CT Dept. of Administrative Services

The Capitol Area System (CAS) in Hartford is a unique opportunity to show how Connecticut can transition away from heating buildings with fossil gas to heating (and cooling) using electricity as the fuel.

In 2019, the State of Connecticut bought CAS, a system of underground pipes that heat and cool 15 large public and private buildings in downtown Hartford. Until recently known as CDECCA, CAS originally consisted of a fossil fuel electric generation plant combined with boilers that produced steam that circulated through the system. The generation turbines were decommissioned in 2021, eliminating what Dr. Mark Mitchell, former Director of Health for Hartford, has called the third largest polluter in the city. 

That means that the CAS now heats its 15 buildings on a  three-mile loop with hot water produced by gas boilers. But the system is outdated, continues to use fossil gas, and needs to be overhauled. The question is whether to rebuild it as a newer fossil fueled system or rebuild in a way that solves the health, greenhouse emissions and cost problems that burning fossil gas produces.

There is more than one electrified solution for a redesigned CAS, but in my opinion, the most likely is something called network geothermal. Individual ground source heat pumps (GSHP) pull heat from the ground in the winter and deposit heat there in the summer, using a closed loop system of pipes. In a network geothermal system, multiple buildings share a thermal loop that can run under a street, with each building tapping into the loop with its own GSHP. The thermal loop can draw heat from the ground via wells, nearby bodies of water, sewer systems, or even other buildings on the loop. 

It turns out that there are substantial installation and operational benefits as compared to multiple individual air source or ground source systems. Massachusetts and New York are among the states actively exploring whether network geothermal can replace fossil gas as a healthier, less costly, and less GHG emitting way to heat buildings in the Northeast. To get a better sense of what a network geothermal system looks like, how it works, and what the benefits are, take a look at this 2 minute video.

YouTube video

What does this have to do with CAS? Well, CAS already is a shared thermal loop system, but currently is powered by a centrally located, fossil fuel plant. The Connecticut Department of Administrative Services (DAS) needs to transition the existing infrastructure to a fossil fuel-free system that may look a lot like network geothermal. If they do, the benefits will be multifold.

Luckily, the DAS seems headed in the right direction, but the final design is not certain. The DAS has made this encouraging statement: “The State is working with consultants who have experience with decarbonization of district heating and cooling systems and is looking at several technologies to meet targets as well as considering operational changes that can help buildings reduce demand.”  However, the DAS lists on the CAS website ‘high efficiency boilers’ as one solution and elsewhere on the website says that the first step is to install high efficiency gas fired hot water boilers to replace the old inefficient steam boilers. Nowhere does DAS commit unequivocally to a non-fossil fuel solution.

The DAS needs to follow through with its partial commitment to make CAS a decarbonized, fossil fuel-free design for the sake of the health of neighborhood residents and the opportunity to reduce greenhouse gas emissions. And if the CAS becomes Connecticut’s first network geothermal system, it will serve as a model for how the state can make a wholesale change in the way it heats buildings. 

Peter Millman is a vice president of People’s Action for Clean Energy