HVAC BASICS and MECHANICAL

  1. Economizer is also known as what, because it does not use any mechanical cooling?
    • “free cooling”
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  2. Dry bulb economizer uses no outside? The most common placement of such a unit is where?
    • A Dry Bulb Economizer uses no outside humidity reference and is most commonly placed on a roof as a roof top unit.
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  3. Enthalpy is?
    the total heat contained in a material.
  4. Enthalpy economizer uses temperature and humidity levels of the outside air to control its operation. The outside air temp and humidity must meet what range?
    The outside Air temp must be below 65F and between 30 and 60% humidity
  5. Compressor compresses what? And they may be of what type?
    refrigerant or other fluid. They may be centrifugal, reciprocating (positive displacement), screw (helical gear compressor), or scroll.
  6. Direct expansion refrigeration systems: parts include what basic components?
    a compressor, condenser, expansion device and evaporator. C.C.E.E.
  7. What are both the condenser and evaporator?
    Both the condenser and evaporator are heat exchangers, where the condensor compresses refrigerant and uses coils to remove the heat, and the evaporator does the same thing as it expands.  The compressor starts the process all over again.... CCEE Compressor, condensor, expansion, and evaporator.
  8. condenser is a?
    heat exchanger that removes heat from high pressure refrigerant vapor. Usually a coil will allow either water or air to pass by and cool the heated refrigerant.
  9. the evaporator medium (used to cool) is what? there are two options.
    The evaporator medium are either air or water.
  10. The expansion device will allow the refrigerant to vaporize and absorb heat as pressure decreases. It is then piped to the….
    evaporator.
  11. evaporator is a?
    Heat exchanger that adds heat to low pressure liquid refrigerant. An evaporating medium (air or water) of higher temperature passes by the refrigerant that cools the medium. The liquid refrigerant vaporizes as it absorbs heat from the medium. It passes though the evaporator across a series of baffles and then to the inlet of the compressor.
  12. Cooling towers allow heat to be ejected where?
    To the outside air.
  13. Direct expansion refrigerant systems the can be?
    reciprocating, screw, or scroll but not centrifugal, as centrifugal compresses refrigerant.
  14. Reciprocal compression units are not common over_____ tons. And may use four or more compressors and a valve can be used to allow bypass for maintenance.
    100
  15. Chillers are between what farenheight temperature range? Include the return.
    42 and 44F and the return is normally between 52 and 55F.
  16. the heat anticipator is wired how?
    In series with the operating contact
  17. a cooling anticipator is wired how?
    this is wired in parallel with the operating contacts
  18. what is the purpose of the solenoid valve in cooling?
    it controls the flow of a fluid
  19. the adding of heat to a refrigerant that has reached its vapor saturation point is referred to as
    superheating the refrigerant
  20. Which of the following is permitted to be used pressure checking a refrigeration system?
    nitrogen
  21. What is a PSC motor?  It is commonly used in cooling and heating applications.
    PSC: Permanent split capacitor motor uses a capacitor (a device that can store and release electrical charge) in one of the windings to increase the current lag between the two windings. Both the capacitor (auxiliary) winding and the main winding remain in the circuit the entire time the motor is running, hence the name “permanent.”
  22. Define a positive temperature coefficient PTC device, and what it is used for?
    start assist for PSC motor. A resettable fuse is a polymeric positive temperature coefficient (PPTC) device that is a passive electronic component used to protect against overcurrent faults in electronic circuits. The device is also known as a polyfuse or polyswitch.Image Upload 3
  23. A thermistor may be used for what regarding a PSC motor, and what is a PSC motor?
    • to provide temperature readout to assist in the starting of a PSC (permanent split capacitor) motor and to stop a motor on an overload condition? Note: Thermistors are commonly used in hot aisles in data centers to determine air temperature. 
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  24. Define a thermistor and what happens to it as it heats up?
    an electrical resistor whose resistance is greatly reduced by heating, used for measurement and control.
  25. What mechanical piece is adjustable on a thermostat?
    • the bi metal strip
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  26. What is a primary cause of hermetic compressor motor overheating and cutting out on the internal overload device?
    refrigerant  under charge is a common cause of this.
  27. which of the following is required when the thermostat subbase designed for two 24 volt power sources is used with one power source
    • A jump wire is required to be connected between RH and RC terminal.  If the air conditioning thermostat has one transformer to power both the heating and cooling system, then the wire from the transformer goes directly to the RC terminal and is called the RC wire. ... This wire is also known as the RH wire.
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  28. What is the difference between a CRAC and a CRAH regarding a chiller plant or chilled water?
    A CRAC unit or Computer Room Air conditioning Unit does not use a chiller plant or chilled water but rather a condenser. A CRAH or Computer Room Air handling unit uses chilled water from a chiller plant.
  29. Refrigerant vapor gets hot when compressed. Why?
    It has a very low boiling point and absorbs heat as it vaporizes.
  30. Volute is?
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    is the opening in a centrifugal compressor that allows you to increase pressure of the refrigerant but not the velocity.
  31. What does DX stand for in Heating Ventalation and Cooling systems.
    Direct Expansion
  32. What is a VAV and what does it stand for?
    It is a variable air ventilation dampener that provides control for hot or cold air by volume through a duct.
  33. What does the acronym VRF stand for in Heating ventilation and cooling? What type of expansion is this used with?
    Variable Refrigerant Flow is VRF in HVAC. This type of cooling is used in Direct Expansion or DX
  34. There are two types of central air conditioning systems, what are they?
    Direct Expansion (DX) type of central air condition plants and Chilled Water type of the central air conditioning plants.
Author
johnbowens
ID
336429
Card Set
HVAC BASICS and MECHANICAL
Description
HVAC MECHANICAL AND COOLING SYSTEMS
Updated