What is Server Delta-T?

Server delta-T is a powerful indicator of your facility’s cooling performance. By comparing the server delta-T, CRAC delta-T, and your IT load, you can:

  • Evaluate the effectiveness of your cooling

  • Calculate how much cooling is required for your IT Load

  • Calculate how much cold air is being wasted and why

What is Server Delta-t?

Server delta-T is the temperature difference between the intake air going into the server and the exhaust air leaving the server. As cold air flow through the server, it will pick up the heat produced by the IT equipment, causing the exiting exhaust air to become warmer (Figure 1: Server Delta-T)

Figure 1: Server Delta-T)

Server Delta-T & Cooling Performance

A simple way to evaluate the effectiveness of your cooling performance is comparing four points within the data center cooling path:

  • Server Inlet - Where the cold air enters the server

  • Server Exhaust - Where the warm air exits the server

  • CRAC Return - Where the warm air returns to the CRAC Unit

  • CRAC Supply - Where the cold air exits the CRAC unit

In an ideal world, 100% of the CRAC supply air would go to the Server Inlet, where the CRAC supply and the server inlet would have the same temperature. Then 100% of the return air from the server exhaust would go to the CRAC return, where the Server exhaust and CRAC return would have the same temperature (Figure 2: Ideal Cooling Circuit)

The reality is some of the some of the cold air from the CRAC Supply will escape and will end up cooling the air returning from the Server Exhaust before it reaches the CRAC return. The phenomenon of the air bypassing the server intake is called bypass airflow. This results in the temperature of the air at the CRAC return being lower than the Server Exhaust (Figure 3: Bypass Airflow)

Figure 2: Ideal Cooling Circuit

Figure 3: Bypass Airflow

Some of the hot air from the Server Exhaust returns to the Server inlet instead of all returning to the CRAC return. This phenomenon is called Recirculation Airflow. It makes the server inlet temperature hotter than the CRAC supply. (Figure 4: Recirculation Airflow)

Figure 4: Recirculation Airflow

Measurement of CRAC Delta-T and Server Delta-T allows one to characterize the airflow management  in a data center. Ideally these values should be as close to each other as possible. Variances between the two are indicators of presence of airflow issues, like Recirculation or Bypass or both. Purkay Labs AUDIT-BUDDY system allows an easy way to measure both in a facility.

How to use AUDIT-BUDDY to measure server Delta-T?

You can use two AUDIT-BUDDY to track the inlet and outlet temperatures over time. The AUDIT-MATE software will use this data to calculate the cooling performance.

  1. Buy or Rent

Buy or rent the at least two AUDIT-BUDDY stands.

2. Conduct Delta-T

Conduct Delta-T Scan, which measures every minute for user defined period of time.

3. Diagnose Cooling Efficiency

Use AUDIT-MATE 2.0 to evaluate how effectively you are cooling your server.

 What Do You Need to Measure Delta-T?

You will need: