AK HVAC flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Sensible heat equation

Btu/h = 1.08 × CFM × temperature difference in °F, using standard air at 0.075 lb/ft³ and 0.24 Btu/lb·°F specific heat.

One ton of refrigeration

A cooling rate equal to 12,000 Btu per hour, originally defined as the heat absorbed by melting one ton of ice in 24 hours.

Sensible heat ratio

The ratio of sensible heat removed to total heat removed by a coil; typical comfort cooling values range from 0.70 to 0.80.

Standard air density

0.075 pounds per cubic foot at 70°F and sea level; density falls about 3.5% per 1,000 ft of elevation, reducing mass flow.

AFUE definition

Annual Fuel Utilization Efficiency; the seasonal efficiency rating of furnaces and boilers, with condensing units typically above 90%.

Combustion air requirement

Approximately 50 cubic feet of indoor air per 1,000 Btu/h of appliance input when drawn from an unconfined space.

Hydronic Btu formula

Btu/h = 500 × gallons per minute × temperature drop in °F, using water at 8.33 lb per gallon and 60 minutes per hour.

Furnace temperature rise

Supply air temperature minus return air temperature; it must fall within the range printed on the furnace rating plate.

Ventilation rate procedure

ASHRAE 62.1 method: breathing zone rate equals people component times occupants plus area component times floor area.

Velocity pressure formula

VP in inches of water equals (velocity in fpm divided by 4005) squared, using the standard air constant 4005.

Heat recovery ventilator

An HRV transfers sensible heat between exhaust and supply airstreams; an ERV also transfers moisture, useful in tight Alaska envelopes.

Duct velocity guidelines

Typical design targets: 600–900 fpm in supply trunks, 400–700 fpm in branches, and 300–500 fpm in return ducts.

Superheat measurement

Actual suction line temperature minus the saturation temperature at suction pressure; target 8–12°F at the evaporator outlet with a TXV.

Subcooling measurement

Saturation temperature at the liquid-line pressure minus the actual liquid-line temperature; target 8–12°F for TXV systems.

Refrigerant glide

The temperature difference between bubble point and dew point in a zeotropic blend such as R-410A or R-407C during phase change.

Recovery cylinder fill limit

A refrigerant recovery cylinder may never be filled beyond 80% of its water capacity by weight, to allow thermal expansion.

Copper tubing types

Type K is heavy wall for underground use, Type L is standard above ground, and Type M is light wall for interior work only.

Equal friction duct sizing

A duct design method that maintains a constant pressure loss per foot of length through the entire supply and return system.

Condensate drain slope

Drains must slope at least 1/8 inch per foot toward the discharge and include a trap at the air handler to prevent air bypass.

Insulation R-value per inch

Approximate values: fiberglass 3.7, closed-cell polyisocyanurate 6.0, and spray polyurethane foam 6.5 per inch of thickness.

Ohm's law and power

E = I × R; single-phase watts = volts × amps × power factor; three-phase watts adds a 1.732 multiplier.

Thermostat terminal letters

R is 24V power, W is heat, Y is cooling, G is fan, C is common, and O or B is the reversing valve.

Motor nameplate ratings

Full-load amps, minimum circuit ampacity, and maximum overcurrent protection determine conductor size and breaker rating for the unit.

Run capacitor tolerance

A capacitor's measured microfarads should be within plus or minus 10% of the nameplate rating; outside that range it should be replaced.

EPA Section 608 certification

Federal credential required to service refrigerant-containing equipment; types cover small appliances, high pressure, low pressure, or universal.

Carbon monoxide properties

CO is colorless, odorless, and slightly lighter than air; it bonds to hemoglobin and is detected only with a calibrated instrument.

Manifold gauge color code

Blue hose connects to the low side, red to the high side, and yellow to the center port for charging or recovery.

Nitrogen pressure testing

Leak testing uses dry nitrogen regulated to the system design pressure; oxygen and acetylene must never be used as trace gases.

Alaska Mechanical Administrator

State license required for mechanical contractor work; the administrator must meet experience requirements and pass a written examination.

Alaska HVAC journeyman licensing

There is no statewide HVAC journeyman license; licensing is handled by municipalities such as Anchorage and Fairbanks.

Alaska Business License

Required for any person or entity conducting business in the state, renewed every two years through the Department of Commerce.

Alaska workers' compensation

Under Alaska Statute Title 23, employers must carry workers' compensation coverage; independent-contractor status is narrowly defined.