Builders Warm to Radiant Cooling
by Linda Anderson, © 2006 Northwest Energy Efficiency Alliance, Inc. All Rights reserved. Northwest Energy Efficiency Alliance grants permission to reproduce this material in whole or in part only for information or education purposes.

Concerns about condensation and a lack of familiarity among builders have hindered the widespread use of radiant cooling in Northwest commercial buildings. However, new control technologies are addressing the condensation issue, and as successful applications become better known in the engineering community, familiarity is expected to rise. Interface Engineering in Portland designed a radiant cooling system when it renovated the 80-year old Lovejoy Building in Northwest Portland. The company also designed a system for a building under construction in the Oregon Health Sciences University (OHSU) River Campus on Portland's riverfront.

John McMichael, principal of Interface, said radiant cooling is more common in Europe, where energy costs are higher than in the United States. Radiant systems also require more analysis determine if they're a good fit," he said. "They're not geared for every building. Radiant systems cool people via cooler surfaces, such as floors, walls or ceilings. The sensation much like entering a basement or walking down the freezer aisle at a grocery store. Cooling tubes can be embedded in ceiling panels that into traditional metal grids, ceiling beams, wall panels and floors. McMichael said concerns about condensation are real. The surface mass can only get so much cooler than the ambient air before it will begin sweating. However, control systems and sensors can accurately control  slab and water temperatures to eliminate the problem.  The Lovejoy Buildings heating and cooling is handled by a radiant floor slab system that temperature-controlled in four zones. Embedded half-inch polyethylene tubing spaced at 6-inch intervals runs throughout the flooring. The is made up of 3 inches of concrete poured over 2 inches of rigid insulation that sits on 80-yearold wood decking. A high-efficiency, closed-circuit cooling tower with a variable frequency drive regulates cooling water temperatures that travel through the tubing. A direct digital control system controls the slab temperatures and the cooling tower. McMichael said a rooftop air conditioning package also was installed, but it is used primarily for ventilation. The air conditioning portion came on only one-half hour, one day, during a four- to five-day hot spell last summer, he said. That's very much less than would have happened in a normal building. The system is used primarily to ventilate and remove carbon dioxide. When outdoor temperatures are above 50 degrees Fahrenheit, ventilation is primarily handled by operable windows and paddle ceiling fans. During other times, building sensors kick on the rooftop unit to flush the building of stale air and bring in outside air. The Lovejoy Building’s radiant cooling system is considered more energy- efficient than moving cool air mechanically.

According to California's Energy Design Resources, A hydronic system can transport a given amount of cooling with less than 5 percent of the energy required to deliver cool air with fans. Although firm numbers are not yet in, Interface Engineering modeled energy savings in the building at 50 percent versus the 2003 Oregon Energy Code. Energy Design Resources pegs radiant cooling systems in general at saving an average of 30 percent in overall energy for cooling and 27 percent in demand charges. The savings are from fan and compressor energy," McMichael said. "Also, because you don't have to run the fan at all for heating, you get that savings too." He said Interface was able to install smaller sized duct work between joists in the office area, rather than the larger ducts required with a traditional heating, ventilation and air conditioning system. Backers of the technology also say radiant cooling improves tenant comfort and air quality because large volumes of air are not recirculated.

 Larry Drake, executive director of the Radiant Panel Association in Loveland, Colo., said ceiling radiant cooling is popular in hospitals for just those reasons. Its very clean and doesn't circulate contaminated air, he said. Its very comfortable, and the same panel can heat and cool. In fact, Drake said ceiling systems work best in almost all applications. Cool air falls, so air that comes in contact with it also falls, and you end up with a convective current, he said. You get a lot of heat exchange. If the cooling is in the floor, you don't get the convective current going. Ceiling applications also avoid conflict with floor coverings, which can play havoc with system performance.

The Lovejoy Buildings floors are made up of scored polished concrete. A part of the OHSU buildings system is also located in  a cement floor in a lobby area. Upper floors of the building will use chilled beams in reception and waiting areas. McMichael said radiant   cooling can offer the right technology for the right situation. I'm not one to put a square peg in a round hole," he said. "If there's a lot of glass, carpet treatments and low mass, that will make it difficult to be the right application. There's no doubt you're paying a premium in this particular case. But you have to have it in the back of your mind when it may work. You need to think of it in terms of life-cycle costs of your building.