Project profile: Satellite chiller plant on campus
As part of Florida International University's Campus Master Planning, the new satellite chiller plant facility has an ultimate capacity of 7,500 tons of cooling capacity, supplements the university’s existing chilled water demand. It serves the existing and future needs of the Academic Health Center located on the northeast corner of the campus as well as other facilities.
Project name: FIU Satellite chiller plant
Project type: New construction
Engineering Firm: SGM Engineering Inc.
Building type: University facilities
Location: Miami, FL
Timeline: March 2011 - June 2013
Florida International University's new satellite chiller plant has approximately 15,000 sq ft of useable interior space with the cooling towers being located on the roof with parapet walls. The service side of the building faces south and the building was kept 30 ft from any known future buildings. The building was designed in compliance with the High Wind Velocity Zone (HWVZ) requirements of the Florida Building code for wind load to the building envelope and cooling towers. The plant is operated automatically with very minimum presence of FIU staff.
The plant energy management system is capable of notifying the FIU staff for any emergency and trouble shooting, such as power outage, maintenance or calibration.As part of Florida International University's Campus Master Planning, the new satellite chiller Plant facility has an ultimate capacity of 7,500 tons of cooling capacity, supplements the university's existing chilled water demand. It serves the existing and future needs of the Academic Health Center located on the northeast corner of the campus as well as other facilities.
In accordance with FIU direction, the project team analyzed and provided additional features for exterior building-envelope to withstand category 5 (157+ mph). That applied to exterior wall panels, exterior louvers, exterior exhaust fans and doors. The total cost for compliance to 157+ mph sustained wind speed was $326,530.
Water distribution system
The water distribution is owned and operated by Miami Dade Water & Sewer Department. The system consisted of an existing 12-in. DIP water main located west of the proposed building location. A 12-in. DIP water main runs east from the existing water main with fire hydrants abutting the new building. Existing water lines are adequate in size for the type of improvements proposed, however a new service was required to the new satellite chiller plant building. The Sewage Collection System was to tie the satellite chiller plant into an existing lift station located south of the satellite chiller plant in the student housing area. If this cannot be achieved then the second alternative is required.
To accomplish the design we required a duplex self contained grinder pump station located just outside the satellite chiller plant building and a new force main extension. Miami Dade Water and Sewer and DERM was coordinated with to apply for sewage allocation capacity.
Storm water piping and catch basins were redesigned. Storm water permitting required approval from Miami-Dade County Department of Environmental Resources Management (DERM) Water Control Section. The site was designed to convey a 5-year storm event on site. In addition 10-year, 25-year, and 100-year 3-day storm event models were run and the 100-yr 3-day model is now utilized to set the finished floor elevation.
This one-story chiller plant houses chillers, pumps, generators, transformers, electric switches and other ancillary spaces on the ground floor, and cooling towers on the roof. The chiller and cooling tower locations were coordinated such that interior column locations are adjacent to the corners of each.
Based on the Geotechnical Report issued by Nodarse & Associates, Inc., the project was founded on shallow foundations with an allowable bearing capacity of 6,000 psf. The slab-on-grade is non-structural, 4-in. thick and reinforced with welded wire reinforcing. The exterior walls are Load-bearing tilt-up concrete wall panels.
This system is common in South Florida but may not be on the FIU campus. With this system, the walls were formed on grade full height and 20 ft in width and lifted up with a crane in one or two days. Then interior columns and roof framing were erected. Benefits included construction speed and economy; appearance (note that the panels function as walls, shearwalls and façade all at once); and masonry and stucco scaffolding is eliminated. This system offers the best combination of aesthetics and construction speed and economy.
The wall panels are cantilever 27 ft above the roof structure. To resist wind forces, the panel ends were formed with 12 x 16-in. returns that act as pilasters (columns at the louvers). Interior columns are cast-in-place concrete. The roof is framed using a structural concrete slab on precast pre-stressed concrete joists and soffit beams (PSI) system. Note that there is the likelihood long-term that steel framing would corrode. Further, the 27-ft parapets caused significant roof diaphragm forces that could not be resisted by bare metal deck. FIU had this facility designed for Category 5 winds as defined by the Saffir Simpson Hurricane Scale. The governing building code, the 2007 Florida Building Code, requires 146 mph wind speed, an Importance Factor of 1.15 and that wind design be per ASCE 7-05, a nationally-renowned code. According to Table C6-2 of ASCE 7-05, 192 mph wind speed over land is the lowest wind speed for Category 5 hurricanes.
Another factor affecting wind pressures is Importance Factor, which is 1.0 for the standard 50-year storm. For buildings designated as essential facilities (such as this one), the Importance Factor is increased to 1.15, which increases wind pressures by 15% and correlates to a 100-year storm. Since pressures are determined in part by multiplying the Importance Factor by the wind speed squared, an Importance Factor of 1.15 effectively increases the wind speed from 146 mph to 157 mph. For this project, we increased the design wind speed to 192 mph, making it greater than a 500-year storm. Therefore, we used an Importance Factor of 1.0.
In deciding whether or not to design this facility for Category 5 winds, note that for the current wind speed of 157 mph, there is to be essentially no damage to the structure, components and cladding. Further, there are load factors and other safety factors. For example, the usual load factor for wind is 1.6. If the higher wind speeds are selected, the design wind pressures would be 50% higher than required by Code. The roof framing system would need to be strengthened, the wall system would become thicker and be more heavily reinforced, and some equipment may not be available; for example, the cooling towers.
The satellite chiller plant was designed for a total of 5 centrifugal chillers with a total capacity of 7,500 tons. During this stage of construction (based on present funding), two chillers were installed and stub outs were provided for the future chillers. All the chilled water and condenser water piping were designed using common header method which allow cross connections between chillers/cooling towers and respective pumps. A hoist beam was provided above the chillers only. The only rooms to be provided with A/C were the communications, restroom and control room.
Centrifugal chillers were used for the chiller plant. Each chiller provided 1,500 tons of cooling at full load. The chiller is producing chilled water at 42 F with an expected return temperature from the campus at 58 F. The chillers were installed on a 6-in. housekeeping concrete pad over neoprene pads for vibration isolation. At the pipe connections flexible hoses were used. All pipe connections were flanged, no mechanical couplings were allowed. Marine boxes were specified for the condenser and evaporator pipes connections. The chiller control system was compatible with the building control systems. An interface card was specified for compatibility. Hardwire of points weren't allowed. Chillers were specified with auto restart in the event of a power failure.
Each cooling tower is a two cell unit with one fan per cell. The cooling towers were constructed with stainless steel material. A solid separator was installed at the condenser water loop eliminating the need of constant basin blow down. The cooling towers fans were controlled with variable frequency drives and isolation motorized valves were installed at the inlet and outlet of each tower. All cooling towers were installed on the roof of the building, vibration isolation was provided at each support. To guarantee performance during raining and humid days the cooling towers were selected with an ambient wet bulb of 81 F.
Pumps and piping
A primary-secondary pump system was used for the chilled water system. The primary loop will be constant flow with one pump per chiller and one extra stand-by pump. The secondary pump system has one pump with one pump standby for this phase of construction with provisions to expand to three pumps. All secondary pumps are controlled by variable frequency drives. The pumps maintain a constant discharge pressure at the chiller plant. The condenser water system is a constant flow with one pump per chiller with one extra stand-by pump. All pumps are horizontal split case and were installed on an inertia isolation concrete pad. Because of the configuration of the pumps and reduced piping space, suction diffusers were used for each pump.
The piping arrangement for the equipment that was used is a reverse return system. By using a reverse return system the water flow is more of a self balance and more energy efficient system. The piping material is steel schedule 40 with welded joints. All equipment connections were flange mount with flexible hoses with exception of the cooling towers. All chilled water pipe was insulated with 2 in. of foamglass insulation and aluminum jacket. All condenser water piping was primed and painted with two-part epoxy paint.
Energy management system
The plant was equipped with an energy management system (EMS) capable of full chiller optimization. The EMS is connected to the campus energy management system. The control system for the chiller plant is BACNet ASHRAE 135 with open protocols. There was an operator computer located in the office but the system was web base available using any web browser. The chillers and frequency drives were provided with an interface card compatible with the control system. BTU meter was provided at the chiller plant supply and return piping to monitor the chilled water consumption and to stage the chillers.