Critical facilities have many of the same HVAC demands as other buildings, except the consequences of unexpected problems can be catastrophic and expensive. Using a data center as an example, reliable power sources and optimal system functioning is required at a minimum. In addition, heat-producing systems must be immediately cooled to maintain the temperature in a narrow range, and the unit must be easily accessible for quick maintenance. To further tax the engineer, servers are often squeezed into small spaces, energy use must be minimal, and designs must be able to accommodate unforeseeable changes.
This is a challenging situation, to say the least! Would it not be wonderful to have a wise design mentor to turn to with jobs like this? Even better, a mentor who is available 24/7, works for free, and only recommends the most energy- and material-efficient, time-tested solutions?
The fact is that this mentor does exist right in front of our eyes. Her name is Mother Nature! Mammals have many of the same restricted space and heat management challenges as buildings, and evolution has ensured survival of only the most energy-efficient and successful designs. Can nature model successful strategies for data center cooling, or at least underscore current engineering methods in the setting of variable heat generation and a tight space? Let’s look at how steady temperatures are maintained in the brains of warm-blooded mammals (like ourselves) and see how the solutions compare to cooling in data centers.
Brain temperature, like all systems, depends on the balance between heat generated and heat dissipated. Every time we have a thought, a feeling, a desire to move or need for functioning organs (all the time), heat is produced by electrical impulses in our brain neurons. This heat production can be widely variable depending whether we are thinking hard, exercising, or resting. Meanwhile, while our body temperature is 36.5º to 37.5ºC, our brain must be kept at a cooler 32.0º to 35.0ºC or massive brain damage will quickly occur. Adding to the conundrum is that, in contrast to other organs such as muscles, the heat produced within our brain is not easily dispersed due to the insulation of our skull.
How does our brain remain cool (hopefully)? Humans have developed an elegant temperature control process, called selective brain cooling (SBC), which can lower the temperature of our entire brain or cool local “hot spots” as needed.
SBC removes excess heat through three well known routes: evaporation, conduction, and convection. Using evaporation, the outermost brain layers are cooled when surface heat is lost directly through scalp and face sweating. Deeper brain cooling occurs through countercurrent heat exchange between venous sinuses (small lakes of blood) within our skull and the two carotid arteries, large vessels close to the surface in our neck. And finally, convection is employed through ventilating cool air in our sinus cavities, which lie close to the brain’s center. In fact, researchers now say that the reason we yawn is to increase cool air convection close to our brain stem when the temperature needs to be lowered, such as prior to sleep.
All of this temperature control is regulated through an integrative center located deep in the brain, the hypothalamus. How the hypothalamus communicates with brain cooling blood and breathing responses is not completely understood, but it seems to involve blood-born chemical neurotransmitters such as norepinephrine, dopamine, and melatonin, as well as direct nerve signals from peripheral thermoreceptors in the body.
So the next time you are challenged by a complicated HVAC design, ask your ever-present and wise mentor.