Part 1 of this topic (August, 2005) covered tenant redundant power supplies and how electricity comes into a building and is distributed to the tenants. This article discusses how an entire commercial building can meet some or even all of its power demand in the event it is removed from the local electrical grid. This issue must be understood by first responders, since it may impact their operations and their safety.
The August, 2003, blackout in the northeast cost businesses millions of dollars in lost revenue and underscored the need to avoid reliance on the local utility company as a consistently dependable power source. When New York went dark, there were several buildings that stayed lit. What did these buildings possess that others did not? The answer is building redundant power sources. The high-profile tenants who occupy space in these properties cannot afford to be without power and sustain substantial losses. Tenants such as banking, trading, law and insurance firms require uninterruptible power supplies to continue doing business when power from the grid is lost. They also cannot lose their electronic security measures. Thus, the idea of Distributed Generation (DG) was proven to be a valid, viable concept.
What is “Distributed Generation”? The generation of electricity by a sufficiently small electrical generating system as to allow interconnection near the point of service at distribution voltages, including points on the customer side of the meter. A distributed generating system may be operated in parallel or independent of the electric power system. It may be fueled by many sources, including but not limited to, renewable energy sources.
COGENERATION
Cogeneration is defined as the simultaneous production of electricity and either steam or high temperature water that is used for a beneficial purpose. Cogeneration is also sometimes referred to as Combined Heat and Power (CHP). Interestingly enough, sometimes the heat product is ultimately used as an energy source to produce air conditioning through the use of an absorption chiller. The simplest uses for waste heat are domestic hot water, winter heat and summer air conditioning. Server farms and high-density data centers are ideal candidates for cogeneration since their electrical demands are high and constant, and the heat load from the equipment requires that the space be air conditioned 24/7. While cogeneration can be feasible in a wide variety of applications up to a 25,000 KW (Kilowatt) commercial installation, they all need a well-matched (and stable) electric demand and a requirement for the heat product. Making optimum use of the waste heat product can raise total fuel efficiency from less than 30% to nearly 80%, far better than the 50% efficiency delivered by the local electric utility. That’s right … approximately one half of the electricity created at power plants never makes it to the customer’s wall outlets (due to losses at the plant and in the distribution network)!
RECIPROCATING ENGINE/INTERNAL COMBUSTION GENERATORS — (LIQUID FUEL AND GAS POWERED)
The true definition of an emergency generator according to the EPA is: “a generator whose sole function is to provide back-up power when electric power from the local utility is interrupted.”
An “engine-generator” is the combination of an electrical generator and an engine mounted together to form a single piece of equipment (see photo 1). This combination is also called an “engine-generator set” or a “genset.” In many contexts, the engine is taken for granted and the combined unit is simply called a “generator.” In addition to the engine and generator, engine-generators generally include a fuel tank (for diesel powered), an engine speed regulator and a generator voltage regulator. Many units are equipped with a battery and electric starter. Standby power generating units often include an automatic starting system and a transfer switch to disconnect the load from the utility power source and connect it to the generator. Standby power generators are permanently installed and kept ready to supply power to critical loads during temporary interruptions of the utility power supply. They can provide emergency power to an individual tenant (single or multiple units, depending on power demands) or they can be arranged in series to provide power to meet all base building power demands and beyond. They can literally be found anywhere in a given building (including even in tenant spaces with attached “day tanks”), but usually are found in the basement or at ground level, on the roof or on mechanical decks within the tower. They can also be located in or on top of adjacent parking garages. Day tanks provide fuel to meet the immediate demands of the generator(s); longer duration operations dictate larger storage tanks in the basement, usually in 5 – 10,000 gallon capacities. If the set(s) are located on the roof, expect to see a fuel riser running up through the core of the building. We pre-planned one high-rise which had 180,000 gallons of diesel fuel in the basement in 18 ten-thousand gallon holding tanks!
NOTE OF INTEREST ABOUT DAY TANKS
The object of a day tank is to provide a “day’s” quantity of fuel that is guaranteed to be clean and dry for the engine. Sometimes it is used to overcome the problem of excessive suction heads on the engine lift pump. It is important to remember that the clean and dry fuel in the day tank will be exposed to the same conditions that cause the fuel in the main storage tank to become bad. Given enough time, the fuel in the day tank will get to the same condition as the fuel in the main tank. A filter and a water separator are still required on the outlet of the day tank. To provide the desired results, this tank must, in fact, be a “Day Tank.” That is, the fuel in this tank must remain there for only a short time. All the problems of long-term fuel storage in the main tank will be present in the day tank if fuel remains in it for long periods of time. Once it ceases to be a “Day Tank,” it must be treated just like any other tank. Neglected, aged fuel is one of the primary reasons for emergency generator failure.
HOW DOES A GENERATOR WORK?
The generator creates an electric current in the conductive wire of its windings. Mechanical energy is manipulated into a rotational force that shoves a magnetic field through a coil of wire and induces a flow of electrons in the wire, converting the mechanical energy into electrical energy. It can do this because electricity and magnetism are two sides of the same coin — the electro-magnetic force. The generator is somewhat analogous to a water pump, which creates a flow of water but does not create water itself. The most common fuel source is liquid diesel fuel, although natural gas and propane can be used as well.
In the majority of high-rise buildings, the typical generator could be expected to be of about 1,000 KW capacity. Sometimes generators are rated in KVAs rather than KWs. The difference between KW (Kilowatt) and KVA (Kilovolt amp) in the simplest of terms would be that KW is “true” power, where KVA is “apparent” power, similar to foam in a beer mug for all you firefighters out there. So, a 1,000 KW generator would be closely equal to 1,200 KVA in output.
Generator Compatibility with UPS (Uninterruptible Power Supply) Systems: A classic operational problem is the starting of other loads on the generator, causing the generator’s output frequency to vary, which then causes the offline or line-interactive UPS to cycle on to battery operation. The problem is especially pronounced with natural gas-powered gensets. This repetitive battery cycling can cause the battery to discharge completely, while significantly shortening battery life. Another potential problem is the generator instability that occurs when the UPS load is transitioned to the generator. The UPS load transfer causes the generator voltage and frequency to sag, causing the UPS to go back to battery operation. Soon thereafter, the UPS senses stable generator output, transfers the load back to the generator, then transfers back to battery operation when generator output dips again. These problems don’t exist for conventional double-conversion UPSes, which rectify the input supply to DC and can accommodate large swings in supply frequency while continuing to provide regulated, stable AC output frequency without the use of the batteries.
Note: During the 2003 Northeast blackout, data gathered afterwards told a surprising story — approximately 80% of the diesel powered emergency generators failed to come on line or even start, due to gelled (aged) fuel or lack of proper maintenance. Another interesting note: In high-rise fires, when emergency generators are called upon to function when base building power is lost, they fail over half the time to function. A lot of this is due to the generators not being run or tested regularly, or not being run with a load placed on them (lights, fans, elevators), which is the environment they will have to operate in when a fire occurs. In other words, do not bank on these working for you when they are needed. During the Meridian Plaza Fire in Philadelphia in 1991, the generator not only failed to run, but the emergency back-up wiring harness in the building core’s vertical chase burned through, causing a complete loss of power to the entire building. The 38-story, 800,000 square foot office tower has since been demolished.
MICROTURBINES
Microturbines are an important emerging technology (see photo 2). They are an efficient, compact, ultra-low emission way to produce power and heat for combined heat and power applications. The microturbine engine is a combustion turbine that includes a compressor, turbine, generator and typically a recuperator (see graphic 1). Microturbines are usually fueled by high-pressure natural gas, which powers the turbine engine, although a wide range of approved fuels can be used. The engine has just one moving part, a shaft with a turbine wheel on one end, a permanent magnet generator on the other and an air compressor wheel in the middle. Air heated from the microturbine is injected along with natural gas into the combustion chamber. Pressure from the continuous combustion process turns the turbine, which generates electricity. The 530 degree F. heated oxygen-rich, near zero pollutant exhaust passes into the Heat Exchanger system, where it heats water for domestic hot water and for building heat. The electricity created from the microturbine is used to power virtually any demand for electricity. It produces dry, oxygen-rich exhaust with ultra low emissions. The system generates and uses high voltages as part of its function. An optional battery pack may exist. If equipped, the typical battery pack is a lead acid type, sealed and “maintenance free” (refer to Part 1 as to what this term really means), with a battery isolation switch.
The system’s gas plumbing is constructed of components that are designed and rated for the gas and pressures used. As part of the quality program, the system is rigorously pressure tested for leaks.
Microturbines can operate using a number of different fuels ranging from land fill methane, to propane, to natural gas and such liquid fuels as kerosene or gasoline with efficiencies in the 28 – 30% range. They can run up to 16,000 hours (two years of continuous use) between routine maintenance inspections. They also start rapidly (less than one minute) and have excellent load following characteristics that makes them ideal for applications where electricity demand can fluctuate rapidly. A microturbine can be compared to a miniature jet engine connected to an alternator and integrated into a unit that can be delivered complete with controls and ready to run (commonly referred to as a “plug and play” model). A 30 KW (Kilowatt) microturbine is about as big as a large refrigerator (see photo 3). The unit can act as a stand-alone generator for standby, backup or remote off-grid power. Multiple systems can be combined and controlled as a single, larger power source, called a “MultiPac” (see photo 4). Microturbines may be configured into an array of up to as many as 100 units. Such an array will operate as a single power generation source and can power an entire building, depending on size/load demands. Already, there are high-rise buildings in California, Texas and Oregon where “Multipacs” power a significant portion of the building’s load demand separate from the city’s power grid.
FUEL CELLS
Fuel cell technology is moving to the forefront of the distributed generation field and is increasingly being promoted as the driving force behind the coming hydrogen economy. Fuel cells offer higher efficiency than microturbines with low emissions, but are currently a more expensive choice. Although fairly new and still developing, fuel cells are the cleanest of all the potential cogeneration technologies. A fuel cell releases the energy in a hydrogen rich fuel source (such as natural gas) by allowing it to combine with oxygen in a catalytic reaction that produces no flame. The outputs of a fuel cell are limited to electricity in the form of a direct current (DC) voltage, water vapor and carbon or carbon dioxide (see graphics 2 & 3). In many ways, a fuel cell is like a large battery that will produce power and heat indefinitely as long as it is provided with a hydrogen rich fuel source. Fuel cells are currently produced in a wide variety of types and sizes ranging from 1KW to 250KW. Commercial-grade units run at extremely high temperatures (600 – 1,000 degrees F). This heat can be used for domestic hot water needs and heating applications.
Without any flame and without moving masses such as turbine blades or reciprocating pistons, fuel cells convert the energy contained in the fuel directly into electricity. The electro-chemical processes employed enable not only high efficiencies, but they also keep emissions at an exemplary low level. The exhaust air is free of noxious gases such as nitrous oxide and sulfur. Up to 30% more electrical power is created in comparison with conventional energy generation from local power plants. They are also very quiet, around 60 decibels. This is equivalent to that of a normal conversation. Why so quiet? No combustion or moving parts.
While the high temperature heat output of fuel cells make them attractive for cogeneration applications, they (earlier models) do have some drawbacks. One is slow start-up time. As a rule, the higher the operating temperature, the longer the start-up time. Another issue is load following capabilities. Microturbines and reciprocating engine generators can adapt to changes in electrical demand from 10% to 100% of rated load in a matter of seconds. Fuel cells are slower to react and have a much narrower throttling range. This is why a commercial application with both a relatively constant electrical demand and heat demand (i.e. a trading or banking data center, telecom facility) is an ideal application for fuel cells. Newer models of fuel cells have overcome these restrictive barriers and have virtually eliminated these two issues as obstacles. Some skyscrapers, such as the Durst 48-story/1.6 million square foot 4 Times Square building in New York employ fuel cell technology.
The future: A highly likely scenario in the not-too-distant future will be where smaller modular fuel cells are situated every three to five floors of new high-rise buildings, providing electricity and heat for heating & cooling and hot water, meeting the full demands of the tenants’ needs. If set-up similar to the microturbine configuration described earlier and connected in a string (or series), full size fuel cells can provide power to run an entire building’s electrical demand from one location (a mechanical room). These units are much larger (see photo 5) and generate greater electrical output versus the smaller modular fuel cell models, which are about the size of a mini-refrigerator. The important thing to remember is that redundant power sources are clearly the way of the future. This, in turn, dictates a clear-cut understanding on the part of the fire service that disconnecting electricity to a given tenant space/floor and even the entire building will take time and assistance from various technical people. This may demand a “hold” approach to firefighting in areas where high-voltage equipment or cabling is located until ALL power is disconnected and verified as to so.
WHAT FIREFIGHTERS NEED TO KNOW
Primary concern: Two or more independent power sources may have to be isolated during a major event, including fires involving electrical chaseways — the utility company feed(s) and the on-site DG (Distributed Generating) feed. Whether the source is emergency diesel or gas-fed reciprocating engine generators, microturbines or fuel cells, this electrical generating source must be located and isolated along with the incoming power feed(s). The time it takes to accomplish this will probably require some patience on the part of the incident commander, because this will not be a 15 minute operation. It will also require personnel from different companies to assist. Pre-planning electrical cutoffs is prudent.
HAZARDS/RISKS
Microturbines:
- Heavy concentrated floor load — unit weights vary between 900 lbs to 3,000 lbs
- The output voltage and residual capacitor voltage is dangerous and can injure or kill
- Flammable fuel connection leaks are possible — Microturbine fuel is flammable and explosive. Without a customer installed leak detector present and tied into an emergency stop device, it is expected that there is a significant probability of a catastrophic event involving a fire and/or explosion should the gas leak and ignite
- Failure danger of relief valves for hot water and steam — High internal temperatures can reach well over 800 degrees F.
- All open flames and other ignition sources need to be kept away from unit
- Unit can store residual power for up to 5 minutes after disconnect with a battery pack (shock hazard) — small amounts of sulfuric acid and hydrogen gas may be a potential threat
- Exhaust must be vented to outside — can produce dangerous emissions from fuel combination process, such as Nitrogen Dioxide and poisonous Carbon Monoxide
- Exhaust airflow and pipes are very hot — up to 700 degrees F. Contacting a hot surface can result in severe burns. Reflex action associated with such a contact could result in a secondary hazard such as an impact on a hard or sharp object. The exhaust is typically located on top of the system which averages over 6′ high and is not easily accessed
- A risk of electric shock may occur if equipment is not properly grounded or if fire personnel inadvertently contact hazardous voltage within the enclosure which may result in severe skin burns or death
- The electrical current created and used by the system has the potential to cause a fire if short circuit protection and grounding measures have not been followed
- Hazardous sound pressure levels may exist when unit is operating — Hearing protection is advised
If On Fire
- Turn off the system
- Open and lock the electrical disconnect switch
- Unplug the batteries or activate the battery isolation switch
- Verify that no voltage is present
- Dry Chemical or CO2 portable fire extinguishers can be used to suppress fires involving the unit — Avoid using CO2 extinguishers on battery fires
Gas Leak
- Immediately cease operation of the equipment
- Close the fuel isolation valve
- Ventilate area
Fuel Cells
- Most of the above noted hazards regarding microturbines apply to fuel cells as well, aside from the loud operating noise levels and dangerous emissions, since there is no combustion process involved with the operation of the unit.
Reciprocating Engine Generators
- The majority of the same hazards apply here also in regards to fuel leaks and possible ignition, shock hazards, exhaust issues, high noise levels, etc.
In summary, the world is a constantly changing landscape. Advancements in technology dictates that the fire service stay on top of these new-age concepts and how they affect both the operation and functionality of modern commercial buildings, as well as their impact on firefighter safety. This series of articles (Firehouse 21st Century High-Rise Training Series) addresses many of these concerns and hopefully will provide a broader perspective on issues which relate to the fire service that can be drawn from and applied to a department’s training regimen. SOPs/SOGs should be reviewed annually and modified to reflect items relative to both safety and the ability to quickly and effectively deal with an incident involving technologically advanced equipment which may not be readily apparent or understood in the arena of emergency response.
Credits: Capstone Turbine, ONSI Fuel Cells, Wikipedia, Bob Lasseter, Dennis Hughes, Ed Lewis, Joe Lechtanski, Steve Boos, Jim Haffey, Jim Jenkins