Evaporators and Condensers Flashcards

What is the temperature difference (TD) across an evaporator and what does it indicate?

Answer: The difference between the air temperature entering the evaporator and the refrigerant saturation temperature; it indicates proper coil sizing and airflow

Evaporator TD is the difference between the entering air temperature and the refrigerant saturation (boiling) temperature inside the coil. A typical TD for comfort cooling is 10°C to 12°C (18°F to 22°F). A higher TD indicates restricted airflow, dirty coils, or an undersized coil; a lower TD may indicate an oversized coil or excess refrigerant.

What is the difference between a fin-and-tube evaporator and a plate evaporator?

Answer: A fin-and-tube uses tubes with attached fins for air-cooled applications; a plate evaporator uses stacked plates for liquid-cooled or direct-contact applications

Fin-and-tube evaporators use copper or aluminium tubes with aluminium fins pressed onto them to increase surface area for air-to-refrigerant heat exchange. Plate evaporators use corrugated stainless steel plates to create channels for refrigerant and the fluid being cooled, offering high efficiency in compact liquid-cooling applications.

What causes frost buildup on an evaporator coil and what problems does it create?

Answer: Operating below the dewpoint of the air combined with coil temperatures below 0°C; it insulates the coil, blocks airflow, and reduces capacity

When the evaporator coil surface temperature is below 0°C and moisture from the air condenses and freezes on it, frost accumulates. Frost acts as insulation, reducing heat transfer, and physically blocks airflow through the coil. This progressively reduces cooling capacity. Heat pump and refrigeration systems use defrost cycles to manage this.

What is the approach temperature on a water-cooled condenser?

Answer: The difference between the refrigerant condensing temperature and the leaving water temperature; indicates condenser efficiency

Approach temperature on a water-cooled condenser is the difference between the refrigerant condensing temperature and the temperature of the cooling water leaving the condenser. A lower approach temperature (typically 3°C to 5°C / 5°F to 10°F) indicates better heat transfer and higher efficiency.

What are the three types of condensers used in HVAC systems?

Answer: Air-cooled, water-cooled, and evaporative condensers

The three types of condensers are: air-cooled (uses ambient air and fans), water-cooled (uses water circulated through a cooling tower or city water), and evaporative (combines air and water spray for enhanced cooling). Air-cooled is most common in residential and light commercial; water-cooled offers higher efficiency in larger systems.

Why is it important to keep condenser coils clean?

Answer: Dirty coils increase head pressure, reduce system capacity, increase energy consumption, and can cause compressor overheating and failure

Dirty condenser coils restrict airflow and insulate the heat transfer surface, causing the system to operate at higher head pressures. This increases compressor energy consumption, reduces cooling capacity, raises discharge temperatures (risking compressor damage), and shortens equipment life. Regular cleaning is essential preventive maintenance.