Compressors & Condensers Flashcards

What is the function of the condenser in a refrigeration system?

Answer: To reject heat from the refrigerant to the ambient medium, condensing the refrigerant from vapour to liquid

The condenser rejects the heat absorbed in the evaporator plus the heat of compression to the outdoor air or cooling water, condensing the refrigerant vapour back into a liquid.

What is the approach temperature of an air-cooled condenser?

Answer: The difference between condensing temperature and entering air temperature

Approach temperature is the difference between the condensing temperature (saturation temperature at condensing pressure) and the entering air dry-bulb temperature, and a low approach temperature indicates good heat transfer.

What effect does dirty condenser coils have on a refrigeration system?

Answer: Higher discharge pressure, higher condensing temperature, and reduced system efficiency

Dirty condenser coils reduce airflow and heat transfer, causing the condensing temperature and discharge pressure to rise, which increases compressor work and reduces system efficiency and capacity.

What type of condenser uses water as the heat rejection medium and is commonly used in large commercial systems?

Answer: Water-cooled condenser (shell-and-tube or plate heat exchanger)

Water-cooled condensers, such as shell-and-tube or brazed plate heat exchangers, use water from a cooling tower or municipal supply to reject heat from the refrigerant, offering high efficiency in large commercial applications.

What is the purpose of non-condensable gas purging in a refrigeration system?

Answer: To eliminate air or nitrogen trapped in the system that raises condensing pressure and reduces efficiency

Non-condensable gases such as air or nitrogen do not condense and accumulate at the top of the condenser, artificially raising discharge pressure and reducing heat transfer efficiency.

What is the 'head pressure control' strategy used on air-cooled condensers in cold Canadian winters?

Answer: Cycling condenser fans off or modulating fan speed to maintain minimum condensing pressure during cold weather

In cold weather, air-cooled condensers can overcool the refrigerant and reduce condensing pressure below the minimum needed for proper expansion device operation, so fan cycling or variable-speed fans maintain minimum head pressure.