Radiant Heat Links
2/28/20
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KSU Abstract Research - Projects Archive - ASHRAE - RP-1037 RP 1037: Development of Simplified Methodology to Incorporate Radiant Heaters Over 300 deg.F into Thermal Comfort Calculations
Kirby S. Chapman, Project Manager chapman@ksu.edu Abstract: High-temperature radiant heaters - those with a surface temperature greater than 300 deg.F - typically are applied in large, open, and occupied spaces such as warehouses and aircraft hangers. These heaters provide an efficient means of delivering thermal comfort to specific work stations without having to condition the entire occupied space. Highly efficient thermal comfort can be delivered because radiant heaters focus thermal energy, and therefore thermal comfort, directly on the occupants, rather than controlling room temperature as do other heating systems. The goal of this research project was to develop a simplified thermal comfort methodology that reliably calculates the thermal comfort effect, as expressed as the operative temperature, of high-temperature radiant heaters. The developed methodology would be an add-on module to the already-existing Discrete-Ordinates Radiation Solver used in the Building Comfort Analysis Program (BCAP), which was developed under ASHRAE project RP-657 (Chapman, 1994). This research report contains: 1) a study of the types of high-temperature radiant heaters and mathematical heat transfer characteristics of each; 2) an examination of radiation models; 3) a review of thermal comfort and radiant heat transfer measures; 4) an explanation of the developed model; and 5) several case studies where the model is applied. The developed method can be used as a design tool for sizing and placing high-temperature radiant systems, possibly in combination with other heating systems as it encompasses a wide range of building materials and operating conditions. This page was last updated: 06/02/2003 12:40 PM
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HOW INFRA-RED WORKS (from Solaronic, Inc.) The amount of radiation produced by a perfect radiator is expressed by the Stephan-Boltzman Law, where:
For ordinary objects, non-perfect radiators, Q is reduced by multiplication of the object's emissive power (always less than one). Thus, at normal temperatures the amount of infra-red radiation produced by an object is relatively low, but as the temperature is increased, radiation increases significantly. For example: An object at 80 deg.F (540 deg. absolute temperature) with an emissive power of 0.85 will produce 124 BTUH/sq.ft. When its absolute temperature is doubled to 1080 deg. its output is increased sixteen fold to 1,984 BTUH/sq.ft. If its absolute temperature is quadrupled to 2160 deg. its output increases two hundred and fifty six fold to 31,744 BTUH/sq.ft.
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Useful Links and Helpful Comments: Thermographic Camera with good Wikipedia overview ASHRAE Technical Committee 6.5 - Radiant Space Heating and Cooling (not maintained) Dynacote A company promoting a coating developed to sheild space vehicles to increase(?) emissivity for fireplaces, chimneys and stoves.* Tulikivi take on radiant heat. Would a masonry heater meet the ANSI Z83.19-2001 standard for high intensity infrared heaters - a "radiant coefficient of at least 0.35"? A masonry heater might be a nice warm surface increasing the mean radiant temperature in a room but, as a source heating a remote space or surface as claimed in the piece on heat distribution a warmers source like a stove or especially a fireplace would be more effective. Remember that radiant energy is proportional to the fourth power of the absolute temperature of the source. The amount of radiation produced by a perfect radiator is expressed by the Stephan-Boltzman Law. As measured by the actual heat in BTUs delivered, most of the heat from a masonry heater is delivered by convection - not radiation.
Elstein Electric Ceramic Radiant Burners Critique of Green Fireplace article by an engineer Jim Hoffman - expert at the high tech end of the IR spectrum Gerald Maxwell - PhD with a Rumford http://www.nfesc.navy.mil/pub_news/tds/7337tds.htm See email dated 7/5/03 to authors, Stephen Cannon and Michael Rocha. Simplified Methodology to Incorporate Radiant Heaters Over 300 deg.F into Thermal Comfort Calculations Kirby S. Chapman and Wen Wang
High Intensity vs Low Intensity Radiant Heaters Emissivity table based on temperature Emissivity table based on wave length See also Heating, Ventilating and Radiant Heat * |
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