The latest greenhouse gas emissions inventory performed for the Town of Truckee showed that the largest share of our emissions comes from our buildings. The vast majority of those emissions come from the burning of fossil gas in furnaces and hot water heaters. The California Air Resources Board has proposed to ban the sale of all gas appliances in the state of California by 2030, which includes the replacement of existing appliances. If this proposal is finalized, any building in Truckee that requires a replacement furnace or hot water heater after 2030 will have to replace it with an appliance that doesn’t burn fossil fuel. Thankfully, existing technology is up to the task.
Heat Pumps 101
Maybe you’ve heard of heat pumps? Heat pumps are like air conditioning units except they not only pump heat out of your house in the summer, they also pump heat into your house in the winter. With the passage of the Inflation Reduction Act reducing the price of heat pump systems for consumers and the war in Ukraine driving up fossil fuel prices, the sale of heat pumps in the United States has exploded. These versatile devices can not only heat and cool the air in your home, they can also heat the water in your home and even dry your clothes.
There are combined heat pump systems that will heat your air and your water with one heat pump. Some novel heat pump systems rolled out recently incorporate water tanks that act like thermal batteries which can give owners of these systems the option to pull energy from the grid when energy is cheapest, or to heat their homes and water during a power outage.
Air Source versus Ground Source
Ground source heat pumps have some advantages in our climate. Air source heat pumps pull heat from the air while ground source heat pumps pull heat from water that runs through pipes under the ground. This system of pipes is referred to as a geothermal heat exchanger. The earth below the frost line (roughly 7 feet below the surface) stays within a very narrow range of temperatures throughout the year. Water in the geothermal heat exchanger going into a house in winter is relatively warm compared to the ambient air. This makes extracting heat from that water more efficient than extracting heat from the ambient air. While modern air source heat pump technology is now fully capable of operating efficiently in sub-zero temperatures, ground source heat pump systems are still more energy efficient and more cost effective over their lifetimes because they pull energy from relatively warm water heated by the earth rather than from the ambient air.
In addition, in some neighborhoods in Truckee/Tahoe where the winter snow pack can obscure second story windows, placing the external units of air source heat pumps in a location that will keep the air flow unimpeded and keep snow and ice shedding off roofs
from damaging the units is challenging to say the least. Ground source heat pumps don’t face these wintertime challenges as the entire unit can be placed within the envelope of the home.
On the other hand, the cost of drilling the holes in the ground to lay the network on pipes for these geothermal heat exchangers significantly increase ground source heat pump system upfront costs compared to air source systems. This is why many people chose to install air source heat pump systems instead of ground source heat pump systems.
Introducing Networked Geothermal Systems
That brings us to networked geothermal systems which rely on ground source heat pump technology. The key is that the geothermal heat exchangers in these systems are owned by a utility rather than the building owner. The utility drills the bore wells for the heat exchangers under the road, lays the pipes and puts a meter on the water going into the home. There are several advantages to this system over having the homeowner own the entire geothermal heat exchange system.
One advantage is financing. Over half of the expense of a geothermal system is in the heat exchanger. The heat exchanger has a lifetime of 50+ years. Most homeowners are not interested in investing in a system for their home with that long of a lifetime. Utilities on the other hand can spread that cost out over the entire lifetime of the system. They also have easier access to low-cost financing.
In Massachusetts, where a lot of pioneering work on utility scale networked geothermal systems is occurring, gas utilities are actively rolling out networked geothermal pilot projects. If these projects prove the viability of these systems, instead of investing billions in dollars in replacing an aging system of fossil gas pipelines, these gas utilities will switch to being thermal utilities. Their workforce of skilled drillers and pipe-fitters will seamlessly transition to working on networked geothermal systems. This would go a long way to making the energy transition a just one.
I should note here that networked geothermal systems have been in existence for decades on college campuses and some housing developments. Gas utilities around the country have expressed interest in this technology recently and are working towards starting pilot projects of their own.
Networked Geothermal in our Region
In Truckee, we could start by implementing systems in new housing developments where natural gas pipe systems have yet to be laid. Or we could transition a group of existing buildings under the same management to networked geothermal. For example, the Truckee Tahoe Unified School District is currently working to address the concerns of its students as expressed in the recently unveiled Energy Efficiency, Clean Energy
and Carbon Neutrality resolution proposed by the students to the school board. The students are urging the school district to swiftly transition to net-zero operations.
One aspect of transitioning our school district to zero emissions energy could be to move the collective Truckee High School, Truckee Elementary, Sierra Expeditionary Learning campus to a networked geothermal system. Because there is a relatively large area on this combined campus to drill geothermal heat exchanger bore wells without disturbing existing infrastructure, this could be a very cost-effective location to demonstrate the effectiveness of these systems.
The Truckee/Tahoe region is under increasing threat of the effects of climate change: rising snow levels, decreased snow pack, persistent drought, and increased intensity and frequency of wildfires. We need to be working on reducing our greenhouse gas emissions from multiple aspects simultaneously. Networked geothermal may not make sense as a solution in all areas of our mountain community, but it could prove to be a crucial piece of our local transition to emission free energy.
Matt Tucker is the Co-Lead of 100% Renewable Truckee. He is a father of two who has lived full-time in Truckee for more than a decade.
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Networked Geothermal, a promising technology for heating cooling ... - Sierra Sun
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