Mine Water to Heat a Building

A new Montana Tech’s Mining Engineering Department project in Butte uses geothermal mine water to heat a building, delivering 88% of the building’s annual heating needs.

This way, they are reducing CO2 emissions 39% and saving $17,000 (40%) per year in utility costs.

This is Tech’s geothermal demonstration project at the Orphan Boy mine shaft, essentially a 50-ton ground-source heat pump that is using the mine’s warmer-than-average water to heat the school's 56,000-square-foot Natural Resources Building.

It’s an intriguing project for Butte because of the hundreds of old abandoned mine shafts below the streets, all filled with groundwater. Until now the water has been useless, contaminated as it is from the remnants of mining.

“What do you do with the mine site once you’re done mining?” said Donald Blackketter, Tech’s chancellor and a mechanical engineer by training.

“I think people look at that mine shaft and perhaps say 'There’s no use for that.' And our point is, no, there is a use for that that’s reasonably economic.”

He has proof, too. According to data from January through July of 2014, shortly after the project was completed, the heat pump delivered 88 percent of the building’s annual heating needs, reduced carbon dioxide emissions 39 percent and saved $17,000 (40 percent) per year in utility costs.

The process involves a closed-loop system with 600 feet of piping installed into the mine shaft. The facility pumps the water, which averages 78 degrees, through the pipes and to the heat exchanger, where it's warmed to 135 degrees and actually can be used either to heat or cool the building.

Leading up to the construction of the building, researchers found that the mine water holds a natural convection, meaning the temperature of the water is distributed equally throughout the shaft, with no hot or cold spots, allowing for more efficiency. And there’s no concern of running out. There’s a lot of water — 332 million gallons of it.

“Cool water falls and hot water comes back up. We always have enough water where you can’t change the temperature in the water significantly. There are so many gallons at 78 degrees that you can’t affect it,” Blackketter explained.

In many ways, the 800-foot deep Orphan Boy Mine, located a little over 1,000 feet from the Natural Resources building, presented a perfect opportunity for Tech. Not to be confused with the much larger, more famous copper pit mines nearby, the Orphan Boy (which is connected to the Orphan Girl) was part of a silver mine built in the early 1900s. A huge slab of granite running thousands of feet into the ground separates it from the copper mines, so the toxicity of the Berkeley Pit water and other ground water is not found here. In fact, the water is safe for livestock to drink.

A bigger question remains as to whether this project can be repeated on a bigger scale for all of Butte, using the mine waters from the many copper-mine shafts.

“There’s a lot of discussion about that because of the immensity of the water (resource),” Blackketter said. “The answer is that’s why we did it. We did it to see if it was economically viable to use that water in the mine shaft to heat and cool a building.”

“The answer is yes,” he said. “You absolutely know it will work. The water in the Berkeley Pit, you wouldn’t have to drop the water temperature much to heat the whole city of Butte.”

First, it would take a large project with a lot of front-end cost. While the Tech project does present a lot of savings, it also cost $750,000 to install, not including all of the research-correlated costs leading up to installation, or the $850,000 tunnel that had to be dug. It could take more than 50 years for the heat pump to pay for itself, though researchers noted that, with lessons learned, project costs could be reduced in the future. Still, it likely wouldn’t have been accomplished had Tech not received a $1 million grant from the American Recovery and Reinvestment Act.

There’s also the question of toxic water. Blackketter said there is a way to harness the warm temperatures of the Berkeley Pit and other underground water, but pipe corrosion issues must be overcome.

The biggest problem is infrastructure. Tech had the foresight to build the Natural Resources building in preparation for the ground source heat pump, and it was already in close proximity to the mine shaft.

“All we had to do was hook that up to the building and we were good to go,” Blackketter said.

Transporting heat to buildings and houses throughout all of Butte could potentially be an infrastructure nightmare.

Also posing a challenge are potential water rights litigation, and the fact that ARCO still owns the mine shafts.

Source: Montana Standard