Energy Modeling, Analysis, and Prioritizing Improvements
Modeling Basics
Understand that energy models are calibrated approximations. Know the inputs that dominate results: envelope areas and R-values, infiltration (CFM50-derived), HVAC efficiency (AFUE, SEER, HSPF), and internal gains. Recognize degree-day methods and the difference between baseline and proposed models. Traps include double-counting savings (e.g., air sealing and duct sealing both reducing infiltration), using nameplate efficiency instead of measured, and ignoring interactive effects.
Prioritization Logic
Rank measures by savings per dollar, but weight by health and safety and durability first. Typical order: combustion safety and moisture fixes, air sealing, insulation, then equipment replacement. Understand interactive effects: tightening a house reduces infiltration savings from duct sealing; adding insulation reduces the value of a high-efficiency furnace. Use marginal cost reasoning, not average cost.
Simple Payback and Life-Cycle
Simple payback = installed cost / annual savings. Life-cycle cost accounts for fuel escalation and equipment life. Know that payback ignores fuel price changes and that low-income programs may prioritize non-energy benefits.
Worked example: A $1,200 air-sealing job cuts 300 therms/year at $1.20/therm = $360/year savings; payback = 1,200/360 = 3.3 years. Trap: if duct sealing in the same scope also claims the same 300 therms, the combined savings are overstated-model them together.
Reporting
Present a clear baseline, proposed scope, estimated savings, and uncertainty range. Avoid promising exact savings.