Javad Hatami, 19 September 2019

7 min read

How to Calculate Weather-Normalized Energy Consumption

If you are an asset manager with properties in regions with different weather conditions or If you are a company
with branches distributed over the whole country or different continents, such as hotel, gas station,
and supermarket chains; You may need to review the energy consumption of your properties and have a reliable
and fair metric to compare your branches to establish energy efficiency strategies and avoid revenue losses
in your business.

In this blog post, we explain you how we calculate this normalization via a standard method. This method will
be also useful for managers who handle one commercial building and want to normalize their consumption over
various seasons (Especially hotel managers).

Heating and Cooling Degree Days

Heating and Cooling Degree Days (HDD and CDD) is a unit of measurement that has been adopted by ASHRAE
organization as the industry standard for weather models. HDD and CDD indicate how hot or cold is outside
for a given day and for how long it was at that temperature. This can be more helpful than knowing the
temperature alone for estimating how much energy you used on heating and air conditioning. National
Grid notes that studying degree-day patterns can help energy managers to evaluate the oscillating trends
in energy bills.

In order to calculate the HDD and CDD, you need to define your base temperature (the temperature at which your
building needs no heating and cooling). For example 20 degrees in a city like Lisbon is the base temperature
for most of the buildings (but it varies building by building related to natural sun lights and ventilation,
age and construction material of the building). Then obtain the average outdoor temperature for a day
(which is available online). If the average outdoor temperature is exactly equal to the base temperature
(20 degrees), the HDD and CDD are zero. If it is above the base temperature, subtract it from the base
temperature to find the CDD and If it is below the base temperature, subtract it from the base temperature
to find the HDD. For example, if the high temperature of a day in Lisbon is 28 degrees and low temperature is 18
degrees, the average temperature is 23 degrees. Subtracting 23 from 20 equals 3, which indicates that there were
3 CDD for this day.

To normalize the electricity consumption of buildings base on HDD and CDD, the following steps should be taken:

- Sum the total heating and cooling degree days for one building for any required period.
- Divide the total kWh consumed in the same period by the total number of heating and cooling degree day.