HVAC Flashcards
What is it called when Vapor and liquid exist at the same time in the same coil?
Saturation
Explain a compressor component.
Low temp low Vapor flows into compressor. Compressor compresses it and turn it into high temp high Vapor. Compressing creates heat, and pressure and heat are directly related. If temp goes up, pressure goes up.
What is the step after compression, what does it do?
High pressure high temp Vapor travels from compressor through condenser coil. The fan blows air on condenser coil and cools the temp. The Vapor turns into a high temp liquid and continues to flow to liquid receiver.
What does the filter drier do?
Removes excess water and contaminants. Water mixed with refrigerant oil creates alcohol and acid.
High pressure high temp liquid travels from liquid receiver to ________
Thermostatic expansion valve (TXV)
What is a TXV, what does it do?
What type of liquid travels from the TXV?
Low pressure low temperature liquid.
What is the function of the evaporator?
Low pressure low temperature liquid travels from TXV into the evaporator coil. Evaporator coil absorbed heat from inside and turns the liquid into a Vapor. Low temp low pressure Vapor flows back outside to the compressor.
What is the term for where low temp low pressure Vapor comes out of the evaporator?
Superheat.
What is the purpose of the TXV bulb? Where is it mounted?
It reads the temperature of the super heat, it is connected to the TXV and depending on if the Vapor is too hot or too cold the TXV will release more or less liquid. It is mounted outside of the Vaporator.
Electric furnaces are made of
Blower heater combination.
Heater resistance elements are layered in 5kw rated pieces to reduce light flickering. Blows hot air up through ducts, cold air back out to return
Where are furnaces usually installed?
Basements or crawl spaces
What is a furnace heat exchanger for? How does it work?
To keep products of combustion seperate from circulated air.
How does a furnace work?
A fan draws air from living room/dining room, blows through heat exchanger, blows out into rooms. Heat exchanger exhausts dangerous fumes through flue.
How efficient are furnaces?
70-80%
How are furnaces usually wired?
120V to supply, low voltage to thermostat. 120v is used to power the blower motor, and there is a 120/24 TX for the control circuit
What is the source of heat for a thermocouple?
Pilot light
What are the typical temperatures for a blow control overheat to operate?
Blower off at 32 (90)
Blower on at 54 (130)
High limit off at 104 (220)
How do humidifiers operate?
Miat water into plenum
What is the rating for duct heaters?
3 - 15kw
What are plenum heaters rated at?
12 - 15 kw
Radiators rely on _______
Convection
Geothermal systems operate in two different loops:
Open and close
What does a damper do?
Regulates air
Two different types of fans
Centrifugal, axial
Theee important principals of fans
Airflow varies with fan speed. Directly changes airflow directly changes fan speed.
Static pressure. Doubling Dan speed makes four times the amount of static pressure.
Power varies.
Doubling can speed makes twice the air flow but 8 times the horsepower
How does a heat pump operate?
Reverses the flow of refrigerant
What is the valve called in a heat pump?
Expansion valve
Hvac controls are usually class _____
2
