Wake Tech East Central Energy Plant Case Study

Project Objectives

From its inception, the design and operating criteria for Wake Tech East's new central energy plant required an innovative integration of leading-edge energy and HVAC equipment technologies. The solution needed to maximize efficiency and meet the demand for decarbonized heating and cooling. Unlike typical central plants distributing hot water from boilers and chilled water from chillers independently, Wake Tech East's facility called for an integrated central heat pump plant with a common set of water source heat pumps to provide hot and chilled water distribution to the entire campus.

The plant's systems were designed to achieve a high degree of sustainability and energy efficiency. System expandability was also a critical requirement for future campus building phases. With Wake Tech East's reputation for providing training in the latest technologies, the facility was also intended to serve as a 'hands-on' classroom for developing talent in high-tech fields and advanced sustainability practices.

A modern educational building with a prominent solar panel array on its roof.

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Project Solution

To achieve its operational, energy efficiency, and sustainability goals, Wake Tech East Central Energy Plant was equipped with two 500-ton Carrier AquaEdge® 19DV centrifugal chillers, serving as both chiller and heat pump. The system design comprises three main water loops: chilled water, hot water, and heat source/sink water, all served by the two 19DVs and a modular heat pump for base loading. Heat rejection and absorption primarily occur via a geothermal bore field connected to the heat source/sink water loop.

The advanced geoexchange system includes 297 closed-loop wells, each 500 feet deep. This system is designed to consume one-third less energy and produce 50% fewer carbon emissions compared to conventional boiler/chiller configurations. The system has been designed for expandability and flexibility for future build-outs.

Interior view of the central energy plant showing large chillers, extensive piping, and insulation.

"By selecting the higher efficiency chillers, we got better long-term energy performance, were able to lower our electric bills and get better operating life out of the equipment. We've seen a wide variety of savings... anywhere from five to ten percent on our energy use, up to over 40% on our energy consumption for our buildings." - John L. Majernik, EI, PEM, CEM, Director, Energy, Sustainability & Transportation, Wake Technical Community College

The Renewable Energy Training Center at Wake Tech East not only supplies heating and cooling but also serves as an immersive educational experience. Its advanced central plant reflects innovative strategies for learning sustainable HVAC and energy practices hands-on. The AquaEdge 19DV centrifugal heat pump chillers were integral to helping Wake Tech East meet its sustainable, energy, and growth goals.

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The System

A schematic illustrating the integrated HVAC system. It shows three main water loops: Campus Hot Water Loop (1), Campus Chilled Water Loop (2), and Heat Source/Sink Water Loop (7). Primary pumps (3) circulate water through the heat pumps, while secondary pumps (4) circulate water in campus distribution loops. Two Carrier Centrifugal HP units and one Modular HP are central. Emergency backup boilers (5) are included. Closed circuit fluid coolers are also shown. The system connects to a geothermal bore field.

The hot (1) and chilled (2) water loops are arranged in a primary/secondary manner, with primary pumps (3) providing circulation through the heat pumps and secondary pumps (4) circulating water in the campus distribution loops. The AquaEdge 19DV units use a common primary pump for both the hot water loop and the heat source/sink loop. The secondary side of the hot water loop includes a 3000 MBH condensing hot water boiler (5) for emergency/backup heat. The heat source/sink loop (6) is also primary/secondary. Its secondary side links to the primary side of the chilled water loop, allowing transitions between heat rejection and absorption modes. The primary means of heat rejection and absorption is via a geothermal bore field (7) tied to the heat source/sink water loop. Future phases will include two 500-ton closed circuit fluid coolers to balance loads on the geothermal field.

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Modes of Operation

Cooling Only

In cooling-only mode, the AquaEdge 19DVs maintain the chilled water supply setpoint temperature of 44°F (6.7°C). Primary chilled water pumps vary speed to maintain flow within the heat pump limits. Secondary pumps adjust flow based on differential pressure setpoints as building valves open and close. On the condenser side, motorized valves isolate the hot water loop and open to the heat source/sink water loop. Primary condenser pumps vary speed to maintain refrigerant head pressure, while the modular unit's pump varies flow based on differential pressure. Heat rejection is controlled by varying the speed of the heat source/sink water loop secondary pumps to maintain a set heat pump entering condenser water temperature.

Heating Only

In heating-only mode, the AquaEdge 19DVs vary capacity to maintain the set hot water supply temperature of 105°F (40.5°C). Primary condenser water pumps run at constant speed, while secondary pumps vary flow based on differential pressure setpoints. On the chilled water side, pumps vary flow to maintain the chilled water supply temperature setpoint, which can be reset lower as return water temperature drops. Heat absorption is controlled by varying the speed of the heat source/sink water loop secondary pumps to maintain the heat pump entering evaporator temperature.

Simultaneous Modes

The system is designed for flexibility in simultaneous cooling and heating modes. The AquaEdge 19DV chillers can operate with cold condenser water for free cooling or hot condenser water for heat recovery. The 19DV's variable orifice ensures robust refrigerant metering and proper levels during variable lift and load conditions, maintaining efficiency. In cooling-dominant simultaneous mode, the 19DV units operate like cooling-only mode, with the modular heat pump acting as a dedicated heat recovery chiller, supplying hot water. Excess heat is rejected to the heat source/sink water loop. In heating-dominant simultaneous mode, all heat pumps control a leaving hot water supply temperature, recovering heat from cooling loads and using the heat source/sink water loop for any remaining heating needs.

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Innovation + Collaboration = Recognition

The Wake Tech East Central Energy Plant represents a paradigm shift in how educational institutions integrate advanced technologies into their infrastructure and programs. It has set new standards in sustainable design through the collaboration of world-class HVAC equipment manufacturers, design/build contractors, architects, and engineers. Designed and constructed by HH Architecture and Skanska USA Building, the facility showcases mechanical systems in accessible, daylit spaces.

The project has earned formal industry recognition, including:

• Green Building Initiative (GBI) 2023 Green Globes Project of the Year: The first project in North Carolina to achieve Green Globes' highest certification level of four Green Globes. The ultra-low GWP refrigerant and exceptional efficiencies of the AquaEdge® 19DV units were a contributing factor.
• Design-Build Institute of America (DBIA) Southeast Region Project of the Year.
• City of Raleigh 2023 Climate Action Award.
• ENR Southeast Regional Best Projects Winner in the Energy/Industrial category.

*Refrigerant R-1233zd(E) has a ~1 GWP according to the Intergovernmental Panel on Climate Change Fourth Assessment Report. GWP is a measure of a substance's climate warming impact compared to CO₂.