(Photo: Lars Hagberg/AFP/Getty Images)

The cannabis industry is not as green as you might think.

Growing marijuana indoors is energy intensive, as it requires various equipment to regulate light, temperature, and moisture levels. Growers account for approximately 1 percent of electricity use in the United States, according to a 2012 study, releasing as much carbon dioxide as three million cars on average. And as more states legalize marijuana, grow houses could put a greater strain on public utilities. For the industry to grow sustainably, more energy efficient systems will need to be developed and adopted—and, as it turns out, there are plenty of points in the growing process ripe for innovation.

In a new study, researchers at the University of California–Davis’ Western Cooling Efficiency Center tested out a new dehumidification system for indoor farms, and found that it was much more energy efficient than traditional dehumidifiers.

Grow houses are typically equipped with multiple dehumidifiers. These dehumidifiers remove moisture from the air but also increase the room temperature in the process, which, in turn, necessitates the use of power-hungry air conditioners to prevent the room from overheating.

This new system, a dehumidifier made by MSP Technology, uses a plate heat exchanger—which mixes incoming and outgoing airflows—and a cooling coil to absorb some of the heat from the air before it is added back to the room. The team found that the new system could reduce energy use by up to 65 percent. Beyond that, 100 percent of the moisture removed from the air was conserved, and could be used to water the plants, the researchers found.

It’s not just big businesses that will have to think about energy use. In November, California, Massachusetts, and Nevada joined Alaska, Colorado, Oregon, Washington state, and the District of Columbia in legalizing marijuana for recreational use. In those states, adult residents can grow up to six plants in their own homes. That can be a huge burden, both on consumers’ budgets and the local electric grid: A report from Oregon’s Northwest Power and Conservation Council found that an indoor system for just four plants could use as much power as 29 refrigerators.

Perhaps it’s not surprising that researchers in California, where electricity costs are some of the highest in the nation, are concerned with energy efficiency.