When it comes to the issue of effectively controlling and dissipating electronic heat in a closed container, there is no shortage of advocates for either a heat exchanger or an air conditioner.
Air conditioning was considered the method of choice for many years. After all, it was effective, particularly in harsh environments, and fairly reliable. Many companies likely viewed the expense of around-the-clock air-conditioning operations to protect enclosed electronics as the unavoidable cost of doing business — a necessary but costly drain on operating budgets.
Likewise, compressed air is an effective and acceptable option, but it, too, has considerable operating costs as well as the need for a compressed air source. In addition, all hot spots must be identified before commencing compressed air flow, which may account some reported incidents in which cabinet doors were left partially open. Operating with the cabinet doors open exposes the electronics to contamination.
Where technology has made a difference is in the development of the heat exchanger and its ability to cool all potential hot spots at slightly above outside ambient air temperatures. Technological improvements have enabled the heat exchanger — a closed loop system with sealed panels — to effectively circulate air inside the cabinet to keep hot spots from forming. Heat exchangers are a proactive form of heat dissipation as opposed to the reactive method of responding to hot spots’ sudden appearance within the enclosure. While the other methods are likely preferable under certain harsh conditions, the heat exchanger is proving to be effective, less costly and adaptable to many applications.
Development of Compact Heat Exchangers
Perhaps the biggest technological impact in the evolution of heat exchangers, which had been produced since the early 20th century, was the development of the compact heat exchanger. Its development was spurred in part by the need for more adaptable exchangers as viable alternatives to the downsides associated with air conditioning. By the early 1980s, air conditioning was viewed as the easiest and most convenient option for cooling waste heat in the burgeoning field of computerized electronics. However, it had its drawbacks in the form of size, weight, energy use, maintenance and relatively short lifespan. It also put enclosures at risk from potentially damaging residual effects of constant operations: condensation settling on the electronics or oil mists. Either or both could render the electronics ineffective.
The change came when IT staff, interested in cost-effective and efficient alternatives, began seriously considering heat exchangers for heat dissipation. Compactness was just one reason. Another was that compact exchangers operate with a closed loop system that protects enclosures from outside air. A third was that technological improvements in the last two decades had increased the efficiency of heat transfer and dissipation through heat exchangers. (By contrast, air conditioning is generally unchanged from the process used decades ago.) One example of the technical improvements made is the heat pipe, which is used in conjunction with fans and aluminum fins. Fans move the heat either closer to or over the pipe, making the heat transfer more efficient. The pipe’s role is to divert heat from the electronics to ensure a longer lifespan.
In its compactness and capability, the heat pipe is an extremely efficient thermal conductor. Its performance is based on the physical principle of latent heat of vaporization — a concept generally associated with condensation or boiling — in which heat is transferred without any significant temperature change. Half of the heat pipe within the unit is exposed to the heat inside the cabinet or enclosure; the other half is exposed to the outside air. Fans circulate the heat inside, allowing the heat pipe to more efficiently transfer the heat outside the enclosure. In addition, plates and fins support the pipe’s ability to move the air more quickly and efficiently. Fans are the only devices that require an external energy source for either heat transfer or dissipation.
Compact heat exchangers are able to keep outside air and contaminants from entering the enclosure thanks to a flange and neoprene gasket — an important component in the unit that ensures against air exchange, either inside or out. The heat pipe technology cools the electronics at slightly above ambient temperatures and keeps hot spots from forming. While manufacturers note that operational costs of heat exchangers are significantly below that of 230 V air conditioners, they also cite their product’s lifespan: as much as 30 years compared with as little as two years for air conditioners that operate constantly in very harsh environments.
Air Conditioners: Positives and Negatives
All of the positives about heat exchangers do not change the fact that air conditioners still have an important role in the cooling of enclosed electronics. They are certainly more effective in high ambient climates such as the American Southwest or the Middle East. The concerns, though, mostly center on costs due to significant energy use required for continuously operating air conditioners, maintenance and wear and tear.
Another potential issue is that many air conditioners still use Freon, a chlorofluorocarbon (CFC) regulated by the U.S. Environmental Protection Agency, which has declared CFCs to be potentially damaging to the planet’s ozone layer. Manufacturers are phasing out Freon from their air conditioners, but many that contain this CFC still operate in various capacities, including enclosure cooling. Freon-based air conditioners pose potential environmental issues that most companies would prefer to avoid in this era of green technology.
With air conditioning, there is no concern about hot spots because cooling occurs at well below ambient temperatures. Information technology professionals, however, are beginning to question whether it is necessary to expend the energy and costs to chill electronics in order to protect them. Heat exchangers effectively prevent hot spots even though the cooling is slightly above the ambient temperatures. For those conditions that require cooling at below ambient, manufacturers have developed air-to-water heat exchangers that use only a gallon of water per minute to achieve the lower temperatures.
In conclusion, finding the most efficient and cost-effective method for heat transfer will always be a challenge due to a number of variables such as internal and external environments, energy usage and corresponding costs, and equipment lifespan. Yet the operating costs associated with vortex systems and particularly air conditioners may not exclude them from being the preferred choice if the outside and indoor plant environments are so harsh that maximum, constant chilling is required at all times.
For many environments where enclosures of electronics operate, however, those cooling demands do not exist. Reduction of heat inside the cabinet at temperatures only slightly above the ambient outside air has proven to be every bit as effective at considerably less cost. While there may be a mindset that colder is always better, analytics prove otherwise and merit consideration when choosing the optimal method of electronic heat dissipation.