Data Center 101: Server Delta-T
Welcome to Keep Your Cool - a blog about simple cooling optimization strategies for the busy data center operators.
Intro
As we wrap up our deep dive into the four major data center cooling Delta-Ts, we turn to Server Delta-T, arguably the most critical of them all. In previous discussions, we covered Cooling Unit Delta-T, Supply Path Delta-T, and Return Path Delta-T. , but Server Delta-T provides the clearest picture of how efficiently a data center is cooling its equipment.
Many data center operators instinctively look at cooling units to determine if their cooling strategy is effective. However, the server itself offers a better indicator of real cooling performance. If the goal of cooling is to ensure that IT equipment receives the right amount of cold air, then monitoring both the air entering and exiting the server is essential.
Why Server Delta-T Matters
Every server follows a basic cooling process: cool air enters through the front, absorbs heat from processors and memory, and exits as hot air through the back. That hot air is then collected and returned to the cooling unit for heat removal.
Most data center managers focus only on the temperature of air entering the server, ensuring it falls within manufacturer guidelines. While this is important, it does not tell the whole story. Without monitoring exhaust temperatures, it’s impossible to determine how efficiently heat is being removed from the equipment. This lack of insight can lead to inefficiencies, unnecessary energy use, and higher operational costs.
A common misconception is that as long as inlet temperatures are within range, everything is operating optimally. However, if exhaust temperatures are low, it often means excessive airflow is being supplied to the server, leading to energy waste. Additionally, factors such as fan speeds, bypass airflow, and air mixing can impact cooling performance, but these issues remain undetected unless both inlet and exhaust temperatures are measured.
Key Takeaways:
Intake temperatures alone do not show how well heat is being removed from the server.
Low exhaust temperatures can indicate overcooling and unnecessary energy consumption.
Fan speeds, bypass airflow, and air mixing can only be properly assessed when both inlet and exhaust temperatures are measured.
What Defines a Good vs. Bad Delta-T? (And What Causes It)
A high Delta-T (a significant difference between intake and exhaust temperatures) generally signals efficient cooling, while a low Delta-T often indicates inefficiencies. But what causes these variations? Several factors influence Server Delta-T and can determine whether a data center is running efficiently or wasting energy.
In well-managed environments, such as data centers with full hot and cold aisle containment, Server Delta-T values typically reach 24°F or higher. These facilities operate with low energy waste and PUE values around 1.3 or even lower.. Their containment strategies, well-placed airflow management, and proper cooling distribution ensure that the right amount of cold air is delivered to the servers—no more, no less.
On the other hand, low Delta-T values (0.5–2°F) often indicate problems such as excessive airflow, bypass air, or hot air recirculation. In data centers without containment or blanking plates, hot and cold air mix freely, causing cooling inefficiencies. This leads to PUE values above 1.5 or higher, meaning higher energy costs and wasted resources.
Several issues contribute to low Delta-T:
Airflow Imbalance – If too much cold air is delivered, it passes through the server too quickly, reducing the temperature differential between inlet and exhaust. If airflow is insufficient, the server may overheat.
Hot Air Recirculation – Gaps in server racks or missing blanking plates allow hot exhaust air to mix with cold inlet air, raising intake temperatures and reducing cooling efficiency.
Bypass Airflow – Cold air escaping through unsealed floor openings or misplaced perforated tiles means that less conditioned air actually reaches the servers, leading to unnecessary cooling.
Inconsistent Rack Arrangements – Uneven distribution of IT loads can create temperature imbalances, making it harder to maintain a stable cooling environment.
Clogged Server Air Filters – Dust buildup in server fans and filters restricts airflow, causing overheating and high Delta-T.
Key Takeaways:
Higher Delta-T values indicate efficient cooling, while lower values suggest inefficiencies.
A well-contained environment improves Delta-T and reduces PUE.
Poor airflow management—recirculation, bypass air, and unbalanced racks—lowers Delta-T and increases energy waste.
How to Improve Server Delta-T
The first step to improving Server Delta-T is measurement. Without knowing your inlet and exhaust temps, diagnosing inefficiencies and optimizing cooling strategies is impossible. This is where Purkay Labs’ AUDIT-BUDDY system provides real-time Delta-T monitoring at the server level across all your server cabinets, allowing operators to track performance and identify problem areas.
Once Delta-T values are measured, the next step is airflow optimization. Sealing gaps in server racks with blanking panels prevents hot air recirculation, while ensuring perforated tiles are properly placed directs cold air efficiently. Implementing containment strategies—such as hot aisle or cold aisle separation—further enhances cooling performance by preventing air mixing. Regular monitoring of fan speeds and adjusting airflow to match IT loads can also significantly improve efficiency.
Routine maintenance is equally critical. Keeping server air filters clean, checking fan performance, periodic cleaning of underfloor or hot air plenums and evenly distributing high-density equipment across racks helps stabilize temperatures and ensures effective cooling.
Key Takeaways:
Measuring server Delta-T throughout the data hall is the first step toward optimization.
Airflow optimization through containment and tile placement reduces inefficiencies.
Regular maintenance of IT equipment and cooling infrastructure ensures long-term performance.
How Purkay Labs Can Help
At Purkay Labs, we specialize in airflow and cooling measurement solutions to help data center operators improve efficiency, reduce energy costs, and optimize containment strategies. Our AUDIT-BUDDY system provides real-time data on all four Delta-T types, allowing operators to quickly identify inefficiencies and take corrective action.
By leveraging real-time Delta-T insights, data centers can:
Identify and correct airflow inefficiencies.
Optimize containment strategies for better energy efficiency.
Reduce cooling costs while maintaining peak IT performance.
For a comprehensive cooling health check, our team can provide expert analysis and tailored recommendations based on Delta-T measurements.
Conclusion
Measuring and managing Server Delta-T is crucial for achieving efficient cooling, lowering operational costs, and ensuring reliable IT performance. By understanding the four Delta-T types, recognizing good versus bad Delta-T values, and implementing best practices, data center operators can create a more energy-efficient and cost-effective cooling strategy.
Take control of your data center’s cooling today—measure your Delta-T with AUDIT-BUDDY and let the Purkay Labs team help you optimize your airflow management strategy.
If you’re interested in learning more about delta-T, or how you can get your data center server delta-T measured, visit us at www.purkaylabs.com or click here.