What's sucking all that juice?

This graph represents the electricity usage of the Department for Energy and Climate Change over 75 days between June 3rd and August 17th 2010.

What has me worried is how they're expending about 50 - 80 kWh per 30 minute period at times when the office is theoretically idle. This appears to be about a third of their consumtion during office hours.

DECC electricity consumption
Data source: http://data.gov.uk/dataset/decc-live-energy-data