Sustainability is defined as a set of environmental, economic and social conditions in which all of society has the capacity and opportunity to maintain and improve its quality of life indefinitely without degrading the quantity, quality or availability of natural, economic or social resources.

There is a general understanding of what makes a sustainable building, but what makes a sustainable substation? It could imply a design that minimizes resource depletion (or maximizes recycling), reduces the impact of pollutants and waste, minimizes the destruction of nature and encourages the use of renewable energy alternatives. In response to society's push for environmentally friendly practices, Connecticut Light & Power (CL&P), a Northeast Utilities company, is partnering with Burns & McDonnell to explore the possibilities of integrating common sustainable design strategies into its substation design standards.

CL&P selected its Sherwood substation in Westport, Connecticut, U.S., as the pilot site to evaluate opportunities for the utility's first sustainable substation study, which was conducted in parallel with the standard design process. The existing site for the proposed development of the Sherwood substation has one residence with a wetland to the west and trees in the remainder of the lot. The site is constrained to the north by a commuter rail line, and to the south and east by local roadways. CL&P evaluated a variety of sustainable design strategies for future substation projects, including stormwater management, material strategies, control building optimization and electric vehicle (EV) integration. The study was rounded out with an evaluation of public education and awareness opportunities.

Stormwater Management

Site development typically increases stormwater runoff, but applying sustainable practices can mitigate this environmental impact. Stormwater regulations vary among states, but most states require limiting stormwater volume and flow rates to predevelopment conditions in addition to requiring partial removal of pollutants carried in stormwater runoff. Connecticut's Stormwater Quality Manual was used as a guide for stormwater requirements. The three criteria analyzed were controlling peak runoff rates, maintaining groundwater recharge and achieving a minimum of 80% removal of total suspended solids.

The sustainable substation design proposed for the study uses a new method of surfacing in the vehicle drive paths within the substation to mitigate effects of the development and minimize the area of disturbance. The proposed surfacing system is comprised of a 12-inch (305-mm)-thick layer of gravel below UrbanGreen Grass and Gravel pavers filled with growing medium. Native low-growing, warm-season, drought-tolerant grasses are proposed in the pavers and would require minimal maintenance. Typical crushed rock surfacing would remain around the equipment and the exterior of the perimeter fence to maintain grounding requirements. The use of this vegetated surfacing system at the pilot site would decrease the amount of graveled impervious surface at the substation by more than 50%.

In the sustainable design, the voids in the rock store runoff while it infiltrates into the native soil, promoting groundwater recharge and runoff rate reduction. The water stored in the rock voids also meets the minimum volume needed to meet the total-suspended-solids-removal requirement. Pavers also decrease the substation footprint by keeping the stormwater management system within the fenced area and eliminating the need for a detention pond.

Perforated underdrains connected to a drain that acts as a spillway at the low end of the substation allows for water to flow from the substation at reduced rates during heavy rains when the native soil infiltration rates are exceeded. Draining the excess water prevents saturating the soil layer of the substation site and eliminates the potential of pooling or rutting.

In addition to capturing runoff and infiltration, maximizing green space and providing a stable working platform and driving surface, this permeable surfacing system lowers the heat island effect. The heat island effect is the absorption of heat to a dark, nonreflective surface, resulting in an increase in the surrounding temperature. Heat islands are especially noticeable in more urbanized areas.

The pilot site was analyzed for the 2-, 10-, 25- and 100-year 24-hour storms. Performance results of traditional and sustainable models were calculated. The sustainable design of stormwater management meets and exceeds the performance of the traditional detention basin design while minimizing the area of disturbance. A benefit of minimizing the disturbance area is the possibility of smaller plots of land needed for substations, reducing site acquisition and development cost, long-term maintenance cost, taxes and public impact. The new sustainable design meets or exceeds permitting requirements and limits the impact on the environment and surrounding landowners.

Material Strategies

The U.S. Green Building Council's Leadership in Energy and Environmental (LEED) manual states that the total solid waste stream in the United States contains nearly 40% construction and demolition wastes. Even small construction projects offer good opportunities to reduce this waste stream.

The goal of a construction waste management plan is to divert construction and demolition debris from disposal in landfills and incineration facilities. The designer must prepare concise specifications for the substation construction contractor. It is important the contractor work in conjunction with the recycler and waste hauler for the project. Depending on the site, recycled and salvaged products may further decrease the overall waste stream associated with the project.

Construction Waste Management Plan

The largest contributing factor in diminishing the total waste stream from a site is to reduce waste from the source. One simple way to address this issue is to work with vendors and suppliers to reduce packaging material or, where possible, use shop fabrication for modular construction.

The Sherwood substation site offers several opportunities to minimize demolition waste, including materials from the existing residential structure, pavement, trees and shrubs. Easily recycled or reusable materials can include metal, concrete, wood, gypsum wallboard, crushed asphalt, masonry and cardboard. Local demolition contractors with experience in recycling and salvaging materials can outline a plan for this methodical process to cost-effectively optimize the amount of waste diverted.

Not only are benefits realized by diverting waste from landfills and incinerators, but certain recyclables, such as metals, may provide some economic payback to the project. Sites with significant clearing can reuse tree and shrub chippings for erosion control, specifically in construction staging areas and entrances to the site.

Sustainable Materials and Vendors

Selection criteria for contractors, vendors and suppliers can be expanded to consider the sustainable practices employed throughout their respective businesses. Developing some metrics to encourage the selection of vendors and suppliers that embrace sustainable practices would further elevate the overall sustainability of the substation design.

Many manufacturers are using recycled materials in block retaining wall systems. Vendors are using recycled concrete, fly ash and plastics as parts of their manufacturing processes. At the Sherwood substation, retaining walls are used to help with erosion control and runoff mitigation into the nearby waterway, which leads directly into Long Island Sound.

Many concrete suppliers use recycled cement and fly ash, and are able to maintain a reasonable level of product quality. Historically, CL&P does not allow fly ash in structural concrete. However, fly ash may be used in non-structural concrete, such as duct banks, as long as it still complies with ASTM International and ACI building codes. Fly ash reduces the carbon footprint of the project by replacing portions of Portland cement, thereby reducing the greenhouse gases produced in its manufacturing process. In addition, fly ash is generally cheaper than the cement it replaces.

Rock aggregate has several simple but important applications in substation design. At the Sherwood substation, several opportunities exist to replace rock aggregate with reclaimed crushed concrete:

  • As a sub-base for the foundations and roads

  • For temporary erosion control

  • For slope stabilization

  • As part of the substation surface and grounding system.

The amount of recycled aggregate for each design opportunity may vary with local governing bodies and utility standards.

The LEED manual indicates that vendors and suppliers should be located within a 500-mile (805-km) radius of the project, especially those who extract and manufacture raw materials. A 100-mile (161-km) radius is preferred for heavier materials such as steel and aggregate. LEED certification considers the benefits of reduced transportation costs and carbon footprint minimization through the use of local suppliers and the local economy.

Buildings and Power

Substation control buildings have little or no occupancy for the vast majority of their service life. This makes a cost-effective use of higher-efficiency devices, such as lighting, more challenging from a first-cost perspective. However, there are opportunities to reduce energy use at the Sherwood substation, such as installing energy-efficient light fixtures and using auxiliary power from photovoltaic panels.

Burns & McDonnell used a light simulation program to determine a 33% reduction, or 1 W/sq ft, of energy use could be achieved through the use of high-efficiency lamps. However, the incidence of usage for those lamps made justifying a change improbable.

Electric power from photovoltaic panels can power the enclosure equipment and the station service auxiliary load. The available area for photovoltaic panels is approximately 300 sq ft (28 sq m). According to an automated solar electric estimate tool, approximately 25% of the annual energy consumption could be offset with photovoltaic panels. The payback on the photovoltaic panels for this project is estimated to be approximately 17 years.

Utilities can promote the use of environmentally friendly EVs and plug-in hybrid electric vehicles (PHEVs) through use on their own systems. CL&P will be expanding the number of electric charging stations around its Connecticut service territory as part of a utilitywide study. CL&P's EV research project is the most comprehensive study of plug-in car recharging in New England. As the EV/PHEV market develops, utilities may choose to integrate charging stations into public infrastructure and make it easier for the public to use EVs and PHEVs, thereby promoting a commitment to sustainability within the community.

Substations located near large populations are positioned in locations that could support large numbers of public vehicle charging stations without the need to upgrade the existing power infrastructure. Sherwood substation is located adjacent to a commuter parking lot for the local rail line. CL&P and the town of Westport selected this location to install an EV charging station that is the first in the nation to offer drivers a pay-by-phone option. Parking passholders at this commuter lot currently may charge their EVs for free.

Little modification to the Sherwood substation would be needed to integrate the types of charging stations on the market today. Multiple options exist to connect the charging stations in the commuter lot to the substation. One option is to connect the load to a service from one of the distribution circuits and treat it like any other customer load. Up to 10 charging stations could be placed in commuter lots similar to the size of the one adjacent to the Sherwood substation. The station load for these alternating-current level-two charging stations is 72 kW. This small load does not affect the overall design and capacity of the substation.

Public Awareness

Educating the public about the sustainability measures implemented is an important part of any sustainability project. Since the Sherwood substation is near a school and directly across from public commuter parking lots, its location offers great opportunities to display educational information about the site's sustainability features.

With three commuter parking lots adjacent to the substation, waiting commuters provide a perfect audience for CL&P's promotional programs. Large display boards with simple sustainability messages and the project website would draw attention to the project and direct commuters to find more information.

Science, technical, engineering and mathematics (STEM) subjects are important to the future of America. This project provides students and teachers with a genuine interest in sustainability and green power an opportunity to learn more about CL&P's programs and future plans, right in their own neighborhood. For example, there is a small private school within 0.25 miles (402 m) of Sherwood substation.

Journey to Sustainable Electric System

Every substation layout and site is unique and presents its own design challenges. Sustainable electric energy design and construction can be applied to electric substations like CL&P's Sherwood substation, resulting in improved long-term operations and maintenance practices, increasing employee satisfaction, meeting regulatory expectations and promoting shareholder value. CL&P's sustainable electric energy design demonstrates the commitment the utility is making to green initiatives and being a good neighbor. It is hoped these concepts spark the creativity of engineers across the industry to embark on the journey to a more sustainable electric system.

Acknowledgement

The authors appreciate the contributions of the following in the development of this article: Kris Aberg, John Morrisette, Amanda Mayhew and Caroline DiDomenico of CL&P; and Marshall Bird, Gene Wyckoff, James Watson and Mike Beehler of Burns & McDonnell.


Kenneth B. Bowes (boweskb@nu.com) is a vice president of energy delivery services for Connecticut Light & Power. He is responsible for CL&P's distribution asset management, field services and capital construction groups. Bowes earned a BSEE degree from the University of New Hampshire and a MSEE degree from Rensselaer Polytechnic Institute. He is the past chairman of the Edison Electric Institute's transmission committee

Jim Hogan (jhogan@burnsmcd.com) is a vice president and director of engineering in the T&D division at Burns & McDonnell. He has worked on major projects for Northeast Utilities, including the NEEWS program and the Northern Pass and Middletown-Norwalk projects. He has more than 28 years of experience at Burns & McDonnell in engineering and managing substation and transmission line projects. Hogan earned a BSCE degree from the University of Missouri-Kansas City and a MSCE degree from the University of Missouri.

Stormwater Flow Summary
Storm event (recurrence years) Pre-construction cfps (L/sec) Post construction
Traditional design cfps (L/sec) Sustainable design cfps (L/sec) Sustainable design runoff reduction (percent change from pre-construction)
2 1.68 (48) 0.62 (18) 0.62 (18) 36.9
10 3.65 (95) 1.39 (39) 1.36 (39) 37.2
25 4.52 (128) 2.61 (74) 1.74 (49) 38.9
100 6.45 (183) 6.27 (178) 4.06 (115) 62.9
New Application of LEED Principles

The U.S. Green Building Council, best known for the development of the Leadership in Energy and Environmental Design (LEED) green building rating system, promotes sustainable building practices among the nation's facility owners, architects, engineers and contractors. The LEED manual is one of the most comprehensive guides to sustainable design and provides many ideas, strategies and implementation techniques for the design of commercial and residential buildings. While the strategies used in this sustainable design concept have been implemented successfully in a variety of industries, these strategies have not yet been applied to unoccupied industrial facilities like electric substations, in part because LEED certification does not apply to this arena.

However, several of LEED's sustainability concepts can be applied to substation design and easily integrated into the design process. With its experience in sustainable facility design and construction, coupled with electric transmission and distribution expertise, Burns & McDonnell is assisting Connecticut Light & Power (CL&P) in evaluating the applications of sustainable LEED-like design parameters in future substations. This exploration of the sustainable substation will move CL&P forward in its efforts to lead by example and meet the ever-changing expectations of its customers, regulators and investors.

Renewable energy sources such as the photovoltaic panel array can serve as a supplemental power source for the substation enclosure equipment and are available to service the auxiliary load. Approximately 25% of the station's annual energy consumption can be offset through photovoltaic arrays.

Companies mentioned:

Burns & McDonnell www.burnsmcd.com

Connecticut Light & Power www.cl-p.com

CONTECH Construction Products Inc. www.contech-cpi.com

Northeast Utilities www.nu.com

U.S. Green Building Council www.usgbc.org