Plus, air simply isn’t as good as other fluids at moving heat. Does your car use an air-cooled engine or a radiator? There’s a reason that even Porsche has moved to radiators in recent years.

Chilled Water – Now we’re talking. We can keep the water at an ideal temperature using ice or some form of chiller. But the problem is keeping it near the body. The good thing is that this problem has been solved.

The first option is to use tubing. This is a common solution and a reasonable one for a few reasons. First, tubing stitched to a garment, allows the fluid to be very near the wearer. Second, the fluid path can be controlled and vectored to target the best areas for heat dissipation. Lastly, tubing is a relatively inexpensive way to move fluid around. Great… Where can I get some? Not so fast.

A tubing solution has some significant draw-backs. First, because plastic tubing is naturally an insulator, the thermal transfer properties of the medium are quite inefficient. Second, because tubing is round and your skin is flat, the actual amount of surface area used to conduct heat from the skin to the fluid is minimal. Third, because tubing, when stitched to a garment, is relatively rigid, it is an unacceptable solution for certain environments like off-road conditions where it can rub ‘into’ the wearer’s skin after repeated large movements against the seat and straps.

If an ideal solution is to pass a chilled fluid next to the wearer’s body while avoiding the pitfalls of tubing-based options, then the best solution would be to use a bladder.

With a bladder-based solution, surface area is multiplied to greatly increase contact area (a good thing) while greatly decreasing pressure points on the skin (also a good thing). And, because bladder film can be sourced with thin and flexible properties… the thermal transfer efficiency of the contact area is greatly enhanced.

Of course bladders can have their own issues as well. Flow problems, purging, and fit/comfort issues. But with proper design and testing, a chilled-fluid based cooling system with a bladder interface for the driver would be the absolute best solution available via standard production means today.

So with this bit of knowledge in hand, you can see why the engineers at 986, Inc. have been so darn excited about our recent breakthroughs in Advanced Driver Cooling technologies.