- list the types of metering devices used in high-pressure chillers.
- list the types of refrigerants typically used in lowpressure chillers.
- state the type of compressor used in low-pressure chiller systems.
The Correct Answer and Explanation is :
1. Types of Metering Devices Used in High-Pressure Chillers
- Thermostatic Expansion Valves (TXVs): Commonly used in high-pressure chillers to regulate refrigerant flow by sensing superheat at the evaporator outlet.
- Electronic Expansion Valves (EEVs): Offer precise control over refrigerant flow and improve efficiency by responding quickly to changing load conditions.
- Fixed Orifice Devices: Simple devices with no moving parts, typically used in smaller systems with stable operating conditions.
- Capillary Tubes: Used in smaller systems, though less common in modern high-pressure chillers due to limited control and efficiency.
2. Types of Refrigerants Typically Used in Low-Pressure Chillers
- R-123 (Dichlorotrifluoroethane): A low-pressure refrigerant with relatively low ozone depletion potential (ODP), used in older systems.
- R-514A: A modern alternative with low ODP and global warming potential (GWP), offering high efficiency.
- R-11 (Trichlorofluoromethane): Historically used, though phased out due to high ODP.
- R-113: Another older refrigerant, also phased out for environmental reasons.
3. Type of Compressor Used in Low-Pressure Chiller Systems
Centrifugal Compressors are commonly used in low-pressure chiller systems.
Explanation:
Centrifugal compressors are widely employed in low-pressure chiller systems due to their efficiency and capability to handle large cooling loads. These compressors use centrifugal force to compress refrigerant vapor. Inside the compressor, an impeller spins at high speed, accelerating the refrigerant outward and increasing its velocity. The kinetic energy is then converted into pressure energy as the refrigerant slows down in the diffuser.
Centrifugal compressors are preferred for low-pressure systems because they perform well with the relatively low pressures and large volumes of refrigerants such as R-123 or R-514A. They offer high efficiency at part-load conditions, making them suitable for large-scale applications like commercial and industrial cooling. Additionally, their simple design and fewer moving parts lead to lower maintenance requirements and extended service life.
In conclusion, the compatibility of centrifugal compressors with the thermodynamic properties of low-pressure refrigerants, coupled with their efficiency and reliability, makes them the standard choice for these chiller systems.