Session: 03-03: Building Performance Simulations for Sustainable Solutions

Paper Number: 169880

169880 - Investigation of Energy Savings Potential and Cost-Effectiveness of Free Cooling Operation With Air-Source Chiller System for Data Centers 

Abstract: 

The rapid digitization of society and the adoption of emerging technologies, such as artificial intelligence (AI), connected energy systems, and autonomous operations, have significantly increased the number of data centers worldwide. This expansion has resulted in a substantial rise in energy consumption and associated carbon emissions, including a major challenge to sustainable development for data centers. Addressing the high energy intensity and environmental impact of data centers requires the exploration of alternative cooling strategies. Traditional direct expansion (DX) cooling systems often incorporate free cooling using a closed loop of water/glycol solution and overlapping indoor and outdoor heat exchangers. When the ambient temperature is sufficiently low, the system pumps the water/glycol solution from the external heat exchanger to the indoor unit to reduce compressor operation. Although this approach can improve operating efficiency and reduce compressor input power, it still has limitations. The high viscosity of the glycol solution requires additional pumping energy, and its lower thermal conductivity reduces overall heat transfer performance under marginal temperature conditions. As an alternative, refrigerant-based free cooling systems have been proposed to avoid issues such as antifreeze leakage and excessive pumping power in free cooling operations using air-source cooling systems. This study evaluates the energy-saving potential and cost-effectiveness of air-source chillers using a refrigerant-cycle-based free cooling strategy in data center applications. Simulations are conducted using the EnergyPlus building energy modeling software tool under various climate conditions. The modeled data center is configured as a single thermal zone equipped with 50 MW of air-cooled information technology equipment (ITE). The proposed system integrates an air-source chiller with an evaporatively cooled condenser, along with supporting components, including a fluid cooler and a fluid-to-fluid heat exchanger, to connect the evaporative cooler to the chiller’s condensing circuit. Performance is compared against a baseline system utilizing an air-to-water heat exchanger for free cooling. A comparative analysis is performed across six U.S. climate zones (1A, 2A, 3A, 3C, 4A, and 5A). Results show that the proposed refrigerant-based free cooling system achieves 10% to 20% energy savings, depending on the climate zone. The number of available free cooling days also increases due to the favorable thermal properties of the refrigerant compared to glycol solutions. Overall, the study demonstrates that the proposed system offers significant improvements in both energy savings and cost-effectiveness, providing valuable insights into the optimization of free cooling strategies for data center applications.

Presenting Author: Dongsu Kim Hanbat National University

Presenting Author Biography: DONGSU KIM received the B.S. and M.S. degrees in architectural engineering from Hanbat National University, Daejeon, South Korea (Republic of Korea), in 2011 and 2013, respectively, and the Ph.D. degree in mechanical engineering from Mississippi State University, MS, USA, in 2019.
From 2019 to 2020, he was a Postdoctoral Associate Researcher with the DOE Building Energy Codes Program, Pacific Northwest National Laboratory (PNNL), USA. He is an associate professor at the Department of Architectural Engineering, Hanbat National University. His research interests include building energy system modeling and simulation, HVAC control and optimization, and renewable energy applications for buildings.