High Mass And Low Mass Construction

By John R. Hall

DENVER - The Radiant Panel Association (RPA) held the first of two RadFests in 2005. RadFest West was held in Denver April 26-27. Approximately 200 people registered for the event, which featured a trade show, "pit stop" product demonstrations, roundtable discussions, guest speakers, and two radiant courses and certification exam.

Ted Lowe, RPA secretary, told The News that the popularity of the daylong radiant courses - radiant basics and radiant precision - drew students from as far away as Alaska and New York. Besides students and contractors in attendance, a total of 56 suppliers and manufacturers displayed their products and services at the trades show.

RPA executive director Larry Drake (right) discusses high mass and low mass systems with Jeff Janetto of Northern Wholesale Supply, Long Lakes, Minn.

High Mass vs. Low Mass

Larry Drake, RPA executive director, hosted one of the roundtable discussions on the pluses and minuses of high mass and low mass construction. Besides Drake, there were radiant contractors from Oregon and New York, a wholesaler from Minnesota, and a manufacturer from Wisconsin.

High mass construction is characterized by concrete slabs, which have the ability to absorb and store a great deal of heat. Radiant systems can "pulse" heat to the concrete slab and the heat will, in turn, spread out over a large area.

Low mass construction is characterized by the inability to store heat. For example, a staple-up radiant floor or a radiant ceiling system does not have the ability to store heat. Constant circulation of warm-to-hot water is needed to maintain temperature.

"The reputation of high mass is that temperatures are hard to control," said Drake. "Most people who install systems in high mass don't understand how they operate."

Some notable characteristics of high mass were discussed at the roundtable, including:

High mass systems offer less design flexibility in architecturally challenging buildings.

High temperatures in slabs can create problems because of the buildup of heat and how to disperse the heat.

System designers often change plans without consulting the in-stalling contractor - and often don't take into account such factors as solar gain.

One contractor suggested that a good way to control temperatures in the concrete slab is to install floor thermometers. A wholesaler suggested keeping water temperatures in the tubing at 90 degrees F. Another suggestion was to tie in the secondary loops from other areas of the building to the primary loop in order to control room temperatures more effectively.

Drake said that low mass systems are easier to control than high mass systems. The roundtable attendees talked about staple-up systems combined with plates to evenly distribute the heat. "Staple-up without plates acts like a high mass system because it takes longer to heat up and cool down."

Most of the attendees combined staple-up with plates, however, there are circumstances where plates may not be necessary, such as in temperate zones where there are few big swings in temperatures.

One contractor said that he doesn't use plates throughout the system, only in areas where the occupants stand or sit for an extended period of time, such as the floor in front of a kitchen sink or around a toilet.

Publication date: 06/13/2005

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