Consider optional features that reduce energy costs. Most of them are inexpensive and easily pay for themselves (table 1). A few examples of energy-saving features are as follows.
More Insulation. If you are considering a new oven, add 1" or 2" of additional insulation to the oven walls. This will make the oven more efficient and is not very expensive, yet it can save you several thousands of dollars over the life of the equipment. An additional benefit is improved temperature uniformity of the heated workspace and, therefore, your product.
Door Limit Switch. When the door on a batch oven is opened and closed to load and unload the parts, the temperature drops temporarily as heat is lost out the opening. This causes the burner (or heaters, in the case of electric heat) to go to high-fire for several minutes while the door is open. This wastes a great deal of heat and fuel. A door limit switch can be used to turn the burner to low fire (or turn the electric heaters off) while the door is open, which can save tens of thousands of dollars over the life of the equipment. Considering the low cost of this device ($300 or so), it is a must-purchase item.
Direct-Drive Recirculation Blower. The oven recirculation blower is an often-forgotten source of energy consumption on convection ovens. Look for an oven supplier that offers direct-driven blowers rather than belt-driven. Belt-drive losses are commonly in the 5 percent to 10 percent range, which translates into roughly $0.30 per hour for a 7.5 hp blower operating at 500°F (260°C), or $1,248 per year assuming two-shift operation. Because a direct-drive blower is driven directly off the motor shaft, there is no belt drive. Another benefit of this blower style is low maintenance as there are no belts to replace. It is also much quieter than belt-driven blowers.
High Efficiency Recirculation Motor. Use a high efficiency motor on your recirculation blower, especially if it is 20 hp or larger. A typical high efficiency motor is 6 percent more efficient than a standard-efficiency motor, and will provide significant savings. For example, a 20 hp high efficiency motor can save $0.50 to $1 per hour and usually will pay for itself within the first year of operation.
Keep Load Carts and Racks as Light as Possible. If your parts are carried into the oven on load carts or racks, design them to be as light as possible. The cart or rack is heated up along with your parts, and this requires additional heat energy. The heavier the cart or rack, the more heat energy will be required, and the higher your operating cost.
Follow a Regular Maintenance ScheduleThe importance of maintaining and properly adjusting your oven equipment cannot be overemphasized and will significantly impact your energy costs.
Be Sure Your Burner Is Adjusted Properly. A burner that is firing too rich (too high gas/air ratio) will consume more gas. Set the burner up with the correct gas pressure and combustion airflow rate as stated in the equipment manual. The burner should be adjusted so you see blue flame with only slight yellow.
Clean the Burner and Combustion Blower Regularly. Over time, the combustion blower will become dirty and inefficient, resulting in improper combustion. This will make your burner fire at a higher rate to maintain the oven setpoint temperature, and consume more gas, which costs you money. Consider a combustion air filter to help keep the blower clean (figure 2).
Replace Worn Door Gaskets. Worn door gaskets can leak hot air, which wastes money. Keep replacement gasket material in stock and replace it whenever necessary. This also will improve your oven temperature uniformity by preventing cold air from leaking into the heating chamber and affecting your product. Considering the low price of gasket material, it is money well spent.
Adjust Your Exhaust Blower Properly. Most exhaust blowers have a manual damper to adjust the flow. In order to meet National Fire Protection Agency (NFPA) codes, the damper should be designed with a stop or cut-away to prevent it being fully closed. You should only open it more than this if necessary for your specific heating process (to exhaust moisture from the heating chamber, for example). If the damper is open more than necessary, you will be wasting energy.
Your oven doesn’t have to cost a fortune to operate. With a little planning and the use of energy-saving features, a properly designed oven system will save you money.