Sound's a Problem—Even on an Island
Sound attenuation for a power plant on an isolated Maine island must balance costs among resident population and an economy based on summer tourists.
Picturesque Monhegan Island lies 12 miles off the coast of southern Maine. Well-known through the paintings of Rockwell Kent and resident artist Jamie Wyeth, the island has been attracting summer residents and day-trippers for over 100 years. Monhegan Island hosts over 200 resident and migrating bird species, and in season can be flooded with herds of binocular-toting birdwatchers. The only access is via ferry, a refurbished Philippine Island cargo ship, which runs daily in the summer but only three times a week once the tourists leave.
The island boasts 17 miles of nature trails but no paved roads. In season the island's 70 or so residents run two hotels, numerous bed-and-breakfast inns, guest cottages, restaurants and shops. In the winter, when the wind sweeps across this 700- square-mile outpost (one-and-a-half miles long and half-mile wide) at a constant of 10-20 mph, the locals put out to sea to fish and tend their lobster pots.
What Monhegan residents and businesses needed appeared simple enough: a year-round supply of quiet, reliable power. What they got was a series of stops and starts, until Northern Power Systems braved bad weather, transportation costs, environmental regulations, and an angry neighbor to give the islanders what they wanted.
For years Monhegan Island's two hotels and most of its residents depended on their own generators. Central power became a reality on the island in the mid-1980s, but problems evolved with the privately-run system sooner than later. The facility housing the power plant and its 500-gallon diesel fuel tank were located ten feet from the primary aquifer, which was the sole source of drinking water. The distribution system was primitive, 208-V cable strung in ditches along the side of the road, sometimes installed in conduit, sometimes not.
“There were horrendous line losses,” says Northern Power Project Director Jim McNamara, describing the system his crew repaired before he got to work on the power plant. “Residents at the end of the line received power at 90 volts, and the system was cranked up so high to get them even that, that people living close to the power plant were receiving 130 volts and popping light bulbs.”
Lack of maintenance plagued the privately owned system most islanders had come to depend on, according to Kathy Boegel, who is president of the Monhegan Plantation Power District (MPPD) and who does triple duty as the wife of a lobster fisherman and owner of the island's general store. Finally the town assessors voted to apply to the Public Utilities Commission to have the system declared a public utility, which subjected it to regulation according to federal and state law. In 1998, with the private power plant down to one generator belching black smoke, Monhegan residents voted to create their own power district.
At the time it took on the Monhegan project, Waitsfield, VT-based Northern Power was known for designing power plants for offshore oil platforms, military and scientific outposts, and nuclear test ban treaty monitoring sites—anyplace, as McNamara puts it, “that's harsh and remote and needs reliable power.” (The company now specializes in large commercial and industrial cogeneration installations.)
The first step to getting centralized power up and running on Monhegan Island was to find a new, more secure location for the power plant, and this turned up its own set of challenges. As an organized territory, Monhegan Island is owned by Maine's Land Use Regulation Commission (LURC), which regulates zoning and land use. LURC would not allow the islanders to build their new facility near the aquifer or anywhere else in the watershed. The least worst site, as Boegel puts it, turned out to be on a hill outside of town in an area designated as a land preserve. The preserve was the brainchild of Theodore Edison, the youngest son of Thomas Edison, who visited Monhegan Island as a child and began buying land in the 1930s to keep it from being subdivided and developed. In 1954, Edison founded one of the East Coast's first land trusts, and Monhegan Associates Inc. safeguards his legacy today.
Eventually LURC gave its blessing and rezoned part of the preserve to allow the power plant to be installed not far from the Marshall Point Lighthouse. The MPPC secured a $100,000 special needs grant, then a $350,000 loan, and Northern Power got down to business. First the company installed the two 480-V gensets the town had rented at the lighthouse site and connected the generators to the existing 208-V distribution system using a 4,160-V feeder line. At the same time, McNamara brought in a team of electricians to make repairs and improvements to the distribution grid until it could be replaced, removing and replacing bad cable junctions and installing boosting transformers to increase voltage in areas that experienced chronic line loss.
For the island's new power plant Northern specced a 300-kilowatt capacity, diesel-fired installation equipped with custom-built switchgear specifically designed for low-budget, isolated, grid applications. The new plant consisted of two 120-kilowatt Kohler generators and one Kohler 74-kilowatt generator, all built on John Deere diesel engines. The sizing was based on a Northern Power load study, which determined the averages and minimums for both the off-season and the May-through-October tourist season.
During the off-season, the 74-kilowatt generator handles most of the load and still runs efficiently during nighttime hours. One of the 120-kilowatt units takes over on the handful of days the peak load exceeds 74 kilowatts. During the tourist season, the situation is reversed. The 120-kilowatt units handle the majority of the load, with the 74-kilowatt generator kicking in about 25% of the time during the day and the majority of the time throughout the night. The second 120-kilowatt unit is for redundancy, allowing the island to meet its entire power needs with any of the units offline.
Each genset has a switchgear cabinet equipped for synchronization with the island's electrical grid. A generator power controller (GPC) in each cabinet controls the engine speed (frequency) and power (voltage and current) to match demand. “At the time we designed this,” says McNamara, “no one made paralleling switchgear to meet our specifications and cost point. Most switchgear manufacturers were offering equipment built for larger or higher voltage applications such as hospital or convention center backup. These were needlessly large and expensive for the island. So we built our own gear based on Encorp paralleling controls.”
In a nod to the island location, Northern Power also incorporated oil change and burn-off systems to alleviate the cost of on-island oil disposal. The simple, robust system also reduces maintenance costs by minimizing costly trips from mainland service providers.
All the work on the plant had to be done in the off-season because there was no housing available during the high season. During the winter the islanders were able to put up workers in their homes, further reducing project costs. All equipment had to be hauled to the island on a landing-craft ferry, and McNamara says one of the primary challenges of the project was thinking ahead “in terms of what we planned to take over there. Otherwise we'd wind up with huge delays.” Once on-island, there were additional transportation challenges. McNamara describes the unpaved road up to the site as a twisting “goat trail” that was washed out half the time. “You couldn't use any kind of equipment that required a flatbed truck to move it around, a consideration which influenced the size of the fuel tanks.”
It was not until the location of the site became common knowledge that concerns about noise surfaced. Islanders objected to the plant being situated in the nature preserve, which was used by residents and visitors alike. “That area has beautiful walking trails,” says Boegel, “and with a museum in the lighthouse we didn't want tourists to be bothered by the sound.” Of more immediate concern was a summer cottage that was located adjacent to the site. Once the news was out about where the plant would be located, the cottage owner immediately declared his intention to block construction.
The island does not have a sound attenuation ordinance, and the neighbor first attempted to convince LURC not to rezone the land. When the agency OK'd the site for the plant, the neighbor hired a sound consultant who recommended 47 A-filter decibels (dBA) at the property line, 75 feet from his house. For four days, Northern Power had taken measurements of the ambient noise in the area, which it determined to be 52-61 dBA—consistent, McNamara notes, with levels referenced from published sound level tables—and 47 dBA seemed reasonable as the standard for the project. It was assumed that ambient noise in the engine room would be 87 dBA.
The power plant building was situated to take advantage of prevailing winds, which were anticipated to help carry and sound away from the neighbor. “The building itself shielded noise,” says McNamara, “and the plant was located in a hollow so we assumed that any sound remaining in the immediate area would hit vegetation, which would attenuate it.”
The building that housed the plant was designed in keeping with the island's gray-shingled architecture. Northern Power designed all the mechanical specifications including the space, amount of air flow required for ventilation and the plumbing for the fuel. To save money, islanders provided the labor. The 11-foot-by-25-foot engine room is housed in a 35-foot-by-41-foot, two-story building that also houses the fuel tank, switchgear, fuel truck parking and the power company's office. The engine room was constructed with sand-filled cinder block walls, an approach that had been suggested by the neighbor's consultant and seized on by Northern Power as being less expensive than installing acoustic material on the engine room walls. The cinder block walls also help the building meet the local fire code.
Inside the engine room, Northern silenced the air ventilation system with Industrial Acoustics Company (IAC) Type S Quiet Duct Silencers and American Warming and Ventilating (AWV) Acoustical Louvers. Both had to be sized for less than 1,098-feet-per-minute free area velocity and .33 inches of water in order to avoid water penetration. All equipment was purchased through HVAC Products of South Portland, ME. Engine silencers were Extreme Application Acute Critical Silencers from GT Exhaust of Lincoln, NE.
“Where the challenge came in,” says McNamara, “was that the duct and louver silencing took up space, and obviously if you constrict airflow it doubles your velocity and you're going to create more noise. We installed the radiators on pads outside the buildings because we didn't want to reject the heat to the interior of the building and we knew fan noise was going to be an issue. The slower you can have your fans running the better, so we went with oversized fans on our remote radiators. But you have to remember that simply going to a bigger fan doesn't always work. The fan may be turning slower, but because the tips are now farther out, the speed may be just as fast despite the fact that the blade is doing fewer rpms. The key thing to note is that you get quieter fans by oversizing the radiator capacity so the same size fan can turn slower.”
To save money, instead of recommending silenced ducts and louvers at the intake and output of the fans, Northern Power specced what McNamara calls a low-tech sound fence: a wood-slat fence lined with a weatherproofed, sound-absorbing material high enough that any sound that escaped would be vectored upward, plus landscaping to attenuate the noise.
Did it work? “I was in the engine room with Chris Smith, the contractor and project liaison who was in charge of construction,” says McNamara, “and of course it was ear-splittingly loud. Then we closed the door and walked outside the building around to the backside and stood next to air intake and outflow. Chris thought the generator must have stalled and went back inside, then came back out again and reported everything was running full tilt. On the outside of the building, the only way you could tell the generator was running was the rain flap on the muffler was lifted. After the plant was installed we re-measured and determined ambient noise levels around the facility were unchanged from what we had originally taken.”
Katy Boegel isn't so sanguine. The facility has been operating for four years now, and Boegel says when she walks through the woods she can still hear the radiator fans. But she knows what the problem is. MPPD never built the sound fence Northern Power recommended to help attenuate fan noise. “I know what we need to do is build the sound fence in front of where the exhaust fans,” says Boegel, “and we need to install the landscaping. But at the moment most of money is going toward the basics, operations and maintenance and paying down the loan. We charge fifty cents a kilowatt hour right now, but we will probably have to raise that because the cost of fuel has risen so dramatically.” Northern Power specced the generators it installed to be effectively integrated with a hybrid solar or wind system, should that ever become a reality, and also installed a wind gauge. But Boegel says islanders have aesthetic and environmental objections to the idea of a hybrid system and will probably be more comfortable paying a higher price for electricity generated under the present system.
Author's Bio: Journalist Penelope Grenoble is a frequent contributor to Forester Media, Inc. publications.
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