Sustainability

How to measure sustainability in the built environment

The calculation for energy consumption in data centres could provide sustainability guidance for the wider built environment. 

In a recent SFG20 report covered in Facilitate, I was surprised to read about “the challenge of tracking sustainability progress” due to the absence of a standardised measurement for better reporting and tracking and overall impact. 

There is a potential solution though and it comes from data centres (DCs) which use a calculation to monitor electric consumption, called Power Usage Effectiveness or PUE. 

PUE=total facility energy consumption/IT equipment energy consumption

A lower PUE indicates higher energy efficiency. An ideal PUE is 1.0, meaning all energy consumed is used directly by IT equipment, with none lost to overhead like cooling or lighting. 

How to calculate PUE in DCs

1. Measure total facility energy – includes all energy used by the entire DC facility, encompassing lighting, cooling systems, power distribution units (PDUs), uninterruptible power supplies (UPS), and the IT equipment itself. This is typically measured by the facility’s utility meter.

2. Measure IT equipment energy – only the power consumed by servers, storage, and networking gear. The most accurate measurement point is after all power conversion and conditioning, typically at the output of the PDUs supplying the server racks.

3. Perform the calculation – divide the total facility energy consumption by the IT equipment energy consumption to determine the PUE ratio. 

So if a data center consumes a total of 50,000 kWh of energy, and 40,000 kWh is consumed by the IT equipment: 

PUE=50,000kWh40,000kWh=1.25

Key considerations 

  • PUE range: Most DCs have a PUE between 1.5 and 2.0, though modern, highly efficient facilities can achieve values of 1.2 or less.
  • Regular monitoring: Energy usage can fluctuate based on the time of day and season. Measuring PUE regularly over time provides a more accurate benchmark.
  • DCiE: The inverse metric is DC infrastructure efficiency (DCiE), expressed as a percentage: DCiE = (1 / PUE) * 100. In the example above, the DCiE would be 80%.
  • Tools: Various PUE calculators and DC infrastructure management (DCIM) software can automate the measurement and calculation process. 

Extrapolating to the wider built environment

Calculating an accurate PUE rate for the wider built environment would require data from as many buildings as possible, categorised according to their functionality; think  hospitals, teaching establishments, accommodation, offices, sports complexes.

In these facilities, the amended definitions should apply:

  • Total facility energy consumption – energy used within the boundaries of the property. These ‘grey spaces’ support the building’s main function and include outside lighting, entrances, maintenance areas, corridors, stairwells, common areas.
  • IT equipment energy consumption – a definition for each type of building will be more difficult but once set it will help to determine which area of a building is in grey space or white space.

For white space consumption, the following should apply:

  • Hospitals – wards, operating theatres, kitchens, treatment and waiting rooms/areas, washrooms, offices;
  • Accommodation buildings – suites, rooms, offices, washrooms, kitchens;
  • Offices – office areas, kitchens, washrooms; 
  • Teaching establishments – classrooms, sports halls, swimming pools, saunas, changing areas, offices, kitchens, washrooms;
  • Sports complexes – halls, swimming pools, saunas, changing areas, offices, kitchens and washrooms; 
  • Warehouse/storage facilities – storage area, offices, kitchens and washrooms; and
  • Factories – manufacturing area offices, kitchens and washrooms.

The calculation would look like this:

PUE=Total Facility/Property Consumption(Grey Space)White Space Consumption

What about time?

When is a building in operation or at rest? Should the total time be used in the PUE calculation or just when it is occupied and being used? 

DCs and hospitals are 24/7 operational facilities but a teaching establishment is not. Accommodation buildings, such as hotels, can be fully occupied, partially occupied, or completely empty.

Further work is needed to determine what level of PUE is acceptable for different building functionality as a hospital will have a different rate from an office which will differ from a sports complex, for example.