Radiant Heating Panel Thermal Analysis
Prepared by: Tim Fleury, Harvard Thermal, Inc. October 6, 2003.
Prepared for: Crown Hill Stone, inc. Analysis Objective•Generate a thermal model of the panel and heating fluid to determine the heat added to the room per panel •Document the thermal analysis results Major Assumptions•Plastic housing on concrete constructed of Polystereor equivalent material with thickness of 0.093 inches •PEX tubing wall thickness = 0.062 inches •PEX tubing deforms to fill the groove in the concrete •Sub flooring consists of ½ inch thick plywood with no insulation •Room temperature remains constant at 68 °F •No material on top of concrete •Radiation emissivity is 0.8 for all surfaces Thermal Conductivity Test-Procedure•The purpose of the test was to determine the thermal conductivity of the concrete •A constant heat load (1.62 Btu/Hr) was applied to one surface ofthe concrete while the opposite surface was clamped to a coldplate •Heat load consisted of a resistor attached to a ¼ inch thick aluminum plate •Thermal grease was used at all interfaces •The sample was heated to a stabilized temperature of 63.5 °F •Coldplate was maintained at a constant temperature of 53.7 °F •A thermal model was generated to verify the test results •Based on the results, the thermal conductivity of the concrete was calculated to be 0.381 Btu/Hr-ft-°F  Specific Heat Test-Procedure•The purpose of the test was to determine the Specific Heat of the concrete •Panel sample was heated to a stabilized temperature (63.4 °F) then allowed to cool down with no heat applied •Coldplate was held to a constant temperature of 53.0 °F •The heat source was then turned off •Temperature difference between the heat source area and cold plate interface was monitored during the cool down period •Based on the results, the Specific Heat (Cp) of the concrete wascalculated to be 0.19 Btu/lbm-°F  Specific Heat Test-Results•Based on heat transfer formula: (T-Tcp)/(To-Tcp) = e –(t/RC) •At t=30 minutes; Tcp = 53 °F, To = 63.4 °F, T = 57.3 °F •Thermal resistance of the sample (extracted from thermal conductivity test) = R = 6.0 Hr-°F / Btu (11.4 °C/W) •The Capacitance, C, = Specific Heat (Cp) x Weight •Weight of concrete sample = 0.489 lbs (222 gms) •Based on the results, the Specific Heat (Cp) of the concrete wascalculated to be 0.19 Btu/ lbm-°F Radiant Panel Model•A model of the radiant panel was generated using TAS (Thermal Analysis System) software •Model included the panel, water flow, plywood subfloor, and convection and radiation •Water inlet conditions were: •0.5 gpm, 90 °F water •0.5 gpm, 140 °F water •2.0 gpm, 90 °F water •2.0 gpm, 140 °F water Material Properties Thermal ConductivityNumber 1 2 3 4 Units Discription Pex Tubing Concrete Plywood Polysterene X conductivity 0.018300 0.031750 0.066600 4.580E-03 BTU/(hr-in F) Y conductivity 0.018300 0.031750 0.066600 4.580E-03 BTU/(hr-in F) Z conductivity 0.018300 0.031750 0.066600 4.580E-03 BTU/(hr-in F)        Summary•The Thermal Conductivity (k) of the concrete was tested to be: k = 0.381 Btu/hr-ft-°F •The Specific Heat (Cp) of the concrete was tested to be: Cp = 0.19 Btu/lbm-°F •The heat transfer rate to the room, per panel, was analyzed to be: 0.5 gpm, 90 °F water:12.1 Btu/hr-ft2(38 W/m2) 0.5 gpm, 140 °F water: 41.9 Btu/hr-ft2(132 W/m2) 2.0 gpm, 90 °F water: 14.9 Btu/hr-ft2(47 W/m2) 2.0 gpm, 140 °F water: 42.7 Btu/hr-ft2(135 W/m2) •The equivalent heat transfer coefficient to the room, per panel, based on a temperature differential between the inlet water temperature and room temperature: 0.5 gpm, 90 °F water:0.551 Btu/hr-ft2-°F(3.13 W/m2-°C) 0.5 gpm, 140 °F water: 1.905 Btu/hr-ft2-°F(3.30 W/m2-°C) 2.0 gpm, 90 °F water: 0.679 Btu/hr-ft2-°F(3.85 W/m2-°C) 2.0 gpm, 140 °F water: 1.941 Btu/hr-ft2-°F(3.37 W/m2-°C) •Half of the heat is transferred through the subfloor •Adding insulation to the subfloor will improve the heat rate to the room
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