The Things You Will Never See: Mechanical, Electrical, and Plumbing Systems
While you were away, the Capitol Crossing project continued to unfold. 250 Massachusetts Avenue, the larger of the two buildings on the Capitol Crossing site, continues to rise. The building’s north tower has risen to the eleventh floor and concrete pours will begin on the twelfth floor later this week. Reshore removal has reached level eight. All of the garage levels of the south tower have been poured and concrete will begin to arrive for the surface level of the tower this week. Peek into the north tower and you will see duct work, sprinklers, and plumbing risers installed on a couple of floors.
Meanwhile, construction workers scurry around the outside and inside of 200 Massachusetts Avenue, installing items large and small as the substantial completion date approaches. Sidewalk pavers that surround Cobb Park on the north side of Massachusetts Avenue are in place and the sub-surface concrete that will support the sidewalk pavers around 200 Massachusetts Avenue is being poured. Doors to the various retail venues along the first floor have been installed and installation of the massive windows surrounding the promenade entrance between 200 and 250 Massachusetts Avenue nears completion. Glass canopies that will cover the main entrances will be arriving during the next two weeks. You can now see the steel support and the glass canopy above the 2nd Street door.
Looking up, we can now see the aluminum coping at the edge of the roof. Installation of the aluminum trim that will rest atop the stone cornice begins this week. Roof skylights have been fitted with electrical lamps and stone tiles are being installed on the roof terrace. The terrace offers a special view of the work going on below and wonderful views of the city itself. The view to the south from the terrace reveals the Capitol, the Library of Congress, and the fall line of the Piedmont as it slopes toward the Atlantic Coastal plain. To the near west, one can watch the dance of the two Capitol Crossing tower cranes hoisting material and concrete for 250 Massachusetts Avenue and the garages below, while noting that major construction continues all around the city. No fewer than twenty tower cranes dot the Washington skyline.
Trim and finishes are being installed inside the building. Bathrooms are completed and inspected and the elevator lobbies are waiting for passengers. Interior stairwell doors are hung and stairwells have been painted, pressurized, and balanced. Everyone knows that leaving a building via an elevator during a fire is dangerous; but few people think about why they are safe in a stairway when fire breaks out. Pressurizing and balancing stairways are critical to ensure a safe exit from a burning or smoke filled building. When fire or carbon monoxide alarms are activated, additional air is pumped into the stairwells to keep them free of smoke or chemicals, permitting safe egress out of the building. The pressure balance must be maintained to keep the air flowing down the stairwell as exit and entry doors are opened.
Farther south, excavation and pile driving continue along the back of Holy Rosary Church and the south side of 501 3rd Street. The support for the excavation has been complicated by the design requirements and the age of the Church. BBC received building construction plans for the church dating from 1919, but were unable to find plans from the construction of the Church bell tower which was added at a later date. Since there was limited information about the construction of the bell tower, engineers had to make assumptions about the structure and add safety features to ensure the integrity of the structure.
The diversity of excavation and support systems made the project complex but interesting. The contractors drove typical soldier piles with lagging boards and tiebacks, installed bracket piles with lagging boards and tiebacks and slurry walls with tiebacks, and dug underpinning pits with tiebacks and dead men — long concrete blocks buried in the ground as anchors. They also used soil mix walls, (secant walls) with tiebacks and various types of braces and walers — horizontal beams used to brace or support a soldier beam. You can see how secant piles are prepared at https://www.youtube.com/watch?v=UF9FLUioZv8 and how soil mix walls are prepared at https://www.youtube.com/watch?v=6xJBbyip4LI Bracket piles with tiebacks were used to support the foundation of Casa Italiana, the parish hall, and to resist the lateral movement of the soil. This type of system is used to support structures, like those along 3rd Street, that are immediately adjacent to the excavation area. They prevent soil erosion from under the existing foundations. A series of underpinning pits were also used to support walls of the Holy Rosary Church and its bell tower. I described this process in an earlier Construction Note. Glass, http://www.law.georgetown.edu/campus-services/facilities/construction-info/index.cfm, August 31, 2017. This system extended the bell tower and Church wall foundations deeper to allow sufficient bearing support to the existing soil. It also added lateral support via the installation of tiebacks and dead men anchors through the face of the pits.
When most people consider great architecture, both their minds and their eyes are usually drawn to a building’s facade. It is what we see first and, if the building is pleasing, we look at it again and again, noticing features we had not noticed before. Beautifully-designed buildings enhance the experiences of our daily lives. They inspire, they delight. They enliven our neighborhoods, lift people’s spirits, and occasionally become part of the cultural vernacular of cities and nations.
Once beyond the front doors, eyes and minds again consider appearance, this time of the interiors. Eventually, however, thoughts of beauty recede as people living and working in a building begin to consider how it works. If the public spaces permit an easy flow of patrons, if people work in offices that are adjacent to colleagues whose work complements theirs, and if natural and artificial light enhance the work space that one inhabits, the building is deemed comfortable, the work produced in it will be performed efficiently, and the residents will be satisfied. When efficiency combines with gracious style, the building adds to the grand architectural spaces of great cities.
Buildings are organic. Like humans, the grandeur or simplicity of their outer shell would be lifeless without a brain to control its life, without arteries and veins to control its warmth and bring nutrients to its body, and without a soul or spirit to animate it and give purpose to its being. The people who live and work in a building provide the spirit or soul that brings expression to its purpose; but it is the mechanical, electrical, and plumbing systems, the brain and vascular system of a building that allows the life inside it to thrive and to emanate its spirit.
Of course, beautiful buildings do not always work. Office buildings today are sometimes deemed sick, so environmentally contaminated that work cannot be performed within them. The beauty of those buildings is soon ignored as the occupants begin to fall ill. Several years ago, occupants of a Richmond, Virginia, office building kept getting mysterious insect bites until a missing set of filters were installed. Loose particles of fiberglass had been blowing through the ventilation system onto employees’ skin and causing the mysterious “bites.” Structural defects may also occur, as when the windows fell to the street many years ago at the Hancock Building in Boston. In some cases, floors or beams collapse, even before the building is occupied. A combination of unexpected wind and incomplete welding brought down beams during the construction of the District of Columbia Walter E. Washington Convention Center. A similar collapse occurred at the David L. Lawrence Convention Center in Pittsburgh. Mechanical systems may prove to be insufficient, electrical circuits too small, plumbing inadequate to the task. These problems were discovered in our own McDonough Hall after it was erected. We have been correcting them ever since.
What permits us to concentrate on the splendor of a beautiful building is not only its design and the absence of major flaws, but also the continuous operation of all the things we never see — the wires, the pumps, the conduit, the pipes, the air handlers, the ducts — all hidden in the walls and floors and even under the ground, all of which we take for granted as we use a building daily. These elements must be designed perfectly and unobtrusively if our eyes and minds are to continue to be drawn to the beauty of the building we live in rather than to its defects or illnesses.
MEP is comprised of three separate systems, mechanical, electrical, and plumbing, although sometimes they overlap. Mechanical refers to almost any service in the building. Elevators, escalators, and heating and air conditioning units, generators, and other similar equipment are all part of the mechanical system. Mechanical systems are relatively new to buildings. Prior to the 20th century, elevators didn’t exist. People got to the higher levels of a building by walking up flights of stairs. Buildings were heated by fire places and coal stoves and cooled by windows or ingenious systems like that created by Montgomery Meigs for the former Pension Building, now the Building Museum. The building Meigs designed provided natural air-conditioning and light for its employees. By using air vents in the exterior walls of the building, he created a ventilation system where hot air escaped through the skylights in the roof. The upward flow of air would draw in fresh air through the exterior wall openings. But this kind of ingenuity slowly led to further advances in the building trades. The industrial revolution and its accompanying mechanization forced major changes to the construction industry, improving our lives and changing the ways buildings were designed.
Electrical refers to the application of electricity to practical uses throughout a building. Like mechanization, practical applications of electricity to the building industry are quite new. In earlier times, candles, whale oil, and later natural gas provided light to darkened homes and cities. The work of Samuel Morse, Thomas Edison, Alexander Graham Bell, and Nikola Tesla in the middle to late 19th century tamed electrical forces and created the need for electrical engineers who designed new power systems for the building trades. The large and beautiful crane that appeared on Monday is a Liebherr LTM 1500 to set precast PEPCO transformer and bus vaults for the future buildings on the Center and South blocks. The crane has a 207 foot-long luffing jib to increase the crane’s horizontal reach. Those future buildings will receive their electrical feeds from vaults along 2nd Street. Based on available lane closures and other logistics, the subcontractor opted to set up one large crane that can reach all 14 vaults from one location rather than several smaller ones.
The engineering to confirm the exact placement on the structure to ensure stability and structural support took several iterations. The farthest life is for a vault weighing 44,000 pounds that is about 205 feet from the main crane boom. The vaults farther away will be set first because the crane can only lift and set to within one hundred feet of the center pin with the jib attached. After those are set, the jib will be removed to allow the telescoping hydraulic sections of main boom to set the closer vaults. The main boom can lift a 600 ton weight if it is stationed right next to the crane. Using the luffing jib reduces the crane’s lift capacity. To prevent tipping when using the luffing jib, the crane is equipped with 350,000 lbs. of counterweight.
Plumbing refers to the system of pipes, valves, pumps, drains, sewers, and fixtures used to distribute potable water and remove waste water from buildings. The development of plumbing systems was very slow. Although aqueducts brought water to Roman cities, the disposal of waste water took years to develop. Almost no progress was made until the 19th century. Until then, stench and disease filled the streets of cities. The old Washington Canal, flowing from the Potomac River to the foot of the Capitol along the Mall was a prime example of fetid waters. Sewer systems and running water systems designed in the late 19th century improved our health and again, caused a redesign of basic building models. By the way, Montgomery Meigs, architect of the Pension Building, also designed Washington’s aqueduct that brought fresh water to the city in 1864. “Let our Aqueduct be worthy of the Nation,” he wrote in a document proposing a system of reservoirs, culverts, and distributing water mains, many of which still function today.
We take MEP for granted today; but once these systems developed, architects and engineers had to design floor and roof spaces to accommodate complex features such as cooling towers, mechanical penthouses, blowers, compressors, pumps, and generators, as well as simple features like sinks, toilets, washing machines, and drinking fountains. Approximately 25 to 35% of the cost of a building, sometimes millions of dollars, goes to mechanical, electrical, and plumbing systems. Engineers and architects have to design space for this equipment. Much of the equipment for 200 Massachusetts Avenue will be placed in the East Concourse. Other equipment will be found on each floor of the building and more will sit on the roof. Twenty-six separate mechanical rooms will serve 200 Massachusetts Avenue.
In modern buildings, we breathe easily, being never too warm, never too cold, as we go about our business. Air handlers noiselessly condition and move the air through a building to keep us comfortable. These air handlers remove excess moisture, foreign particles, and odors from the air to increase our comfort. The condenser water system provides a majority of the heating and cooling through a thermodynamic heat transfer process. Interestingly, there are no boilers for heat in 200 Massachusetts Avenue. Supplemental heat comes from electric heating elements, body heat, and everyday heat-producing equipment like computers and generators. The chillers and cooling towers help in the cooling process. The building’s air is recycled where it is cooled and filtered and redistributed throughout the building to maintain a consistent temperature. The capacity of the chillers is 850 tons. An air conditioner for a typical Capitol Hill house has less than three tons capacity. Because Capitol Crossing sits above the I-395 highway, sixteen fans as large as aircraft jet engines have been installed to push air though the tunnel, clearing smoke from the highway and preventing smoke from coming into the building should a fire occur below the deck.
Water literally surrounds most buildings and this is especially true in Washington, D.C. If you recall, the Tiber Creek once ran south and east of the Capitol Crossing site. Though it was encapsulated into a sewer system in the late 1800s, remnants of it and other streams still produce underground water. The underground water is pumped out before the foundations are laid but it soon returns. Building foundations must be waterproofed to prevent the migration of water into the building. Because intruding water can weaken a foundation and produce mold, the underground water is collected around the west side of the building’s foundation via drains that feed it into the water treatment process.
The below grade foundation of 200 Massachusetts Avenue is waterproofed like any conventional building. A building itself must also be water- and vapor-proofed to create a barrier that controls the flow of humidity through an exterior wall. Glass buildings, when properly sealed, are vapor proof and water proof. A heavy duty vapor barrier material is placed under the lowest concrete slab in the building. This barrier helps prevent water from entering the basement through the floor slab. The weatherproof barrier then goes to the face of the glass and then follows the roof line. As such, 200 Massachusetts Avenue is a weatherproofed six-sided box.
Inside the building, plumbing engineers weave intricate copper and cast iron pipe patterns that bring needed water into a building while ensuring that unwanted water moves out. Water pumps distribute hot and/or cold water for toilets, sinks, and water fountains, while other pumps distribute water to standpipes for fire hoses and for the fire sprinkler-pipe system that lines the ceiling on each floor. 27,000 linear feet (more than five miles) of copper pipe move water through 200 Massachusetts Avenue. Waste water flows out of the building though cast-iron pipes into the city’s sewers where it flows to treatment plants and finally into the rivers that flow through the city. Interestingly again, so called “grey” water from the roof and from subsurface ground water is captured, treated, and recycled to conserve fresh water. This grey water is used for irrigation and at the cooling tower for cooling. There are also slot drains in the Pedestrian Way between 200 and 250 Massachusetts Avenue that will collect rain water and send it into the treatment process. Other drain tiles collect water running down the building’s facade and direct it to filters before it reaches the storm drains. 29,000 linear feet (nearly five and one half miles) of cast iron pipe move grey water around the building and waste water out of the building.
In modern buildings, we turn night into daylight with the flip of a switch. For this magic to occur at 200 Massachusetts Avenue, wires and cables move from four ten- or twelve-foot-deep electrical vaults under the street, through duct banks into the building, and then through a system of conduit to twenty-nine electrical closets before they reach those switches and other electrical outlets. During construction, they also provide temporary power for the cranes and other construction equipment before they eventually illuminate and power the finished building. Architects and engineers design hundreds of circuit breakers and check overloads to prevent electrical fires. Moreover, no matter what the size of a room, the light must always be appropriate for the surroundings. Lighting engineers calculate the precise measurements of lumens to ensure that lighting in all areas within a suite enhance the work within it. All this is made possible by the 15,575 feet (almost three miles) of conduit and 63,000 feet (twelve miles) of electrical wiring that course through the building.
None of these processes are left to chance. Engineers spend months calculating mechanical, electrical, and plumbing needs and plotting the architecture of the systems throughout the building. Once calculated, the requirements are often increased beyond recommended standards to ensure that the building operates efficiently and consistently. The placement of the myriad of pipes, conduit, wiring, cables, and ductwork require an artist’s eye, an engineer’s sense of order, and a computer’s speed and logic to create ceiling plans like the one pictured below. The resulting choreography emulates an intricate ballet.
Computers have made the coordination of the various systems easier to achieve. Capitol Crossing is using Building Information Modeling (BIM) and clash detection to coordinate the mechanical, electrical, plumbing, and fire protection (FP) systems. The process starts when the design teams creates architectural, structural, and MEP design models using 3-D modeling software. The design team at Capitol Crossing is using Autodesk Revit for most content development. Some documents are created using 2-D CAD files (Autodesk AutoCAD). CAD (Computer Aided Design) is an image file. These same 3-D models and 2-D CAD files are used to create the contract documents.
Soon after all of the subcontracts are awarded, a BIM meeting is held to begin the trade coordination process. This meeting sets the standards and expectations for a successful process, referred to as the BIM Project Execution Plan (PXP). Prior to this initial coordination meeting, the design teams will have conducted their own internal PXP process geared towards design authoring and drawing creation. After the initial meeting, each MEP and FP trade begins creating its own 3-D models in trade-specific software to create shop drawings.
Using the BIM system, BBC’s Process Manager coordinates with the design teams and subcontractors virtually to solve many of the design and construction issues so that the field crews can install the MEP systems quickly and easily. Their models are split by building and by level and linked together with the other trades’ models and the architectural and structural models into Autodesk Navisworks. Within Navisworks, MEP coordinators use a clash detection module to find collisions between trades and to provide architectural and structural checks.
During weekly BIM coordination meetings, subcontractors, designers, the developer, and Balfour Beatty work their way through the major collisions to identify needed shifts and pathways for each system. Each trade then works simultaneously making the assigned adjustments to their models.
All of the drawings and updates from every discipline have to be analyzed to gain a clear understanding of what systems are locked in place and which ones have the flexibility to shift around. The BBC Process Manager spends much of her time analyzing the composite models and clash reports, trying to find open paths, and studying how the systems can be organized, either horizontally or vertically, while meeting the various constraints within each system. Once major collisions are avoided, the team removes the smaller clashes. When an area is clash free, the Process Manager approves the design and releases the trades to produce shop drawing submissions for approval and then for fabrication.
Capitol Crossing is a complex project, making precise coordination essential. The East Concourse is one of the shared spaces between multiple projects and has utilities locked into specific elevations as they cross through the structure over the highway. Moreover, some of the MEP systems will be installed in the future; yet it all has to be studied, analyzed, and coordinated in advance.
The elegance of an architect’s hand is usually easy to see. Architects can become well-known and often become celebrities — and well they should when they design buildings that inspire the populace and beautify the city. But these mechanical, electrical, and plumbing engineers, all coordinated by BIM engineers, labor in anonymity. These artisan/engineers create magically elegant systems of calculated complexity that are skillfully placed within the walls and ceilings of the building by expert craftsmen and women. But they, like their work, remain hidden once the building is completed. The patrons of the building will go about their business, feeling secure in their building, but oblivious to the grandeur of the things they will never see.
Wally Mlyniec
SOURCES
Many people contributed content to this Construction Note;
Barron Collier, Superintendent, Balfour Beatty
John Clements, Senior Project Manager, Balfour Beatty
William Compton, Sr. Project Manager, Dynalectric Company
Stephen R Daneker, Project Manager, The Bowers Group, Mechanical Construction
Katie Eller, Process Manager, Balfour Beatty
Brian Markel, Project Engineer, Balfour Beatty
Robert C. Robidoux, Purchasing Director, Balfour Beatty
Joe Tyeryar, Senior Project Engineer (Field), Balfour Beatty
Betsy Kuhn provided editing assistance.
Editors, Mechanical System, Encyclopædia Britannica, https://www.britannica.com/technology/mechanical-system
Editors, Plumbing, Encyclopædia Britannica, https://www.britannica.com/technology/plumbing
Donald G. Fink John D. Ryder, Electrical and Electronics Engineering, Encyclopædia Britannica, https://www.britannica.com/technology/electrical-and-electronics-engineering
King County WTD, Construction Shoring Methods: Soil Mix Walls, https://www.youtube.com/watch?v=6xJBbyip4LI
National Park Service, The Pension Building, https://www.nps.gov/nr/travel/wash/dc40.htm
Piling Contractors, Secant Pile Walls, https://www.youtube.com/watch?v=UF9FLUioZv8
Professional Systems Analysis, Inc., Commercial Stairwell Pressurization Testing Service, http://psatab.com/stairwell-pressurization-testing
Erica Sloan, Everyone Forgot the Washington Aqueduct Was a Political Football — Until Trump Talked About Selling It, Washingtonian, September 5, 2017, https://www.washingtonian.com/2017/09/05/everyone-forgot-washington-aqueduct-political-football-trump-talked-selling/
Wiki Group 14: Sally Ostendorf, Blake Gifford, Jessie Hunter, David L. Lawrence Convention Center, https://failures.wikispaces.com/David+L.+Lawrence+Convention+Center+Truss+Collapse
