GA HVAC flashcards
GA 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.
- Manual J
- Manual J is the ACCA method for calculating residential heating and cooling loads from room-by-room envelope, infiltration, internal gain, and design-condition inputs.
- Manual S
- ACCA Manual S is the equipment selection procedure that matches manufacturer performance data to calculated Manual J loads and checks sensible and latent capacity at design conditions.
- Sensible heat formula
- For standard air near sea level, sensible heat in Btu/h equals 1.08 times airflow in cfm times the dry-bulb temperature difference in degrees Fahrenheit.
- Ton of cooling
- One ton of cooling equals 12,000 Btu per hour, the approximate heat removal rate of one ton of ice melting over 24 hours.
- Superheat
- Superheat is the difference between measured suction-line temperature and refrigerant saturation temperature at the same suction pressure; it indicates evaporator feed and protects the compressor.
- Subcooling
- Subcooling is the difference between refrigerant saturation temperature at liquid-line pressure and measured liquid-line temperature; it indicates liquid seal and charge in the condenser.
- TXV function
- A thermostatic expansion valve meters refrigerant into the evaporator and modulates flow to maintain a set superheat at the evaporator outlet under changing load.
- A2L refrigerant
- A2L refrigerants have lower flammability than A3 refrigerants but are mildly flammable; examples include R-32 and R-454B, and they require specific handling and charge limits.
- AFUE
- Annual fuel utilization efficiency is the ratio of annual heat output to annual fuel energy input for a furnace or boiler, expressed as a percentage on the rating plate.
- Furnace temperature rise
- Furnace temperature rise in degrees Fahrenheit equals output Btu/h divided by 1.08 times measured airflow in cfm; it must fall within the nameplate range.
- Heat pump balance point
- The balance point is the outdoor temperature at which heat pump capacity equals building heat loss; below it, supplementary heat is needed to maintain indoor temperature.
- Condensing furnace condensate
- A condensing furnace produces acidic water condensate from flue-gas water vapor; it must drain through a trap and often a neutralizer to a suitable location.
- Equivalent length
- Equivalent length converts duct fitting and component pressure losses into added straight-duct length so total effective length can be used with available static pressure.
- ASHRAE 62.2
- ASHRAE Standard 62.2 sets ventilation and acceptable indoor air quality requirements for low-rise residential buildings, including whole-house and local exhaust ventilation rates.
- Duct leakage
- Duct leakage is air escaping or entering a duct system through seams, joints, and penetrations; it reduces delivered airflow and efficiency and is measured by pressurization testing.
- Sediment trap
- A sediment trap, or drip leg, is a capped pipe section installed at a gas appliance connection to collect dirt and condensate before gas enters the controls.
- Natural gas manifold pressure
- Natural gas appliance manifold pressure is commonly about 3.5 inches water column, but the nameplate rating for the specific appliance always governs adjustment.
- Dielectric union
- A dielectric union separates dissimilar metals, such as copper and steel, to reduce galvanic corrosion at a piping connection while maintaining a pressure-tight joint.
- MCA
- Minimum circuit ampacity is the minimum conductor ampacity listed on HVAC equipment nameplate, calculated with code-required margins for the largest motor and continuous load.
- Capacitor microfarad test
- A capacitor is tested by measuring microfarads with a meter after discharging it; a reading outside the nameplate tolerance indicates a weak or failed capacitor.
- C terminal
- The C terminal is the common side of the 24-volt transformer secondary; it provides continuous power for thermostats and controls that require a common wire.
- Nitrogen purge
- Nitrogen purge means flowing dry nitrogen through refrigerant piping while brazing to displace oxygen and prevent internal oxidation scale that can damage compressors and valves.
- 500 microns
- A vacuum of about 500 microns absolute indicates removal of moisture and noncondensables from a refrigerant system; a standing decay test confirms the vacuum holds.
- Pitot tube traverse
- A pitot tube traverse measures velocity pressure at multiple points across a duct; average velocity pressure is converted to airflow using duct area and air density.
- Fan laws
- Fan laws state that airflow varies with speed, static pressure with speed squared, and power with speed cubed for a fixed fan and system.
- Delta T
- Delta T is the temperature difference between return and supply air across equipment; it is compared with the expected range to assess airflow, charge, and capacity.
- Frozen evaporator causes
- A frozen evaporator can result from low airflow, low refrigerant charge, restricted metering, or low return-air temperature; each causes coil temperature below freezing.
- Lockout/tagout
- Lockout/tagout isolates hazardous energy, such as electrical or gas, with locks and tags before servicing equipment to prevent unexpected startup or release.
- GFCI
- A ground-fault circuit interrupter detects imbalance between hot and neutral conductors and opens the circuit to reduce shock hazard in wet or outdoor locations.
- Permit
- A permit is official authorization from the local authority to install or alter regulated equipment; work must follow approved plans and pass required inspections.
- Manual D
- ACCA Manual D is the residential duct design method that selects duct sizes and fittings based on available static pressure, total effective length, and room airflow.
- Combustion analysis
- Combustion analysis measures flue-gas oxygen, carbon dioxide, temperature, and carbon monoxide to calculate excess air and steady-state efficiency and verify safe burner operation.