Keeping it Cool
One sure way of wrecking your day, is allowing excessive heat to wreak havoc in your cabinet. Put simply, it can greatly reduce the life expectancy of components, lead to stoppages in work, and potentially create a hazard to employees. So, let’s avoid all of that and talk about protecting your cabinet from out of control temperatures.
Conservation of Energy
I guess the best place to begin is to talk about the conservation of energy.
Smart Person Speak: The total energy from all sources flowing into a defined, fixed region (e.g. an enclosure or specific component) must equal the total energy flowing out to maintain a stable temperature. Temperatures of system components will change to make this happen when in steady-state operation.
Me: Basically, energy (in this case watts of electricity being used in the enclosure) going in must equal energy (heat being dissipated by the thermal solution) going out. So, the components of your system will respond to changes, either increasing or decreasing in temperature, until thermal equilibrium is reached. Preferably at a temperature equilibrium lower than the one when the “fireworks” start.
Why it’s so Important
Smart Person Speak: According to the Arrhenius law, Electromechanical and other processes accelerate roughly two times with each 10°C rise in temperature.
Me: Blink… Blink… What? Gonna need more coffee for this…
Kidding aside, what does this mean for your components? It means that the service life of your components such as electrolytic capacitors and batteries decrease with temperature increase. Given that information, it is pretty important to consider your device capacities or ratings as they are frequently limiting factors such as performance and lifespan.
Figure 1: (Image Source: www.istockphoto.com)
Before I go too far, it’s probably best to go over a few thermal management terms.
Smart Person Speak: Conduction is the heat transfer between two physically connected components within a system.
Me: When a hot piece of metal is connected to another piece of metal the heat transfers between the two until they are the same temperature.
Smart Person Speak: Convection is the transfer of heat through the circulation of air or fluid.
Me: A really hot object transfers its heat through the air (or other fluid) to another object until they are equal.
Smart Person Speak: Radiation is the transfer of energy particles from one object through an intervening space and absorbed by another object.
Me: Think Toaster.
Smart Person Speak: Thermal Modeling is the process for the making of basic thermal analysis calculations in electronic applications.
Me: Hey look, a link! (EEwiki article)
Closed vs. Open System Cooling
There are two conventional methods typically used when cooling your cabinet. A Closed system means there is no movement of coolant (air or fluid) from within the cabinet to outside the cabinet. All cooling is done through conduction. Like any good decision, there are pros and cons. Let’s consider a couple. First, there is no need for filtration meaning there is less maintenance. This is great for a particulate heavy environment. It also means your equipment within the panel will stay clean longer. Of course, this also means that temperatures will run higher due to the limitations of a conduction process. The heat will need to transfer through the enclosure wall before being released into ambient air. In high temperature environments, this could create a very big problem as this process by itself is not good for dissipating large amounts of heat. Something to consider though, perhaps adding a closed loop cooling system within the panel that stirs captivated liquid to pull heat from your components.
The next option would be the Open System. This system allows air or fluid to enter your cabinet through the use of a filtration system and circulates it through the cabinet leveraging convection. This will permit the cabinet to typically operate at a lower temperature than a closed system. It does, however, require maintenance. With the filtration system, the filter will need to be changed out regularly to prevent air flow restriction and eventual component degradation. There are limitations on the Open System. The required fluid (typically air) flow rate is dependent on the thermal capacity of the cooling fluid, intake and exhaust temperatures, and permissible component temperatures. Also, it’s worth noting that the inner cabinet temperature will still be higher than that of the exhaust temperature.
Extra Information and Helpful Links
Fan Selection & Application Guide: Navigating parametric attributes (EEwiki article)
Some available options: