This article examines the liquid injection system in scroll compressors, a crucial technique for reducing discharge temperatures in freezing applications. This method protects the compressor and ensures reliable operation under extreme conditions, such as the high compression ratios typical in low-temperature applications.
Purpose of the Liquid Injection System
The primary goal of liquid injection is to lower the refrigerant discharge temperature, protecting the compressor and enhancing performance in critical conditions. The system activates when discharge temperatures exceed 115 °C, maintaining them at safe levels around 95 °C.
System Operation
- Temperature-Triggered Activation
- The liquid injection process is controlled by a temperature sensor, thermostat, capillary tube, or solenoid valve.
- When discharge temperatures reach 115 °C, the solenoid valve opens to inject liquid refrigerant.
- Automatic Regulation
- Once the temperature drops to a safe level (e.g., 95 °C), the solenoid valve closes.
- If temperatures exceed 125 °C despite the system being active, the compressor’s temperature protector engages to prevent damage.
- Impact on Energy Consumption
- Activating the system slightly increases the compressor’s energy consumption due to the added refrigerant to compress.
- However, this is offset by the ability to handle higher compression ratios without overheating risks.
Technologies and Configurations
- Discharge Temperature Control (DTC) Valve
- The DTC valve eliminates the need for additional components like capillary tubes or solenoid valves.
- It directly detects discharge port temperatures and injects only the necessary amount of liquid refrigerant as required.
- Scroll Compressor Models
- Some scroll compressors are specifically designed for liquid injection.
- Others combine liquid and vapor injection, enhancing refrigerant subcooling at the condenser outlet and compressor protection.
- Advanced models feature wet vapor injection, simultaneously integrating liquid and vapor to optimize system efficiency.
- Compatibility with Inverter Technologies
- At high speeds, liquid injection significantly improves compressor efficiency and reliability.
- At low speeds, it may present drawbacks in terms of energy use, capacity, and adiabatic efficiency.
Benefits of Liquid Injection Systems
- Compressor Protection: Prevents overheating in demanding applications.
- Increased Reliability: Supports higher compression ratios without compromising performance.
- Design Flexibility: Adapts to various compressor configurations and technologies.
