When investing in a new tempering line, energy consumption is always a critical consideration. Why? Because the tempering process is energy-intensive, and energy costs are a significant part of the overall operating expenses. That's why tempering equipment manufacturers are constantly striving to improve energy efficiency. However, this drive for better energy performance has led to some misleading claims about energy consumption in the market.
To put things into perspective, we can draw a parallel with the automotive industry. Over recent years, car manufacturers have focused on creating vehicles that consume less fuel and produce fewer emissions. This trend has been driven by stricter regulations and rising fuel costs. While these innovations have led to more environmentally friendly cars, some manufacturers have been caught exaggerating their performance numbers to make their cars appear more fuel-efficient than they actually are. Similarly, the glass tempering industry faces similar challenges with inflated energy-saving claims.
This is why it's important to dig deeper into the specifics of energy consumption in the tempering process.
Understanding the Basics of Tempering
Glass tempering involves two main stages: heating and quenching. First, the glass needs to be heated to a temperature well above its transition point of +567 °C but below the softening point of +710 °C. In most cases, the glass is heated to a minimum of +630 °C to achieve a high-quality tempering result. Once heated, the glass undergoes rapid cooling (quenching) to below the strain point of +510 °C. Only after this phase can the glass be cooled to a safe handling temperature.
Key Terminology for Energy Consumption in Tempering
When discussing energy consumption, it’s crucial to understand the key terms used in the industry. While these terms may vary slightly from company to company, it's essential that all figures provided include everything from heating to cooling. This includes energy consumption in the heaters, convection, as well as energy losses from the furnace and blowers. Additionally, ensure that the data reflects continuous, real-world production conditions.
Here are the most common terms you'll encounter:
Connected Power: This refers to the total power of all electrical components connected to the tempering line. Contrary to common belief, connected power doesn’t directly correlate with energy consumption. A high connected power is necessary for the furnace to process large loads without delays, allowing it to recover quickly between production cycles.
Heating Power: The total power required to heat the furnace, including both heater power and convection energy.
Quenching Power: The power used by the blowers to cool the glass during the quenching process.
Energy Loss: This refers to the wasted energy that radiates through the furnace walls. However, in modern furnaces with good insulation, energy loss due to radiation is minimal compared to total energy consumption.
Energy Consumption in Production: This is the total energy consumed during production, typically measured in kWh/m². This metric includes heating, quenching, and energy loss from the furnace.
How to Evaluate Energy Consumption Data Accurately
When you’re evaluating energy consumption data, be cautious of misleading claims. Here’s a quick checklist to ensure you’re getting reliable information:
Always Compare: Compare the provided energy consumption figures to the minimum energy requirements necessary for your production needs.
Account for All Components: Make sure the data you receive includes all relevant factors like heating, quenching, and energy loss.
Know the Minimum Requirements: A good rule of thumb is 0.475 kWh/m²*mm, which is the minimum energy required for heating the glass. For example, for 10 mm glass, this would mean a minimum of 4.75 kWh/m² is needed just for heating. If the data provided shows lower energy consumption, you can be sure that something is off.
In the next part of this blog series, I’ll dive deeper into the physics behind these numbers and explain the heating and cooling process in more detail. With this knowledge, you’ll be able to better evaluate the energy efficiency of tempering lines and avoid being misled by false data.
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