Hotel Service Unit 11 Q5

The basic principles of refrigeration revolve around the transfer of heat from one location (the refrigerated space) to another (the environment). This process is achieved by utilizing a refrigerant, a substance that readily changes its state between liquid and gas, and by applying the laws of thermodynamics.

Here are the key principles:

1. Heat Transfer:

• Heat always flows from a warmer body to a colder one.
• Refrigeration systems exploit this principle by creating a low-temperature environment (the evaporator) where heat from the refrigerated space is absorbed by the refrigerant.
• The refrigerant then carries this heat to a higher-temperature environment (the condenser), where it’s released into the surroundings.

2. Refrigerant Properties:

• Refrigerants are chosen for their specific properties, including:
  • Low boiling point: This allows the refrigerant to evaporate at low temperatures, absorbing heat from the refrigerated space.
  • High latent heat of vaporization: A large amount of heat is absorbed during the phase change from liquid to gas, making the refrigerant an efficient heat carrier.
  • Suitable pressure-temperature relationship: The refrigerant’s pressure and temperature change in a controlled manner throughout the system, facilitating heat transfer and efficient operation.

3. Refrigeration Cycle:

• The refrigeration cycle is a continuous process involving four main stages:
  1. Compression: The refrigerant, in a gaseous state, is compressed by the compressor, increasing its pressure and temperature.
  2. Condensation: The high-pressure, high-temperature refrigerant gas flows into the condenser, where it releases heat to the surroundings and condenses into a liquid.   1. www.numerade.com www.numerade.com
  3. Expansion: The high-pressure liquid refrigerant passes through an expansion valve, reducing its pressure and temperature drastically.
  4. Evaporation: The low-pressure, low-temperature refrigerant enters the evaporator, where it absorbs heat from the refrigerated space and evaporates back into a gas, completing the cycle.   1. www.numerade.com www.numerade.com

4. Laws of Thermodynamics:

• The refrigeration cycle operates based on the fundamental laws of thermodynamics:
  • First Law: Energy is conserved, meaning the heat absorbed in the evaporator is equal to the heat rejected in the condenser plus the work done by the compressor.
  • Second Law: Heat naturally flows from a higher temperature to a lower temperature. The refrigeration system works against this natural flow, requiring external energy input (from the compressor) to pump heat from the cold space to the warmer environment.

In summary, the basic principles of refrigeration involve heat transfer, utilizing a refrigerant with suitable properties, and applying the laws of thermodynamics in a continuous cycle to move heat from a cold space to a warmer environment.Sources and related content

A direct expansion (DX) free-standing mechanical refrigeration system is a common type of refrigeration system used in various applications, including commercial and domestic settings. In this system, the refrigerant directly absorbs heat from the refrigerated space, making it efficient and relatively simple in design.

Main Components:

1. Compressor:

• Function: The compressor is the heart of the system, responsible for circulating the refrigerant throughout the circuit. It compresses the low-pressure refrigerant gas from the evaporator, raising its pressure and temperature.   1. The Refrigeration Cycle – In easy to understand descriptions & diagrams! – Torr Engineering www.torr-engineering.com2. The 4 Main Refrigeration Cycle Components | The Super Blog www.superradiatorcoils.com
• Type: Depending on the system size and application, various compressor types may be used, such as reciprocating, rotary, or scroll compressors.

2. Condenser:

• Function: The condenser receives the high-pressure, high-temperature refrigerant gas from the compressor. It facilitates heat transfer from the refrigerant to the surrounding environment, causing the refrigerant to condense into a liquid state.   1. What’s the difference between an A/C compressor and an A/C condenser? – Ernst Heating & Cooling www.ernstheating.com
• Type: Common condenser types include air-cooled condensers (using fans to dissipate heat) or water-cooled condensers (utilizing water circulation for heat removal).   1. Difference Between Air Cooled and Water Cooled Condenser – Glen Refrigeration glenrefrigeration.com

3. Expansion Valve:

• Function: The expansion valve, also known as a metering device, controls the flow of refrigerant from the high-pressure liquid line into the low-pressure evaporator. It reduces the pressure and temperature of the refrigerant, preparing it for heat absorption in the evaporator.   1. The Thermal Expansion Valve (TXV) Explained – United CoolAir www.unitedcoolair.com2. Air Conditioning – Expansion Valve www.swtc.edu
• Type: Several types of expansion valves exist, including thermostatic expansion valves (TXVs), capillary tubes, and electronic expansion valves (EEVs), each with its own control mechanism.

4. Evaporator:

• Function: The evaporator is located within the refrigerated space and is responsible for absorbing heat from the surroundings. As the low-pressure, low-temperature refrigerant flows through the evaporator coil, it absorbs heat and evaporates into a gas.   1. Direct Expansion Air Conditioning Systems – Basic HVAC – BC Open Textbooks opentextbc.ca2. [Solved] In a refrigeration plant, in a direct expansion evaporator: – Testbook testbook.com
• Type: Evaporators can be of various designs, such as finned-tube coils, plate evaporators, or shell-and-tube evaporators, depending on the application and required cooling capacity.

5. Refrigerant:

• Function: The refrigerant is the working fluid that circulates through the system, absorbing and releasing heat to achieve the desired cooling effect.   1. The 4 Main Refrigeration Cycle Components | The Super Blog www.superradiatorcoils.com
• Type: The choice of refrigerant depends on the system’s operating conditions, environmental considerations, and safety regulations. Common refrigerants include hydrofluorocarbons (HFCs), hydrocarbons, and natural refrigerants like ammonia or carbon dioxide.

6. Other Components:

• Filter-Drier: Removes moisture and contaminants from the refrigerant to protect the system and ensure efficient operation.   1. Filter driers: just the facts – Danfoss www.danfoss.com
• Accumulator: Collects liquid refrigerant and prevents it from entering the compressor, protecting it from damage.
• Sight Glass: Allows visual inspection of the refrigerant flow and condition.
• Pressure Gauges: Monitor the pressure on the high and low sides of the system for troubleshooting and diagnostics.
• Controls and Safety Devices: Thermostats, pressure switches, and other controls regulate the system’s operation and ensure safety.

Refrigeration Cycle:

The refrigerant flows through these main components in a continuous cycle:

1. Compressor: Compresses the refrigerant gas, raising its pressure and temperature.   1. The 4 Main Refrigeration Cycle Components | The Super Blog www.superradiatorcoils.com
2. Condenser: The hot gas releases heat to the surroundings and condenses into a liquid.
3. Expansion Valve: The liquid refrigerant expands, lowering its pressure and temperature.   1. Air Conditioning – Expansion Valve www.swtc.edu
4. Evaporator: The cold liquid absorbs heat from the refrigerated space and evaporates into a gas.   1. Direct Expansion Air Conditioning Systems – Basic HVAC – BC Open Textbooks opentextbc.ca
5. The cycle repeats as the refrigerant gas returns to the compressor.

This continuous cycle facilitates heat transfer from the refrigerated space to the external environment, achieving the desired cooling effect.  

1. Understanding the Refrigeration Cycle : A Guide to Cooling – Industrial Cold Room & Equipments – Frigosys