BPI Building Analyst flashcards

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

Stack effect

Buoyancy-driven pressure difference caused by indoor-outdoor temperature difference; warm air rises and exits high, drawing cold air in low.

Neutral pressure level

The height in a building where indoor and outdoor pressures are equal; above it air exfiltrates, below it air infiltrates.

Thermal boundary

The continuous layer of insulation separating conditioned from unconditioned space; it should align with the air barrier.

Vapor retarder classes

Class I below 0.1 perm, Class II 0.1 to 1.0 perm, Class III 1.0 to 10 perm; placement depends on climate and assembly.

Blower door CFM50

Airflow in cubic feet per minute needed to hold the house at 50 Pa pressure difference; the standard metric of envelope tightness.

ACH50

Air changes per hour at 50 Pa, calculated as CFM50 times 60 divided by conditioned volume in cubic feet.

Pressure pan test

A gauge placed over a register grille measures pressure relative to the house; readings above 1-2 Pa indicate duct leakage.

Duct leakage CFM25

Duct airflow measured at 25 Pa reference pressure with registers sealed; reported as a percentage of total system airflow.

Grade I insulation

Insulation installed in full contact on all six sides with no gaps or compression, delivering the nominal R-value.

Rim joist sealing

The band joist at the floor perimeter is a major air leakage path and should be sealed and insulated to wall R-value.

Attic baffles

Rigid channels that keep a one-inch ventilation path at the roof deck and prevent insulation from blocking soffit vents.

Manual J

ACCA method for calculating residential heating and cooling loads from envelope, infiltration, and internal gain inputs.

Sensible heat ratio

Sensible capacity divided by total capacity; oversizing raises SHR and reduces latent moisture removal.

Subcooling method

Charge verification for TXV systems; measured liquid-line temperature minus saturation temperature, typically 8-12 degrees F.

External static pressure

Total pressure resistance of the duct system and filter, measured in inches of water column; keep below about 0.5 in. w.c.

Air-free CO

Measured CO multiplied by 20.9 divided by 20.9 minus measured O2; normalizes flue CO to zero excess air.

Worst-case depressurization

Test that runs all exhaust fans and dryers with doors closed, then verifies combustion appliance draft remains within specification.

ASHRAE 62.2 rate

Whole-house ventilation formula: 0.03 times floor area plus 7.5 times bedrooms plus one, in CFM.

Spillage

Flue gases escaping into the living space instead of up the vent; indicates failed draft and requires appliance shutdown.

Degree-day method

Estimates annual energy from UA, heating degree days, and efficiency; assumes a 65 degree F balance point by convention.

Model calibration

Adjusting model inputs so predicted consumption matches at least 12 months of utility data within about plus or minus 5 percent.

Simple payback

Installed measure cost divided by annual energy savings; ignores measure life, financing, and fuel escalation.

Interactive effects

When one measure changes the savings of another, so savings cannot be summed linearly across a retrofit package.

Savings-to-investment ratio

Present value of lifetime savings divided by installed cost; a ratio above 1.0 indicates a cost-effective measure.

Test-in and test-out

Baseline diagnostic measurements taken before work and repeated after, used to verify performance improvement.

Change order

Written authorization for work outside the original scope, signed by the client before the additional work proceeds.

Sensible heat equation

Q equals 1.08 times CFM times temperature difference in degrees F, giving Btu per hour for air at standard conditions.

Latent heat equation

Q equals 0.68 times CFM times humidity ratio difference in grains per pound, giving Btu per hour of latent load.

Psychrometric chart

Graph of air properties including dry-bulb, wet-bulb, dew point, humidity ratio, and enthalpy at a given pressure.

Thermal bridging

Heat flow through framing members that bypasses insulation, reducing whole-assembly R-value below the cavity value.

Effective leakage area

Estimated equivalent hole size in square inches at 4 Pa, often approximated as CFM50 divided by 18 for homes.

Leakage curve exponent

The exponent n in Q equals C times pressure to the n; residential values typically fall between 0.6 and 0.75.