Insight

Heat wave more than doubles cooling energy consumption in commercial buildings

In July, a record-breaking heat wave hit Europe. High temperatures can have large effects on building energy consumption, and with higher probability of occurrence and surging energy prices, building operators need to be aware of how a warmer climate affects their building components and operational budget.

Using energy and weather data from the Ento Labs database (currently 7000 buildings), we set out to investigate the effects of heat waves on building energy consumption.

Building energy consumption is highly sensitive to temperature

A core part of the Ento Labs analysis is to model energy consumption while taking into account weather data, among a broad range of variables that drive consumption in commercial buildings. From these models, we can extract cooling profiles that show how building energy use is affected at certain temperatures. (A cooling profile is a plot of cooling system energy consumption as a function of outside temperature.)

A typical cooling profile for buildings in a relatively cold climate, e.g., Northern Europe, has a nonlinear temperature dependency. As it gets hotter, the cooling system consumes energy at a higher rate, so the cooling profile curves upwards, as seen in the figure below. The cooling profile also shows a characteristic “kink” at the outdoor temperature where the building’s cooling system switches on. This gives information about cooling system setpoints and building insulation quality, information that is important when selecting buildings to renovate or optimize.

Heat waves lead to significant excess cooling needs

How did the recent heat wave affect energy usage for cooling in buildings? By analyzing energy consumption data from more than 7000 public and commercial buildings, we find a significant increase in energy consumption for cooling during the heat wave. In the figure below, we show the distribution of the percentage increase in cooling electricity consumption during the heat wave. The effect is clear across building types, but we see some differences between supermarkets, retail stores, and office buildings.

Supermarkets average around 129% increase in energy consumption for cooling, retail stores around 125% and offices see a 165% increase! This data indicates that heat waves have a large effect on building energy consumption.

According to Energy Data Specialist at Ento Labs, Poul Abilgaard, this result is due to the combination of two effects. The cooling systems of many buildings have a relatively high cooling setpoint and so only run for a few hours during a normal summer day at these latitudes, when the sun is highest in the afternoon. During a heat wave, however, the temperature is high all day, so cooling systems must run longer to maintain the same internal temperature.

The second effect is the greater need for mechanical cooling as temperatures rise. No building envelope can be perfectly insulated against heat exchange with the outside. This leads to a relatively higher power consumption for cooling per degree that the outside temperature is greater than the desired indoor temperature. This increase is the origin of the non-linear increase in energy consumption seen in the cooling profiles. In simple terms, a poorly insulated building consumes lots of energy when trying to keep cold.

The financial effects of heat waves

Looking at energy prices during the heat wave, it seems that prices were higher than expected. In Denmark, the spot prices for electricity increased by 32% compared to the rest of July. In the UK, South London residents experienced times where prices went up by 5.000%.

Heat waves in Northern Europe are stressing the entire economy. According to economists and climate experts, researchers estimate that, on average, heat waves lowered overall annual GDP growth across Europe by as much as 0.5 percent in the past decade. Demand increases because of higher temperatures, and this pushes power producers to the limit due to high energy prices.

Heat waves are becoming more common due to climate change

Heat waves like the one at the beginning of July are becoming more common due to climate change. In the coming decades, we will see more fluctuations in cooling electricity consumption during the summer months. The consequences will be requirements for higher capacity electricity infrastructure, higher electricity prices and operational and financial challenges for the building operator.

From UK climate projections for the next decades, we see a significant increase in the frequency of heat waves. We expect there to be more heat waves, each of which may last longer.