Analyse the energy usage and compare it with weather adjustment

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Hi there,

the new energy dashboard is great. It gives a very good live insight into the energy consumption and the correlation to the way of use of the building.

In germany we have a system called “weather adjustment” (“Witterungsbereinigung”) to compare the energy usage without the influence of the weather of the actual day. That enables

  • Comparison of the energy usage accross different times of the same building, e.g. compare the energy usage of the building between November and March.
  • Comparison of the energy usage accross different buildings, e.g. compare the usage of my building with the usage of other building (e.g. from the community)

This helps to analyse, if measures to optimize energy consumption are successful or not.

The system in germany ist based on a local rule (VDI 2067) and this rule depends on data from weather stations, that are nearby the building. This system is made, to calculate a forecast of the energy consumption for planning purposes. The system is based on so called “Gradtagzahlen”. This can be possibly translated to something like “Degree day number”. The Gradtagzahl is defined , as

Degree day number (also degree day number, GTZ, Gt) and heating degree day (HGT, G) are used to calculate the heating demand of a building during the heating period. They represent the relationship between room temperature and the outside air temperature for the heating days of a design period and are thus a tool for determining heating costs and heating fuel requirements.

Degree-day figures and heating degree-days are given with the unit Kelvin (K, or °C), so they have the same dimension as temperature (or as heat sum in Kd or °Cd, degree-days). However, they are also related to a heating period or a calendar month and are then meaningful for seasonal fluctuations. In each case, there is a value for the long-term climatic mean, and a value for the current weather (meteorological measurement).

The degree day number Gt is calculated only over those days of a period when the outdoor temperature is below the heating limit temperature. The degree day number is the sum of the differences between an assumed room temperature of 20 °C and the daily mean value of the outdoor temperature. The degree-day number is a location-dependent parameter that reflects local climatic conditions. A distinction is made between a GTZnorm for the long-term mean, and a GTZspez for the current measurement. The latter is used, for example, for the climate adjustment of consumption measurement values.

According to VDI 2067 Space heating: Calculation of costs of heat supply systems:

image

with

  • Gt20/15: Degree day number with ti of 20 °C and heating limit of 15 °C.
  • z: number of meteorological heating days
  • ti: average assumed room temperature (indoor temperature), here 20 °C
  • ta: mean outdoor temperature of the respective heating day.
  • The degree day number of a day (heating degree day value) is the difference between indoor air temperature and the daily average outdoor temperature.
  • The degree day number for the heating period is the sum of the differences between the average indoor temperature of 20 °C and the daily averages of the air temperature over all heating days in the local heating season (September 1 and May 31).
  • The degree-day figure for the heating season includes only those heating days that fall within the heating season.
  • The degree day number of a month is the sum of the temperature differences over the month.

(Thank you, Deepl)

In HA we would not need a weather station, since HA itself is sort of a weather station and has the values evene on time, per second, minite, hour, or whatever you choose as an intervall for your weather sensors.

I am wondering, if such a system, like the VDI 2067 exists in other countries as well, and how they compare to another.

Reading the wikiperdia article I have learned, that there are similar systems in Austria ( ÖNORM B 8135) and Swiss ( SN 565381-3). But what about other countries?