CRES Plant Provides Sustainable, Efficient Energy

Thursday, January 20, 2022
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Inside of Cress Plant
Inside of Cress Plant

Sustainability has been a key focus of the Nebraska Innovation Campus (NIC) since its inception. The CRES system (or Centralized Renewable Energy System) that heats and cools the campus plays an integral role in this Sustainability mission.

Built on the former grounds of the Nebraska State Fair and running parallel to Salt Creek, Innovation Campus is located adjacent to the City of Lincoln’s Theresa Street Wastewater Treatment Plant. While many would have considered the proximity to a wastewater treatment facility to be an issue, planners and engineers in the early stages of NIC development recognized the unique opportunity to utilize byproducts of the treatment process as a renewable energy resource in a modern, highly efficient system.

Efficient Campus Heating and Cooling

Traditional campus heating and cooling systems – like those on UNL’s City and East campuses – generate steam and chilled water at a central utility plant and distribute them to building heat exchangers for conditioning. These systems typically rely on natural gas-fired boilers and large electric-driven chillers to generate enough heating and cooling for campus buildings.

Traditional Campus Energy System

Traditional Campus Energy System

In contrast, buildings at NIC were designed to use commercial heat pumps. Like a home heat pump system, the same equipment can be used to switch between cooling and heating modes. While a typical home heat pump system uses an outdoor fan unit to exchange heat with the atmosphere, the NIC building heat pumps exchange heat with water from the CRES campus loop distribution operating between 55°F and 75°F.

CRES System. Image from Olsson

CRES System. Image from Olsson

While the traditional system certainly has its merits, the heat pump system offers several unique advantages:

-          One distribution system handles both heating and cooling, so there is no need for separate piping systems.

-          In cooling mode, heat pump efficiencies are very similar to chillers in the traditional system, each getting 4-6 units of cooling out for each unit of electricity put in. In heating mode, the heat pump can produce the same performance, while the traditional system gets just 0.8 units of heating output for each unit of natural gas put in.

table of outputs/inputs unit statistic

Source: US Department of Energy

-          The campus loop allows buildings to “share” energy needs. For example, if one building has a lot of large heat-generating equipment, it may need cooling even in the winter. The energy put into the campus loop from this building can be used to heat other buildings on the loop, reducing the need for energy from outside the system.

-          Because the campus loop operates in a low temperature range, heat pump systems can incorporate low-temperature energy sources to condition the campus loop. This eliminates the need for high-energy fossil fuels like natural gas or heating oil.


Renewable Energy

During development of the CRES system, the team of engineers and planners from UNL, the City of Lincoln, and Olsson recognized the unique combination of resources and technologies available thanks to NIC’s location adjacent to the Theresa Street Wastewater Treatment Facility.

At the last stage of the wastewater treatment process, treated effluent water is discharged from the Theresa Street Plant to Salt Creek. This effluent water operates between 57°F and 78°F all year long, an ideal temperature range for the campus loop and heat pump system at NIC. The CRES plant “borrows” a portion of the reclaimed effluent stream before it’s discharged and pumps it to heat exchangers at the CRES plant.

These large heat exchangers use the effluent water on one side to heat or cool the campus loop on the other side before returning the effluent back to the wastewater treatment facility, where it’s combined with the rest of the effluent water and discharged to Salt Creek.

Pumps (dark green), piping (light green and blue), and heat exchangers (dark blue frames at the back) at the CRES Facility

Pumps (dark green), piping (light green and blue), and heat exchangers (dark blue frames at the back) at the CRES Facility

This system eliminates the need for burning fossil fuels to heat campus. The system is similar to a geothermal heating & cooling system, though instead of exchanging heat with the earth through an extensive underground piping system, it uses the waste product of an essential process occurring next door. Effluent water provides a truly renewable resource that operates in a stable temperature range needed for conditioning the campus loop. It also eliminates the extensive drilling or digging required to install an underground geothermal system in favor of a few hundred feet of piping from the wastewater plant to the CRES building.

The CRES System, one of the first of its kind in the world, provides a fantastic example of thinking creatively about how our campuses and communities use the resources we already have available to us and seeing waste streams as opportunities.

Aaron Evans has been an engineer with UNL Facilities since 2015, working with both building systems and utility plants. He is a professional engineer and certified energy manager who currently serves as the Engineering Supervisor for Utility Services.