Cooling For Plant Floor Computers

The placement of computer systems on the plant floor is growing at a rapid pace. The proliferation of manufacturing-based software systems that can be run by these PC's in a stand-alone or network basis has served to fuel this growth. As these PC's end up on the plant floor there is a large question that most end-users are eventually faced with. This question is, "Since my plant floor/process area is typically warmer and many times more humid than our normal office environment, do I need additional protection for my computer system?". This is a valid question since the number one threat to computer life on the plant floor is high temperature and humidity.

There is a "thermal fatigue factor" that is associated with the continuous use of a PC in an ambient temperature that is reaching the maximum "allowable" operating temperature rating of that PC. Above a certain threshold, computer life will decrease by 50% for every ten degrees Fahrenheit (10° F) temperature rise. This is an alarming concern because many of these computer systems are critical to the batch operations and even more critical to the continuous process applications they might be involved with. Once this threat is recognized the most common question is, "How much cooling do I need?". Before answering that question three factors must be known:

1. What is the maximum ambient temperature in the area that these computer systems will be operating?
   
   
2. What is the heat generation of the computer system measured in watts or BTU/hour? This information can typically be found in the computer manufacturer's spec sheet.
   
   
3. How much heat/temperature can this computer system tolerate? Again, this information can be found under the manufacturer's spec sheet; "Maximum Operating Temperature".

Although most manufacturers have a "safety factor" in their thermal specifications, it is not advisable to run these systems at their maximum temperature, due to the "fatigue factor". In fact, many computer system warranties state that if temperatures exceed a certain level for a period of time, any failure due to heat will not be covered by the warranty. Computers that are applied on the plant floor, in a hot environment are typically enclosed in a standard workstation enclosure. A cooling device can then be applied to this enclosure to create an internal ambient that is within the tolerable range of the computer system. An additional benefit of the enclosure is that it will prevent the typical dust and particle build-up on the printed circuit board and hard drive of the computer system which will serve to create "hot spots" on the printed circuit board, which is a primary cause of computer failure. By keeping the electronics clean and reducing the temperature to a tolerable range computer life will be prolonged.

The effect of putting a computer system in an enclosed container such as a workstation enclosure has an initial negative impact in the sense that you are "containing the heat" generated by the computer within the enclosure. The positive effect is that you now have a smaller environment in which to control temperature. Generally, there are three levels of thermal control:

1. Thermal/Convection Cooling - This is accomplished simply through heat being dissipated through the skin of the enclosure, through a heatsink arrangement, or by some form of fan/filter system. This can be used in areas where temperature is not high enough to warrant an active cooling system, but enough to warrant relief from the internal heat buildup within the enclosure.
   
   
2. Near Ambient Cooling - The next level is an active air-to-air heat exchanger which utilizes internal heat pipes to absorb the internal heat from the enclosure and transfer that heat to the outside environment. The collection of this heat and the dissipation to the outside world is accomplished by both internal and external fan assemblies. This typically is a medium-cost approach to cooling and does provide a degree of heat relief within the enclosure up to five degrees Fahrenheit (5° F) of the maximum ambient temperature. This approach will not cool below ambient and should therefore be used only in areas where the ambient temperature outside is ten degrees Fahrenheit (10° F) below the maximum operating temperature of the computer system. This approach, as well as the convection approach above are generally low maintenance styles of cooling.
   
   
3. Below Ambient Cooling - When the external ambient exceeds the maximum operating temperature of the computer there is a need for "below-ambient cooling". This can be accomplished by traditional freon-based air-conditioning systems, solid state air conditioners and vortex-style air coolers. These devices typically are thermostatically controlled and provide below-ambient cooling only when the need arises.
   

When selecting the level of cooling required it is recommended the user provide the enclosure manufacturer with the parameters relative to, 1) the maximum ambient temperature, 2) internal heat load, and 3) maximum allowable temperature for the computer system. Armed with this information the manufacturer can then determine the level of cooling required, if any, for the particular application. There are calculations that will be performed by the manufacturer relative to the overall enclosure size since a certain degree of heat will either be dissipated or absorbed via the surface area of the enclosure. Care must also be taken not to oversize the cooling system as to create a condensation problem within the enclosure which could eventually result in corrosion and/or computer failure which is what we are trying to prevent from the beginning.