Geothermal in Newport
Geothermal heat pumps [a.k.a. “Geo Exchange” or “ground-source”] have been in use since the late 1940’s. Geothermal systems have a heat exchanger in contact with the ground to extract or dissipate heat, instead of the outside air. The lower temperature differential and the near-constant temperature of the earth results in higher efficiency–even on the most frigid winter nights–compared to air-source heat pumps. The tradeoff is that geothermal systems have a higher initial cost, due to the need to drill wells in which to place the pipes that carry the heat exchange fluid. While the lower installation cost makes traditional air-source heat pumps more common, they unfortunately become less efficient during periods of extreme cold or heat because they use outside air as a heat exchange medium.
IN MORE DETAIL…
Several major design options are available for geothermal systems: direct exchange systems circulate refrigerant underground, closed loop systems use a mixture of anti-freeze and water, and open loop systems use natural groundwater. Closed loop tubing can be installed horizontally in trenches or vertically as a series of long U-shapes in wells. Vertical loop fields are typically used when there is a limited area of land available, but the required drilling can be costly. The length and quantity of the loops depends on the soil type and moisture content, the ground temperature, and other thermal characteristics of the building itself.
THE NEWPORT FIREHOUSE
Because of the tight building lot, a vertical loop configuration seemed a natural fit. The heating and cooling loads of the building required an 800’ deep well—the drilling took 2 ½ days and caused quite a ruckus and resulted in a huge geyser! Fluid pumped through the closed loop absorbs heat from the earth and carries it to a heat exchanger in the basement mechanical room. Here, the warm water is compressed by pumps to a higher temperature and distributed throughout the firehouse, via radiant flooring and warm air. In summer, the process is simply reversed, to expel heat from the firehouse to the cooler earth. Payback of the initial investment for the firehouse’s geothermal system is expected to be +/- 8 years, depending on price of oil in near future. With a life-expectancy of the system being at least 30 years, the decades to come should be quite comfortable—physically and financially!
But the heating and cooling system comprises only part of our holistic approach to energy conservation at the firehouse. On the roof, an array of solar tubes collects the sun’s energy to provide domestic hot water [with surplus heat being directed through the basement radiant floor]. Electricity is purchased from “People’s Power + Light”, a RI non-profit which uses wind turbines to create power. The re-built firehouse is a ‘super-insulated’ building. Spray-applied cellulose [aka “wet-spray cellulose”; R-value = 3.8 per inch] from recycled newsprint fills all wall and ceiling cavities, providing both a thermal + acoustic barrier. Rigid insulation [R-value = 6.0 per inch] was added to roof and within brick veneer walls. An open floor plan, combined with ceiling fans and huge operable track doors at the roof deck allow for fantastic breezes throughout the home during the warmer months. During the construction process, special attention was given to properly air-sealing the entire building envelope. Using the most durable materials throughout the home will result in less required maintenance and help ensure a very long “second life” for this special Newport structure!