Interval data heat maps: what an hour by day view tells a property team

Interval data is the electricity consumption of a meter recorded every hour, or more often, rather than once a billing cycle. In Ontario it is available to commercial and multi-residential customers through Green Button, which the province required its electricity and gas utilities to implement, with certification by the Green Button Alliance, by November 1, 2023. Fifty-five utility platforms were certified by that date.

The problem with interval data is not getting it. It is that a month of hourly readings is 720 numbers per meter, and a line chart of 720 points looks like noise. A heat map turns those numbers into a picture a property manager can read in ten seconds.

What the grid shows

Rows are hours of the day, columns are days of the month, and each cell is shaded from low to high consumption. Above the day numbers is a weekday row, with weekends tinted, so that Saturday and Sunday columns are obvious. An outline marks the hours of interest, for example 9 AM to 5 PM for an office or a property management schedule, so the eye separates occupied from unoccupied hours. Below the grid, rows of daily high and low temperatures explain days that are hotter or colder than their neighbours.

In the VE-MAP dashboard the heat map is interactive on the M&T tab; in the monthly review report it is printed with a findings paragraph beside it.

Five patterns worth knowing

1. The base load band

The colour of the 2 AM to 5 AM rows on a weekday is the building's base load: everything that runs regardless of occupancy. In a multi-residential building that is corridor lighting, elevators on standby, ventilation, domestic hot water recirculation and parking. If the overnight band is more than about half the shade of the afternoon peak, the base load deserves a look. Base load is the cheapest thing to reduce because the savings accrue 8,760 hours a year.

2. Schedule edges

A well scheduled building shows a crisp horizontal edge where equipment starts and stops. A blurred edge or an edge that has moved earlier means a schedule crept, often after a complaint, a contractor visit or a time change. Compare the edge across months to catch the drift.

3. Weekend columns

Weekend columns should look like the overnight band all day in commercial buildings and like weekdays in residential ones. A commercial building whose Saturday looks like a Tuesday is running its full schedule on the weekend.

4. Weather-driven days

A column that is darker top to bottom on a day with a high temperature in the weather row is cooling load. A column that is darker in the morning on a cold day is electric heating or pre-heat. The weather rows keep the reviewer from reading a heat wave as an equipment fault. For the monthly totals the same idea is handled with degree days, which Environment and Climate Change Canada defines against an 18 degree Celsius base; the heat map is the daily, visual version of that adjustment.

5. The isolated dark cell

A single hour that is much darker than its neighbours is an event: a test, a fault, a large motor starting. If it recurs at the same hour on the same weekday, it is a schedule. If it is random, it is a maintenance question.

Heat maps at the calendar scale

For meters without interval data (most gas and water accounts, and electricity accounts where Green Button is not yet connected), the same idea works at a coarser scale: a month by year grid shaded by consumption, with peak month marked. It shows seasonality and year over year change at a glance and is the view we use to spot a missing or doubled month before it reaches the benchmark.

A worked example

A mid-rise residential building's common-area meter shows a heat map where the overnight band is nearly as dark as the afternoon. The weekday and weekend columns look alike, which is expected for residential. The finding is a high base load. The operations team checks the parking garage ventilation and finds the exhaust fans running continuously because a carbon monoxide sensor was bypassed after a nuisance alarm. The fans go back on sensor control, the following month's heat map shows a lighter overnight band, and the CUSUM slope on the electricity M&V chart turns upward. The saving is verified from the utility meter; the heat map is what found it.

The same building's month by year gas heat map shows one February cell far darker than the surrounding years. The validation checks find two bills for that period, one re-issued; one is superseded and the cell returns to normal. Without the visual, the doubled month would have reached the annual benchmark report and the EWRB filing.

Getting the data

1. Authorize Green Button Connect My Data for each electricity account with the utility. The Green Button Alliance describes Connect My Data as the standard by which utilities provide access to interval usage and billing data to authorized third parties.
2. The platform pulls the readings, stores them per meter, and keeps a history so months that age out of the utility's window stay available.
3. Readings are aggregated to daily totals for trend charts and kept at full resolution for the heat map.
4. Bills for the same meter are captured from PDFs and compared against the Green Button record over the same period; see validation.

What interval data adds to M&V

Whole-building M&V runs on monthly totals and degree days, as explained in weather normalization, CUSUM and RETScreen M&V. When the CUSUM slope changes, interval data is how you find out why: the heat map for the month before and the month after shows whether a schedule moved, base load rose, or weekends changed. Without it, the reviewer has a symptom and no diagnosis.

FAQ

Do residential buildings have interval data?

Common-area and house meters in multi-residential buildings are usually interval metered in Ontario, and Green Button covers them. Individually metered suites belong to the residents and are outside the property's data.

What about gas interval data?

Gas meters are generally read monthly, so gas appears in the month by year heat map rather than the hour by day grid. Green Button gas data still provides billing-period consumption and cost.

How far back does interval history go?

It depends on the utility's Green Button window. The platform retains everything it has pulled, so history grows from the day the account is connected. Details on the about page and the data path in turning utility bills and meter data into a portfolio view.