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Why Does Plastic Resin Drying Use So Much Energy in Injection Molding Plants?

2026/09/09 By le zhan

Why Does Plastic Resin Drying Use So Much Energy in Injection Molding Plants

In the daily operations of an injection molding plant, drying plastic resin often consumes the most energy because a dehumidifying dryer does more than heat plastic pellets once. It must continuously heat the resin, circulate large volumes of air, remove moisture, regenerate the dehumidifying medium, and typically also maintain the material’s temperature. At the same time, it awaits processing in the injection molding machine. This complex operating pattern creates a significant energy-efficiency challenge. Even after the material reaches the required dryness level, the dryer may continue running its heaters and blowers at high power.

Topstar’s TCDE energy-saving dehumidifying dryer effectively addresses this high energy consumption issue by combining variable-frequency control, heat recovery, constant-temperature maintenance logic, and an anti-overdrying function. Under applicable operating conditions, this comprehensive energy-saving strategy can achieve overall energy savings of up to 60%.

Energy Consumption in the Plastic Resin Drying Process

A dehumidifying dryer does not simply remove moisture by heating the resin. It heats the process air and forces the airflow through the material bed, causing moisture to migrate from inside the pellets into the airflow. For hygroscopic engineering plastics, this process can last for several hours.

The basic heat requirement can be understood using the following formula:

Heat requirement ≈ mass × specific heat capacity × temperature rise

As resin throughput increases, the mass of material the dryer must heat per hour also increases. Similarly, higher drying temperatures increase the temperature difference between ambient conditions and the required process temperature. As a result, large hoppers create a significant electrical heating load during continuous operation.

Energy Consumption in the Plastic Resin Drying Process

Plastic Resin Drying Requires Additional Energy to Generate Low-Dew-Point Air

For PA, PET, PC, PBT, and other hygroscopic plastics, heating alone is insufficient. These polymers not only retain moisture on their surfaces but also absorb moisture into their interiors. Therefore, dehumidifying dryers must use dry air with an extremely low dew point to create a strong moisture-transfer gradient.

In honeycomb desiccant wheel dehumidifying dryers, the dryer continuously processes two air streams:

  1. Process air: Used to dry the material;
  2. Regeneration air: Used to remove moisture adsorbed in the dehumidification rotor.

The regeneration process requires heat.

This means a portion of the electrical energy the system consumes is not used to heat the pellets, but to restore the dehumidification capacity of the system.

Plastic Resin Drying Requires Additional Energy to Generate Low-Dew-Point Air

Power is Also Required to Keep the Blower Running Continuously

The dry air must flow through the following path:

Dehumidification section → Heater → Drying hopper → Return air circuit.

A fan or blower generates this airflow.

In traditional fixed-speed systems, the blower may run at a power level close to its rated output even when the actual drying load is low.

For example, the machine may require maximum airflow during the initial stage. However, after a few hours, the resin may have warmed up and approached the target moisture content. If the blower and heating system continue to run at the same output power, some energy consumption becomes unnecessary.

Power is Also Required to Keep the Blower Running Continuously

Energy Waste Occurs When Production Demands Do Not Match Drying Demands

Material consumption rates in injection molding production rarely remain absolutely constant. Injection molding machines may experience downtime for mold changes, low-load operation, maintenance waits, or production interruptions. Material consumption may fall below the dryer’s designed processing capacity.

However, a large amount of hot resin may remain inside the dryer at this time. Even when very little new material enters the hopper, traditional systems may continue to supply the full volume of heated drying air. This leads to two problems:

Unnecessary energy consumption and over-drying.

Over-drying does not simply mean that the material becomes “extremely dry.” Certain materials may undergo undesirable changes after prolonged exposure to high temperatures. Therefore, an efficient drying system should adjust to actual material requirements, rather than running at maximum output power throughout the entire production shift.

Topstar Energy-Efficient Dehumidifying Dryer—Reducing Energy Consumption in Plastic Resin Drying

Topstar’s energy-saving solution does not rely on a single component; it achieves energy savings by reducing consumption across multiple stages of the drying cycle.

The TCDE Energy-Efficient Dehumidifying Dryer integrates the following features:

Variable-frequency control, heat recovery, temperature maintenance, and protection against over-drying.

Depending on specific operating conditions, this comprehensive energy-saving strategy can achieve overall energy savings of up to 60%. It also features a 7-inch touchscreen for operation and alarm logging, weekly scheduled start/stop functions, and RS485/MODBUS RTU communication, simplifying operation and control.

Topstar Energy-Efficient Dehumidifying Dryer

Achieving Energy Savings Through Variable Frequency Control

Topstar’s energy-saving dehumidifying dryer utilizes variable frequency control technology, which reduces motor output power when full airflow is not required.

This adjustment is particularly effective after the initial drying phase.

During startup, the material requires significant heat input for heating and dehumidification. Once the resin reaches a stable drying state, the energy required to maintain that state is lower than the energy required to heat it from ambient temperature to that state. Variable-frequency control lets the equipment adjust to actual demand, avoiding unnecessary full-speed operation.

Our energy consumption test data also shows that, over a recorded nine-hour operating period, equipment configured with variable-frequency control had lower cumulative energy consumption than comparable equipment without this feature.

Heat Recovery During the Drying Process

Waste heat discharge is another major source of energy waste.

Conventional dryers often exhaust hot air directly after consuming electrical energy and generating heat. If subsequent processes require reheating fresh air, this effectively repeats the same energy consumption cycle.

Topstar combines variable-frequency operation technology with heat recovery technology.

The system uses a heat exchanger to capture useful thermal energy during drying and cooling and transfer it to the incoming airflow at the right time.

This reduces the need for additional electric heating.

For compact 3-in-1 dehumidifying dryers with a processing capacity of 100 kg or less, Topstar employs an air-cooled configuration equipped with a multi-layer plate heat exchanger. This design offers two practical advantages:

No need to connect cooling water, simplifying installation and equipment relocation
Recovering thermal energy generated during drying and cooling improves energy efficiency.

Utilizing Constant-Temperature Maintenance Instead of Repeated Full-Power Heating

Once the resin has completed the primary drying phase, it typically no longer requires the high heating power needed during the initial heating stage. The TCDE energy-saving dehumidifying dryer’s insulation or constant-temperature maintenance function alters the operating strategy after drying is complete.

Instead of continuing full-power drying, the system maintains the resin at an optimal thermal state while consuming less energy. This helps avoid the following common cycle:

Full-power heating → Unnecessary heat loss → Temperature drop → Full-power heating again

By maintaining the material at an optimal state, the system reduces the need for repeated heating.

This feature is particularly valuable when the injection molding machine experiences temporary shutdowns or intermittent resin consumption.

Improving Energy Efficiency During the Drying Process

Plastic resin drying consumes so much energy because it requires simultaneous resin heating, air heating and circulation, dehumidification system regeneration, and maintaining the material at the drying temperature for extended periods.

Topstar’s energy-efficient dehumidifying dryer addresses these energy-waste issues by integrating variable-frequency control, heat recovery, temperature maintenance, and over-drying prevention features. Under optimal operating conditions, this equipment can achieve energy savings of up to 60%. The most effective way to reduce drying energy consumption is not simply to lower the drying temperature, but to have the dehumidifying dryer precisely provide heat, airflow, and regeneration capacity based on the material’s actual drying requirements.

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