- The Performance Indicator combines PUE, thermal conformance and thermal resilience.
- There are four levels of PI assessment in which inlet temperatures are measured.
- You can determine how changing one metric affects the others before making any changes.
- PUE ratio determines how close you are to the low end of your PUE range and indicates how much energy you may be wasting. If your current PUE is 1.5 and your range target is 1.35, your PUE ratio is 90 percent (1.35/1.5).
- Thermal conformance (TC) is defined as the amount of equipment falling within the maximum inlet temperature range divided by the total amount of equipment. The temperature specifications are based on ASHRAE guidelines or other standards as required by your facility or equipment manufacturers.
- Thermal resilience (TR) is the worse case scenario for thermal conformance. In other words, TR shows how much IT equipment is receiving cool air within the recommended temperature ranges when redundant cooling units aren't operating.
TR helps you determine if it's safe to have fewer cooling units operating and how long you can tolerate high air temperatures without having an outage. Measure for TR when the units are down for maintenance, or use modeling software to simulate the conditions. When these three metrics are combined, you can predict the performance of your entire facility under different scenarios.
PUE, TC, and TR are inter-related. Changing one affects the other two. Therefore, once you calculate all three metrics, plot them on a triangle or spider diagram, with each metric at one apex.
You'll find out which triangle is the best fit for your business so you can set a target. For instance, an enterprise data center usually has to sacrifice efficiency to reduce or eliminate the risk of downtime.There are four levels of PI assessment in which inlet temperatures are measured in relation to thermal performance:
- Only takes measurements at the rack level with three points per rack recommended
- Takes measurements at every server (requires data center infrastructure management software)
- Uses rack-level temperature readings to create simulations (requires modeling software)
- Provides a more detailed model calibrated using as many temperature readings from as many points as possible
With a three-dimensional model, you can visualize your facility's cooling performance and determine how a change in one metric affects the others in different scenarios before making any changes. You can answer the following questions:
- Where should I relocate equipment?
- Where is cooling recirculation air needed?
- Which equipment requires maintenance?
- Do I need to install additional equipment?
- How much can I increase my inlet temperature?
- Do I need customized blanking panels?
With PI, you'll know how different IT loads should be distributed for maximum efficiency. You'll improve your PUE without damaging equipment or increasing risk. You'll reduce asset costs by extending equipment life. You'll avoid unnecessary capital investments by not installing equipment you don't need.
Image sources: iStock, Green Grid (redrawn)