Daylight saving time can reduce the total amount of energy needed for cooling office buildings in summer by nearly 6%, according to a new study. The findings add a new dimension to the ongoing debate about whether to do away with the twice-yearly switching of clocks that happens in many countries and use either standard or daylight time year-round.
“A lot of the discussion surrounding daylight saving time focused historically (and still is) on electricity savings from artificial lighting,” says study team member Sven Eggimann, an urban infrastructure and sustainability researcher at EMPA, the Swiss Federal Laboratories for Materials Science and Technology in Zurich. “However, building heating and cooling energy demand is much bigger” than lighting energy demand. And building energy use is a major contributor to carbon emissions, so figuring out how to cut energy demand for heating and cooling is important in fighting climate change.
Eggimann and his colleagues modeled how much energy would be needed to heat and cool office buildings with and without daylight saving time. They analyzed simulated small and large office buildings in 15 U.S. cities spanning different climate zones.
Because climate change itself affects heating and cooling demand, the researchers analyzed the effects of daylight saving time in the current climate as well as in future climate change scenarios in the year 2050.
Setting the clocks forward for daylight saving time means that workers arrive at the office an hour earlier, in the cool of the morning, and leave the office an hour earlier in the afternoon, which is typically when demand for cooling is greatest. So, daylight saving time reduces the amount of energy needed for climate control in office buildings, the researchers report in the journal Environmental Research Letters.
“Shifting working hours impacts the interplay between heating and cooling energy demand,” Eggimann says. Daylight saving time reduces the amount of building cooling energy needed by up to 5.9%, depending on the climate zone. Meanwhile, building heating energy demand increases by up to 4.4% because of more work conducted during those cool morning hours.
Much more cooling than heating energy is needed during the summer. So overall, daylight saving time yields a net savings of building energy. The overall savings work out to roughly a couple of percent of the total energy demand.
“With climate change, cooling demand will increase,” Eggimann says. But the researchers found that under a middle-of-the road climate change scenario, daylight saving time still reduces overall energy demand. As cooling demand increases, the relative cooling energy savings from daylight saving time decreases, but the absolute savings remains roughly the same.
The overall energy savings from daylight saving time under climate change varies by climate zone, with a maximum of 3%.
The researchers focused on office buildings because they generally require more energy for cooling than residential buildings (due to their preponderance of windows, concentration of people, and heat-generating office equipment). But pandemic-related shifts in work habits could add another wrinkle to the analysis. “If everyone works from home, then of course this has major implications for energy use in offices,” Eggimann says.
There are other complexities to consider. Heating and cooling can be provided by different systems with different levels of climate impact; in some cases it might be more climate-friendly to reduce heating demand than to reduce cooling or even overall energy demand. If both heating and cooling are electric – from highly efficient heat pumps, for example – then the impact on the grid of any changes in working hours will need to be considered.
Still, the climate impact of daylight saving time should be part of policy discussions, the researchers argue. And such discussions could also expand to consider other strategies to reduce energy consumption in offices, from undertaking building retrofits and adopting shorter work weeks to turning off lights and adapting workplace dress codes.
Source: Eggimann S. et al. “Climate change shifts the trade-off between lower cooling and higher heating demand from daylight saving time in office buildings.” Environmental Research Letters 2023