Your energy data is yours: export it, keep it, share it with your energy manager

In a Brick system, temperatures, states and consumption are logged minute by minute and stay on the controller, inside the building. It is a deliberate choice, which we discussed in the articles on home automation without the cloud and where thermostat data ends up: the data belongs to whoever uses the system.

Owning your data, though, also means being able to use it: export it when needed, keep it for years and give it to people who can read it. This article explains how, especially when you need to export Home Assistant energy data for an energy manager.

Where the data lives in Brick

In a Brick system the data lives in two places, with different jobs.

The Home Assistant database. It keeps the detailed history of every sensor, usually for a few days, and long-term hourly statistics, such as energy consumption, for much longer. This is what you see in the app, in the History and Energy panels.

The time-series database that feeds Grafana. It keeps per-minute readings for months or years, according to the retention policy set. This is what is used for analysis, as in the plant room dashboard.

Both live on the controller. No copy leaves the building unless whoever manages the system decides so.

Exporting to CSV

The simplest and most universal format for exporting data is CSV: a text file with one row per reading and columns separated by a character. It opens in any spreadsheet and any analysis software, today and in twenty years’ time.

There are three ways to get one, depending on the period and the detail needed.

• From the Home Assistant app. In the History panel, choose the sensors and period, then download the data. It is the quickest way to get a few days’ extract.
• From Grafana. Every panel on a dashboard lets you inspect the data it shows and download it as CSV. It is the most convenient way to get long periods and data that is already aggregated, such as daily consumption.
• With a scheduled export. A Node-RED flow can prepare a file each month with that month’s data, in the agreed format, and save it to a shared folder in the building or email it to whoever needs it.

A file people can understand

A useful CSV is more than a column of numbers. For the recipient to use it without phone calls, follow a few rules:

• dates in a standard format, year-month-day plus time, with the time zone stated;
• one column per reading, with a clear name and unit: underfloor_flow_C, gas_m3, heat_pump_kWh;
• the same interval for every reading, for example one value per hour, rather than irregular readings;
• a short accompanying note explaining what each column measures, where the sensor or meter is, and what changed in the system during the period.

The last point is the most neglected and, in our experience, by far the most useful. A jump in consumption in mid-January makes immediate sense if the note says the heating curve was changed that day.

How long to keep it, and where

Consumption data becomes more valuable over time, not less. One year shows how the system works. Three or four years let you compare different winters and prove the result of an upgrade.

A sound policy is:

• per-minute readings for one year, on the controller;
• hourly averages and daily totals for many years, even ten, which take up very little space;
• a backup copy off the controller, in the building or with the installer, alongside the configuration backups.

That way a controller failure doesn’t wipe out the system’s history.

What an energy manager needs

An energy manager preparing an energy audit needs data that shows how the building uses energy. Audits follow a method set out in standards such as EN 16247, but the data required is largely the same:

• hourly or daily consumption of gas and electricity, for at least one season;
• outdoor temperature, to calculate degree days;
• flow and return temperatures and the heat source’s running hours;
• zone temperatures and schedules, to understand how the building is used;
• changes made to the system, with dates.

These are the readings described in the article on the six readings in a plant room. A system that has logged them for a year allows a much more precise audit, and a cheaper one, than an audit based on bills alone.

Sharing without losing control

Sometimes someone needs the data on an ongoing basis: an energy manager who follows the building all year, an engineer who looks after its maintenance. Rather than sending a file every month, you can grant access.

The local-system principle applies here too. Access is given through a personal user account, with read-only permission on the dashboards needed, over the system’s private network. It is revoked when the relationship ends. That is very different from uploading data to an external platform whose rules you don’t control: there remains a single copy, in the building, and whoever consults it does so on the owner’s terms.

The privacy of the people in the building

Before handing data to anyone, stop and ask what it actually contains and who it describes. Room-by-room, hour-by-hour temperatures show when people are present. In a private home the decision is the owner’s. In an office, a hotel or an apartment block, it concerns other people too.

The solution is often simple: an audit only needs plant room data and totals per zone or per floor, without room-level detail. Exporting only what is needed is the simplest way to protect everyone.

The value of an archive

There is one last reason to look after consumption data: it is worth something. When selling or letting a building, applying for an incentive, choosing between two upgrades, or showing a public body that a measure worked. A system that keeps its own data, and hands it over in an open format, puts that value in the hands of its owner.