New Men’s Prison Utilizes State-Of-The-Art Cooling System|
In the 17 years that they have been serving the greater Las Vegas area, Harris Consulting Engineers (HCE) has designed many large-scale heating, ventilation and air conditioning (HVAC) systems. But according to president Tom Harris, P.E., the HVAC system they designed for the new $100 million High Desert State Prison represents one of the largest cooling systems in Southern Nevada. Harris also noted that the overall project was challenging on many different levels.
"First and foremost, due to the remoteness of the prison (located 40 miles Northwest of Las Vegas), we had to design this as a completely self-sustaining site. The prison has its own 26,000-square-foot infirmary, full laundry, 5,300-square-foot armory, a culinary building and a completely secured power plant. Even if the line from Nevada Power is cut, due to a lightning strike, auto accident, fire, whatever, this facility can be self-sustaining with just the emergency generators for up to 5 days in winter — even longer in summer."The three 1,750-kilowatt emergency generators provide over five megawatts of stand-by power and are fueled by four huge diesel tanks capable of holding 40,000 gallons of fuel.
Another "unfortunate" challenge was designing for growth of the prison, which sits on more than 160 acres and includes 13 buildings, seven guard towers, four miles of razor-wire fencing and 1.7 miles of electrified fencing. Phase I, completed in September, now houses 1,000 prisoners, and Phase II will increase the population to approximately 2,500. However, even more space will be needed to relieve overcrowding at other Nevada prisons. Therefore, HCE designed the centrally located power plant to serve a mirror image expansion of the prison. Additional boilers and chillers will be added to serve the expansion, and will be connected to the power plant.
The biggest challenge for HCE, which also designed all the plumbing and electrical for the site, was designing an adequate, yet cost-effective, cooling and heating system. Plans were changed several times, with the Nevada Department of Prisons finally choosing to go with two basically different systems.
"The buildings housing the administrative functions, employees and prison guards are served by chilled and hot water hydronic systems," Harris said. "The hydronic loops extend more than 15,000 feet from the powerhouse. In addition, these buildings have variable volume air distribution systems that respond to the heating/cooling requirements as they vary from morning to night and from summer to winter."
HCE designed the power distribution system to the wells, pumping stations and reservoir. The reservoir system has a holding capacity of 3 million gallons and serves domestic and service requirements for the entire facility.
Air conditioning for inmate housing is provided by indirect/direct evaporative cooling systems. These units cool by evaporation of water in cascading stages; the first stage is indirect and the second stage is direct. Initial costs and operating costs for these systems are considerably less than refrigerated air conditioning.
Following Arizona’s lead in using indirect/direct evaporative cooling for inmate housing, the Nevada Department of Prisons reduced the refrigeration capacity from 2,400 tons to 600 tons, a substantial savings, noted Harris, with few drawbacks. "The evaporative cooling system maintains comfort conditions on all but the most humid days."In addition to serving the employee, guard and administrative buildings, the heating plant serves the entire facility for both space heating and domestic water heating. Space heating hot water directly serves heating coils in the air-handling units, while domestic water is indirectly heated through a shell and tube heat exchanger. "Combining the space heating and domestic water heating systems reduced the plant space and provided a more economical and efficient operation," Harris said. "Both the chilled and hot water systems are designed to accommodate expansion of another prison of the same size."
Security was another major factor in the design of the prison. The kitchen/dining facility, capable of serving 7,500 meals per day, is segregated into six separate dining rooms. This allows different housing units to be served separately, so that trouble in one unit is isolated from other units.
The culinary building also houses the laundry facilities. A separate steam boiler plant was designed to generate steam for both cooking and laundering. Steam pressure requirements for the various cooking and laundering systems ranged from 25 pounds per square inch to 125 pounds per square inch. Steam was generated at 150 pounds per square inch and reduced to the pressures needed at the various pieces of equipment. For security reasons, and to prevent vandalism, components of the steam system had to be concealed. The routing of all the piping systems presented a real challenge, according to Harris.
"Many of the ceilings in this facility are "secure" ceilings and are made of steel plate; once welded into place, they are inaccessible. Sprinklers, sprinkler piping, ductwork, chilled and hot water piping, electrical security systems, alarm systems, power systems, all had to be designed so that access was not necessary. Items requiring service had to be located away from prisoner access. Ceiling access doors in inmate areas had to be vandal proof approved for prison use. Steam can be a fairly dangerous system so vandalism had to be taken into consideration. All the valves, duct works and pipes had to be kept out of site. Plus we had to provide the steam boiler with its own fuel supply, which also had to be secured."
The cells in the "dog-bone" shaped inmate units were designed with stainless steel toilet/sink units, "pick-proof" grout, and security bar systems in the ceiling. HCE designed the utilities so that guards control everything from a central location, including flushing the toilets, turning on the lavatory water, and turning on the lights.
"All-in-all," Harris said, "this is an extremely secure, self-sustaining prison. It was almost like designing a small, state-of-the-art city."