Case study: Integrated resort project
By integrating the lighting and HVAC systems, a resort saved on overall energy use.
Energy is one of the primary drivers of innovation in modern building design. As energy costs continue to increase, the industry is turning to engineers to take an active role in designing systems that result in more efficient buildings. Why is it so important that the engineers drive this effort? The answer is simple; it is the building infrastructure (lighting, cooling and heating systems, hot-water systems, etc.) that accounts for much of the energy usage.
Figure 3 illustrates the expected energy usage of a recently designed integrated resort project. It is evident that lighting and the HVAC systems account for more than 75% of the overall energy usage in the building. Using LED lighting and high-efficiency cooling systems, incremental changes in these systems can have a dramatic effect on the overall energy usage.
For example, one of the most common methods of recognizing energy savings in building cooling systems is to centralize the cooling function into a central utility plant (CUP). The size of the CUP and the cooling equipment installed within is a function of the building location, type/use, size, and the calculated cooling loads. The resort project referenced used a centralized chilled-water system, which circulated chilled water to the various cooling coils throughout the property.
The largest energy consumers in the cooling system are the chillers (see Figure 4). Reducing this consumption is not as easy as increasing chiller efficiency. There are other components that influence the performance of the overall system: chilled-water temperature design, condenser-water temperature design, cooling tower fan energy, pump configurations, pump energy, use of variable frequency drives, air handling unit coil sizing, etc. The challenge presented to the engineer is how to design the mechanical systems to minimize energy consumption while maintaining low first costs and maximizing the use of available space.
To better understand how designers can use the operational-driven design model to overcome these challenges and provide owners with innovative designs, we will take a closer look at how the chilled-water system was optimized for this integrated resort project. The project was a mixed-use facility consisting of a three-level underground garage, two high-rise hotel towers, and a multilevel podium, which included a casino, shopping area, food and beverage venues, nightclubs, a state-of-the-art theater, and various back-of-house functions.
The total project area was approximately 3.9 million sq ft with plans for a future expansion of 1.2 million sq ft. During the design, it became evident that the building program and the incoming electrical service would not support a traditional chilled-water design. The system would need to be redesign to fit the project parameters. Some of the factors that influenced this decision included:
- Limited electrical capacity for the site
- Limited space available in the central plant
- Reduction in calculated load based on operational data
- Owner’s desire to increase operating efficiency while decreasing operating costs
- First-cost savings to the project.
The design of the integrated resort during the schematic phase followed more closely with the traditional model described in Figure 2. The design team calculated preliminary system loads for the property based on the original area program. The loads were used to develop several system concepts to present to the owner. Preliminary central plant equipment and central air handling systems were sized to determine the electrical loads while system information was provided for the rest of the spaces to calculate an electrical allowance for secondary HVAC systems. This information was coordinated with the electrical engineer, who began negotiations with the utility company to size the incoming service and the main electrical distribution gear.
As the design progressed into the design development stage, it was apparent to the team that the electrical capacity for the site was going to become a concern. If the site exceeded 30 MW, the utility would require the owner to construct a high-voltage substation to serve the property. Based on the schematic level loads, the building demand exceeded this limit and would require a dedicated substation.
Because the property was constructed with a zero-lot line, there was no place to install the substation. The design team needed to find ways to reduce the overall electrical load. The largest load in the building was related to the chilled-water system; this was the most logical place to start.
The design team revised the schematic cooling loads to incorporate more detailed building program information. At the same time, several different chiller configurations were being evaluated based on maximizing chiller efficiencies. During the re-evaluation process, the owner decided to hire an energy engineer and a CxA to provide a different perspective. It became apparent very quickly that each consultant had an area of expertise that could benefit the project. The chilled-water optimization project was now going to follow a nontraditional model, the operation-driven design model.
The base system design consisted of eight water-cooled centrifugal chillers using a variable-flow pumping arrangement to circulate chilled water. Four large-capacity heat pumps were used to provide heating hot water to the building while pretreating the condenser water serving the chillers (see Figure 5 for base equipment list).
Because the energy engineer had already completed several energy retrofits at the owner’s other properties, they had access to a wealth of information. The energy engineer had firsthand knowledge on how integrated resorts were operated and how to improve upon standard chiller designs. Most important, they had 2 years of operational data, which was analyzed and used to rationalize a smaller building load based upon actual building operation of similar use groups (see Figure 6).
The team then used the rationalized load to develop different concepts to determine the system with the best operating efficiency. The optimized design consisted of three pairs of series-counterflow chillers using a variable-flow pumping system. A variable speed drive was installed on one chiller to provide improved part-load performance. Two double-bundle machines, which can be used as either a heat pump or a chiller, were used to provide heating hot water during heat pump mode or base load the building in chiller mode (see Figure 7 for optimized equipment list).
During the optimization phase, the team relied heavily on the operational experience of the CxA, who reviewed each of the options to identify control issues that would cause problems during the commissioning phase. Adjustments were made to the control diagrams and sequences to fine-tune control of the system and maximize system performance.
To close the coordination loop, the design team reviewed the final system concept with the electrical engineer to make sure that the proposed configuration could be supported by the electrical infrastructure. The electrical team evaluated the various operating modes to make sure that the system did not exceed the power threshold required to maintain the building electrical demand below 30 MW.
Through the close coordination effort during the design development phase, the design team identified a serious issue that would have had a significant impact on both the project schedule and budget. The design team, assisted by nontraditional consultants, rationalized reduced building loads, analyzed multiple system options, and optimized the chilled-water system to reduce overall electrical consumption. This process resulted in an innovative solution to a complex issue and provided the owner with a high-performance building that will save energy for many years to come.
Hans Grabau is executive director of mechanical at NV5. His expertise is in multiple market sectors including large mixed-use gaming and hospitality projects, mixed-use commercial developments, mission critical facilities, and central plant design both domestically and internationally.