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.

By SGM Engineering Inc. November 3, 2014

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

Building details

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.

Building envelope

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.

Mechanical details

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.

Cooling towers

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.

Piping design

The Chiller Plant was provided with new domestic cold and hot water piping systems. Water was distributed to plumbing fixtures and equipment utilizing Type ‘K’ soft-drawn copper pipe and soldered or pressed fittings underground and Type ‘L’ hard-drawn copper pipe and soldered or pressed fittings above ground. Underground piping was encased in polyethylene. All pipe, fittings, and joining materials were certified as lead-free. Water piping was sized to limit velocity to 8 fps to reduce the damaging effects of water hammer. Isolation ball valves were installed at the water main entrance and at each group of plumbing fixtures. An instantaneous electric water heater was provided within the janitor closet to provide hot water to the mop sink and lavatory sink. All domestic hot water piping was insulated with pre-molded fiberglass or elastomeric insulation. A sanitary drainage system was provided to serve all plumbing fixtures and equipment within the new Chiller Plant. The sanitary system was routed by gravity through the building to a point 5 ft outside the building where it connects to the site underground sanitary sewer system. This system was constructed utilizing schedule 40 solid-wall PVC pipe and DWV fittings with solvent cement joints. Cleanouts were located to provide easy access and cleaning.

All plumbing fixtures are commercial grade. Accessible fixtures are specified to comply with the Florida Accessibility Code. All plumbing fixtures were provided with low flow type faucets, valves and fixtures. Water Closets were wall hung vitreous china with battery powered sensor operated flush valves designed for 1.28 gal per flush. Lavatories were vitreous china, wall mounted type, with ADA approved trim. Faucet sets are self closing with 0.5 gpm discharge and laminar flow outlet. Lavatories are cold water only. ADA lavatory p-traps and supplies were provided with insulation. Electric Water Coolers are self-contained, semi-recessed units with single or bi-level dispensers, as required and meeting ADA mounting requirements. Service Sinks were wall hung 20-in. wide by 11-in. deep minimum enameled cast iron type with wall mounted faucet set, hose and bracket, mop hanger, and stainless steel bumper and wall guards. A 3-in. diameter floor drain was provided in front of the sink to catch spillage. Floor Drains are located within the toilet room, janitor closet, and chiller and pump room and were provided with automatic trap primer valves. Heavy duty floor drains were utilized within the mechanical area. Hose bibs for cleaning purposes were provided within mechanical rooms near the entry doors and were placed at 18 in. above the finished floor. Hose bibs were keyed type with chrome plated finish. Wall hydrants were provided at 100 ft intervals on the exterior of the building. Wall hydrants were installed at 18 in. above grade or finished floor. Wall hydrants are encased, keyed type with chrome plated finish.

Electrical design

The electrical distribution was 480V/3 phase with (2)-3000 amp switchboards to serve the current 2 chillers and layout with conduit stub ups for (3) -3000 amp switchboards for future chillers/cooling towers. Underground conduit rough was also provided for the future pumps. The local 120/208V loads were supplied from a dry type transformer and panel board provided within the plant.

The large mechanical equipment and lighting were served from the 480/277V distribution panels. The 208/120V, 3φ, 4-wire branch panels are supply power for receptacles, small appliances and miscellaneous equipment as required. The utility transformers are supplied by Florida Power & Light (FP&L) and were placed inside a transformer vault with 3-hr rated walls and proper ventilation. Primary conduits were provided for with concrete encasement.

Transient voltage surge suppression were installed at the main switchboard and panel boards for two levels of coverage. Parallel connected surge protection devices (SPD’s) were used and they are connected to minimize the lead length of the SPD. The SPD was selected to match the available fault current at the equipment it protects.

Motor control

The chillers were supplied with unit mounted Wye-Delta starters. To make the distribution more efficient and cost effective with the use of VFD’s, there is no MCC-motor control center. The building was provided with space provisions for the future addition of (2) 2000 kW generators with automatic transfer switch. The layout was for the generators to handle the entire load of the plant as required by the first phase of this plan. This included (2) 1500-ton chillers, (2) 250 hp secondary pumps, (2) 30 hp primary pumps, (2) 125 hp condensed water pumps, (4) 50 hp cooling tower fans, and the miscellaneous lighting, power, HVAC load for the chiller plant building.

Lighting design

Interior lighting used T-8 industrial vaportite fixtures inside the chiller plant. The average maintained foot-candles within the plant shall be 50 fc. All fluorescent lamps are 4100K with a CRI of 80. Emergency lighting was provided in accordance with FBC section 1006 by the use of wall mounted emergency battery units. Exit lights are LED type with battery backup power. The emergency lighting and exit signs have a laser pointer device activated test switch. Exterior lighting is fluorescent wall sconce type fixtures with no up light. Interior lighting is controlled with motion sensors for energy conservation. Lighting on the roof (cooling tower areas) was provided with a photocell and local switch for control.

A rooftop lightning protection system was provided. All new air terminals, bonds to rooftop equipment and other metallic items, down conductors, buried counterpoise conductors and ground rods, all as per NFPA 780 and UL 96A. The system was installed by an LPI approved installation contractor. Any roof penetrations were made with thru roof assemblies equal to Harger 230 series pre-manufactured base plate/cable connector, threaded riser bar, 2 3/8-in. OD PVC tubing support, and cap/cable connector. All connections were made with exothermic welding below grade and compression connectors above grade. Roof conductors were NFPA Class 1 stranded aluminum. Down conductors was NFPA Class 1 stranded copper with bi-metallic transitions to the aluminum roof top conductors. All down conductors were concealed from public view. Air terminals will be ½-in. diameter Class 1 aluminum. Appropriate bases for the mounting surface were utilized and coordinated with the roofing manufacturer.

Communication system

Since the communications requirements within the plant were minimal, the FIU standards for buildings were reduced, but still allowed for future expansion of the system for the building. Data and phone outlets were provided within the control room and for the EMS and fire alarm systems as required. Cat 6 horizontal cabling in accordance with EIA/TIA 568-B.2-1 standards were provided to each outlet.

Fire and security

The fire alarm system for the building is an addressable microprocessor controlled system by Notifier or Johnson controls and be fully compatible with either of the two central fire alarm systems located in FIU’s Central Utilities Building. System components included new fire alarm control units, manual pull stations, horn/strobes, and heat or smoke detectors. The system utilized class B wiring circuits. The system required a dedicated branch circuit for the primary power source for the fire alarm control units. This circuit disconnect means have a red marking, be accessible only to authorized personnel, and is identified as "Fire Alarm Circuit". The location of the circuit is permanently identified at the fire alarm control unit. The secondary power supply consists of storage batteries dedicated to the fire alarm system. The secondary power supply is of sufficient capacity to operate the fire alarm system under quiescent load for a minimum of 24 hours and, at the end of that period, is capable of operating all alarm notification appliances used for evacuation for 5 minutes.