Computers and other sensitive electronic components are being used in increasingly hostile surroundings, where the inherent vulnerability of these devices has become a major consideration. High temperatures, contaminant-laden air, and humid or corrosive atmospheres can wreak havoc on electronic equipment. Few plants in today’s lean manufacturing environment can afford the costs associated with repairs, downtime and lost data due to inadequate protection. However, enclosure cooling systems can be large, awkward and expensive, and because they require maintenance and increase energy consumption, they add cost. How can a company protect its technology investment without increasing the complexity of its operation?
Thermoelectric solid-state cooling systems are one possible solution. Compact, versatile and lightweight, these electronic devices require minimal maintenance and can provide years of reliable service. With relatively low energy requirements and the ability to provide both cooling and heating when needed, these systems are becoming increasingly popular for enclosure cooling applications.
Principle of OperationThe underlying technology that permits construction of thermoelectric cooling systems is known as “The Peltier Effect.” The technology uses two elements of a semiconductor constructed from doped bismuth telluride. Upon application of a direct current (DC) power source, the device generates a cooling action that is countered by a generation of heat on the opposite side (figure 1). With the right packaging, the cooling properties of these devices can be harnessed into modular air conditioners that can dissipate loads of 200 to 1,500 BTU/hr, which commonly are found in industrial plant applications. For some applications with higher cooling requirements, multiple thermoelectric systems can be used to provide the necessary cooling.
The thermoelectric devices themselves are small and lightweight - for example, a 200 BTU/hr system might weigh as little as 9 lb and measure as small as 8 by 6 by 7". Unlike many compressor-based cooling systems, which typically are mounted in a single orientation to prevent oil loss in the compressor, thermoelectric devices can be mounted in any configuration. This flexibility allows them to be used in plant retrofits and upgrades where space limitations might preclude the use of traditionally mounted cooling technologies.
While many enclosure cooling systems are limited to applications below 125°F (52°C), thermoelectric air conditioners can be used in applications up to 140°F (60°C), and some thermoelectric devices can be designed to operate in conditions well beyond this limit. For plants that are located in desert regions or that need to protect and cool electronic equipment in high-temperature operations, the high temperature limit of thermoelectric systems can provide a significant benefit.
Additionally, because the cooling air is generated within the device, no air is exchanged between the outside (ambient side) and inside of the enclosure to achieve cooling (figure 2). As a result, particulates and contaminants in the surrounding air remain outside the cabinet, and the air within the cabinet remains clean.
Minimized MaintenanceThermoelectric systems are solid-state devices; they have no moving components other than a few fans, and they do not require filters or refrigerant. As a result, minimal maintenance is required to keep the systems running smoothly. A typical thermoelectric system might operate for 5 to 10 years or more before needing maintenance. The most common service requirement is a simple fan cleaning or change-out.
In testing performed to evaluate the mean time before failure (MTBF) of various thermoelectric components, the fans exhibited a lifetime of 50,000 to 80,000 hours, which translates to roughly 6 to 10 years. The thermoelectric modules inside the unit were rated for more than 200,000 hours (more than 20 years) in applications at 122°F (50°C). Also, the system’s power supply was rated for more than two million hours (more than 200 years).
Because of their reliability, thermoelectric cooling systems often are used in remote-mounted locations, where they provide trouble-free service with minimal monitoring.
A Versatile OptionSome types of enclosure cooling systems rely on compressed air for cooling. These can consume considerable energy. Some plants may reduce their energy consumption while maintaining the desired level of cooling by using one or more thermoelectric air conditioners. While thermoelectric coolers do, of course, use electricity, they can be designed to minimize current draw. For instance, a 400 BTU/hr cooler operating from standard 120 V AC power might have a current draw of only 2 A, while a 1,500 BTU/hr unit, also operating from 120 V AC power, might have a draw of only 6.3 A. These levels often may be lower than those required for compressor-based systems.
Extreme cold can be just as damaging to electronic components as extreme heat. For outdoor enclosures in regions that experience hot summers and cold winters, thermoelectric systems that can both heat and cool can provide a way to protect sensitive equipment year-round. In some thermoelectric systems, the switch from cooling to heating is accomplished by reversing the polarity through the device. However, this effect can shock the thermoelectric modules and reduce their useful life.
Other thermoelectric devices use embedded cartridge heaters in the base of the cold-side heat sinks. These heaters ensure that the system remains above a minimum temperature in the winter and below a maximum temperature in the summer without compromising the reliability or durability of the thermoelectric modules.
Numerous options exist for cooling and protecting electronic components in enclosures. Plants that need a flexible system with minimal maintenance requirements and low energy consumption can turn to thermoelectric cooling systems for reliable performance.