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definition of insulation terms & calculations Post New Topic | Post Reply
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Posted: Apr 12, 2008 08:37 PM
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definition of insulation terms & calculations
the rate of measurement for construction insulation is the amount of heat flow through one square foot, per hour, per degree (*f) of temperature differential. this btu is expressed in either "K", "C","F",or "U" values..."C" Factor(thermal conductance): the measurement of heat flow through any single material greater/less than 1" is expressed: C=K/T... (note:K & C are the same for one inch of material)Example: if insulation thickness is required to meet C = 0.10, the calculation for polyurethane spray foam thickness would be as follows: T = K/C = 0.16/0.10 = 1.16 inches... "K" Factor(thermal conductivity): the heat flow measurement through one inch of any single homogeneous material, by lab tests is written: "K" = BTU/(hr)(sq. ft.)(*F/inch)... BTU (british thermal unit): the amount of heat required to raise the temperature of one pound of water one degree F. Btu equivalents: 1 therm=100,000btu 1 watt = 3.413 btu 1 kilowatt = 3,413 btu(aint math great?)1 cu ft of natural gas = 1,000 btu 1 gallon of fuel oil = 140,000 to 150,000 btu 1 lbs coal = 7,000 to 14,000 btu 1 cu ft mfg gas = 500btu... "U" Factor (overall coefficient of heat transmission): after total thermal resistance (RT) of the system is determined, the U value (or heat flow) can be calculated as follows: U=1/(RT) the U value is the measure of btu that will flow through a composite system (wall-floor-roof) per hour, square foot or surface, degree F temperature difference between the two sides fo teh system. U= btu/(hr)x(sq ft)x (degree F)... "R" Factor (thermal resistance): since K and C values change and become lower as the material insulation value increases, it is imposssible to add K and C values. therefore, R is the reciprocal of C, and is determined by dividing C into One, or by dividing the materials K factor into its thickness ("T") ,,,, R=1/C or R=T/K to find insulation thickness needed to achieve a specific r-rateing use formula: T=RxK,,, each material in a roof or wall assembly has a resistance value which, when added together, obtains the composite system's total resistance to heat flow... R1+R2+R3+R4+R etc = R total sunspots baby..sure had a real good time... |
