THE OWNER BUILT HOME & HOMESTEAD
(Page 12 of 15)
January/February 1971
By Ken Kern
The ancient Romans, and later Count Rumford and Ben Franklin, and now heating engineers and physiologists have speculated on the heating process in relation to health and fuel economy. From all available evidence, I am reasonably directed toward using radiative means of heating rather than convected, warm-air types. It is important to realize that the purpose of heating a building is not to put heat into the occupant, but to keep him from losing heat. We are comfortable when we give off heat effortlessly at the same rate that we produce it. The only purpose of a heat-system is to aid the body's mechanism in maintaining balance between its rate of heat loss and its rate of heat generation.
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In the case of convected heat, the air-temperature in a room must reach 68 to 70 degrees F. for basic comfort; yet this temperature unfortunately is too high for us to emit heat rapidly enough. Our pores tend to "open" (through certain nervous and endocrine reactions) and more blood flows to the surface of the body, so that it can radiate more heat to the outside air. The result is a feeling akin to exhaustion as on a hot, humid day.
Comfort at lower air temperatures can be achieved by using radiative heating methods—thereby promoting the generation of heat within the body, and the exhilaration that goes with brisk activity. In a conventionally heated room, hot air rises from the convector (usually located beneath a window) and then sweeps across the ceiling and falls down the opposite wall. Temperatures at the ceiling level are highest where they actually do the least good, comfort-wise. A temperature of 100 degrees at the ceiling may produce only a 70 degree temperature at the living zone! A smaller range of air temperature from floor to ceiling is possible by using radiant panel heating methods. Where a 70 degree air temperature is required in convected heating, less than 65 degrees is required using radiative means, resulting in a 30% saving in fuel consumption.
The sun or an open fire emits radiant heat rays. The Romans, by circulating hot gases from charcoal fires through ducts to warm walls and floors, created radiant heat 2000 years ago in England. The traditional Korean "ondol" heating adapts the radiant principle; combustion gases from the kitchen stove flow through a labyrinth of chambers under the floor-slab to a chimney at the far end of the room. Radiant heat then comes from the floor. Frank Lloyd Wright revived radiant heating in the Western world in developing the "gravity heat" system. He used it (1937) in the Johnson Wax Building.
About 90% of currently installed radiant panels use hot water as a circulating medium, but a hot air radiant system is definitely less expensive to install and operate. Most water systems use steel or copper pipes buried an inch or two beneath the top surface of the concrete floor slab. This is no doubt less costly than ceiling or wall installations, but the hot-water radiant ceiling has many points in its favor. In order to achieve maximum efficiency, the water temperature in a radiant floor slab must be maintained at from 80 to 90 degrees. Yet a floor temperature of over 70 degrees will cause a rise in foot temperature and consequently an undesirable disturbance of normal heat emission from various areas of the body, since the temperature of the lower extremities is normally several degrees lower than that of the trunk and upper areas.
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