Raleigh s District Cooling Solution:

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1 Feature Story Raleigh s District Cooling Solution: Performance contracting finances system upgrades John S. Andrepont, President, The Cool Solutions Company; Kevin P. Gillespie, PE, Energy Engineer, Pepco Energy Services; and Richard B. Beversdorf, PE D istrict energy is once again at the heart of an economically attractive solution to complicated energy issues at the North Carolina State Capitol Complex in downtown Raleigh, N.C. This solution entailed a self-financing, energy service performance contract to improve energy efficiencies and energy costs while upgrading aging energy infrastructure within existing buildings and within an existing, limited district cooling system. A team of designers, suppliers, and contractors led by Pepco Energy Services recommended fairly typical energy conservation measures plus an inventive departure from the initially requested approach: The company chose to invest heavily in district cooling rather than merely replacing existing in-building chillers. As is increasingly common with performance contracting for federal and state entities, the entire project is self-financed by the energy cost savings relative to the state s base case energy utilization. The combination of four key elements district cooling, thermal energy storage (TES), a packaged chiller plant and pressureindependent flow control is creating maximum savings and value that would otherwise be unattainable if one or more of those elements were excluded from the project. The Challenge The North Carolina state government occupies numerous buildings clustered in the capital of Raleigh. A strong commitment to reducing energy consumption, renewal of aging infrastructure, budget cuts and rising energy costs caused the state to explore the use of performance contracting to modernize its energy infrastructure while avoiding the associated capital investment. A selected performance contractor, or ESCO (energy service company), would finance the project and utilize a portion of the savings in the state s operating energy budget to recover the project capital costs. In late 2004, the state issued a request for proposals from performance contrac- Most of the buildings in North Carolina s State Capitol Complex in Raleigh, including the State Capitol itself (center bottom), are connected to the district cooling system. The system s old central chiller plant is located within the quadrangle of buildings shown just above the State Capitol building grounds. The new chilled-water tank (not shown in this older photo) is located beyond the tallest building on the left side of the photo. Reprinted from Fourth Quarter 2007 District Energy magazine with permission of IDEA. Fourth Quarter

2 The Solution The successful solution involved an approach integrating existing assets that were modernized and improved as well as new equipment and infrastructure. These improvements involved four groups of energy conservation measures: lighting upgrades in various buildings, HVAC and control improvements within the buildings, water conservation initiatives, and a major expansion and modernization of the district cooling system. The latter included a new TES system, a new packaged chiller plant, upgrades to existing chillers and the existing TES system, system control modifications to ensure a high delta T throughout the chilled-water system, and expansion of the existing cooling loop to accommodate additional and future facilities. The project benefits are as follows: More than $2 million per year in energy savings 8 District Energy Courtesy Natgun Corporation. tors. The RFP specified that numerous and varied types of energy conservation measures could be included within the scope of the project. The RFP also requested that several concerns be addressed regarding specific inefficient and poorly operating cooling systems. These included (1) an aging and relatively small district cooling plant that serves a core of 10 of the state s oldest buildings; (2) an old, unused 740,000-gal chilledwater TES tank associated with the old cooling network; and (3) aging, inefficient chillers and degraded cooling towers in four large buildings remote from the existing district cooling network. (Their capacity was to be replaced, presumably within those buildings.) (Note: The state complex is also served by an existing steam district heating network that was not included in the RFP.) The state selected the proposal offered by Pepco Energy Services. The company then performed the detailed audit phase of the project throughout the first half of Project implementation began in November 2005, with completion of the energy conservation measures in late 2006 and The expanded district cooling system was commissioned and placed in service during spring 2007 and commissioned during the summer. Raleigh s upgraded district energy system includes a new 26,270 ton-hr thermal energy storage tank. Designed to blend architecturally with an adjacent parking structure, the tank was partially buried, which minimize its height and aesthetic impact. Approximately $18.9 million in new infrastructure Reductions in energy usage of more than 20,000,000 kwh/year Reductions in water consumption of more than 10,000,000 gal/year Improved building comfort More than $7 million in future capital cost avoidance Expanded cooling capacity and system redundancy The district energy solution was dependent on the integrated use of four important elements: district cooling, thermal energy storage, packaged chiller plant and improved chilled-water delta T. District Cooling Is Backbone The energy services contractor based its unique and successful proposal not on replacing the four large in-building chiller plants with new in-building plants, but rather on a major expansion of the existing district cooling network to include those four buildings as well as other new additions. The old central chiller plant, which had served 10 state buildings totaling 1.3 million sq ft of space, was modernized; the existing unused chilled-water TES tank was repaired and re-commissioned. However, the primary investment in new chiller capacity was focused on an all-new, larger-scale, highly energy-efficient packaged chiller plant located at a more centralized site within the expanded district cooling network. The expanded system now serves 20 buildings that total 3.5 million sq ft. No new chillers were purchased for any individual buildings. The new packaged chiller plant became the primary source of chilled-water generation. The old, rehabilitated chilledwater plant became a secondary source at a satellite location. Additionally, the most reliable and efficient of the remaining inbuilding chiller plants became available as distributed, local, tertiary sources of chilled-water generation, used only for peaking capacity or emergency backup capacity in extreme cooling conditions. The majority of the new piping used in the district cooling system is directburied, high-density polyethylene (HDPE) pipe. HDPE was chosen due to its ease of installation, longevity, and life-cycle-cost considerations. Insulated steel piping is used for all above-ground and in-building applications. TES Enhances Solution Critical to the successful economics of the project, in addition to rehabilitation of the old, relatively small TES tank, was installation of a new 2.7 million gallon TES tank, located at the site of the new packaged district cooling plant. This large, new stratified chilled-water TES tank provides two key economic benefits: It minimizes the use of chillers during high-cost, on-peak utility periods, greatly reducing demand costs and also benefiting from Reprinted from Fourth Quarter 2007 District Energy magazine with permission of IDEA.

3 Courtesy Natgun Corporation. time-of-day energy rates, and it reduces total capital cost relative to a conventional (non-tes) chiller plant installation. The new TES tank was partially buried. Though adding cost, this was done to minimize its height and aesthetic impact. The partially buried tank configuration supported the choice of a concrete tank, which uses a precast, prestressed design in accordance with American Water Works Association standard D110, Type III. The new TES tank and the adjacent new packaged district cooling plant comprise the Energy Conservation Center, the heart of the expanded district cooling system. The tank s façade was also designed to architecturally blend with the existing multilevel parking structure immediately behind the Energy Conservation Center. The new TES tank and the adjacent new packaged district cooling plant comprise the Energy Conservation Center, the heart of the expanded district cooling system. The existing underground TES tank had a nominal 740,000-gal volume (33 ft wide x 100 ft long x 30 ft deep). Installed in 1988, the concrete, stratified chilledwater TES tank was unused prior to this performance contract for a number of The Energy Conservation Center serving the North Carolina state government complex includes a new packaged chiller plant with a 2,900-ton cooling capacity. reasons, including a high rate of water leakage, poor stratification performance and difficulty controlling the flows of water to and from the tank and the water level within the tank. These issues were addressed as part of the performance contract. During the detailed audit phase of the project, scuba divers and underwater video identified the sources of the tank leakage (occurring at the sleeves around the piping penetrations of the concrete tank walls and in one of the distribution lines leaving the tank) and the cause of the poor stratification performance (attributable to broken PVC pipe flow diffusers in the original TES tank design). During project execution, the tank wall penetrations were repaired using leak-resistant sleeves, and new internal flow diffusers were designed and installed by the new TES tank supplier using primarily welded-steel piping. In addition, the TES tank pumping and valving interface with the balance of the district cooling network was redesigned to accomplish simple and reliable control of flow and level. This TES tank, though originally designed to provide approximately 5,300 ton-hr of capacity at a 12 degrees F delta T, had been providing no TES capacity due to its past operational problems. Now it can provide more than 7,000 ton-hr of capacity at a 16 F delta T. Prioritizing Investments for Energy Efficiency Existing Chilled-Water Plant The existing plant had three aged (and dissimilar) chillers piped in parallel; the two oldest chillers were specified for a 12 F delta T and the newest for a 10 F delta T. However, all three chillers were typically operating at only a 6-9 F delta T. The plant capacity was also constrained by the existing cooling towers and the electric power feed. Each of these factors contributed to limiting the operation to a maximum of two of the three chillers at any one time. The congested plant layout and equipment age and inefficiency dictated that only limited capital should be invested at this site, in lieu of a more justified investment in primary capacity at the new Energy Conservation Center. The cooling towers and electrical service were upgraded, and the three chillers were upgraded and re-rated for operation at supply and return temperatures of 39 F and 55 F, consistent with the expanded district cooling system design. New District Cooling Plant The use of a turnkey, design-built, packaged district cooling plant, rather than the conventional stick-built plant, provided multiple significant benefits to the project. They included a much smaller required plot plan for easier siting and less visual impact; a much shorter overall schedule and on-site installation schedule; high energy-efficiency compressors, with 39 F supply temperature and high delta T; low installed capital cost per ton; and single-point responsibility with guarantees of total plant tonnage and kw per ton. The installed capacities of the new and old chillers and new and old TES are summarized in table 1, along with the peak design day cooling loads. Optimizing High Chilled-Water Delta T Another crucial aspect of achieving the economically successful district cooling solution was the use of a relatively high temperature differential between the chilled-water supply and return temperatures. The small, pre-existing network suffered from operating at very low chilledwater delta T (typically 6-9 F). Increasing the delta T resulted in very significant benefits: smaller new pipes with lower capital cost and more capacity in existing piping; smaller new pumps with lower capital cost; more capacity in existing pumps and lower pump horsepower with associated lower operating costs; more capacity in the existing TES tank; and a smaller new TES tank with lower capital cost and less concern with issues of space allocation and aesthetic impact. The higher delta T was accomplished by both lowering the chilled-water supply temperature at the new and old plants and by assuring a high chilled-water return temperature at the buildings cooling loads. The latter result was accomplished by the installation of pressure-independent flow control valves at all major air-handling units throughout the connected buildings. Some buildings are now achieving a delta T of 18 F, even at below-design loads. Reprinted from Fourth Quarter 2007 District Energy magazine with permission of IDEA. Fourth Quarter

4 Table 1. Chiller and TES Capacity and Design Day Cooling Loads. Primary Chiller Capacity (New Packaged Chiller Plant) Secondary Chiller Capacity (Rehabilitated Chiller Plant) Peaking & Reserve Chiller Capacity Administration Building Albemarle Building New Revenue Building Highway Building TES Capacities New Chilled-Water TES Tank Old Chilled-Water TES Tank Total Available Capacity Chillers Only Chillers Plus TES Discharge Design Day Peak Load Design Day 24-hr Average Load The existing in-building chillers, which can provide peaking and reserve cooling capacity, are not designed for the low (39 F) chilled-water supply temperature. However, they are used on a limited basis, and are not planned to feed the district cooling network. In those instances when in-building chillers are dispatched, they are used solely to serve load within their own individual buildings, effectively shedding that load from the district cooling system. Results and Benefits Management of Energy and Energy Costs Each state building is now independently metered and billed in accordance with that building s applicable standard electric utility tariff. Because buildings have been connected to the district cooling network, the Energy Conservation Center can be used to adapt to and control the load profiles of the individual buildings. This is made possible primarily though the use of the TES. These strategies allow the state to select the most advantageous electric rate tariff for each building, further increasing the energy cost savings. Through the avoidance of inbuilding chiller operation in many of the 2,900 tons (operates off peak and, often, as needed, on peak) Approximately 1,800 tons (operates off peak and, at times, as needed, on peak) (operates only rarely and always off peak) 485 tons 450 tons 750 tons 375 tons (discharges on peak, recharges off peak) 3,700 tons of discharge (26,270 ton-hr total) 800 tons of discharge (7,100 ton-hr total) 6,760 tons 11,260 tons With Initial Buildings Only 4,872 tons 5,881 tons 3,500 tons 4,162 tons Also With Legislature and Legislative Office Building large buildings, the state can benefit from the use of the more economical Small Time-of-Use tariff. The old chiller plant and the new Energy Conservation Center, each with a nearby TES tank, are billed on the attractive TES tariff. Excess storage and chiller capacity also allow both chiller plants to avoid operation during the day-time peak periods of high demand and energy charges during the cooler months. Additionally, water flow within the network is managed through the use of variable speed pumps to further enhance system efficiency and control. A new custom-applied Siemens Energy Management Control system monitors, controls and coordinates the two chiller plants, the TES systems, the individual building chilled-water needs and the district cooling flow. Also, each facility served by the system is metered to determine the actual flow rates and temperature differentials. Expandability for Future Load Growth Several steps were taken in designing the project to accommodate future district cooling system expansion. First, the piping headers were sized large enough to accommodate the incorporation of two additional large existing state buildings and three large future buildings. Second, the new TES tank was oversized beyond that necessary for leveling present peak day loads not an idle investment, as it can be used now to shift larger cooling loads and achieve larger electric demand management. Third, the new packaged chiller plant was designed to allow for easy future capacity expansion. Reliability and Redundancy The project now provides a minimum of N+1 redundancy in critical mechanical items such as chillers and pumps. The use of an integrated district cooling system permits this to be economically achieved, whereas it would not have been economically feasible if serving each building only with its own in-building chiller plant. This added redundancy and reliability is a benefit that the state did not previously enjoy, and would not now be enjoying without the use of district cooling. The upgrade of Raleigh s state government energy infrastructure, under the direction of Pepco Energy Services, achieved an innovative and extremely beneficial result. The magnitude of the project benefits, and even the economic viability of having a project at all, was dependent on the integration of the key technical elements: district cooling, TES, packaged chiller plants, pressure-independent flow control valves and the tactical use of various existing assets. The project is a showcase of what district energy can deliver, especially when it is leveraged with complementary technologies that are not as readily deployed on the scale of individual building systems. The result for the performance contractor is an attractive rate-of-return applied to a large investment, thus creating a large net present value. The result for the state is a much better-than-anticipated solution to their cooling issues, with much more new infrastructure, much 10 District Energy Reprinted from Fourth Quarter 2007 District Energy magazine with permission of IDEA.

5 larger levels of energy conservation and energy cost reduction, the realization of reliability and redundancy that could not have been economically achieved with individual in-building chiller systems, and the ease of expandability of all those benefits to even more buildings in the future. The project is a showcase of what district energy can deliver, especially when it is leveraged with complementary technologies that are not as readily deployed on the scale of individual building systems. Authors Note: The authors recognize the foresight of the State of North Carolina in supporting this important energy conservation and cost-reducing district cooling development. Specifically they wish to recognize the North Carolina Department of Administration, including Speros Fleggas, Greg Driver, Michael Hughes, Hany Botros and Cindy Browning of the North Carolina State Construction Office, as well as Larry Shirley, director of the North Carolina State Energy Office. In addition, the authors acknowledge the key members of the district cooling project team: Pepco Energy Services, performance contractor/team leader; The Cool Solutions Company, district cooling and TES consultant; Affiliated Engineers Inc., engineering consultant; TAS Ltd., packaged district cooling plant; Natgun Corporation, TES tank; Cool Systems Inc./Flow Control Industries, pressureindependent flow control valves; Siemens Building Technologies, controls; Progress Energy, electric utility. John S. Andrepont is the founder and president of The Cool Solutions Company, which provides professional consulting services in the areas of thermal energy storage, district cooling and turbine inlet cooling. Andrepont served on IDEA s board of directors for five years and has cochaired three IDEA cooling conferences. He has also held leadership positions in the American Society of Heating, Refrigerating and Air-Conditioning Engineers and the Turbine Inlet Cooling Association. A graduate of Rensselaer Polytechnic Institute with bachelor and master degrees in mechanical engineering, Andrepont is the named inventor on more than one dozen U.S. patents. He can be reached at [email protected]. Kevin P. Gillespie, PE, is an energy engineer for Pepco Energy Services, an energy services company that develops, installs and finances projects designed to improve the energy efficiency and maintenance costs for facilities of all types. Gillespie provided design guidance throughout the project implementation stage as well as managed final commissioning of all interrelated mechanical systems. A graduate of North Carolina State University with a bachelor s degree in mechanical engineering, he is a registered professional engineer in North and South Carolina. He can be contacted at [email protected]. Richard B. Beversdorf, PE, also contributed to this article. Sustainable Campus Energy We Get It! University and College campus energy dynamics are rapidly shifting. It has become imperative for campuses to provide sustainable energy solutions that are reliable and flexible for future technologies, but can also efficiently meet today s needs. AEI is a national expert for planning, analyzing, designing and implementing: Whole Campus Energy Systems Master Planning Utilities Master Planning Carbon Footprint Analysis Emissions Control Alternative & Renewable Fuel Analysis Chilled Water Underground Utility Distribution Thermal Storage CHP Steam/Steam Condensate Commissioning Hydraulic Modeling Building Management/ Control Systems Compressed Gases Contact Jerry Schuett, P.E., Principal, at to discuss your campus energy needs. Chapel Hill, NC Champaign, IL Chicago, IL Gainesville, FL Houston, TX Madison, WI Metro DC Phoenix, AZ Seattle, WA Tampa, FL Walnut Creek, CA Reprinted from Fourth Quarter 2007 District Energy magazine with permission of IDEA. Fourth Quarter