Energy Fundamentals and the Building Profile

Why buildings matter

Buildings account for a substantial share of global energy use and emissions, and for most organisations the estate is either the largest or the second largest source of operational emissions. It is also the area where reductions are most directly within the facilities manager’s control, which makes energy management one of the highest-value activities in the discipline.

Units and the basics

• Power is the rate of energy use, measured in kilowatts. Energy is power over time, measured in kilowatt hours. A ten kilowatt load running for ten hours consumes one hundred kilowatt hours.
• Fuel is billed in various units — cubic metres, litres, kilograms — and is converted to kilowatt hours for comparison using calorific values.
• Peak demand — the maximum power drawn, which frequently attracts a separate and substantial charge in commercial electricity tariffs. Reducing peak demand can save money without reducing total consumption at all.
• Power factor — poor power factor increases current for the same useful power and attracts charges; correction equipment is a straightforward fix where it applies.
• Load factor — how evenly consumption is spread. A low load factor means sharp peaks and expensive supply.

Where energy goes in a typical building

Proportions vary greatly by building type, climate and use, and a typical office profile is dominated by:

• Heating — usually the largest single end use in cooler climates.
• Cooling and ventilation — fans and chillers, and fans frequently consume more than people expect because they run continuously.
• Lighting — a large share in older buildings and much reduced where efficient sources and controls have been installed.
• Small power and IT — equipment at desks and in server rooms, which has grown as a proportion as other loads have fallen.
• Hot water, lifts, catering and specialist loads.

Do not assume the profile. Measure it, because intuition about where energy goes is frequently wrong and money spent on the wrong end use achieves nothing.

The base load

The most revealing single analysis in building energy management is the overnight and weekend consumption — the base load. A building that is empty should consume very little, and in practice most consume a substantial proportion of their daytime load around the clock. Causes include plant running continuously, lighting left on, equipment never switched off, and control schedules that were set once and never reviewed.

Identifying and eliminating unnecessary base load requires no capital investment and is almost always the largest single saving available. It is the first place to look in any building.

Degree days and weather correction

Heating and cooling consumption varies with weather, so comparing one year against another without correction is meaningless — a mild winter flatters performance that has not improved. Degree days provide a measure of how cold or warm a period was relative to a base temperature, allowing consumption to be normalised. Use weather-corrected figures whenever comparing periods or assessing whether a measure has worked.