Radiant Cooling an Option to Conventional A/C
The panel included Mark Evans, product manager for Viega NA; Dick Bourne, director of the University of California, Davis Western Cooling Efficiency Center; and Larry Drake, RPA executive director.
Simply defined, radiant cooling systems rely on chilled water pipes to distribute cooling throughout a building rather than a conventional system that uses chilled air and ductwork.
Radiant cooling systems rely mainly on the direct cooling of occupants or objects by radiative heat transfer (such as the sun’s warming effect on an object in its direct path) because the pipes, which are commonly run through ceilings, maintain the surface at temperatures of about 65°F. Through radiative heat transfer, people in the room will emit heat that is absorbed by the radiant cooling surface.
To manage indoor humidity levels and air quality, a separate ventilation system to supply fresh air is needed.
According to www.toolbase.org, “There are at least three methods of delivering chilled water in radiant cooling systems. The panel system is the most common of these. Aluminum panels that carry tubing can be surface-mounted or embedded on floors, walls, or ceilings. Another, the capillary tube system, consists of a mat of small, closely spaced tubes that are embedded in plastic, gypsum, or plaster on walls and ceilings. Or, similar to hydronic heating systems, a concrete core with embedded tubes can provide the conduit and thermal storage capacity for a cooling system.
“In each of these systems, the water is mixed with glycol and cooled by an air-to-water heat pump, a cooling tower, a ground-source heat pump, or even well water. Because the radiative surface is typically a whole floor or ceiling surface, the water can be as warm as 65° and still provide comfort.”
THUMBS-UP TO RADIANT COOLINGThese types of radiant cooling systems fall into the new green technologies classification, which is why they are becoming so popular, according to Evans. “Radiant cooling is becoming more mainstream because people are building more thermally efficient buildings,” he said. “And what is the most efficient comfort system available? The one that you never have to turn on.”
He said that radiant cooling works best in areas of the country where daily average temperatures average 65 degrees or below. In these areas, radiant cooling “adequately services the sensible cooling load,” said Evans.
Evans pointed out that in radiant cooling systems, a ¾-inch pipe can transfer as much energy as a 14-inch duct, in part because the goal of radiant cooling is to cool an object or occupant rather than an entire space. Radiant cooling systems can be installed in suspended ceiling panels or embedded capillary tubes in the floor, wall, or ceiling.
Evans said that radiant cooling is ideal for building retrofits where spot cooling is needed for certain areas. “For example, older buildings that have new computer rooms require more cooling,” he elaborated.
Bourne said that radiant cooling is growing but is still considered a niche market. One of those niche markets is big box retailers, who often need to keep a close control over climate conditions within their buildings. Bourne said this niche provides an excellent opportunity for contractors selling radiant cooling because:
• Of the high internal heat gains during long cooling seasons;
• Operating schedules often include 24/7 schedules, contributing to high-energy costs;
• There are large open spaces with very little zoning;
• There are significant numbers of ‘hard floors’;
• Retailers are looking for cost-effective energy solutions;
• New technologies can often be rolled out quickly when a building changes ownership or use.
“There is potential for business owners to save 45 percent or more in energy costs using radiant cooling,” Bourne said.
He told RPA members about a case study involving a California convenience store that utilized a radiant cooling system over conventional air conditioning. The energy cost savings paid for the system within the first year. “This was very unusual for a prototype store,” Bourne said. “But the maximum payback period is usually only three years.”
Drake followed Bourne and said he prefers to think smaller when it comes to radiant cooling systems. “It’s hard for me to think in terms of 100,000 square feet,” he said. “I think of smaller, simpler systems.”
Drake discussed two homes he owned in Minnesota where he had installed radiant cooling and remarked, “I have never been more comfortable with any other type of cooling system.”
But he said that in order to get the most out of a radiant cooling system, building occupants have to “learn how to live with the system.”
“These are just like radiant heating systems,” he said. “You have to set the thermostat and leave it. The system needs to run at a constant load.”
For more information, visit www.radiantpanelassociation.org.
Publication date: 09/10/2007