# Carbon footprint

## Equipment Categories and CO2 Emission Calculation

### Equipment Categories

A Data Center uses three main categories of equipment:

* **Compute equipment** (e.g., ESX servers based on X86 processors, IBM servers based on Power processors, etc.), which host the various instances.
* **Storage equipment** (e.g., data storage arrays, object storage arrays, backup and archiving storage arrays).
* **Network equipment** (e.g., network switches, firewalls, BigIP, etc.), which enable internal and external flow exchanges between services and instances.
* **Note**: These three categories themselves consist of subcategories that allow for a more detailed calculation of CO2 emissions per user instance. For simplicity, these subcategories will not be included in the calculation method outlined below.

### Energy Consumption Collection

The energy consumption of each piece of equipment is collected every minute (instantaneous power in watts) and stored in a database (MIMIR key-value database).

Additionally, we collect the following elements to calculate the associated CO2 emission:

* The **PUE** (Power Usage Effectiveness), calculated daily for the data centers we operate and monthly for colocation data centers.
* The **CO2 emission factors** (in kgCO2e/kWh), which are updated annually based on data from ADEME and suppliers.

### CO2 Emission Calculation for Equipment

The CO2 emission of a piece of equipment is calculated on a daily basis:

* Convert the instantaneous consumption into kWh/day from the data collected in the key-value database.
* Apply the PUE of the data center:
  * If a piece of equipment consumes 1000 kWh/day and the PUE of the data center is 1.3, the actual consumption of the equipment will be 1300 kWh.
* Convert the kWh/day into CO2 (kg) using the CO2 emission factor from the supplier:
  * If 80% of the energy used by the data center comes from a supplier who emits 0.008 kg of CO2 per kWh, and the remaining 20% comes from a second supplier who emits 0.01 kg of CO2 per kWh, the equipment’s emission will be: 1300 \* 0.008 \* (80 / 100) + 1300 \* 0.01 \* (20 / 100), which equals 10.92 kg of CO2 per day.

## CO2 Emission Calculation for a Global Service

### Reminder

A **Global Service** is the logical grouping of resources (primarily Instances) that use resources from different categories of physical equipment (Compute, Storage, and Network). The carbon footprint of a Global Service will therefore be the sum of the CO2 emissions of its resources.