BEMP cheat sheet

Conduction: q = U × A × ΔT = A × ΔT / R_total, where R_total = Σ(L/k) for each layer plus inside and outside film resistances.

Sensible air heat: Q_s = 1.08 × CFM × ΔT (Btu/h) or 1.21 × L/s × ΔT (W); latent heat: Q_L = 4,840 × CFM × ΔW with ΔW in grains/lb.

Degree-day estimate: E = (UA × HDD × 24) / η; accuracy requires the balance point to match the building balance temperature rather than a fixed 65°F.

EER = 3.412 × COP. SEER and HSPF are seasonal ratings and cannot be converted to steady-state COP by a single factor.

Fan and pump affinity laws: flow ∝ speed, head/pressure ∝ speed², shaft power ∝ speed³.

SHGC = directly transmitted solar plus the fraction of absorbed solar that flows inward; it and visible transmittance trade off in glazing selection.

Infiltration driving forces are stack effect (indoor-outdoor temperature difference) and wind; models use either effective leakage area (crack method) or air-change rates.

Steady-state whole-building balance: internal + solar + HVAC gains equal envelope + infiltration + ventilation losses; thermal mass makes the real problem transient and shifts peaks.

ASHRAE Standard 140 (BESTEST) defines analytical, empirical, and comparative validation cases; Standard 90.1 Appendix G defines baseline modeling rules.

Zone rule: one thermal zone per HVAC control zone; interior spaces with no envelope exposure can often be aggregated without loss of accuracy.

Weather selection: TMY3/IWEC/CWEC typical-year files for annual energy and Appendix G compliance; design-day (ASHRAE 99.6%/0.4%) conditions for sizing runs.

Time step: 15-minute to hourly is default; shorter steps (e.g., 10 min) are needed when controls, economizers, or thermal-mass interaction govern results.

Layer order matters: placing insulation outside the mass keeps mass inside the conditioned envelope and changes peak timing compared with insulation placed inboard.

Appendix G baseline HVAC is assigned by building type and conditioned floor area, with prescribed fan power limits (e.g., 0.35 W/cfm for VAV) and economizer requirements.

Equipment performance curves (biquadratic/cubic) are fits valid only in the rated range; extrapolation outside it produces unrealistic capacity and power.

Calibration thresholds per ASHRAE Guideline 14: monthly NMBE within ±5% and CV(RMSE) ≤15%; hourly NMBE within ±10% and CV(RMSE) ≤30%.

Every conditioned zone requires a thermostat; spaces left unassigned default to uncontrolled, a common source of silent model errors.

Schedules are fractional multipliers (0 to 1) applied to a design level (W/ft², cfm/ft², people/ft²) for each hour of the year.

EUI = annual site energy (kBtu) ÷ conditioned floor area (ft²); source EUI applies site-to-source multipliers that include generation and delivery losses.

90.1 Appendix G acceptance checks: unmet load hours ≤300 per year, and proposed design energy cost not exceeding the baseline budget.

Report energy and demand together - annual kWh/therms plus peak kW and time-of-use cost - because measures that cut peaks may barely change annual consumption.

Comfort evaluation uses ASHRAE Standard 55: PMV within ±0.5 and PPD ≤10%, plus zone temperature exceedance hours in addition to unmet load hours.

Normalize savings for weather using regression on heating and cooling degree days before comparing simulated results with measured data.

Benchmark end-use results against CBECS or ENERGY STAR ranges before drawing conclusions; an EUI far outside the range signals an input error.

Attribute savings with parametric runs that change one variable at a time, separating design effects from modeling-assumption effects.

Baseline and proposed models must share identical schedules, setpoints, and weather files; otherwise the comparison is invalid.

ASHRAE Standard 209 defines modeling cycles (simple box, conceptual, detailed loads, HVAC, compliance); fidelity increases only as design decisions are fixed.

ASHRAE Guideline 14 governs savings determination, calibrated simulation, and uncertainty analysis; IPMVP defines measurement boundary options A through D.

QA checklist: geometry versus drawings, space/zone assignment, schedule totals, fan and pump power, outside-air rates, and equipment capacities versus schedules.

Energy balance reconciliation: modeled end uses plus unaccounted losses must be consistent with envelope loads driven by the weather file.

Document the weather file name, software name and version, code version, and every assumption not derivable from drawings.

Version control: a unique run identifier for each simulation, with input file, output report, and assumptions memo archived together.

Check for convergence and simulation warnings or errors before any results are analyzed or reported.

Independent peer review with a rerun of at least one key parametric case verifies reproducibility before results are released.