GeoMicroDistricts in Retrofit Magazine

Extracted from June issue of Retrofit magazine here:

A study Advocated for a Utility-scale Approach to Replace Existing Gas Lines with Ground-source Heat Pumps

GeoMicroDistrict: GCHP closed vertical systems could be installed in a single row along an existing utility corridor. Vertical boreholes and service connections could be located between existing infrastructure.

In 2019, 97 percent of natural gas pipelines in the U.S. were made of plastic or steel. Cast and wrought iron pipes make up the remaining 3 percent and are among the oldest gas lines in the country. Nearly half of all iron pipes are concentrated in four states including Massachusetts, New York, New Jersey, and Pennsylvania. If cast iron (and bare steel pipelines) are left in the ground beyond their service life instead of being replaced, utilities have to spend millions of dollars repairing leaks on old pipelines. When left unattended, leaking gas pipes release methane which is a highly combustible gas that poses significant health, public safety, and environmental risks.

In September 2018, a natural gas leak resulted in 131 fires and 3 explosions in three communities in Merrimack Valley, Massachusetts. Thousands of people from city of Lawrence, and towns of Andover and North Andover were forced to evacuate their homes. About 25 people were injured and one person died in the incident. In the winter months that followed, more than 8000 customers had no access to heat, hot water, and gas. After a yearlong investigation, the National Safety Transportation Board determined that inadequate planning and management by Columbia Gas of Massachusetts’ led to over pressurization in the Valley’s aging cast-iron gas pipes.

Massachusetts Rethinks Gas Infrastructure

Massachusetts has the second oldest gas infrastructure system in the country, with 6,000 miles of aging and leak prone pipes, which make up 26 percent of the State’s gas system. In recent years, natural gas companies have faced great deal of backlash due to pipeline failures and methane leaks from aging pipelines. Gas companies are therefore actively replacing aging pipelines with corrosion-resistant high-density polyethylene plastic pipelines. It is estimated that repairing and replacing the State’s leaking gas system can cost taxpayers over $9 billion over next 20 years. This does not include the price of lost gas that customers and businesses already pay in their monthly bills, which is estimated at $90 million per year in Greater Boston area alone.

Currently, nearly 70% of Massachusetts electricity and 50% of heating energy loads are met by natural gas, all of which is imported from other regions in the United States and overseas. During peak winter season, the State faces massive gas shortages, increasing the wholesale price of gas as well as the cost of power production. To address this energy security problem and overarching climate issues, the State has required electric utilities to use more renewable energy each year and has heavily invested in energy efficiency programs. At the current pace, clean energy alternatives are poised to undercut gas prices in coming years.

The decreasing cost of renewables will likely accelerate the pace of renewable deployment and building electrification, which will decrease gas consumption. If gas consumption declines, the utilization of gas pipelines will drop, inadvertently increasing the financial burden of maintaining the pipelines on a shrinking pool of gas customers. While it is imperative to maintain gas lines for public safety, continually replacing leaking pipelines with new ones will not only cost taxpayers billions of dollars but also lock some gas customers into another 40 to 70 years of fossil-fuel dependency. These macroeconomic factors have forced Massachusetts policy makers and industry leaders to rethink future expansion of gas infrastructure.

Following the aftermath of Merrimack Valley, the Home Energy Efficiency Team (HEET), a local environmental non-profit, began exploring potential substitutes for gas infrastructure. Long known for their work on energy efficiency retrofits and methane leak studies in Massachusetts, HEET wanted to explore an alternative business model where customers could purchase renewable thermal energy, instead of natural gas. In early 2019, HEET selected Buro Happold to lead a Feasibility Study to assess the replacement of aging natural gas infrastructure with a network of ground source heat pumps (GSHP).

Viability of GeoMicroDistricts

During the development of the Study, the term “GeoMicroDistrict” was coined to refer to the GSHP network that serves a street segment i.e. the length of street between two intersections or an intersection and a dead end. The GeoMicroDistrict would contain a shared loop running through an array of boreholes installed within public right-of-way (ROW). The ambient water circulating in the shared loop would serve as the heat exchanging medium between the ground and heating and/or cooling distribution systems housed within individual buildings. In theory, the concept is to incrementally replace leaking gas pipes with GeoMicroDistricts that are eventually interconnected to create a district-scale energy system.

District-scale GSHP systems are not a novel idea. In the United States, universities like Colorado Mesa, Ball State, and Furman, and many large-scale residential development projects have successfully installed and operated district-scale GSHP systems for years. However, strategic replacement of natural gas pipelines with GSHP systems is certainly a unique proposition. For successful execution of this concept various risks pertaining to site suitability, building compatibility, high upfront capital costs, operational reliability (energy load and capacity management), need to be mitigated.

PSS: Layout of prototype street segments (PSS) representing common building and land use characteristics across Massachusetts.

To address these constraints, the GeoMicroDistrict Feasibility Study examined the engineering and economic viability of installing shared loops in four prototypical street segments (PSS). The PSS represent distinct building and land use typologies prevalent in Massachusetts. Each PSS is composed of two contiguous lines of residential and/or commercial properties on either side of a 40-foot wide, 500-foot long public ROW.

To avoid site conflicts with underground infrastructure systems (potable water, telecom, data cables, sewer, stormwater systems etc.), borehole installation area is limited to the two-foot wide gas utility corridor. The engineering layout is informed by the State’s geological and seasonal parameters and designed to operate in balanced condition so as to prevent ground overheating or overcooling. The heating and cooling demand profiles of each PSS are then compared with the ground’s thermal capacity to assess annual thermal loads met by interconnected GeoMicroDistricts.

The Study concluded that interconnected GeoMicroDistricts can provide nearly 100 percent of the annual thermal loads in low to medium density residential and mixed-use commercial areas. High density neighborhoods would require supplemental heating and cooling energy. The Study strongly advocates for a utility-scale approach wherein existing gas companies install, operate, and maintain the GeoMicroDistricts. It is assumed that any costs associated with systems outside the building are borne by the gas company. As the customer base increases, the load diversity, efficiency, and economies of scale would improve. Furthermore, the utility would also be responsible for scaling and managing system capacity while integrating thermal energy storage and backup energy systems, as needed.

Results: Annual thermal loads met by interconnected GeoMicroDistricts.

At this conceptual stage, it is assumed that customers would pay for monthly thermal energy consumption and any additional costs associated with heat pump installation or improvements needed inside the buildings, with financial support from the State. The performance and cost for retrofitting existing buildings can therefore vary significantly based on their type, size, height, and age of the building and the original space conditioning system. Installing heat pumps in new buildings is relatively easier than renovating existing buildings. GSHPs in existing buildings, are generally more compatible with forced-air and hydronic system as the distribution system can be reused with minor adjustments in the ducts, pipes and controls. However, buildings utilizing steam distribution systems and electrical baseboards are not well suited to GSHPs and may need a gut rehab. Furthermore, gas-powered appliances like domestic hot water heaters, stoves, ovens, and cloth dryers etc., would also need to be replaced with electric appliances. It is also critical that existing buildings are made as efficient as possible prior to or during the conversion. This would allow for the installation of smaller and less expensive systems, reducing upfront costs and energy bills for the customer.

Safety First

GeoMicroDistricts represent a viable “safety first” alternative to natural gas heating, along with a host of additional benefits including climate change mitigation, infrastructure resilience, and air quality improvements. The concept promotes equitable transition to a renewable thermal system that can be deployed in any neighbourhood, city, or region. Allowing gas utilities to operate GeoMicroDistricts will help them retain their current organization purpose, structure and workforce. Installing GeoMicroDistricts will not be an easy or inexpensive feat, and will require significant coordination with public utilities, policy makers, and communities. It is safe to say that investing in heat pumps and building electrification is certainly a better utilization of billions of taxpayer dollars that are currently being used for funding an obsolete energy system.

Following the public release of the GeoMicroDistrict Feasibility Study, HEET and their supporting partners filed an Act for utility transition to using renewable energy (FUTURE). The FUTURE Act was developed with legislative leaders to pass laws to improve regulations for gas distribution systems and to accelerate the transition to renewable energy. The FUTURE Act will grant utilities the permission to bill customers for renewable thermal credits (or BTUs) instead of gas and proposes a renewable thermal credit market for the gas industry. The Act calls for flexible regulations allowing municipalities to choose energy alternatives and requests for funding and financial incentives to encourage gas companies to distribute thermal renewable energy instead of gas. The bill was supported by 13 municipalities at the Telecommunications, Utilities, and Energy Committee hearing on November 12, 2019. HEET is currently supporting Eversource Gas to pilot the GeoMicroDistrict concept in 2021.


  6. For further details on engineering and economic assumption please refer to the GeoMicroDistrict Feasibility Study.

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