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By Barbara Knecht

Running hot and cold

Serenity and comfort are a high priority for the national engineering firm Flack + Kurtz, says senior vice president Dan Nall, even as he readily acknowledges the difficulty of satisfying every single person’s perception of thermal comfort. He is a proponent of environmental conditioning systems that more directly create individual comfort than ones that simply change the temperature of the air. These include a number of methods of delivering heating and cooling and mitigating climatic impacts that have been much more common in Europe than in the U.S.

 

SMWM Architects’ renovation of Pier One on San Francisco’s waterfront includes a radiant heating and cooling system. Pipes are laid before the concrete floor is poured (left). The vertical element is the manifold, which connects each radiant zone with zone-control values. Photography: © Tim Hursley

Conventional air systems rely on creating an even air temperature from which some radiant comfort will result, while radiant systems concentrate on changing the temperature of surfaces in a space. According to the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), the mean radiant temperature, which is a measure of surface temperatures in a space, has more impact on human comfort than the air temperature. ASHRAE has also indicated that people are comfortable at lower temperatures with radiant systems.

 

Pipes are laid before the concrete floor is poured. The vertical element is the manifold, which connects each radiant zone with zone-control values. Photography: © Alan Monpelier

Although radiant floor heating is not common in the U.S., radiant cooling is quite rare. Both these systems have been used much more extensively in Europe for some very good climatic reasons, explains Nall. “Western Europe has a much less humid summer climate than most of the U.S. east of the Rocky Mountains. London, like San Francisco, is damp, but the temperatures are cool. The difference lies in the dew-point temperature, which combines with air temperature and measures humidity. The percentage of the year when the dew-point temperature is in the uncomfortable range is as follows: zero in London, 2 percent in San Francisco, rising to 7.5 percent in Chicago, and 41 percent in Houston. The high humidity causes condensation, or “puddling,” on a cool floor. Air systems, which are able to adjust the humidity and velocity, have some inherent benefit over radiant systems in humid environments.