Ceiling systems can usually react fairly quickly to changing demands for heat, because of their relatively low mass. Downward convection from a warm ceiling is poor, however, leading to lower overall efficiencies and a stratum of cool air at floor level, a defect made worse by the infrared shadows that tables and desks cast on people's legs and feet.
Small, high-temperature infrared heat sources with focusing reflectors are highly effective if installed so as not to cast shadows. They are especially useful where high air temperatures cannot be maintained, as in large industrial buildings or even outdoors, where they can produce heat instantaneously when it is needed and beam it precisely to where it is needed. Open fires and stoves are less efficient radiant heat sources because of their omnidirectional, inverse-square radiation and because of the relatively large amount of fuel that they convert to warm air rather than radiant energy. Because of its thermal similarity to solar radiation, infrared heat from either low- or high-temperature sources feels very pleasant on the bare skin. Swimming pools, shower rooms, and bathrooms are particularly appropriate locations for such systems.
Our means for lowering the mean radiant temperature of an interior location are somewhat more restricted than our means for raising it. We cannot, for example, cool our bodies by exposing them to a small surface at a very low temperature. Whereas we can easily heat an electric filament or gas flame to a temperature a thousand or more degrees above body temperature, there are only a few hundred degrees with which to work between body temperature and absolute zero, and devices for producing very low temperatures are expensive to build and operate. Furthermore, a very cold surface quickly frosts over with moisture condensed from the air, thereby losing most of its effectiveness because of the insulating properties of the frost. Even a moderately cold surface becomes moist and unpleasant in warm summer weather, which is why we do not actively cool floors and ceilings except in rare cases when we can control the humidity at a level low enough to eliminate condensation. What we can do instead is to shade roofs, walls, and windows against the summer sun, surface them on the exterior with highly reflective coatings whenever practical, insulate them well, and provide enough thermal capacity in the interior surfaces of the building to ensure the maintenance of cool temperatures throughout the day. We can also, in some cases, open a building to the night sky, allowing our bodies and the warm surfaces of the building to radiate heat into space.
Our prototype building combines radiator and storage overhead and controls radiant flux by means of overhead shutters. This is inexpensive and effective yet it is so different people may not accept it in many kinds of buildings. In this case we intend to use blow-molded mats in the ceiling, pumping warm or cool water through from storage tanks as desired.
In many climates a Di-thermal roof can save 40,000 to 100,000 BTUs per square foot per year in heat. Compared to $.10 per kWh electric heating, this would save $1.20 to $3.00 per square foot per year. (With propane @ $1.10 per gallon savings are 50% as great.) During the cooling season the Di-thermal roof does all the cooling. It saves about 2 kWh per square foot per year or $.20 per square foot per year and more important replaces the capital cost of a compressor.
The success of the Di-thermal roof will likely depend on marketing the luxury of radiant heating and cooling as a necessity to save energy.
Source: Zomeworks. Text extracted by OCR from scanned document.
PDF: 2002-01-01-dithermal-roofs-2.pdf