Delta-T 101: Supply Air to Server Inlet Delta-T
Welcome to Keep Your Cool—a series tackling simple cooling optimization strategies for busy data center operators.
We’re in Week4 of our Delta-T 101 series. We started with the four different Delta-Ts of data center cooling, and then broke down the cooling unit delta-T and the return path delta-T. This week we’re exploring the supply path delta-T.
Introduction
The final Delta-T we will discuss in this series is the Supply Air to Server Inlet Delta-T—a crucial but often overlooked aspect of data center cooling. While much attention is given to CRAC/CRAH unit performance, ensuring that cool air actually reaches the server inlets at the right temperature is just as important. In this article, we’ll break down how cooling works from the supply output to the server inlet, what constitutes a good Delta-T, and how to improve efficiency by addressing common airflow issues.
How Cooling Works in a Data Center
A data center’s cooling system operates by pushing conditioned supply air from CRAC (Computer Room Air Conditioning) or CRAH (Computer Room Air Handling) units into the cold aisle, where it enters servers to cool them before exiting as hot exhaust air. This airflow cycle is essential for maintaining proper temperatures and preventing overheating.
In a raised-floor environment, cold supply air is distributed through an underfloor plenum and delivered through perforated floor tiles. Ideally, this air should travel directly to server inlets without unnecessary warming. However, factors such as air mixing, bypass airflow, and underfloor obstructions can cause supply air to warm before it even reaches the equipment, leading to inefficiencies.
What is Supply Air to Server Inlet Delta-T?
Supply Air to Server Inlet Delta-T refers to the temperature difference between the air leaving the CRAC/CRAH units and the air entering the server inlets. Ideally, this temperature should be as close as possible—meaning the air supplied by the cooling unit is effectively reaching the servers without unnecessary warming.
However, several issues can cause supply air to warm up prematurely, leading to higher temperatures at the server inlets. Common causes include:
Venturi Effect: High-velocity supply air can create low-pressure zones near perforated tiles, pulling warm air into the underfloor space before it reaches the servers.
Underfloor Obstructions: Cables, pipes, or poorly positioned floor panels can disrupt airflow, creating low-pressure pockets that allow hot air to mix with the supply air.
Rack Openings: Unsealed gaps in server racks allow hot air from the exhaust side to recirculate into the cold aisle, raising inlet temperatures.
Floor Tile Misalignment: If perforated tiles are not properly aligned with server inlets, cool air can disperse inefficiently, leading to temperature variations.
Plenum Leaks: Openings in the raised floor, often used for cable routing, can reduce the pressurization of the plenum, limiting the flow of cool air to server inlets.
What is a Good vs. Bad Delta-T?
A good Delta-T occurs when supply air reaches the server inlets at a temperature close to what the cooling system intended. For example, if a CRAC unit supplies air at 55°F, the server inlets should ideally see temperatures close to this range, ensuring optimal cooling.
A bad Delta-T occurs when supply air is significantly warmer by the time it reaches the server inlets. If the supply air starts at 55°F but reaches server inlets at 65°F or higher, it means cooling efficiency is being compromised, likely due to air mixing or obstructions. This forces cooling units to work harder to compensate, increasing energy consumption and operational costs.
How to Improve Supply Air Delta-T
To minimize supply air warming and optimize Delta-T, data center managers should focus on airflow management best practices, including:
Eliminate Underfloor Obstructions: Keep cable runs and piping organized to prevent disruptions in underfloor airflow.
Optimize Floor Tile Placement: Ensure perforated tiles are properly aligned with server inlets to maximize the delivery of cold air.
Seal Openings and Gaps: Use brush grommets and sealing materials to prevent air leaks in raised floors and server racks.
Manage Air Containment: Implement hot aisle or cold aisle containment to prevent hot and cold air from mixing.
Monitor and Adjust Airflow: Measure Delta-T regularly to identify inefficiencies and adjust supply temperature or airflow distribution as needed.
About Purkay Labs
Purkay Labs provides advanced cooling measurement solutions to help data centers optimize airflow and cooling efficiency. Our AUDIT-BUDDY system allows operators to measure Delta-T across the supply air and server inlets, providing real-time insights into cooling performance. The software automatically calculates cooling efficiency, helping you identify inefficiencies and improve airflow management.
Conclusion
Understanding and optimizing Supply Air to Server Inlet Delta-T is critical for maintaining efficient cooling in a data center. By identifying and addressing common airflow issues, data center operators can ensure that supply air reaches the servers at the correct temperature, reducing energy costs and improving cooling performance.
Start measuring your Delta-T today with AUDIT-BUDDY and take control of your data center’s cooling efficiency.