Some manufacturers suggest you can save energy by heating the furnace from room temperature in just one hour at the start of each shift. Does this approach actually reduce energy consumption? Let’s take a look at whether this promising claim holds up.

One shift – and turn off

If you only run one shift per day and turn the furnace off overnight instead of leaving it in so-called hot store mode, it’s highly unlikely that you’re actually saving any energy.

Incomplete heating leads to quality issues

Heating the furnace from room temperature to almost 700 °C in only one hour means furnace structures won’t be completely heated when production starts. This will cause quality fluctuations, resulting in glass rejections. In the end, you’ll waste more glass and effort from the uneven heating. Moreover, constantly ramping the temperature up and down will increase wear and tear of the furnace significantly. This negatively affects performance of your furnace over time and leads to higher maintenance costs.

Damage to the furnace from rapid heat-up

Even more important, rushing the heating process puts extreme stress on the furnace’s steel structures. Over time, you’ll see significant wear and tear which will shorten the furnace’s lifespan and increase maintenance costs. A controlled heat-up is essential to prolong the lifetime of your equipment.

What’s the better approach?

Instead of turning the furnace off, we recommend keeping it in hot store mode at around 550 °C. This protects the furnace’s structures while ensuring it is quickly ready for stable production.

In fact, the energy used in hot store mode, combined with what is required to reach production temperature, is usually less than the energy consumed by turning the furnace off completely and reheating from room temperature the next morning.

The only way that turning the furnace completely off would save energy is if there are significant leakages in the furnace, for example, from ceramic roller openings.

In this blog, you will find some more practical tips on cutting energy consumption in tempering line operations.

What’s the conclusion?

Turning a tempering furnace off brings no real energy savings, more wasted glass and unnecessary stress and wear on the furnace. Not exactly a tempting trade-off.

While modern tempering technology does offer real opportunities for energy savings, misleading claims like this one can easily steer glass processors down the wrong path.

When evaluating furnace energy efficiency, make sure you base your decisions on facts – not on overly optimistic claims that can end up costing you more. Reach out to a knowledgeable and trustworthy partner who can help you cut through the noise and avoid costly mistakes.

Check out our previous articles on other false energy-saving claims.

• Glass tempering energy consumption video
• Tempering energy-consumption claims – don’t fall for them
• Glass tempering energy consumption: If the numbers look too good, they probably are
• Glass tempering energy consumption: how not to be misled by false data (Part 1/2)
• Glass tempering energy consumption: how not to be misled by false data (Part 2/2)
• 3 ways to reduce energy consumption in glass tempering
• Understand your tempering line energy consumption – then minimize it effectively
• The Volkswagens of the glass tempering business

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