HVAC Flashcards
What would you expect to happen to a chiller if the only condenser water pump failed and the flow switch failed also?
Chiller would trip on high pressure.
In what state is the refrigerant just after the compressor but before the condenser?
Hot gas
Why is blow-down needed on a condenser water circuit?
To eliminate dissolved solids from the water.
What is the purpose of an expansion tank on a closed water loop?
To allow for thermal expansion
What is a possible cause of an evaporator coil becoming iced?
Low refrigerant charge or low airflow.
What would you expect to happen to a chiller if the only chilled water pump failed and the flow switch failed also?
Chiller would trip on low pressure or low temp.
Why is the oil kept warm in an off-line chiller?
To prevent the migration of refrigerant into the oil.
What is the purpose of the metering device in a refrigeration circuit?
To allow pressure drop to the evaporator.
What happens to the efficiency of a cooling tower on a very humid day? Why?
Decreases, evaporation is not as efficient.
What is chiller approach?
Tells you the efficiency of your chiller
What would cause a high “small temperature difference” (approach)?
Fouled tubes
What is Eddy Current Testing?
Uses electromagnetic induction to detect flaws in the chiller tubes
How is a capacitor measured?
Farad
What type of chiller would you see a purge unit on and what is it used for?
Low pressure chiller. It removes air from the system that may have been brought in from a leak in the chiller’s refrigerant system.
What is CFM and what is it used for?
Cubic Feet per Minute. Measures air flow.
Name the four major components of a refrigerant circuit.
Compressor, condenser, expansion device and evaporator.
What does BTU stand for and what is a BTU?
British thermal unit. The amount of energy needed to raise one pound of water one degree Fahrenheit.
How many BTUs are in one ton of refrigeration?
12,000 BTU
Name at least three different types of refrigeration compressors.
Reciprocating, centrifugal, screw, etc…
What is superheat? As it relates to a refrigerant circuit.
Superheat is the temperature of the refrigerant vapor above its saturation temperature.
Name at least three possible reasons why an evaporator coil may ice up.
Dirty air filter, Dirty evaporator coil, faulty belt or blower motor, faulty TXV, low refrigerant charge, low outdoor temperatures, etc…
Name at least three possible reasons for a refrigeration circuit to be operating with a high head pressure.
Dirty condenser coil, faulty condenser fan motor, over charged, not enough condenser water flow, etc…
What process is used to cool the water in a cooling tower?
Evaporation.
Name two types electrical diagrams?
Pictorial diagram and ladder diagram(schematic)
What is the normal position of a high pressure switch in an HVAC system?
Closed
Is a chilled water loop open or closed?
Closed
What is latent heat?
The heat required to change the physical state of a substance (solid to liquid, liquid to vapor). This heat does not raise the temperature.
Briefly describe how evaporative cooling cools the air in a space.
Sensible heat is converted into latent heat as it evaporates the water. This effectively lowers the sensible heat in the air.
Define Humidity.
It is basically moisture content in air or it is the quantity of water vapour retained by gas.
What is Psychrometer?
Psychrometer is a device that uses the bulb thermometers to measure humidity. It is also used in air conditioning systems for maintaining humidity.
What is Ambient Temperature?
The average or mean temperature of the surrounding air which comes in contact with the equipment and instruments under test.
Define Boiling Point
The temperature at which a substance in the liquid phase transforms to the gaseous phase.
Which transducer converts heat energy into electrical energy
thermocouple
What is the purpose of a Hot Gas Bypass valve?
Capacity control
