BEMP flashcards

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

U-factor

The overall heat transfer coefficient of an assembly, equal to the reciprocal of its total thermal resistance R; expressed in Btu/h·ft²·°F or W/m²·K.

Sensible heat equation

Q = 1.08 × CFM × ΔT for air in English units, since 1.08 = 60 × 0.075 lb/ft³ × 0.24 Btu/lb·°F; the SI form is Q = 1.21 × L/s × ΔT.

Degree-day method

Estimates annual heating or cooling energy as UA × HDD × 24 divided by system efficiency. Accuracy depends on using a balance point near the building's actual balance temperature.

Thermal mass effect

Mass in the envelope or interior stores and releases heat, shifting and dampening peak loads. Effects are largest with wide daily temperature swings and night ventilation.

COP versus EER

COP is dimensionless cooling output divided by energy input at a rating condition. EER equals COP × 3.412 in Btu/Wh, while SEER is a seasonal rather than steady-state rating.

Fan affinity laws

For a fixed system, airflow varies with fan speed, pressure with speed squared, and shaft power with speed cubed, so VFD savings scale roughly with the cube of flow.

Solar heat gain coefficient

The fraction of incident solar radiation admitted through a fenestration, including directly transmitted solar plus absorbed solar that flows inward; lower SHGC reduces cooling loads.

Unmet load hours

Hours in which a zone's HVAC system cannot hold the setpoint. ASHRAE Standard 90.1 Appendix G limits the annual total to 300 hours for both baseline and proposed models.

Thermal zone definition

A building volume served by one HVAC control zone or sharing a single thermostat. Splitting zones more finely than the HVAC system increases run time without improving accuracy.

Typical meteorological year

A weather file built from 12 representative months selected from multi-year records, preserving typical rather than extreme conditions; used for annual energy, not equipment sizing.

Fractional schedule and design level

Hourly schedule values between 0 and 1 multiply a design level, such as W/ft² or cfm/ft², to produce the actual load in each hour of the simulated year.

Biquadratic performance curve

An equation fitted to manufacturer data that expresses equipment capacity or power as a function of two variables, typically entering water temperature and entering air wet-bulb temperature.

Baseline model per Appendix G

A budget building derived from the proposed design but with envelope, lighting, and HVAC replaced by prescriptive baseline values, simulated with identical weather and schedules.

Economizer high-limit control

Free cooling that allows up to 100% outdoor air when conditions permit, then disables above a dry-bulb, enthalpy, or dew-point high limit set by climate zone.

Night setback and setup

Unoccupied thermostat setpoints that reduce heating or cooling during off-hours. Realized savings depend on building mass, reset schedule, and system recovery time.

CV(RMSE)

The coefficient of variation of the root mean square error, used to judge calibration under ASHRAE Guideline 14; thresholds are 15% for monthly data and 30% for hourly data.

Energy use intensity

Annual site energy divided by conditioned floor area, usually reported in kBtu/ft²·yr, used to benchmark a model against CBECS or ENERGY STAR targets.

Site versus source energy

Site energy is measured at the building meter. Source energy adds upstream generation and delivery losses using national or regional conversion factors.

300 unmet load hour limit

The Appendix G cap on hours per year when HVAC cannot meet zone setpoints. Exceeding it requires correcting the model before compliance or savings results are reported.

PMV and PPD

ASHRAE Standard 55 comfort indices: predicted mean vote on a −3 to +3 scale, and predicted percentage of dissatisfied. Acceptable comfort is PMV within ±0.5 and PPD ≤10%.

Weather normalization

Adjusting measured or modeled energy to a common climate using regression against heating and cooling degree days, so periods with different weather can be compared fairly.

Peak demand versus annual energy

Measures such as demand-controlled ventilation can reduce peak load while barely changing annual consumption, or the reverse; both metrics must be reported and analyzed separately.

End-use breakdown

Allocation of annual consumption among heating, cooling, fans, pumps, lighting, plug loads, and service hot water; used to confirm the model behaves plausibly before comparing designs.

Life-cycle cost analysis

Present value of capital, energy, maintenance, and replacement costs over a study period, discounted at an assumed rate; Appendix G uses a 30-year study period.

Basis of design

The document stating owner program, design assumptions, weather location, code version, and modeling scope; it defines what the model is required to represent.

ASHRAE Standard 209

A framework for simulation-aided design that defines numbered modeling cycles, from simple box through compliance, whose rigor increases as design decisions are finalized.

Quality assurance checks

Verification of geometry, zoning, schedules, and equipment inputs, plus mass and energy balance and comparison of EUI with benchmark ranges before results are released.

Model version control

Named, dated, archived copies of the input file plus a change log for every simulation run, so any reported number traces back to its exact model.

Archiving deliverables

Retaining input and output reports, the weather file, software name and version, and the assumptions memo so results can be reproduced years later by another modeler.

Independent model review

A second qualified modeler checks inputs against drawings and specifications, reruns at least one key parametric case, and signs off on assumptions before submission.

ASHRAE Guideline 14

Provides methods for determining measured energy savings, including calibrated simulation and whole-building metering, along with statistical thresholds for declaring a model calibrated.

Modeling scope statement

A written agreement listing which systems, spaces, and end uses are represented, which are excluded, and the intended use of results, preventing later disputes over expectations.