BEMP key terms

A software-based method that predicts annual energy consumption by simultaneously solving envelope heat transfer, internal loads, and HVAC system performance for every zone at each timestep.

A rigorous load calculation technique that writes an energy balance on each interior and exterior surface and on the zone air, solving all equations simultaneously rather than sequentially.

A simplified cooling load calculation that uses periodic response factors and radiant time factors to convert heat gains into loads, approximating heat balance results with far less computation.

A set of coefficients relating heat flux at one face of a wall or roof to past fluxes and temperatures, capturing transient conduction without solving for internal layer temperatures.

The ability of building materials to absorb, store, and later release heat, which delays and reduces peak cooling loads and smooths indoor temperature swings.

A space or group of spaces with a common setpoint and control, modeled by the simulation engine as a single well-mixed air volume at one temperature.

A synthetic 24-hour weather profile representing near-extreme conditions for a site, used to size equipment rather than to estimate annual energy use.

A hypothetical HVAC system that supplies exactly the heating or cooling each zone requires with no efficiency or distribution losses, isolating zone loads from system effects.

Unintentional outdoor air leakage through cracks, joints, and openings in the envelope, driven by wind pressure and by indoor-outdoor temperature differences.

The quantity of outdoor air intentionally supplied to a space for acceptable indoor air quality, usually set by code or standard based on occupancy and floor area.

An assumption that connected loads or occupants are not all at full value at the same moment, so realistic peak demand is lower than the simple sum of components.

A relationship describing how equipment capacity and efficiency change below rated capacity, essential because most equipment runs at part load for most of the year.

The ratio of useful heating or cooling delivered to the energy consumed, evaluated at a specified rating condition for a chiller, heat pump, or packaged unit.

An hourly, one-year weather dataset assembled from long-term site records to represent typical conditions, used as the driver for annual simulations.

The interval at which the simulation solves its governing equations; shorter steps generally improve accuracy for fast-responding systems but increase run time.

An hourly or sub-hourly profile defining occupancy, lighting, plug loads, or setpoints across the year, which strongly drives modeled loads and energy use.

The simulation engine's automatic calculation of equipment capacities, airflows, and water flows from design-day loads, replacing manual capacity assumptions.

A sizing run uses design-day conditions to fix equipment capacity, while the annual simulation applies those capacities across a full weather year to estimate energy.

A batch of simulations in which selected inputs are varied systematically, allowing results for alternative designs or control strategies to be compared directly.

A control strategy that brings in cool outdoor air for free cooling when conditions allow, reducing or eliminating mechanical cooling energy.

Modulating outdoor air intake in response to measured or estimated occupancy, such as carbon dioxide sensing, to avoid unnecessary fan and conditioning energy.

Energy gained or lost by air or water distribution systems running through unconditioned space, which must be modeled to avoid overstating savings.

The number of hours a zone drifts outside its allowed throttling range because the system cannot meet the load; a primary indicator of model and sizing quality.

Annual energy consumption per unit of floor area, reported as site or source energy, used to benchmark a design against peers, targets, or code.

The allocation of total modeled energy among categories such as heating, cooling, fans, lighting, and plug loads, used to target efficiency measures.

Adjusting model inputs within justifiable ranges so that simulated energy use closely matches measured utility data for the same period.

The root-mean-square error between simulated and measured data divided by the mean measured value and expressed as a percentage; lower values mean a better fit.

The average difference between simulated and measured values over a period, expressed as a percentage of measured data, revealing systematic over- or under-prediction.

Summing first cost, operating, maintenance, and replacement costs over a study period and discounting them to present value so alternatives can be compared.

The tariff that converts modeled consumption and demand into cost, including energy charges, demand charges, and time-of-use pricing periods.

Systematically varying key inputs to see how much outputs change, revealing which assumptions dominate results and deserve the closest scrutiny.

A written agreement defining modeling objectives, deliverables, level of detail, schedule, software, and responsibilities before analysis begins.

The chosen granularity of geometry, zoning, and system representation, matched to the purpose of the analysis and the available budget and data.

Tracking model file revisions, input changes, and software versions so that any reported result can be traced to a specific, reproducible model state.

A structured check of model inputs and outputs, covering geometry, schedules, loads, unmet hours, and energy balance, to catch errors before results are used.

A written record of modeling assumptions, input sources, software and version, and results, allowing a reviewer to understand and reproduce the analysis.

A documented alternative modeling approach approved by the rating authority when the simulation tool cannot represent a particular technology or system.

A standardized procedure, such as the method in ASHRAE 90.1 Appendix G, prescribing how baseline and proposed models are built and compared to rate efficiency.