BPI AC/Heat Pump flashcards

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

Sensible heat formula

Q_s = 1.08 × CFM × ΔT, where Q_s is sensible BTU/h, CFM is airflow, and ΔT is dry-bulb temperature difference. Used at sea level for air.

Latent heat formula

Q_l = 0.68 × CFM × ΔW, where ΔW is humidity ratio difference in grains per pound. Represents moisture removal or addition in BTU/h.

Total heat formula

Q_t = 4.5 × CFM × Δh, where Δh is enthalpy difference in BTU/lb. Combines sensible and latent loads for coil capacity.

Superheat definition

Suction line temperature minus evaporator saturation temperature at the bulb. Target 8–12°F for fixed orifice, 5–10°F for TXV systems.

Subcooling definition

Condenser saturation temperature minus liquid line temperature. Target 8–12°F for TXV, 5–10°F for fixed orifice; indicates charge and condenser performance.

Heat pump reversing valve

A four-way valve that swaps evaporator and condenser roles. In heating, outdoor coil becomes evaporator and indoor coil becomes condenser.

Defrost cycle initiation

Triggered when outdoor coil temperature falls below about 30°F or a pressure/temperature sensor detects frost. Terminates on time or temperature.

Manual J load calculation

ACCA method that calculates room-by-room heating and cooling loads using orientation, insulation, windows, infiltration, and internal gains.

Sensible heat ratio (SHR)

Sensible load divided by total load. Equipment SHR should closely match structure SHR to avoid humidity control problems.

Manual S equipment selection

ACCA procedure for selecting equipment using manufacturer expanded performance data at design conditions rather than nominal capacity ratings.

Manual D duct sizing

Sizes ductwork using friction rate = available static pressure ÷ total effective length. Typical supply friction is 0.08–0.10 in. w.c. per 100 ft.

Balance point

Outdoor temperature at which heat pump capacity equals building heat loss. Below this point, auxiliary heat supplements the heat pump.

ASHRAE 62.2 ventilation

Requires mechanical ventilation when natural infiltration is below 0.35 ACH. CFM = 0.03 × floor area + 7.5 × (bedrooms + 1).

Nitrogen purge brazing

Flow 1–2 psig nitrogen through tubing while brazing to prevent internal oxidation. Use silver-phos or 15% silver alloy depending on joint type.

Evacuation to 500 microns

Evacuate system to 500 microns or below and hold for 10 minutes with pump isolated. Rising microns indicate leak or moisture.

Weigh-in charging

Charge refrigerant by weight when line set length differs from factory charge. Adjust per manufacturer table, typically 0.6 oz per foot of 3/8-inch liquid line.

Temperature split check

Return air dry-bulb minus supply air dry-bulb. Normal cooling split is 18–22°F; low split suggests low airflow or charge issue.

Condensate trap requirement

Trap depth must be at least total static pressure; drain slope 1/8 inch per foot. Secondary pan with float switch is required.

External static pressure

Measured pressure resistance of duct system and components. Compare to fan performance table; target 350–450 CFM/ton cooling, 400–450 CFM/ton heating.

High superheat diagnosis

High superheat with low suction pressure indicates undercharge or restriction. Low superheat with high suction pressure indicates overcharge or overfeed.

High subcooling diagnosis

High subcooling with high head pressure indicates overcharge or condenser airflow restriction. Low subcooling with bubbles indicates undercharge.

Compressor amp draw check

Measure compressor amps and compare to nameplate RLA. Amps above RLA with high head pressure suggest mechanical or electrical fault.

Capacitor microfarad test

Use a multimeter with capacitance function to measure microfarads. Replace capacitor if reading is outside ±10% of rated value.

Leak detection methods

Electronic leak detector, UV dye, or nitrogen pressure test at 150–300 psig. Never use oxygen or acetylene for pressure testing.

Balometer airflow verification

Measure CFM at each register with a balometer. Total measured airflow should match design within ±10%.

Thermostat voltage check

Verify 24 VAC ±10% at R–Y, R–G, and R–W terminals during call. Check anticipator or cycle rate settings for proper operation.

Lockout/tagout procedure

Disconnect power at breaker, verify with meter, and apply lock before servicing. Never rely on thermostat off position.

R-410A pressure safety

R-410A operates at about 1.6 times R-22 pressure. Use gloves and eye protection; never heat a sealed system or mix refrigerants.

EPA Section 608 certification

Technicians must be certified to purchase or handle refrigerant. Recovery is required before opening system; venting is prohibited.

Electrical safety verification

Test 24 VAC control voltage and line voltage separately. Treat all conductors as live until tested with a meter.

Startup documentation

Record model/serial, refrigerant type and charge, filter sizes, startup readings, and deficiencies on invoice for warranty and reference.

Fall protection threshold

Use fall protection on roofs above 6 feet. Wear safety glasses, gloves, and steel-toe boots as personal protective equipment.