## Canada Builds |

BUILDINGS

Angle of Incidence

Ashrae Window Test

Doors

Exposed Bldg Face

Fire Protection

Fire Walls

Floors

Footings

Foundations

Height Area and Use

Means of Egress

Mezzanines

Newton's Cannon

Roofs

Thermal Massing

Vegetation

Walls

Ventilation

ENERGY

Solar Energy

Solar PV Panels

Geothermal Energy

Cost of Energy

RESOURCES

Measuring Height

Size a Radiator

Size a Wood Beam

Size a Steel Beam

Deflection Calculations

TANGENTS

The Area of a Circle

Stonehenge

World Population

Bouncing Ball

The Number One

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Angle of Incidence

Ashrae Window Test

Doors

Exposed Bldg Face

Fire Protection

Fire Walls

Floors

Footings

Foundations

Height Area and Use

Means of Egress

Mezzanines

Newton's Cannon

Roofs

Thermal Massing

Vegetation

Walls

Ventilation

ENERGY

Solar Energy

Solar PV Panels

Geothermal Energy

Cost of Energy

RESOURCES

Measuring Height

Size a Radiator

Size a Wood Beam

Size a Steel Beam

Deflection Calculations

TANGENTS

The Area of a Circle

Stonehenge

World Population

Bouncing Ball

The Number One

The work of
Stefan and
Boltzmann
in the late 1880's proved that the amount of radiation emitted from a 'perfect radiator' or
'blackbody' is proportional to the fourth power of the Kelvin Temperature. It is possible to use the Stephan-Boltzmann law of radiation to size a
radiator
with the excel sheet below. The equation can be derived as follows:

H = σ (T_{1} ^{4} - T_{2} ^{4})

Where:

H = Heat radiated in kilocalories per second per square metre or kcal / sec m^{2
}T_{1} = Kelvin Temperature of the radiating body

T_{2} = Kelvin Temperature of the surroundings

σ = Radiation Constant with a value of 1.35 x 10 ^{-11 }kcal / sec m^{2
}K^{4} (or 5.67 x 10 ^{-8} W / m^{2} K^{4})

Example:

A radiator is operating with a surface temperature of 180 °F with an effective
surface area of 10 square feet. How many Btu's per hour (or Btuh) will the
radiator emit to a room whose average temperature is 70 °F (21 °C)? Use the
excel worksheet below to place these values into the equation.

A note on the chart below - You can type values into the chart below to see and compare calculations. Type only the red numbers. If you type another cell, the formula will get erased. If this happens, simply hit F5 or 'refresh the page'.

In essence, the information you get from this calculation is the amount of btu/hr that a radiator of a certain size at a certain tempertature will give off. For instance, a radiator with a surface area of 10 square feet that is heated up to a temperature of 180 degrees farenheit will emit about 6000 btu/hr into a surrounding area (i.e. a room) that is 70 degrees farenheight. We could convert to metric and use units other than those listed above. First though you want to get a sense of what is going on and what is being described in common language. Metric makes it much more complicated. Especially when you go out to buy a radiator or a furnace to see that they are sold and advertised based on their 'btu' output. For this reason, you might be better off using imperial calculations and converting once finished.