MI HVAC flashcards
MI HVAC · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- AFUE
- Annual Fuel Utilization Efficiency: the ratio of annual heat output to annual fuel energy input for a furnace or boiler, expressed as a percentage.
- Temperature rise
- The difference between supply air temperature and return air temperature across a furnace; it must fall within the range printed on the rating plate.
- Heat pump balance point
- The outdoor temperature at which heat pump capacity equals the building heat load, below which supplemental heat is required.
- Hydronic Btuh formula
- Btuh equals 500 times gallons per minute times the water temperature drop in degrees Fahrenheit for water-based hydronic systems.
- Steam trap
- A device that passes condensate and non-condensable gases while preventing steam from escaping, maintaining heat delivery in steam systems.
- Condensing furnace
- A high-efficiency furnace with a secondary heat exchanger that recovers latent heat from flue gases, requiring a condensate drain and plastic venting.
- Superheat
- Suction line temperature minus the evaporating saturation temperature; it indicates how far refrigerant vapor is above its boiling point.
- Subcooling
- Condensing saturation temperature minus liquid line temperature; it measures how far liquid refrigerant has cooled below its condensing point.
- Tonnage of cooling
- One ton of cooling equals 12,000 Btu per hour of heat removal, the standard unit for expressing air conditioning capacity.
- Sensible capacity formula
- Sensible Btu per hour equals 1.08 times airflow in cfm times the dry-bulb temperature difference across the coil.
- TXV
- Thermostatic expansion valve: a metering device that modulates refrigerant flow to maintain a set superheat at the evaporator outlet.
- Dirty condenser effect
- A fouled condenser raises condensing temperature and pressure, which increases compressor amp draw and reduces cooling capacity.
- Equal friction method
- A duct sizing method that selects a constant friction rate, commonly 0.1 inch of water per 100 feet, and reads sizes from a duct calculator.
- Velocity pressure
- Velocity pressure in inches of water column equals the duct velocity in feet per minute divided by 4005, then squared.
- Equivalent length
- The straight-duct length that produces the same pressure loss as a fitting, used to add fitting losses to total effective length.
- Duct leakage test
- A test that pressurizes the duct system to 25 pascals and reports leakage as cubic feet per minute per 100 square feet of conditioned floor area.
- Manual J
- The ACCA residential load calculation procedure that determines room-by-room heating and cooling loads from envelope, orientation, and internal gains.
- Manual D
- The ACCA procedure for sizing ducts and selecting registers based on room airflow requirements and available static pressure.
- Sensible heat ratio
- The sensible load divided by the total load; it indicates what fraction of cooling capacity removes temperature rather than moisture.
- Oversizing penalty
- An oversized air conditioner short-cycles, runs less efficiently, and removes less moisture, leaving the space cool but humid.
- Design conditions
- The winter and summer outdoor temperatures and humidity values used as inputs to load calculations for a specific location.
- Ohm's law
- Voltage equals current times resistance; combined with watts equal to volts times amps, it supports troubleshooting electrical circuits.
- High-limit switch
- A temperature-actuated safety device that opens the burner circuit when supply air temperature exceeds a set maximum.
- Flame sensor
- A rod that detects the presence of flame through current rectification; a dirty sensor prevents the burner from staying lit.
- Locked rotor amps
- The current a motor draws when the rotor cannot turn; a compressor reading near this value is failing to start.
- Float switch
- A device in the condensate pan that interrupts the cooling circuit when water rises, preventing overflow and water damage.
- Natural gas heating value
- Natural gas contains roughly 1,000 Btu per cubic foot, while liquefied petroleum gas contains about 2,500 Btu per cubic foot.
- Combustion air rule
- Unconfined spaces should provide about 50 cubic feet of volume per 1,000 Btu per hour of appliance input for proper combustion.
- Carbon monoxide
- A colorless, odorless gas produced by incomplete combustion that is hazardous to health and indicates a burner or venting problem.
- Manifold pressure
- The gas pressure measured at the burner manifold; natural gas appliances are commonly set near 3.5 inches of water column.
- Mechanical permit
- Authorization issued by the local enforcing agency before HVAC work begins; inspections verify compliance before concealment and at final.
- Mechanical contractor license
- A state-issued credential required to contract for HVAC work in Michigan, obtained by examination and maintained with fees and insurance.