3.11.2 Lighting Updates
Besides all of the electronic equipment that is found in the data center, another significant consumer of electricity is the lighting system. Fluorescent lighting was the defacto standard for many, many years, and is typically fed with 277VAC in larger commercial buildings or data centers. Since fluorescent lamps vary by type and length, they operate on varying voltages and currents. A fluorescent ballast is used to adjust the supplied voltage and regulate current accordingly. In an effort to improve fluorescent lighting efficiency, the electronic ballast was invented in the 1970s. Besides adjusting the supplied voltage, electronic ballasts also changed the frequency from 60 Hz to 20,000 Hz or higher, which substantially eliminates flicker while also providing higher system efficiency.
LED lighting retrofits are available to replace fluorescent bulbs in existing fixtures, or the fixtures can be modified to bypass the ballasts. The LED bulb emits the same amount of lumens and can be produced to match any temperature (color) level. It is taking over the lighting industry in today’s environment to conserve energy since it is a simple alternative. It uses a fraction of the power fluorescents require and also gives off a fraction of the heat, which relieves some stress on the HVAC system.
Almost all new lighting installations are LEDs other than specialty lighting for stages or displays. In fact, most municipalities around the country have adopted LED lights or retrofits for all of their street and roadway lighting. Another benefit is fewer circuits are required since the load per light is a fraction of an amp. LED lights have also brought about better controls or wireless controls. The fixture can have an IP address associated with a wireless wall switch or ceiling occupancy sensor to operate a single or battery of fixtures
By supplying the lighting system with DC, we eliminate another power conversion and improve data center efficiency even further.
Figure 3.6 Electronic Ballast
(Courtesy of Antron Electronics Co., Ltd)
3.11.3 DC Storage Options
The fact that electrical energy is most easily stored in batteries as DC is the primary reason power conversions is necessary when AC distribution is used in the data center. The two types of batteries that are most commonly used in conjunction with a UPS are lead‐acid wet cell (flooded) and valve regulated lead‐acid (VRLA) or variations thereof. Lithium ion batteries are gaining popularity since they have excellent weight to power density, can cycle or discharge many times without losing capacity, do not off gas during charging, and have a longer life than VRLA’s. They are mainly being deployed on smaller UPS’s below 300kW, and some state or local city codes have special requirements or are hesitant to allow them to be installed in buildings since they are a newer and thought of as unproven. This will change over time as more and more installations become common. For additional information, see Chapter 10 – UPS.
Another storage technology are flywheels that store kinetic energy and can discharge DC power to a UPS. Conventional batteries and flywheels are covered in more detail in the UPS chapter. Also worth mentioning here are some new battery storage technologies called Zinc‐Bromine Flow Batteries and a megawatt‐class of batteries that use a sodium‐sulfur electrolyte – which are both, by nature, DC sources. Both of these batteries have the potential to be used in grid‐storage class applications and may undergo many deep discharges without suffering ill effects.?? Various battery manufacturers are developing battery storage banks so that excess power produced from solar panels or other renewable sources during the day can be used at night, or other sources like hydropower can charge batteries at night for discharge during peak daytime hours reducing demand loads on fossil fuel plants. For additional information, see Chapter 10 – UPS.
As of this writing, sodium‐sulfur batteries have already been installed at several locations globally, including a wind farm in Japan and a bus depot in Garden City, NY. Zinc Bromide batteries have yet to prove themselves in anything more than a handful of demo installations, but the technology seems promising for the storage of electricity from intermittent sources and load‐leveling applications, similar to sodium‐sulfur batteries.
3.11.4 Renewable Energy Integration
Solar power is the most common renewable resource that can be used for the on‐site generation of electrical power for a data center. Since photovoltaic (PV) arrays produce DC electricity, it is easily integrated with a DC distribution system. Only a voltage regulator is required, or a charge controller if the PV array is used to charge battery storage.
Wind power is another option. Inverter‐based wind turbines already produce AC power. The power conversion that would normally be needed to convert the DC to AC is not required, eliminating the inverter and any need for synchronization.
Although technically not a renewable energy source, fuel cells are being used to convert natural gas to electrical power locally at data centers and other sites. The output power is synchronized with the utility service and feeds the data center loads through the same distribution. Multiple units can be paralleled to feed a building. Some advantages are that fuel cells are very efficient and will continue providing base power at night when solar panels cannot, or winds die down, and wind power is not fruitful. Another advantage is that excess heat is produced in the conversion cycle that can be used for heating or hot water in the building or used to feed an absorption chiller. Several cons include a natural gas service of sufficient size is required at the site or a tank farm with liquid propane, or other hydrogen‐rich fuel is needed, they are relatively heavy and need to be located outdoors or in a remote structure.
3.11.5 DC and Combined Cooling, Heat & Power
Combined Cooling, Heat & Power (CCHP), also known as cogeneration, is an ideal strategy for improving data center energy efficiency. This is accomplished by using some form of power generation equipment that also produces thermal energy as a by‐product. Since data centers typically require 24x7 cooling, the recovered thermal energy can be used to activate absorption chillers that turn the waste heat into free cooling.
There are two types of power generating equipment that can be easily integrated with a DC distribution system. One is a fuel cell. The fuel cell is an electrochemical device that produces DC electricity, much like a battery. Only a voltage regulator is needed to match the DC voltage of the fuel cell to the DC distribution voltage or an inverter to create AC power that can be synced to a building’s electrical supply or used independently. Since the chemical reaction within the fuel cell produces heat, this thermal energy can be recovered and used to drive an absorption chiller.
Figure 3.7 Absorption Chiller
(Courtesy of Yazaki Energy Systems, Inc.)
Figure 3.8 Typical Fuel Cell
(Courtesy UTC Power)
The microturbine is another prime mover that can produce DC power. Microturbines operate on the Brayton cycle to rotate a small permanent magnet alternator at very high rpm to generate high‐frequency AC, which is rectified to DC. A voltage regulator can be used to match this DC to the DC distribution voltage, or an inverter can convert the DC power to 60hz AC. The turbine exhaust can be run through a heat recovery absorption chiller to make chilled water.