Data and methods
How the estimator and calculators work, and what they leave out.
Estimator calculation
Baseline emissions (tCO₂e) = annual electricity (MWh) × grid factor (kgCO₂e/kWh). The units reduce directly: 1 MWh × 1 kg/kWh = 1 tonne.
After measures = max(MWh × (1 − demand reduction) − on-site solar, 0) × grid factor. On-site solar means PV generation consumed behind the meter, treated as displacing purchased grid electricity one-for-one. Exported energy, battery losses, export limits and your inventory boundary are not modelled, so the result is a planning estimate, not a verified GHG inventory, and it does not by itself show that a hospital has reached net zero. Always state the factor year, geography and boundary you used.
Boundaries
- Location-based Scope 2 (purchased electricity) only.
- Excludes Scope 1 (fuel, refrigerants, anesthetic gases) and Scope 3 (supply chain).
- No market-based accounting, hourly matching, or marginal emissions.
Data
- The site stores no hospital data. The estimator runs in your browser.
- The default grid factor is an example. Replace it with your own published factor and keep a note of its year.
- Primary sources are listed on the resources page with the date last reviewed.
Calculator formulas
Every calculator is a pure function of its inputs, checked against hand-calculated cases. Constants live in one table (reference data).
- Carbon footprint. Scope 2 tCO₂ = kWh ÷ 1,000 × eGRID rate (lb/MWh) ÷ 2,204.62 ÷ (1 − T&D loss). Scope 1 = natural gas therms × 0.005291 t (0.1 mmBtu × 14.43 kg C/mmBtu × 44/12), diesel × 0.01018 t/gal, gasoline × 0.008887 t/gal. eGRID rates are at the point of generation and exclude transmission and distribution losses, so a loss adjustment is offered (EPA uses 5.1%).
- Equivalencies. tCO₂e divided by EPA's published factors per vehicle-year, home-year, gallon, mile, tree seedling, wind turbine-year and coal railcar.
- EUI. (kWh × 3.412 + therms × 100 + other kBtu) ÷ gross floor area. The comparison is with the ENERGY STAR national median site EUI for general medical and surgical hospitals. It is a screening comparison: weather, hours, imaging, bed mix and campus services all move the answer.
- Chilled water. Tons = GPM × ΔT(°F) ÷ 24 (water, 500 ÷ 12,000). kW/ton = plant kW ÷ tons. COP = 3.517 ÷ (kW/ton). EER = 12 ÷ (kW/ton).
- Life-cycle cost. Following the FEMP method in NIST Handbook 135: uniform present value UPV = [1 − (1+d)−N] ÷ d for flat costs; modified factor UPV* = [(1+e) ÷ (d − e)] × [1 − ((1+e) ÷ (1+d))N] for energy savings escalating at real rate e (equals N when d = e). NPV = savings × UPV* − O&M × UPV − initial cost. SIR = PV savings ÷ (initial cost + PV O&M). Discounted payback counts years until cumulative discounted net cash flow turns positive. IRR is a real internal rate of return found by bisection. The default real discount rate is the 3.0% in the 2025 Annual Supplement.
- Solar PV. Year-1 energy = kWdc × specific yield from PVWatts. Later years apply (1 − degradation)t−1. Carbon offset multiplies energy by the grid factor and assumes all output displaces purchased electricity.
- Refrigerants. Leaked lb = charge × leak rate; tCO₂e = lb × 0.45359 ÷ 1,000 × GWP, using IPCC AR5 100-year values and blends computed from component mass fractions.
- Anesthetic gases. tCO₂e = mL × density × GWP ÷ 106 for liquid agents and kg × GWP ÷ 1,000 for nitrous oxide. GWP and density are editable because published values differ by source.
- LEED trackers. Sum your points against published category maximums and compare with the 40, 50, 60 and 80 point thresholds. They do not model credit-level requirements.
Corrections
Found an error? Email info@hospitalnetzero.com. Corrections are made on the page and noted here. Last reviewed 2026-11-04.