As telecommunications providers respond to growing service demands with ever-increasing power density, a need has arisen for additional equipment to handle the load while reducing the facility's total cost of ownership (TCO).
One way of reducing TCO is to reduce the frequency of battery replacements and interruptions of service by using backup battery systems that are designed and manufactured to meet the demands of the application. These backup battery systems typically use lead acid batteries, which provide the power density that telecommunications networks require.
A significant factor that affects the life of lead acid batteries is temperature. Lead acid batteries function best at an average of 77 degrees F (25 degrees C); high temperatures severely reduce life expectancy. For every 15 degrees above 77 degrees that a valve regulated lead acid (VRLA) battery experiences, the float life is reduced by half. The environment in which the batteries are used, such as in the open air, can subject them to high temperatures that compromise their service life.
Two options in the selection of backup battery systems can reduce the facility's TCO with technology that addresses high-temperature environments.
Option 1: Outdoor placement
In order to make better use of indoor facility space in the face of additional equipment, some telecommunications facilities have chosen to "take it outside"; i.e., to move the backup battery system out of the building and into an outdoor enclosure designed for the purpose. Unlike constructing a new facility, outdoor enclosures reduce costs by being simple to install and maintain. Maintenance should be performed in compliance with the manufacturer's guidelines, and any questions should be directed to a battery professional.
An ideal battery temperature can be difficult to maintain if the battery's outdoor enclosure is not equipped with thermal management technology, especially for cooling. Enclosures will be subjected to significant heating from solar exposure if they are not insulated and cooled. In these cases, temperatures can reach 50 degrees F above outside ambient temperature. Any electronics, such as rectifiers or radio equipment, that are located inside the enclosure with the batteries can generate significant heat load and contribute to elevated internal temperatures.
Features that make outdoor housing viable are enclosures with thermal management capability, which keep backup batteries near their optimal temperature of 77 degrees F, even when outside ambient temperatures are extreme. Thermally managed enclosures can improve service life, reduce maintenance and require less frequent battery replacement by protecting the batteries from extreme temperatures, inclement weather and other outdoor conditions.
Among the cooling options available for thermal management are direct air cooling (DAC), air conditioning (AC) and zone cooling, in which the division of the enclosure into multiple thermal zones allows the support of a range of equipment to maximize reliability and reduce TCO.
DAC, also referred to as free air cooling, uses a fan with a particulate filter to cool the enclosure. This type of system can ventilate the heat load from sun exposure and from batteries and other electronic devices that are inside the enclosure. The advantage of a DAC is low operating cost and low maintenance requirements. DAC systems are best used in mild climates since they cannot cool the chamber below ambient conditions. In hotter climates, the service life of the batteries can be affected with a DAC system.
AC cooling is a better choice for enclosures that will be exposed to high temperatures on a regular basis. A properly sized AC unit will maintain the ideal battery temperature for maximum service life. An AC unit will have higher operating costs and maintenance requirements, so the TCO must be carefully evaluated, with consideration of geographic location, to determine the lowest cost solution.
Enclosures that have zone cooling are divided into multiple thermal zones that use combinations of DAC and AC units. Any electronic equipment that generates significant heat and can tolerate greater temperature extremes can be cooled at a lower operating cost with a DAC unit or an AC unit set at a higher temperature. A separate battery compartment with a lower heat load can then be cooled with an AC unit to maximize the battery service life and performance. This type of design is best when electronic equipment and batteries are in the same enclosure.
Taking the backup battery system outside can take less than one day to install once a concrete pad is poured. Modularity of outdoor enclosures also enables additions to the existing unit when expansion is needed.
The enclosure, however, is one of two options available for backup battery systems; the other is the batteries themselves.
Option 2: Better batteries
Telecommunications facilities have an additional cost-reduction option in reserve power system selection: batteries that feature thin plate pure lead (TPPL) technology. Batteries with TPPL technology use 99.99% pure lead for the battery grids and active material. In addition, the high-purity electrolyte provides an extremely low float current and high recombination efficiency, which slows the drying out of the electrolyte and corrosion of the plates to extend service life.
For applications in telecommunications infrastructure, TPPL batteries can withstand higher temperatures than conventional lead acid batteries. As a lead acid battery is exposed to higher temperatures, the corrosion rate of the grid increases. The corrosion of the positive grids is a primary determinate in the service life of lead acid batteries. The use of pure lead alloy for the positive grid slows the corrosion enough to enable the batteries to perform with a 10-year service life at 50% higher operating temperature than conventional VRLA batteries can withstand.
Conclusion
Telecommunications operators have options to reduce their TCO in the selection of backup battery systems. These options include housing batteries in thermally managed outdoor enclosures and using batteries with TPPL technology. The selection of the right thermal management solution and battery type to minimize TCO can depend on location. A reputable battery professional who has experience with enclosures and batteries deployed in backup power systems can provide a detailed analysis to find the ideal solution for each particular site. Finding the right solution can provide significant cost reductions in initial capital, lower operating cost, less maintenance and less frequent battery replacement.
Jason Zerbe is systems marketing manager at EnerSys.
