OSP Magazine August 2015

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CABINETS & ENCLOSURES

Today’s cell sites are expanding into remote locations that are often inaccessible and characterized by unstable grids. This presents many challenges. As such, they require hybrid

solutions incorporating energy storage to handle frequent, multiple outage events.

The batteries used in these applications must be able to recover quickly and survive partial states of charge (POC), harsh weather, and extreme temperatures. Keeping batteries at their optimal temperature range helps ensure high-performance and long life, with high reliability and low operating expenses.

The best way to ensure that batteries perform at their peak in rugged, outdoor environments is with thermally managed outdoor cabinets.

Survivors!Protecting Your Investment in Remote Cell Sites By Joel Fastow and Erin Bresnahan

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Figure 1. Airflow with a DAC System. Figure 2. Components and airflow with a TEC System.

5 Cabinet Selection Considerations This article discusses the 5 considerations to evaluate when looking

for the right hybrid battery and enclosure system for today’s remote

cell sites.

Consideration #1 Surviving Remote Locations

Remote locations frequently are inaccessible, and are plagued by

unstable grids. This necessitates hybrid solutions that incorporate

energy storage that can handle frequent outages and batteries that

can recover quickly and survive partial states of charge (POC) and

harsh weather.

South America is one example characterized by an unstable grid,

plagued by frequent outages and extreme and varied weather

conditions. It is not uncommon for sites there to experience 10 to 20

micro events weekly that last less than a minute, as well as 3 events

lasting more than 3 hours. A hybrid approach involving generators,

solar, and batteries helps keep the network running.

Consideration #2 Optimizing Energy Storage

In an ideal world, you want to optimize battery ownership.

Therefore, you need batteries with higher cycles, quicker recharge

rates, and longer life, to reduce run time and the fuel costs for

generators. Meantime, some manufacturers are building new

eco-efficient enclosures with no additional cooling. While this

reduces costs, it subjects the battery to higher temperatures. You may

also have older cabinets for which you are seeking the same efficien-

cies by reducing run time on air conditioning. Both scenarios drive

demand for temperature-tolerant batteries.

Battery manufacturers such as EnerSys are turning to specialized

manufacturing processes to develop batteries that reduce ownership costs,

while outperforming other batteries.

A cabinet system should be able to:• Accommodate the full range of

applications needed -- from initial deployment to large capacity backup power systems.

• Grow with your application.

• Offer a wide range of thermal system technologies to handle seasonal temperatures and humidity, as well as the thermal load produced by the active equipment and components deployed within it.

• Prevent moisture entry.

• Have minimal parasitic power consumption.

Additional features that users may appreciate include zoned cooling and security and intrusion prevention measures.

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Thin Plate Pure Lead (TPPL) batteries with ultra-thin,

corrosion-resistant plates and uniquely designed jars offer

roughly 30 percent more power density and about 11

percent more energy density than similarly-sized Valve

Regulated Lead Acid (VRLA) batteries. They also

provide a shelf life of up to 24 months without a charge,

compared to 6 months for a traditional lead-calcium

battery. TPPL batteries also are less likely to fail in

extreme temperatures and can be used from -40 to 122 F.

These features make TPPL batteries ideal for unattended

locations with minimal or no climate control system. As

such, they offer tremendous reliability and reduced owner-

ship costs -- ideal for system hardening in today’s data-

saturated market.

Consideration #3 Thermal Management

While some batteries may be more temperature-tolerant

than others, all batteries in remote locations can benefit

from the protection of a thermal-controlled enclosure.

Many factors affect the thermal performance of an

outdoor cabinet -- primarily the range of seasonal

temperatures and humidity, the thermal load produced

by the sun, and the thermal load produced by the active

equipment and components deployed inside. More than

any other feature, the thermal management system may

have the largest impact on ongoing operational expenses.

Figure 3. Components and airflow within an A/C System.

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Today’s manufacturers offer a range of technologies and

capacities to match the user’s thermal management

requirements. The trick is that you must weigh their options

based on technology, performance, reliability, and cost.

Today’s options include Direct Air Cooling (DAC),

Thermoelectric Cooling (TEC), Air Conditioning (A/C)

and Zone Cooling. These help optimize the thermal

environment for the equipment, while minimizing

ownership costs over the cabinet’s lifetime.

Direct Air Cooling (DAC)DAC systems provide excellent above-ambient thermal

management performance that is ideal for deployments

in locations with moderate annual temperatures. DAC

uses open-loop systems that bring outdoor ambient air

into the cabinet’s interior for cooling purposes. DAC

systems typically employ inexpensive mesh filters to

prevent particulate contamination from entering the

cabinet or, alternatively, can be equipped with high-per-

formance hydrophobic filters that prevent moisture entry.

DAC systems are highly reliable and consume little

energy, which makes them well suited for operation

during commercial power outages due to their low

parasitic power consumption from the batteries. They

also have long life expectancy; the only moving parts are

the fans. (See Figure 1.)

Thermoelectric Cooling (TEC)TECs use the Peltier effect,1 in which current applied

across 2 dissimilar materials causes a temperature differen-

tial. TECs offer variable and scalable incremental cooling

and heating in a compact form factor and are ideal for

deployment in any temperature climate. TECs offer high

reliability and long life expectancy because the fans that

circulate air are the only moving parts. They require no

maintenance and can operate on battery backup during

commercial power outages. In general, a TEC will

consume more power than a DAC. (See Figure 2.)

Air Conditioning (A/C)A/C offers among the highest performance thermal

management technology, as it is able to support high heat

loads and cool an enclosure’s interior far below ambient

air temperatures. Most A/C units deployed in support of

outdoor enclosures are closed-loop systems based on a

vapor compression cycle: The refrigerant undergoes a

change of state (from a liquid to a gas) that absorbs

thermal energy from within the enclosure and transfers it

to the outside air. This process also removes humidity

from the enclosure. (See Figure 3.)

“ It is not uncommon for sites in South America to experience 10 to 20 micro events weekly that last less than a minute, as well as 3 events lasting more than 3 hours.”

Zone CoolingThis thermal system option separates the cabinet into

multiple zones, each using a thermal management

technology optimized specifically for the equipment or

components deployed in each zone. This capability is

especially useful for cabinets that house both batteries

and electronics.

Consideration #4 Security and Intrusion Prevention

Security is a critical concern today. Unauthorized access

to equipment can result in not only the loss of or damage

to valuable assets, but possible network downtime, reduced

service revenue and unsatisfied customers. Considering

that the cost of an unplanned data center outage is likely

to exceed almost $8,000 per minute per incident,2

protecting a system is of the utmost importance.

Features that can enhance security include:

Interior Door Hinges: Hinges on all access doors

ideally should be accessible only from inside the cabinet,


Figure 4a. Initial Deployment. Figure 4b. Increased Capacity Deployed at Later Date.

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and reside inside the cabinet’s exterior gasket area so they

are protected from exposure to the elements. The hinge

should not be visible or accessible when the cabinet door

is closed. Unlike interior hinges, exterior hinges can be

easily knocked off the cabinet, thus allowing the removal

of the door and access to the interior.

Door Latches and Frame: Some cabinets feature

exterior doors with multi-point, captive latching mecha-

nisms located in the cabinet’s interior to ensure that all

door corners and edges are secured and inaccessible when

the door is closed. Latches that aren’t captive can easily be

compromised. Ideally, there should be minimal gaps

between the edge of the door and the cabinet frame, and a

flange along the interior of the door to prevent intrusion.

The door-latching hardware and mechanisms should

be capable of withstanding serious torque (up to 400

in-lbs.) without physical distortion or a loss of function-

ality. Look for a model where, in the event that the

exterior handle is compromised, the latching mechanism

is not accessible to external tampering and stays in the

locked position.

Intrusion Alarms: Intrusion alarms can be configured

to alert in case of an unauthorized or unscheduled

opening of the door.

Consideration #5 Expandability and Flexibility

When specifying an enclosure for a remote location,

it is important to consider future needs. Ideally, the

enclosure system should be able to accommodate

changing application needs and various environments

where your equipment is deployed. An enclosure with

numerous configuration options enables you to standard-

ize with one enclosure model, while providing the

flexibility for the different equipment configurations and

deployment challenges presented by unique environ-

ments. Features such as additional equipment bays,

power and battery backup, and thermal management

capacity ensure that the cabinet will meet deployment

demands today and tomorrow, without the need for

expensive and limited custom development.

One way to ensure future adaptability is to make sure

that the enclosure architecture can accommodate

horizontal expansion, typically called a line-up. Features

that enable horizontal expansion include aligned bolt

patterns for mechanical joining of the adjacent walls, and

alignment of knockouts on the walls that allow cable

pass through between connected bays.

Customers can select the capacity that meets their

needs and minimizes initial costs, then incrementally

increase capacity over time, as demand and requirements

change. As shown in Figure 4, an initial deployment

could consist of a single bay 3-tier cabinet that includes a

DC rectifier system. The initial deployment could be

configured with a single string of batteries, allowing for

growth of another string of batteries in the future, or

Figure 5. A dual bay battery cabinet.

“ Considering that the cost of an unplanned data center outage is likely to exceed almost $8,000 per minute per incident, protecting a system is of the utmost importance.”

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could be initially configured with 2

strings of batteries.

If more than 2 strings are required

in the future, a second single bay

3-tier cabinet can be installed next to

the original cabinet. The second

cabinet is physically attached to the

first, presenting a unified monolithic

cabinet that now supports DC

rectifiers and up to 5 strings of

batteries.

Dual bay battery cabinets (See Figure

5.) are designed for applications that

require large-capacity, such as backup

power, energy storage, and uninterrupt-

able power systems. A dual bay battery

cabinet supports up to 40 battery blocks

@ 12Vdc that can be arranged as 10

strings @ 48Vdc, 4 strings @ 120Vdc

strings, or 1 string @ 480Vdc string.

SummaryIn conclusion, remote cell sites are

here to stay, which means you can’t go

cheap when it comes to protecting

your investment. The best way to

accomplish that is to insist on quality

-- both with the batteries themselves

and the cabinets protecting them.

Endnotes1. “The Physics of Cooling Techniques,” S.H. Price, March 26, 2007, http://ffden-2.phys.uaf.edu/212_spring2007.web.dir/sedona_price/phys_212_webproj_home.html2. “2013 Cost of Data Center Outages,” Ponemon Institute, December 2013, http://www.emersonnetworkpower.com/documentation/en-us/brands/liebert/documents/white%20papers/2013_emerson_data_center_cost_down-time_sl-24680.pdf

Joel Fastow is Marketing Manager, Telecom, EnerSys®. He has over 30 years of experience in commercial marketing. For more

information, email [email protected]. EnerSys provides stored energy solutions for industrial applications, manufactures and distributes reserve power and motive power batteries, battery chargers, power equipment, battery accessories, and outdoor equipment enclosure solutions. The company provides aftermarket and customer support services to customers through its sales and manufacturing locations in over 100 countries worldwide. For more information, visit www.enersys.com.

Erin Bresnahan is Product Manager, Purcell Systems. She has over 6 years of experience in marketing and product management. For more information, email [email protected] or visit www.purcellsystems.com.

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OSP Magazine August 2015