Fixing a building's degree-day baseline

Nearly everything you might want to do with degree days involves setting a baseline characteristic for the building you are currently studying. The process starts with weekly (or more usually monthly) meter readings, complemented by the corresponding degree-day figures.

The consumptions are then plotted against degree-day values on an x-y scatter diagram (as illustrated here). Once the points have been plotted, a straight line can be superimposed to represent idealised behaviour.

The straight line relates expected fuel consumption (E) in a given week or month to D, the degree-day value for that period. The straight line has an equation

E = k₀ + k₁D

in which the constant k₀ represents the non-weather-related demand (per week or per month) and k₁ is a coefficient representing the incremental fuel used per degree day (you may recognise this equation from your school days as y=mx+c ).

Values for k₀ and k₁ are the key 'outputs' from this process.

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