Modular central plants can streamline engineering

Modular central plants can be less expensive to build, simplify design and specification, and require less space than traditional mechanical rooms.

By Joe Cantwell, Johnson Controls Rental and Modular Solutions, Milwaukee, Wis. April 26, 2011

Modular central plants (MCPs) are emerging as smart, efficient alternatives to traditional "stick-built" mechanical rooms. These prefabricated, self-contained systems are up to 15% less expensive to build than conventional utility plants. MCPs simplify design and specification, require less space, and deliver both the technology and flexibility that facility owners and managers require. In short, they can add value to mechanical/electrical design.

An MCP is, simply put, a central utility plant in a box. The manufacturer pre-engineers and fabricates all the equipment according to the consulting engineer’s specifications, including boilers, chillers, pumps, cooling towers, starters, and controls. The components are packaged in an enclosed skid that is pre-piped, wired, tested, and shipped to the job site as a module. Once the module is placed on-site, only water and power connections need to be made.

Consulting engineers may specify MCP operating parameters and output (for example, load profiles and total heating/cooling capacity) and then supervise the plant design done by the MCP manufacturer. Alternatively, they may choose to actively manage plant design using 3-D modeling and specifications for unique requirements or environments.

The MCP represents an approach to plant design that can be faster and more cost-effective for the architect, engineer, construction manager, and ultimately, the owner. In retrofit and expansion projects, the MCP requires no interior space and its capacity can be increased by adding another module. The modules lend themselves to facilities that are moving from air-cooled chillers to a central water-cooled-chiller plant for the first time, as well as projects that require additional chilled/hot water capacity and have interior space constraints. Projects on short design and construction cycles and those that require refrigerant replacements are also candidates for an MCP installation.

Additionally, an MCP can incorporate the latest central plant technology (e.g., variable-speed drives and quick-restart capability for chillers in mission-critical applications) and security and fire safety solutions, as well as testing and certification that compares favorably to ground-up, site-built plants.

For all of these reasons, MCPs are an attractive alternative to traditional builds. As the U.S. economy begins to show signs of recovery, the benefits of MCPs will become increasingly clear in four specific markets poised for growth, as listed below.

1: Healthcare facilities

The population is aging and living longer. According to the Administration on Aging, the number of older persons (65 years or older) will double between 2000 and 2030 to about 72.1 million. Hospitals must plan for that future growth without compromising present service levels.

The key is flexibility. As campuses grow or the demands of existing buildings increase, MCPs will give hospitals the ability to add capacity with little or no disruption in service. MCPs also can be moved to make way for future construction or to move capacity to another location in the case of consolidation.

In addition, today’s MCPs are compact, requiring about two-thirds of the space of a conventional plant. That leaves more space available for patient-directed activities. Aesthetically, today’s modular plants have come a long way. MCPs now feature custom paint colors and can be designed to match existing siding, brick, wood, or stone. Exterior panels can be made to control sound for acoustic-sensitive applications, such as hospitals, where noise must be kept to a minimum.

2: Data centers

The U.S. data center industry is in a major growth period. A survey conducted by Digital Reality Trust shows 83% of large firms surveyed in North America are planning to expand their data center facilities in the next 12 to 24 months. MCPs can help address the challenges posed by data center development. MCPs can grow with the business, allowing facility managers to plan for the future, but build and pay for only what is needed now.

MCPs can also be designed to meet the demanding uptime and redundancy requirements for Tier I to Tier IV data center certifications. Because they are pre-engineered, designed, built, and tested by experts in a quality-controlled environment, the risk of delays or failure during start-up is minimized. An MCP can be designed to maximize power usage effectiveness (PUE) ratios and incorporate essential features like power-interruption protection and fast restart of cooling equipment so that chilled-water temperature can be re-established quickly if a power event occurs. Some chillers equipped with advanced electronic variable-speed drives provide quick-restart capability in seconds, not minutes.

3: Educational facilities

College enrollment rates are at an all-time high. According to a recent U.S. Labor Dept. report, the rate has been trending up for decades and is continuing to rise, partly because the weak job market is encouraging more people to pursue higher education. Campuses are stretching their HVAC capacity to accommodate increased enrollment.

Heating and cooling capacity can be added easily when needed and, because MCP footprints are compact, the units require less campus real estate than conventional site-built plants. Modular plants can be situated outdoors in a remote area, so they are not occupying interior space needed for classrooms and other uses. Perhaps most importantly, modular central plants can be built quickly; lead times are reduced by as much as 40% compared to site-built plants, and they can easily be commissioned during slower summer months.

4: Industrial applications

Although the U.S. economy may be showing signs of recovery, businesses of all sizes remain under pressure to cut costs and increase efficiencies. MCPs offer facility and plant managers a cost-effective cooling option, leaving more dollars available for revenue-generating operations.

While the MCP layout is compact, it is carefully configured for ease of access, operation, and maintenance with a floor plan that allows multiple service technicians to work in the same area simultaneously. Many of today’s MCPs offer features such as pump and chiller hoist rails, wide service doors, removable wall panels, and overhead roof hatches.

Finally, MCPs are easier to keep clean than conventional plants. Inside a MCP, lipped draining trays under the condensers eliminate cross-contamination from one module to another. In addition, all surfaces are steel plate or aluminum, compared to the hard-to-maintain concrete surfaces of a conventional build.

In these four markets poised for growth, as well as other applications, MCPs offer a cost-effective, flexible, efficient HVAC option. The benefits are magnified when MCPs are incorporated into a plant designed for energy efficiency. When combined with building management systems that monitor energy usage and energy-efficient equipment, such as chillers with variable-speed drives, MCPs help facility managers lower operating costs and address green building and sustainability goals.

Design considerations

The specifications engineers consider for modular plants are similar to those for a conventional central plant and include location, capacity, pressure drops, efficiency, and equipment selection. However, the modules engineers ultimately specify are unlike traditional plants. The MCP is pre-engineered, packaged, optimized for efficiency, and tested by the manufacturer prior to delivery.

MCPs require engineers to write overall plant specifications rather than specifications for individual components, saving significant amounts of time associated with designing the plant, selecting individual components, choosing suppliers, and going through an extensive bid process. Engineers may realize additional time savings with the elimination of certain field tasks, including job site inspections and punch-list items. As a result, engineers can focus greater attention on design issues in the building’s interior space, including indoor air quality and optimization of the entire mechanical and electrical system.

The use of MCPs also allows for a more competitive construction-bidding process by including contractors who may not be (and do not need to be) specialists in large, central plant design and construction. Project bidding is available to all qualified firms that can install ductwork and piping to the interior of the building.

Single-supplier benefits

Because MCPs come from a single supplier, they also mitigate risk for engineers and consolidate responsibility for central plant performance. Modules are constructed in a temperature-controlled environment that allows efficient fabrication. The proximity and availability of in-house quality control inspectors makes it easy to implement a quality assurance plan. Modules can be tested and inspected before shipping so that MCPs arrive at job sites with guaranteed performance, efficiency, and minimal problems at commissioning.

Owners also benefit from the simplicity of working with a single provider for the entire plant. They also can be assured they are receiving advanced central plant technology, including plant optimization capability. In fact, with weather data, load profiles, facility use plans, and so forth, factored into the MCP design in advance, the module can arrive with optimized control settings and sequences already pre-programmed. Commissioning and fine-tuning is always done in the field, but accomplishing most of the programming at the factory provides additional time, cost, and quality advantages.

Saving time

Because building construction and central plant construction happen in parallel, not in series, general contractors benefit from shortened construction time. System construction is not dependent upon site construction permits or civil works completion. Additionally, because the modules are constructed off-site, building owners are not subject to change orders as the result of space or trade coordination.     

MCPs also simplify central plant installation, further reducing construction time. Less skilled labor is required at the job site, since connections for installation are straightforward and the module has been factory-tested. The primary site work associated with the modules is preparing the foundations, setting the modules, and connecting the supply/return piping and the electrical power feed.

Finally, MCP providers offer a wide range of special designs, from various pumping schemes to certifications for nonexploding central plants, emergency power criteria, earthquakes, hurricane-force winds, blast forces, and even bioterrorist attack. Engineers will find few, if any, limitations in incorporating modular central plants into their designs and specifications and will certainly find value in terms of cost, time, and space savings, and advanced technology and design flexibility.

Cantwell is marketing manager at Johnson Controls Rental and Modular Solutions. He has been with York and Johnson Controls for 15 years.

A Modular Application: Le Bonheur Children’s Hospital

Hospitals have historically designed and built their central plants using the conventional on-site construction method. However, an increasing number of healthcare facilities are turning to modular central plants (MCPs) as they face pressure to increase flexibility and maintain costs. In Memphis, Tenn., Johnson Controls installed a 13-module central plant at newly expanded Le Bonheur Children’s Hospital, where an empty 12,000-sq-ft pad was transformed into an installed modular central plant in just a fraction of the time it would have taken using traditional construction methods. This plant provides service to the $340 million, 610,000-sq-ft, 12-story facility and represents one of the largest MCPs in the United States, which includes chillers, boilers, and generators.

“We chose a modular central plant because it gives greater flexibility for repairs and replacements. More importantly, the cost savings of modular construction gave us flexibility to use our budget for other priorities,” said Dave Rosenbaum, vice president of facilities management at Le Bonheur Children’s Hospital.

Project statistics

  • Investment: $15 million
  • Site: 12,000-sq-ft pad
  • Equipment:
  • Three 1,100-ton chiller and pump modules
  • Three 1,100-ton cooling towers and pumps
  • Three 1,500-kW generator modules
  • Three 700-BHP steam boiler modules
  • One de-aerator and water treatment module
  • One main/emergency gear module
  • One control room and automatic transfer switch module
  • One fire pump module

Note: Site includes room for expansion to include the addition of one boiler and one chiller module with the associated cooling tower and hydronics.

Click here to view a fly-through video of the Le Bonheur Children’s Hospital MCP.


 View more fly-through videos of MCPs:

  • Electrical Control Room Assembly
  • Boiler Modules Assembly
  • Generator Assembly