AEE Certified Energy Auditor cheat sheet

ASHRAE Level 1 (walk-through) uses 12 months of utility bills plus a brief site walk to identify no- and low-cost measures and a preliminary EUI benchmark.

Level 2 (energy survey and analysis) adds an end-use breakdown, a bin or hourly model, and cost and payback estimates for each recommended measure.

Level 3 (detailed analysis) requires a calibrated simulation, design-level scoping of capital measures, and a measurement and verification plan.

Define the audit boundary and baseline period (typically 12 consecutive months) before collecting data, then normalize for weather, occupancy, and floor-area changes.

EUI = annual site energy (kBtu or kWh) divided by conditioned floor area; benchmark it against ENERGY STAR Portfolio Manager medians for the property type.

Energy Cost Index (ECI) = annual utility cost divided by floor area; use it to rank buildings within a portfolio before committing audit effort.

Per ASHRAE Guideline 14, a monthly utility-bill regression baseline needs CV(RMSE) of 15% or less and NMBE within plus or minus 5% to be defensible.

Screen measures by simple payback first, then re-rank by life-cycle cost or NPV before recommending capital-intensive projects.

Energy balance rule: purchased energy = end-use consumption + distribution losses + conversion losses; unaccounted energy above roughly 10% of the total signals a metering or model gap.

Load factor = average demand divided by peak demand over the period; values below about 0.40 point to demand-charge exposure or oversized equipment.

Degree-day model: E = a + b x HDD for heating, E = a + b x CDD for cooling; the intercept a is the weather-independent base load.

A four-parameter model adds both HDD and CDD and is required when the building carries significant heating and cooling load.

Check demand ratchet clauses (for example, 80% of the highest monthly peak billed for 11 months) before claiming any demand savings.

The bin method multiplies annual hours in each temperature bin by equipment part-load performance to estimate HVAC energy without a full simulation.

Benchmark EUI against CBECS or ENERGY STAR medians, but adjust for operating hours, plug-load intensity, and climate zone before drawing conclusions.

Typical commercial end-use split is HVAC 40-60%, lighting 15-25%, and plug loads 10-20% of site energy; reconcile the split against bills rather than assuming it.

Unit conversions: 1 kWh = 3,412 Btu; 1 therm = 100,000 Btu = 29.3 kWh; 1 ton of refrigeration = 12,000 Btu/h = 3.517 kW.

Interval data at 15-minute resolution supports load-shape, peak-demand, and schedule analysis; monthly bills cannot resolve peaks or after-hours operation.

Clamp-on power meters are typically accurate to plus or minus 2% of reading; verify CT ratio, phase orientation, and true-RMS capability on VFD-fed circuits.

For engineering measurements, a common sampling target is 90% confidence with plus or minus 10% precision.

Cross-check sub-metered totals against utility bills; a discrepancy over 10% indicates missing loads, CT errors, or unbilled fuel.

Power factor = kW divided by kVA; values below about 0.90 can trigger utility penalties and reduce usable transformer capacity.

Weather-normalize with TMY3 or actual station data for the baseline period, not long-run averages, when regressing consumption.

Document every data gap and the method used to fill it (interpolation versus engineering estimate); each number in the report must be traceable.

Simple payback (years) = total installed cost divided by annual savings; it ignores the discount rate and all savings after the payback date.

NPV = sum of [cash flow in year t divided by (1+i)^t] minus initial cost; accept measures with NPV greater than zero at the organization's discount rate.

IRR is the discount rate that drives NPV to zero; compare it against the hurdle rate, commonly 8-12% for public and higher for private capital.

Capital recovery factor CRF = i(1+i)^n divided by [(1+i)^n - 1]; annualized cost = initial cost x CRF.

Life-cycle cost analysis must include energy escalation, O&M, replacement, and salvage over the study period, typically 20-30 years.

Use real discount rates with real escalation rates, or nominal with nominal; mixing the two distorts NPV.

Levelized cost of conserved energy = (annualized capital + incremental O&M) divided by annual kWh saved; compare it with the utility's marginal rate.

Value demand savings at the marginal demand charge plus any ratchet effect, and value energy savings at the marginal rather than average energy rate.

Efficacy in lm/W: incandescent 10-17, halogen 15-25, T8 fluorescent 85-100, metal halide 60-100, high-pressure sodium 80-140, LED 100-160 and higher.

Lumen method: N = (E x A) divided by (lumens per luminaire x CU x LLF), where E is the target maintained illuminance and A is the area.

LLF = lamp lumen depreciation x luminaire dirt depreciation x ballast factor; typical design values fall between 0.70 and 0.85.

LPD = total connected lighting watts divided by floor area; compare against the ASHRAE 90.1 space-by-space allowance before proposing a retrofit.

Occupancy sensors save roughly 20-30% in intermittently occupied spaces such as restrooms, private offices, and conference rooms.

Photosensor daylight dimming in perimeter zones typically saves 20-40% of the lighting energy in those zones.

Replacing T12 fixtures with magnetic ballasts by T8 lamps with electronic ballasts cuts lighting energy about 35-45% at comparable light output.

For any LED retrofit, verify delivered lumens, CCT, CRI, L70 driver life, dimming compatibility, and that existing wiring and voltage drop support the new load.

COP = cooling output in kW divided by electrical input in kW; EER = Btu/h divided by watts; EER = 3.412 x COP; kW/ton = 12 divided by EER.

Affinity laws for fans and pumps: flow varies with speed, head with speed squared, power with speed cubed; a 20% speed reduction cuts power about 49%.

An air-side economizer is beneficial when outdoor air enthalpy (or dry-bulb in arid climates) is below the return-air condition.

Chilled-water supply reset upward and condenser-water reset downward each save roughly 1-2% of chiller energy per degree Fahrenheit within design limits.

Boiler stack loss rises about 1% per 40 degrees Fahrenheit of excess flue-gas temperature; target roughly 15% excess air on natural-gas boilers.

Condensing boilers only capture latent heat when return water is below about 130 degrees Fahrenheit; without low return temperature the condensing premium is lost.

Demand-controlled ventilation with CO2 sensors saves fan and conditioning energy wherever occupancy varies widely.

Night setback saves roughly 1-3% of heating or cooling energy per degree Fahrenheit of setback held for 8 hours, depending on envelope and thermal mass.

Verify economizer dampers, linkages, and changeover sensors during the audit; failed economizers are common and invisible in utility bills.

DHW energy: Q in Btu = gallons x 8.33 lb/gal x 1.0 Btu/(lb x degree F) x temperature rise; divide by system efficiency to get input energy.

Store hot water at 140 degrees Fahrenheit or above where Legionella risk exists, and temper down to no more than 120 degrees Fahrenheit at the fixture to prevent scalding.

Standby loss dominates low-use DHW systems; inspect tank insulation R-value, pipe insulation coverage, and recirculation loop controls.

Continuous recirculation can waste 15-25% of DHW energy; timer-based or demand-controlled recirculation reduces that loss substantially.

Heat-pump water heaters deliver COP of 2-3 but need roughly 700-1,000 cubic feet of tempered air and add a space-cooling load.

Condensing gas water heaters reach UEF above 0.90, while atmospheric units with standing pilots typically rate 0.55-0.65.

Low-flow fixtures (1.5 gpm showerheads, 0.5 gpm aerators) cut hot-water draw without requiring occupant behavior change.

Drain-water heat recovery units reclaim 40-60% of the heat in greywater and perform best on showers with high simultaneous flow.

Motor efficiency classes are IE1 standard, IE2 high, IE3 premium (NEMA Premium), and IE4 super-premium; size motors to run in the 75-100% load band.

Slip-method load estimate: load fraction = (synchronous speed - measured speed) divided by (synchronous speed - rated full-load speed).

Rewind versus replace: replace when rewind cost exceeds about 50-60% of a new premium-efficiency motor or when rewind efficiency loss exceeds 1-2%.

VFDs on variable-torque loads such as fans and pumps capture cube-law savings; on constant-torque loads, savings scale linearly with speed.

Compressed air specific power is typically 18-22 kW per 100 cfm at 100 psig, and one horsepower of compressor delivers roughly 4-5 cfm.

Lowering system pressure by 2 psi reduces compressor energy about 1%; every 2 psi of unnecessary pressure carries a measurable annual cost.

Leaks typically waste 20-30% of compressed air output; an ultrasonic leak survey belongs in every compressed-air audit.

Storage sizing: 1-3 gallons per cfm for demand events, up to 5 gallons per cfm on highly fluctuating systems, located near the largest loads.

Heat recovery from air- or oil-cooled compressors can supply 50-90% of compressor input energy as useful hot water or space heating.

Conductive heat flow Q = U x A x delta-T; the U-factor is the reciprocal of the R-value (U = 1/R).

Insulation R-values add in series only; thermal bridging through steel studs, slab edges, and shelf angles substantially reduces the effective assembly R-value.

Blower-door CFM50 divided by roughly 20 approximates natural infiltration, and 0.1-0.3 ACH50 per 1,000 square feet of envelope is a common tightness range.

Window performance requires three numbers: U-factor for conduction, SHGC for solar gain, and visible transmittance for daylight.

In cooling-dominated climates specify SHGC of 0.25-0.35 to cut solar gain; in heating-dominated climates keep higher SHGC on south-facing glass.

Cool roofs are characterized by solar reflectance and thermal emittance, which combine into the Solar Reflectance Index.

Air sealing typically saves 5-15% of heating and cooling energy, but only when the envelope is a dominant loss and ducts sit inside the boundary.

Continuous rigid insulation above the roof deck avoids the thermal bridging that batt insulation between joists leaves in place.

BAS architecture: field sensors and actuators feed DDC controllers, which report to a supervisory workstation over BACnet, Modbus, or LonWorks.

EMCS is the legacy term for a building automation system with energy functions such as scheduling, duty cycling, demand limiting, and optimal start.

PAS (process automation system) applies the same control and trending logic to industrial process loops, where setpoint and sequencing savings often exceed HVAC savings.

Optimal start uses indoor and outdoor temperature and building mass to reach setpoint exactly at occupancy, eliminating unnecessary pre-conditioning hours.

Scheduling and night setback are the highest-value, lowest-cost BAS measures; audit the programmed schedule against actual occupancy.

Reset schedules for supply-air temperature, chilled-water temperature, duct static pressure, and condenser-water temperature deliver persistent savings with no hardware.

Trend logs at 15-minute intervals supply the data for measurement and verification and for fault detection; confirm the trends exist and cover the baseline period.

Demand limiting sheds non-critical loads as interval kW approaches a target, reducing demand charges and ratchet exposure.

Fault detection and diagnostics rules catch simultaneous heating and cooling, stuck dampers, and sensor drift that utility bills cannot reveal.

PV annual energy (kWh) is approximately system kW x peak sun hours x 365 x derate factor, where derate is typically 0.75-0.85 for wiring, inverter, soiling, and temperature losses.

Standard test conditions are 1,000 W/m² irradiance at 25 degrees Celsius cell temperature; module output falls roughly 0.3-0.5% per degree Celsius above 25.

Wind power scales with air density x rotor area x velocity cubed; the Betz limit caps extraction at 16/27, or about 59.3%, of the wind's kinetic energy.

CHP efficiency = (electric output + useful thermal output) divided by fuel input; well-designed systems reach 75-85% versus about 50% for separate generation.

Storage sizing: usable kWh = rated kWh x depth of discharge; delivered kWh = usable kWh x round-trip efficiency, which is 85-95% for lithium-ion.

Storage value streams include demand-charge reduction, time-of-use arbitrage, peak shaving, backup capacity, and demand-response revenue.

Ground-source heat pumps reach COP of 3-5 by exploiting stable ground temperature; ground-loop sizing dominates first cost.

Net metering and interconnection tariffs set the value of exported generation; confirm the tariff structure before sizing the array.

Fleet fuel use = miles divided by MPG; report gallons per 100 miles so vehicles of different sizes can be compared on equal footing.

Idling burns roughly 0.5-1.0 gallon per hour in light trucks; anti-idling policy and auxiliary power units eliminate that consumption.

Fuel economy drops sharply above 50 mph because aerodynamic drag rises with the square of speed; speed governance is a measurable efficiency measure.

Under-inflated tires raise fuel consumption about 1-3% for every 10 psi below the recommended cold pressure.

Electric vehicle efficiency is expressed in miles per kWh; a typical light-duty EV uses 0.25-0.35 kWh per mile.

Tailpipe CO2 is about 8.89 kg per gallon of gasoline and 10.18 kg per gallon of diesel; well-to-wheel accounting adds fuel production and delivery emissions.

Route optimization and telematics typically cut fleet fuel 5-15% through fewer miles driven and improved driver behavior.

Alternative-fuel decisions require total cost of ownership: vehicle price premium, fuel cost per diesel-gallon-equivalent, infrastructure, and maintenance.