Solution of the Month: Discreet Heat

Sep 17, 2012 by


Solution of the Month:

Discreet Heat

In a house museum in north Georgia, buy an orthodox approach to historic interpretation minimizes heating and cooling load.

By David Sokol
August 2012
Photo © Jonathan Hillyer / Atlanta

Lamartine G. Hardman was an entrepreneur, prescription farmer, physician, and, between 1927 and 1931, head of the State of Georgia. But he was no decorator. When the former governor owned a 173-acre farm outside Helen, Georgia, in the early 20th century, he barely touched the 1870 house at the compound’s core. Gasoliers were partly electrified and the original furnishings remained. Although UV rays were fading zinc-painted trim and the calcimine on walls and ceilings, Hardman never refinished the plaster.

Hardman passed away in 1937, and fascinatingly, the time warp remained untouched. The Georgia Department of Natural Resources (DNR) acquired the property from the Hardman family in 2002—still only partly electrified, originally furnished, and unpainted.

DNR tapped architect Lord, Aeck & Sargent (LAS) to restore the 5,160-square-foot farmhouse with Dublin, Georgia–based design-builder Garbutt Construction. The intactness of the historic artifact sparked all imaginations. LAS project manager Julie Arnold says the project launched with a three-prong strategy: “to retain as much of the historic fabric as we could; to pursue aggressive sustainability strategies; and to create a museum-quality environment for the house, which would entail temperature, humidity, and particulate control.”

Because the building had never been conditioned, the design team then recognized that museum-quality climate control may be in conflict with other objectives. Installing mechanical systems would mean cutting through the untouched plaster, and sealing the house for maximum interior climate performance could radically alter the composition of materials that had acclimated to decades of thermal cycles.

A computational fluid dynamics model supported revising this aspect of the mission. Thanks to passive solar orientation, shading devices like a wraparound porch and operable shutters, and stack effect enhanced by the house’s Italianate cupola, “The model determined that there were very few hours when the temperature inside the house exceeded 80 degrees, and then only late in the day, when the sun strikes the west walls,” Arnold says. Employing only natural ventilation, the house would be comfortable enough for summertime visitors, in which case they could experience the 1915–1925 reference decade in both look and feel.

“Then came the concern about heating,” Arnold recalls. The cracked plaster walls would be repaired only minimally, with elastic filler that would be left unpainted. “We didn’t want the house experiencing freeze-thaw conditions with the new materials we were introducing to the house.” Mechanicals of some type would have to be introduced into the pristine environment.

LAS considered several heating options for maintaining a minimum temperature of 65 degrees on the ground floor and 55 degrees upstairs. It assessed these choices within a matrix of criteria that included lifecycle cost, energy efficiency, physical impacts on the historic interior and exterior, maintenance, and thermal comfort. Alternative systems were compared against a traditional high-efficiency split system.

Baseboards were nixed, since each room would require four or five of the visually intrusive elements. Ducted systems had similar cons. “A hydronic floor system with an electric water heater was the most expensive option regarding energy consumption and operating cost, while a hydronic system with a liquid propane gas boiler seemed to be the most moderate between them,” Arnold concludes. By holding second-floor temperatures to a different standard and presuming continued stack effect, the design team left the upstairs mechanically untouched. “We wanted to achieve this balance between efficiency and historic impact, and by not doing anything on the second floor we felt we were starting to achieve that balance.”

A basement crawl space allowed installation of the hydronic floor system to take place unobtrusively. Long runs of radiant tubing are stapled into the joist cavity beneath the floor, with a water-glycol mix running through the closed loop. Insulated sheeting hides the cavity from underneath.

What Governor Hardman lacked as an aesthete, he made up for in tinkering. He was an early adopter of crop rotation and indoor plumbing, and he only electrified a few lamps in his gas chandeliers because the power technology was not yet proven. He most surely would have approved of the progressive, almost inconspicuous changes made to his farmhouse, then. In addition to the LPG hydronic system, Georgia’s next State Historic Site includes a 3.2-kilowatt photovoltaic ground array installed in a picketed area near the residence to offset much of the electricity it demands. And last year the National Center for Preservation Technology and Training, a research division of the National Park Service, awarded the DNR a two-year grant to collect temperature and humidity data and measure plaster movement to verify all aspects of the project’s performance.

via greensource

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