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HCE Uses Efficiency Expertise To Help |
Recycle And Reshape AWT Building
The 38,500-square-foot Clark County Sanitation District Advanced Wastewater Treatment (AWT) Laboratory was designed to meet the current needs of the rapidly growing communities it serves, and to provide today’s water testing requirements as well as the progressive future testing requirements of the Environmental Protection Agency (EPA).
HENV Architects was hired to redesign the existing building, as recycling an existing structure could be done more efficiently and economically than a new smaller building could be erected.
Harris Consulting Engineers
(HCE), a professional mechanical and electrical engineering firm serving the Las Vegas area since 1983, was hired to design the heating, ventilation and air conditioning (HVAC) systems, as well as plumbing and electrical systems for the project.
“The recycling of this building saved a sound existing structure, and did not require use of additional land for a new facility,” said Tom Harris, President of HCE. “We are glad we could be part of this important endeavor.”
Although the redesigning and restructuring of an existing structure did help contain expenses on a project already estimated to cost $10,000,000, there were a number of special challenges for HCE. For one thing, the design of mechanical system components was made difficult because the building was originally designed to house and support heavy equipment used in separating liquids and solids, therefore, had extremely thick reinforced concrete structural floors and walls.
“It was necessary for air distribution ductwork and liquid distribution piping to penetrate these structures to deliver air and liquid heat transfer mediums for comfort control throughout the building,” said
Harris. “Plus, the comfort control systems were secondary to the primary functions of the laboratory equipment and had to yield to their preferential locations and arrangements. This coupled with the existing arrangements of the building left difficult design aspects for the larger components of the HVAC systems.”
Harris noted that the HVAC systems were unusual because of the different occupancies within the building. Laboratories needed to be served by heating and refrigerated cooling systems capable of controlling temperature, humidity, exhaust, ventilation make-up air, and interior pressures relative to other occupancies. Administrative areas required heating and refrigerated cooling systems capable of controlling temperature and ventilation. And receiving, shipping and holding bays required heating and evaporative cooling systems capable of controlling temperature exhaust and make-up air.
The overall objective of the EPA is to provide a safe, pollution-free environment for future generations. Therefore, the nature of this project was to provide environmental protection from the hazards of untreated wastewater that travels downstream through other communities and lakes. With such a project, it was overseen by a number of agencies.
“The laboratory environment control systems had to comply with regulations of the EPA, National Fire Protection Association (NFPA), Uniform Building Code (UBC), Uniform Mechanical Code (UMC), Uniform Plumbing Code (UPC), and the National Electrical Code (HFPA 70),” said Harris. “Each of these agencies was administered by separate entities, and some of the codes and regulations overlapped each other. Coordination of the varying regulations with the multiple agencies was a formidable task to say the least.”
Another challenge for
HCE was the design of the air conditioning system for the AWT Laboratory. The main air-handling unit serves both low and medium pressure air distribution as well as both constant and variable temperature supply air. However, spatial limitations did not permit the use of two separate air-handling units; therefore, one unit was required to have two compartments: one for low pressure, constant supply air temperature; the other for medium pressure, variable supply air temperature. In addition to providing heating, cooling and building pressurization, the main air-handling unit provided the make-up air for the laboratory exhaust systems.
Airflow was another crucial element in the mechanical design. “Gases emitted during laboratory testing must be contained to prevent contamination of occupied spaces,” explained Harris. “Airflow was used to prevent the cross flow of contaminated air from the laboratory testing areas to the laboratory general environment and to the administrative and storage areas. Containment was accomplished by exhausting more air from the contaminated areas than is made up. Exhaust airflow was provided to maintain negative pressure relationships increasing from the least contaminated areas to the most contaminated areas.
“Electronically controlled modulating dampers in the supply and exhaust ducts serving each space are monitored and positioned in response to pressure sensors by a computer to lag the supply airflow rates behind the exhaust airflow rates to provide the desired negative pressures.”
Laboratory plumbing design was challenged by the many systems required in laboratory testing of water to meet EPA standards. Among the required piping systems are: standard plumbing soil waste and vent, acid waste, deionized water, vacuum, compressed air, nitrogen, steam, natural gas, acetylene gas, and argon gas. Special challenges included those penetrating the heavy concrete structures, coordinating the safety requirements of the NFPA for volatile and toxic gasses, compliance with building codes for hazardous materials, and the installation of these piping systems in the seventeen supporting structures serving the laboratory test areas and hoods.
HCE also supplied the electrical design for site and building lighting, power distribution, fire alarm, telephone and data systems.
“Although HCE did provide design engineering services for a similar, but smaller laboratory facility for the City of Henderson, Nevada,” Harris said, “recycling this enormous building presented some very unique engineering challenges. We thank all the other firms involved in this project for making it go as smoothly as it did.”
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