BY ERIC CORZINE,
Product Manager- Climate Control
Rittal Corp.
The reliability of electronic systems is paramount to all sorts of industries today, from commercial ISPs who run large data centers to automobile manufacturers who depend on electronic controls to keep their factories running. And the biggest threat to those systems is heat: the operating life of semiconductor devices is generally cut in half for every 10ºC rise in their internal junction temperature.
Compounding the problem is the fact that, to protect electronics from contaminants in the surrounding environment such as dirt, dust, and even water or paint spray, commercial data center and industrial electronics are typically installed in large enclosures. But enclosing electronics tends to make the heat they generate stay put, thereby endangering the performance life of the electronics. For that reason, enclosure designers have come up with a variety of ways to remove heat from enclosures. As will be seen, the most recent techniques are extremely efficient, and result in many additional benefits for users.
Traditional cooling approaches
To begin, let’s look at some of the traditional approaches to removing heat from enclosed electronic systems. In the past, heat has sometimes been removed from enclosures passively using either heat conduction or convection, depending on whether the enclosure is open (air-permeable) or closed (air-tight). With an open enclosure, the heat can be removed from the enclosure simply by natural air circulation, that is,. thermal conduction, from inside to outside. On the other hand, if the enclosure has to remain closed, the heat can only be dissipated via the enclosure walls, that is, through convection. Such approaches have the advantage of not adding additional costs to the enclosure and not requiring any energy. However, the maximum amount of heat such approaches can handle is only to about 350 W, and hot spots may occur in the enclosure.
To improve heat dissipation by convection at the enclosure walls, circulation fans are sometimes used. By circulating the air inside the enclosure, these fans offer better heat distribution inside the enclosure and at the enclosure walls, and limit internal hot spots. Still maximum cooling is still only 350 W, and it requires that power be added for the fans (fig. 1 ).
Fig. 1: Passive systems, even those like the one shown here using circulating fans, are not able to provide the amount of cooling most electronic systems need today.
Many systems today rely on active cooling methods to overcome limits on heat removal. The world's most widely used solution for the dissipation of heat from enclosures and electronic cases is the enclosure cooling unit. By using this unit, the enclosure internal temperature can be cooled to well below the ambient temperature, for example, with an ambient temperature of 45°C, the internal temperature can easily be kept to 35°C.
These systems work on the same principle as a refrigerator or air conditioner (fig. 2 ). In the cooling unit, a refrigerant (type R134a) is used as the cooling medium. The gaseous refrigerant is compressed by a compressor, causing it to heat up. The refrigerant is led through refrigerant pipes to an external heat exchanger (condenser), where the heat of the refrigerant is dissipated to the ambient air (cooled).Due to this cooling, the refrigerant liquefies and flows via the filter dryer to the expansion valve. Pressure reduction takes place here. The refrigerant is depressurized and flows through the second internal air heat exchanger located inside the enclosure. The heat from the enclosure is absorbed by the refrigerant in this heat exchanger. Due to heating, the refrigerant is gaseous once more and is compressed by the cooling compressor, and the cycle begins again.
Fig. 2: Traditional refrigerant-based cooling systems can be effective at moving large amounts of heat energy, but do so at the cost of significant power consumption.
While such cooling units are effective, and can easily handle cooling of up to 5,000 W, they tend to consume a great deal of energy, making them expensive to operate.
A cooling breakthrough
Thanks to a game-changing, patented hybrid technology, a series of cooling units called Blue e+ changes the cooling paradigm for enclosures. The units, introduced recently by Rittal, are more efficient in both performance and energy consumption than any traditional cooling units. This advanced cooling technology employs two parallel cooling circuits working together; the degree to which each circuit is employed depends on temperature difference between the enclosure and their external ambient environment.
In Blue e+, one cooling circuit is passive, while the other is active. The passive circuit is based on heat pipe technology (fig. 3 ). In the heat pipe cooling circuit, a liquid refrigerant inside an evaporator coil evaporates, absorbing energy from inside the enclosure and turning into a gas. The gaseous refrigerant then rises inside the pipeline up to the condenser, where it cooled down, releasing its heat energy to the external ambient environment and returning to its liquid state. The now-liquid refrigerant then flows, due to gravity, back down through the copper pipe to the evaporator coil, where the cooling cycle begins again.
Fig. 3: Use of passive heat pipe technology significantly reduces the power consumption needed to achieve optimal cooling.
The heat-pipe system has the advantage of not requiring any energy to circulate the refrigerant, but is not by itself able to handle large differential temperature difference between the ambient and internal environments. Thus passive technology is coupled with an active one, essentially the air conditioning system described above, so that the combined system can provide the desired cooling in the most efficient manner.
Key to this operation is an intelligent cooling-speed regulation system. In this system, the required cooling output in the enclosure is calculated and fan and compressor speed are centrally controlled via the inverter. This results in significantly less thermal cycling in the enclosure (fig. 4 ) and thus provides greater protection of components because it maintains a constant cold air outlet temperature. Furthermore, the cooling unit can adapt flexibly to temperature changes in the enclosure.
Fig. 4: The reduced thermal cycling that Blue e+ makes possible can significantly increase the reliability and lifetime of electronics.
This operation also results in providing the highest seasonal energy efficiency ratio (SEER) available today. Whereas the energy efficiency ratio (EER) is calculated using an assumed ambient temperature (also referred to as hall temperature) of 35°C, in reality, temperatures are usually significantly lower than 35°C, and fluctuate over the course of the year. To precisely calculate energy efficiency, it is necessary to consider the seasonal temperature variation. Thus SEER is a better, truer measure of efficiency.
Because Blue e+ is newly developed, it responds to major industrial trends in ways that other system haven’t. For instance, Blue e+ is designed to operate with all the common power system around the world, whether they are 50 or 60 Hz and regardless of voltage level. Then too, the control mechanisms for the unit are state-of-the-art, providing a simple handheld device that uses near-field communications (NFC) to let maintenance personnel communicate with systems to obtain performance data and set parameters using simple plain statements in local languages (fig. 5 ).
Fig. 5: An NFC device with touch control lets user gather data and adjust settings on the fly.
As a result, Blue e+ can provide the kind of performance that companies need to be certain their systems provide the up-time they need to compete in markets today.
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