The rapid growth of integrated networks and systems has led to an increasing demand for dependable and continuous power. To support a reliable supply of electrical energy to power these networks and systems in the event of an outage on the electric grid, the Uninterruptible Power Supply (UPS) system serves as a source of nearly instantaneous backup power. Strings of batteries typically power these UPS systems, providing energy that is available to support critical operations when an outage occurs.
As integrated networks and systems quickly evolve, new challenges arise that demand innovative solutions. These challenges include occupying valuable indoor space, exposing backup batteries to the UPS system’s radiant heat, and consumption of additional energy to power air conditioning at a low enough temperature to maintain an optimal environment for backup batteries.
Take It Outside: Equipping the Battery Backup System for Outdoor Placement
When selecting the proper UPS backup batteries, the expected operating temperatures should be taken into account. An ideal ambient temperature can be difficult to maintain if the battery backup system is not equipped with thermal management technology, especially for cooling. While the electronic components in the UPS system typically tolerate a much wider range of temperatures than the batteries, it is also easier to direct cooling air to them than it is to batteries, which often get minimal cooling, if any.
When this equipment is located indoors, the task of maintaining temperatures that are ideal for UPS and other backup power equipment is complicated. Many UPS systems lack adequate cooling for the backup batteries, especially in the case of modular and containerized UPS systems. This often places additional energy demands on the facility’s air conditioning system, as the indoor environment must be kept cool enough to safeguard backup batteries.
The placement of UPS systems indoors also takes up valuable facility space, which can be used for other, more profit-producing equipment and additional workspace for personnel. This is especially critical in operations with a high value on floor space, such as hospitals.
An alternative solution is to “take it outside”; i.e., to move the battery backup system into a specially designed exterior enclosure. Thermal management technology, which includes air conditioning and heating, provides an environment for optimum performance and longevity of UPS batteries that are housed in outdoor enclosures.
Most air conditioning units deployed in support of outdoor enclosures are closed-loop systems based on a vapor compression cycle: The refrigerant changes from liquid to gas (evaporation), which absorbs heat from within the enclosure and transfers it to the outside air. This cools and removes humidity from the enclosure. Air conditioning is energy efficient, as there is a small amount of energy loss during the cycle, and it can manage a large heat load, making it reliable in even very high-temperature climates. Managing a large heat load makes air conditioning among the highest performing thermal-management technologies, as it is able to cool an enclosure’s interior far below high ambient air temperatures. Thermal management technology will also heat the interior far above low ambient air temperatures.
Thermally managed enclosures help enable the batteries to operate for their entire service life, reduce maintenance and require less frequent replacement by protecting the batteries from extreme temperature, inclement weather, and other outdoor conditions.
Thermally Managed Outdoor Enclosures
To maintain the proper operating temperature for backup batteries in the most extreme environments, thermally managed UPS outdoor enclosures are equipped with efficient air conditioning and heating for minimal energy consumption and reduced cooling costs. For example, the VaultFlex UPS outdoor battery enclosure from EnerSys is designed to operate in an ambient temperature range of minus 22°F (minus 30°C) to 113°F (45°C). Constructed of corrosion-resistant aluminum with steel racks and rails, the VaultFlex UPS outdoor enclosure is rated for outdoor use.
The thermal management features of these UPS outdoor enclosures deliver the following benefits:
- Additional indoor space – Moving the housing of backup batteries for UPS systems outdoors will make additional space inside of the facility available for other equipment and personnel. Even though the battery backup system is outdoors, it is still protected from the elements and extreme temperatures.
- Air conditioning set at higher temperatures – If the UPS enclosure is installed inside of the facility, it is no longer necessary to set the air conditioning at a lower temperature for that room, provided all other equipment in the room will tolerate higher temperatures, which is typical of most installations. By using the enclosure’s air conditioner to maintain a temperature specified for the backup batteries, the facility’s air conditioning does not need to be set at an artificially low temperature, which results in savings on cost and consumption of energy.
- Placement adjacent to UPS system – The battery backup power system can be installed in a position that is adjacent to modular, containerized UPS systems, which typically lack adequate cooling to protect the batteries from premature failure. The UPS outdoor enclosure should be capable of maintaining a temperature of 68°F (20°C) in low ambient temperatures, and slightly below 77°F (25°C) in high ambient temperatures.
Temperature levels activate the thermal management features of the UPS outdoor enclosure. If the ambient temperature drops below 3°F (0°C), the heater will maintain a temperature of 68°F (20°C) inside of the enclosure. If the ambient temperature rises above 46°F (8°C), the air conditioner will maintain a temperature of 77°F (25°C), and for temperatures up to 110°F (43°C), the air conditioner will keep the temperature inside of the enclosure from exceeding 86°F (30°C).
VaultFlex UPS outdoor enclosures also include passive ventilation that mitigates hydrogen gas. They are constructed to protect backup batteries from earthquakes in compliance with seismic certifications IBC (2015), ASCE 7-10, CBC (2016), and California OSHPD healthcare infrastructure requirements. They are also CSA certified to UL 1778.
Backup Batteries for UPS Applications
The enclosure, however, is only part of the overall battery backup system for UPS applications; the other important element is the batteries themselves. Needs have evolved from the 15-minute rate discharges required of UPS systems to support main frame computers of the past to rate discharges of five minutes or less that modern, globally interconnected networks now demand. Trends such as cloud storage, the availability of data/communications equipment and bandwidth to retail customers for rent, and modular and containerized power, as well as shorter run times and higher ambient temperatures, have placed new demands on UPS batteries. In response, a new generation of batteries featuring Thin Plate Pure Lead (TPPL) technology has been introduced for UPS applications.
EnerSys DataSafe XE batteries, constructed with TPPL technology, have plates that are manufactured in a proprietary, continuous, and highly controlled grid fabrication process for maximum consistency. Advanced, high-purity lead and acid provide more efficient energy consumption. The use of proprietary manufacturing processes and pure materials also results in less electrical resistance and greater conductivity by forming a unique, solid reaction surface.
The TPPL technology also fosters greater conductivity and lowering resistance by greatly reducing both grid corrosion and grid growth common in conventional alloyed lead acid batteries, which typically experience calcification. Another advantage of high-purity materials is reduced gas generation within the cell. As a result, TPPL batteries have an extended operating temperature range of minus 40°F (minus 40°C) to 122°F (50°C), enabling users to reduce cooling costs. The lack of impurities also improves the battery’s service life, and extends shelf life by as much as three times that of conventional batteries.
The use of pure lead in TPPL technology enables plates to be made as thin as 1 millimeter (as opposed to a thickness of 2 to 4 millimeters for conventional alloyed lead acid batteries), so that as much as 20% more plates will fit in each two-volt cell than conventional Absorbed Glass Matte (AGM) batteries. Pure lead plates are denser and require less space between them. This results in increased surface area, better active materials utilization, and greater power density. With this energy-dense design, smaller, lighter batteries are able to achieve the same run times as larger conventional lead acid batteries, with reduced recharge rates. Following a full discharge, the TPPL battery can achieve 100% State of Charge (SOC) in 50% less time, compared with conventional lead acid batteries.
The enhanced density of TPPL batteries like the DataSafe XE battery provides discharge rates from 30 seconds to five minutes, and a wider operating temperature range that requires less cooling of the UPS system’s environment. TPPL technology also enables the batteries to have a higher cyclic capability, as much as 25% longer service life (seven years or longer) and a longer shelf life (17 months) than lead-calcium batteries at 77°F (25°C).
As integrated networks and systems grow, indoor space is becoming increasingly valuable. At the same time, backup batteries are being exposed to the UPS system’s radiant heat. A battery backup system comprised of TPPL batteries housed in a thermally managed UPS outdoor enclosure is among the most effective solutions for placement outdoors, adjacent to modular and containerized UPS systems, or even indoors with room air conditioning set at temperatures as much as 10°F (approximately 5.5°C) higher.