[L1] 1 Overview of the Refrigeration Cycle [L2] 1) Definition [L4] - Refrigeration: Refers to maintaining a system at a temperature lower than that of its surroundings. [L4] - A device that constitutes a refrigeration system by supplying external work is called a refrigerator. [L4] - Refrigeration involves a continuous cyclical process (cycle) of removing heat from a low-temperature object and transferring it to a high-temperature object via a medium called a refrigerant. [L5] * The process of extracting heat from a low-temperature heat reservoir, receiving work required for heat transfer, and releasing this energy to a high-temperature heat reservoir. [L2] 2) Reversed Carnot Cycle [L4] - While the direction of the Carnot cycle is clockwise on a T-s diagram, the direction of the reversed Carnot cycle is counter-clockwise. [L4] - The reversed Carnot cycle rotates counter-clockwise and is a reversible cycle composed of two adiabatic processes and two isothermal processes. [L4] - The reversed Carnot cycle is an ideal model for refrigeration cycles. [L2] 3) Refrigeration Cycle Diagrams [c] P-H Diagram [c] T-S Diagram [L1] 2 Refrigeration Calculations [L2] 1) Definition of Coefficient of Performance (COP) [L4] - The ratio of output energy to input energy, i.e., efficiency. [L4] - Also known as Coefficient of Performance or Performance Coefficient. [L4] - The efficiency at 100% full-load operation under specified temperature conditions. It refers to the average energy consumption efficiency for heating and cooling. [L5] * The power consumption or gas consumption during rated cooling and rated heating, expressed as cooling or heating capacity per 1 kW. [L4] - Since COP does not reflect the efficiency under actual operating conditions, it was changed to Integrated Part Load Value (IPLV). [L5] * For absorption chillers/heaters using gas, the high-efficiency certification standard was changed from Coefficient of Performance (COP) to Integrated Part Load Value (IPLV) starting in 2017. [L5] * COP is used only for limited and temporary reference. [L5] * IPLV = Full Load (100%) x 1% + Part Load (75%) x 42% + Part Load (50%) x 45% + Part Load (25%) x 12% [L2] 2) Refrigerators and Heat Pumps [L3] ① Refrigerator [L4] - A device that performs heat transfer by inputting work to move heat from a low-temperature object to a high-temperature object. [L3] ② Heat Pump [L4] - A device used when the heat from the heat rejection part of a refrigeration cycle is utilized for a specific purpose. [L4] - A device that absorbs heat from the outside by inputting work and releases the remaining heat for heating. [L4] - Used in a comprehensive sense to include combined heating and cooling devices. [L5] * In the case of system air conditioners, they are used for both cooling and heating by adjusting the cycle direction. [L5] * There are electric and engine-driven types depending on the refrigerant circulation method. [L2] 3) Calculation of Coefficient of Performance for the Reversed Carnot Cycle [L4] - Refrigerator Coefficient of Performance (maximum value through reversed Carnot cycle, COP) [L4] - Heat Pump Coefficient of Performance (reversed Carnot cycle, COPh) [L4] - Generally, the coefficient of performance for a refrigeration cycle refers to the COP of a refrigerator. [L1] 3 Standard Refrigeration Cycles [L2] 1) Simple Standard Vapor-Compression Cycle [L4] - Actual refrigeration cycle [L4] - Related graph [L2] 2) Improved Standard Refrigeration Cycle [L4] - Improved vapor compression efficiency is possible by subcooling the refrigerant. [L4] - Increasing cycle efficiency by enhancing the refrigeration effect (4->4'). [L4] - A method to superheat the refrigerant after it exits the evaporator (2-3 -> 2'-3').