313A Evaporators and Condensers 2

Question 1

What is a flooded evaporator and where is it typically used?

Accepted Answer

An evaporator where the tubes are submerged in liquid refrigerant, used in large chillers to cool water flowing through the tubes

Answer

A flooded evaporator is a shell-and-tube design where refrigerant floods the shell side, submerging the tubes that carry the fluid being cooled (typically water). Liquid refrigerant is maintained at a level covering the tubes, ensuring efficient heat transfer. This design is common in large centrifugal and screw chillers.

Question 2

What is the split between sensible and latent cooling in an evaporator?

Accepted Answer

Sensible cooling changes temperature; latent cooling removes moisture — the ratio affects both comfort and coil selection

Answer

Evaporators perform both sensible cooling (lowering air temperature) and latent cooling (removing moisture by condensing it on the coil). The sensible heat ratio (SHR) describes the proportion of each. In humid climates, more latent capacity is needed; in dry climates, mostly sensible cooling is required. Coil selection and airflow affect this ratio.

Question 3

What is a direct expansion (DX) evaporator?

Accepted Answer

An evaporator where refrigerant expands directly inside the coil to cool air or fluid passing over or around it, with the metering device controlling flow

Answer

A direct expansion (DX) evaporator is the most common type in residential and commercial HVAC. Refrigerant from the metering device expands directly inside the evaporator tubes, absorbing heat from air passing over the finned coil. The metering device controls refrigerant flow to maintain proper superheat.

Question 4

What is the purpose of a condenser fan cycling control?

Accepted Answer

To maintain adequate head pressure during low ambient temperatures by cycling condenser fans on and off

Answer

In cold weather, the condenser can reject too much heat, causing head pressure to drop too low for the metering device to function properly. Condenser fan cycling controls turn fans off or reduce their speed to maintain minimum head pressure, ensuring proper refrigerant flow and system operation.

Question 5

How does a cooling tower work with a water-cooled condenser?

Accepted Answer

The cooling tower cools the condenser water through evaporation of a portion of the water, then returns the cooled water to the condenser

Answer

A cooling tower cools condenser water by spraying it over fill media while ambient air is drawn through. A small portion of the water evaporates, absorbing heat from the remaining water (evaporative cooling). The cooled water collects in the basin and is pumped back to the condenser. This allows water-cooled systems to reject heat very efficiently.

Red Seal HVAC 313A Practice Test

Red Seal HVAC 313A Practice Test

313A Evaporators and Condensers 2