What are heating and cooling degree days?

They measure how much and for how long outdoor temperature was below or above a base temperature. Higher heating degree days mean colder weather; higher cooling degree days mean warmer weather.

Why normalize energy use for weather?

So that changes in consumption reflect operations and equipment, not weather. It lets teams compare this year with last year, or one site with another, on a fair basis.

How much data do I need to weather normalize?

Typically at least a year of monthly data so the model sees a full set of seasons. Interval data gives more detail but is not essential to start.

Is weather-normalized EUI used in regulations?

Some building performance standards and benchmarking programs use weather-normalized metrics. Check the specific law that applies to your building for the exact metric it requires.

Glossary

Operations and asset management

What is Weather normalization?

Definition

Weather normalization is the practice of adjusting energy consumption for differences in weather, usually with heating and cooling degree days, so that one period can be compared fairly with another and one site with another. It separates the effect of weather from the effect of operations, equipment and behavior.

What it is

Heating and cooling loads rise and fall with outdoor temperature. A building can use more energy in a hot month without anything going wrong, and less in a mild month without anything improving. Weather normalization removes that noise.

The usual method is regression. Consumption is modeled against heating degree days and cooling degree days, and sometimes against occupancy or production. The model then predicts what use would have been under different or typical weather.

Degree days measure how far, and for how long, outdoor temperature sat above or below a base temperature. The base temperature should reflect the building's balance point rather than a fixed default.

Where it is used

Weather normalization is used in benchmarking, building performance standards, measurement and verification, energy budgeting and portfolio comparisons. ENERGY STAR Portfolio Manager reports weather-normalized metrics, and several building performance laws set weather-normalized targets.

How it is measured

A normalized result needs consumption data, weather data from a nearby station, and a model whose fit has been checked.

Monthly bills or interval meter data
Heating and cooling degree days for the matching periods
A regression model with fit statistics
Normalized use or EUI for the period being reported

How Aqueduct helps

Weather normalization is the core of aQ EnergySmart baselining. Every site gets a model that separates weather from waste.

Regression on usage plus cooling and heating degree days for each site and meter
Day-one baselines from 6 to 12 months of uploaded utility bills
Ongoing comparison of actual use against the weather-adjusted expectation, with deviations flagged
Rate configuration that turns the normalized delta into money