CA CEG common mistakes
CA CEG · Understand the traps and how to avoid them.
Treating simple payback as the sole decision metric and rejecting projects whose payback exceeds an arbitrary cutoff, without computing life-cycle cost, net present value, or internal rate of return over the equipment life.
Simple payback is the easiest calculation and appears in most introductory examples, so candidates default to it and forget that it ignores cash flows after the payback point, time value of money, and salvage value. Long-lived measures such as envelope upgrades or variable-frequency drives then look unattractive.
What to do instead
For every economic question, state the metric being asked for and its assumptions. Practice converting the same cash-flow stream into payback, NPV, IRR, and savings-to-investment ratio, and note explicitly which metric handles long horizons, capital rationing, and mutually exclusive alternatives.
Applying a blended or average utility rate to savings calculations when the measure reduces consumption in a specific block or time-of-use period, or ignoring demand charges entirely.
Candidates see a single cents-per-kWh figure on the bill and use it uniformly, missing that energy is billed in tiers or time-of-use periods and that demand, ratchets, and power factor penalties can dominate savings for load-reducing measures.
What to do instead
Before calculating savings, reconstruct the tariff: energy blocks, time-of-use periods, demand charge structure, ratchet clauses, and power factor or reactive power charges. Assign each hour of avoided consumption to its correct rate and compute demand savings separately from the monthly peak reduction.
Confusing measured energy savings with measured consumption change, i.e., reporting the difference between post-retrofit and pre-retrofit bills as savings without adjusting for weather, occupancy, production, or other baseline conditions.
The intuitive comparison of before and after utility bills is simple and persuasive, and candidates under time pressure skip the regression or bin analysis that separates true measure effects from confounding variables.
What to do instead
Always establish a baseline model relating energy to relevant independent variables (degree-days, production volume, occupancy), then compute avoided energy use as baseline-model prediction minus actual post-installation consumption. State the adjustment method, the baseline period, and the uncertainty.
Using nominal or design airflow and static pressure to estimate fan power instead of applying the fan laws to actual operating conditions, and ignoring part-load behavior when estimating motor and drive savings.
Fan and pump affinity relationships are memorized in simplified form, so candidates apply the cube-law reduction across the full load profile without accounting for system curves, static pressure setpoints, bypass, or throttling that limit actual savings.
What to do instead
Sketch the system curve and the control method, then apply the affinity laws only within the range where they hold. Weight savings by an annual load profile (hours at each flow fraction) and account for minimum flow, static pressure reset, and drive and motor efficiency at part load.
Sizing or evaluating motors and drives on nameplate horsepower alone, neglecting efficiency class, load factor, power factor, and the difference between input power and shaft output.
Nameplate data is the most visible information, and candidates equate rated horsepower with actual draw, missing that a lightly loaded premium-efficiency motor may operate far from its best-efficiency point and that power factor correction affects billing.
What to do instead
Convert between shaft power and electrical input using efficiency at the actual load fraction. Estimate load from current, slip, or input power measurement, then compute annual energy with the part-load profile. Evaluate power factor separately and check whether capacitors or a synchronous condenser are justified.
Performing a walk-through audit and presenting it as a full investment-grade audit, omitting end-use breakdowns, measured data, and uncertainty ranges needed for financing.
Time pressure and the desire to deliver recommendations push candidates to skip submetering, trending, and engineering calculations, so the report lacks the rigor a lender or executive needs to commit capital.
What to do instead
Match audit scope to purpose: screening, targeted, or investment-grade. For investment-grade work, specify measurement duration and instruments, develop an end-use breakdown that reconciles to the utility bill, document assumptions and their uncertainty, and present savings ranges rather than single-point values.
Ignoring combustion efficiency versus thermal efficiency and failing to account for stack losses, excess air, and blowdown when evaluating boiler plant improvements.
Candidates treat boiler efficiency as a single number and focus on the burner, missing that flue gas temperature, excess oxygen, scaling, and blowdown rate determine real fuel use, and that heat recovery options depend on dew point and load.
What to do instead
Compute stack loss from flue temperature and oxygen or carbon dioxide readings, distinguish gross from net calorific value bases, and quantify blowdown and radiation losses. Evaluate economizers and air preheaters against acid dew point limits and part-load operation.
Designing envelope or HVAC recommendations without checking for moisture, infiltration, and ventilation interactions, such as adding insulation or air sealing without addressing combustion air, make-up air, or internal gain removal.
Candidate thinking is compartmentalized by domain, so an envelope measure is evaluated on conduction savings alone, missing that tighter envelopes change infiltration, pressure relationships, and ventilation adequacy, and can create backdrafting or indoor air quality problems.
What to do instead
For any envelope or air-sealing measure, evaluate the whole-building effect: combustion appliance zone testing, ventilation rates per ASHRAE 62.1, pressure balance, and interaction with economizer and fan schedules. Present savings net of any added ventilation or humidification energy.
Assuming a renewable or combined heat and power project's savings equal the displaced utility energy at retail rates, without accounting for interconnection limits, standby charges, export compensation, or thermal load matching.
The simple avoided-cost framing is intuitive, and candidates overlook that export rates are often below retail, that standby and demand charges persist, and that CHP economics depend on coincident thermal load duration.
What to do instead
Build an hourly or monthly energy balance matching generation to site load and thermal demand. Apply the actual export or net metering tariff, include standby and interconnection costs, and compute the thermal load duration curve before sizing CHP. Report savings under multiple tariff scenarios.
Reporting emissions or sustainability benefits using a single generic emission factor and ignoring scope boundaries, baseline choice, and units, so claimed reductions cannot be reconciled or verified.
Emission factors are often taken from memory or a headline source, and candidates mix units (pounds versus kilograms, carbon versus carbon dioxide equivalent) or double count purchased electricity and on-site fuel, producing numbers that fail review.
What to do instead
State the boundary (scope 1, 2, or 3), cite the emission factor source and year, convert all quantities to a consistent unit such as metric tons of carbon dioxide equivalent, and show the calculation chain from energy to emissions. Distinguish location-based from market-based electricity accounting.