Refrigeration Cycle Flashcards

What happens to the refrigerant in the condenser?

Answer: It rejects heat and changes from a high-pressure superheated gas to a high-pressure liquid

In the condenser, high-pressure superheated refrigerant gas from the compressor rejects heat to the surrounding medium (air or water). As it loses heat, it desuperheats, condenses from gas to liquid, and may subcool further. This heat rejection is what removes the heat absorbed by the evaporator plus the heat of compression.

What is the purpose of the compressor in the refrigeration cycle?

Answer: To raise the pressure and temperature of the refrigerant vapour so it can reject heat in the condenser

The compressor raises the pressure and temperature of the refrigerant vapour from the evaporator. By increasing the pressure, the condensing temperature rises above the ambient temperature, allowing the condenser to reject heat to the surroundings. The compressor is the component that drives the entire cycle.

What is a pressure-enthalpy (P-h) diagram used for in HVAC?

Answer: To graphically represent the refrigeration cycle, showing the state of the refrigerant at each point and the energy involved in each process

A pressure-enthalpy (P-h) diagram plots refrigerant pressure on the vertical axis and enthalpy (heat content) on the horizontal axis. It shows the saturation curve, the state of the refrigerant at each point in the cycle, and allows calculation of system capacity, COP, and heat transfer at each component.

What is the saturation temperature of a refrigerant?

Answer: The temperature at which the refrigerant changes state (boils or condenses) at a given pressure

Saturation temperature is the temperature at which a refrigerant changes between liquid and vapour states at a specific pressure. At saturation, liquid and vapour coexist. Every refrigerant has a unique pressure-temperature relationship that technicians use for system diagnosis.

In a heat pump system, how does the cycle differ from a standard air conditioning cycle?

Answer: A reversing valve changes the direction of refrigerant flow, allowing the system to heat or cool by swapping the functions of the indoor and outdoor coils

A heat pump uses a reversing valve (four-way valve) to reverse the direction of refrigerant flow. In cooling mode, the outdoor coil is the condenser and the indoor coil is the evaporator. In heating mode, the functions are reversed — the outdoor coil absorbs heat (evaporator) and the indoor coil rejects heat (condenser).

What is latent heat and why is it significant in the refrigeration cycle?

Answer: The heat energy absorbed or released during a phase change (liquid to gas or gas to liquid) without a temperature change

Latent heat is the energy absorbed or released when a substance changes phase without changing temperature. In refrigeration, the large amount of latent heat absorbed during evaporation provides the cooling effect, and the latent heat released during condensation is how the system rejects heat. This is far more effective than sensible heat transfer alone.