Q. Please explain how to calculate the heat load capacity of a paint baking oven, using aluminum alloy wheels as an example. H.T.

A. Energy consumption in an oven is primarily related to radiant loss through the oven panels; energy required to raise the product, racks and conveyor to temperature; and exhaust losses. To determine the energy use, you will need to calculate these three factors and then add them to get the total.

Panel Loss
To calculate the loss of Btu/h through the oven panels, multiply the total square feet of oven panel surface area by the panel loss factor (see table) and then by the temperature difference between the oven start-up and the controller setting.

Formula: Square feet of oven surface × panel loss factor × temperature rise

Example

Oven Size: 20 × 50 × 10 ft (W × L × H)

Operating Temperature: 300°F

Oven Start-up Temperature: 70°F

Panel Thickness: 4 inches

Oven Surface Area

Sides: 10 × 50 = 500 × 2 sides = 1,000

Ends: 10 × 20 = 200 × 2 ends = 400

Top and bottom: 20 × 50 = 1,000 × 2 = 2,000

Total: 1,000 + 400 + 2,000 = 3,400 sq ft

Temperature Rise

300°F – 70°F = 230°F

Panel Loss

3,400 sq ft surface area × 0.35 panel loss factor × 230°F temperature rise = 273,700 Btu/hr

Product Loading
To calculate the Btu/hr required to support the product loading, multiply the total load (parts, rack, conveyor chain and trolleys) by the specific heat (Btu required per lb °F) by the temperature rise. The factor 0.226 is used for aluminum. Different materials will require a different multiplier, and the table below shows the specific heat values for different metals.

Read more: Calculating Oven Heat Load Capacity