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New Hampshire has found the place it wants to test an intriguing power source known as the Stirling engine: In the laundry room of the state hospital.

On Thursday the state asked for companies to bid on its plan for a Stirling engine – a variant of gas-powered engines that has shown promise for more than a century but never been truly commercialized – in the state facility at 127 Pleasant St. in Concord. The installation would go ahead as part of the transition of heat sources from Concord Steam to natural gas that is happening in all the state properties in the Hugh Gallen Office Park.

Although the official Request For Proposals issued Thursday doesn’t single out any particular company to run the demonstration project, there’s an obvious front-runner: DEKA Research and Development Corp., the company started by Manchester inventor Dean Kamen, who has long been a fan of Stirling engines.

DEKA has developed a refrigerator-sized Stirling engine that it says can generate 10 kilowatts of electricity and 40 kilowatts of heat. Several are installed in office buildings in the Manchester Millyard, where DEKA has its offices.

It was DEKAs offer last year of a free Stirling engine test that got the ball rolling on this idea. Legislators balked at giving DEKA a free reign and instead passed Senate Bill 489, allowing anybody to bid on the project.

A Stirling engine is named after Robert Stirling, a Scottish minister who developed one of the prototypes some 200 years ago is similar to an internal-combustion engine with two major differences.

One different is that it uses an external heat source to create energy and move parts around rather than an internal heat source such as a spark plug igniting gasoline inside a car engine.

The other difference is that the Stirling engine is a closed-cycle engine. The fluids and gases stay inside it, unlike the exhaust released by car engines.

In theory, these differences make the Stirling engine more efficient and less polluting than internal-combustion engines, as well as more flexible, since they can use any external heat source. In reality, however, problems with heat transfer through materials, sealing of fluids and other engineering issues have kept them from working on a useful scale except in a few limited applications.

Under the RFP, the winning bidder must install a Stirling engine “for heat and/or electricity at the New Hampshire Hospital Laundry Facility at no cost to the state,” must maintain and repair the machine for free, and must remove it any time if the government decides the project isnt working, also at no cost to taxpayers. The project can run anywhere from one to five years and at the end of the time the site “shall be returned to its original condition or better.”

These stipulations sound pretty extreme, but were part of DEKAs original proposal.

Bids must be received by next month, and a winning company will be announced by the end of September. For more information, check

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