Chicago Energy Cost Savings Calculator
Estimate annual energy cost savings by upgrading heating, cooling, or lighting systems in Chicago-area buildings. Uses ComEd/Peoples Gas average rates and Chicago climate data (HDD/CDD).
Building & System Info
Formulas Used
Heating Savings:
Annual Heat Load (therms) = UA × HDD × 24 / (100,000 × AFUE_current)
Savings (therms) = Annual Load × (1 − AFUE_current / AFUE_new)
Dollar Savings = Savings_therms × Gas Rate
UA auto-estimate = Floor Area × 0.5 BTU/hr·°F·ft² (Chicago typical)
Chicago HDD (base 65°F) ≈ 6,497 degree-days/year (NOAA 30-yr normal)
Cooling Savings:
Annual kWh_current = (Capacity_tons × 12,000 BTU/ton × Equiv_Full_Load_Hours) / (SEER_current × 1,000)
Annual kWh_new = same numerator / (SEER_new × 1,000)
Dollar Savings = (kWh_current − kWh_new) × Electricity Rate
Chicago Equivalent Full Load Hours ≈ 750 hrs/year (based on ~750 CDD base 65°F)
Lighting Savings:
kWh_saved/year = (W_current − W_new) × Fixtures × Hours/day × 365 / 1,000
Dollar Savings = kWh_saved × Electricity Rate
Net First-Year Savings = Dollar Savings + (Rebate × Fixtures)
Assumptions & References
- Chicago Heating Degree Days (HDD, base 65°F): 6,497/year — NOAA 30-year normal, O'Hare International Airport
- Chicago Cooling Degree Days (CDD, base 65°F): ~750/year — NOAA 30-year normal