A client-side engineering calculator that estimates annual cooling energy usage for rooftop air conditioning units (RTUs) using the bin method of analysis. It compares a high-efficiency candidate unit against a standard-efficiency baseline and provides economic metrics for the investment.
The calculator simulates hour-by-hour cooling energy for two rooftop units across all temperature bins for a selected U.S. city. It accounts for:
- Sensible and latent load modeling with building-type-specific load profiles
- Multi-stage, single-stage, and variable-speed compressor operation
- Economizer integration (when enabled)
- Psychrometric corrections to capacity and power at each temperature bin
- Occupied and unoccupied schedule periods with setback
Economic results include life-cycle cost (LCC), simple and discounted payback, rate of return (ROR), and savings-to-investment ratio (SIR).
Controls.html Main page — form UI and results display
controls.js Page-level logic — form handling, results rendering, charts
help_viewer.js Help modal overlay
load_header_footer.js Dynamic header/footer injection
engine/
engine_module.js Core bin-method engine (ES module)
performance_module.js Correction factors, S/T ratio, staging, fan/condenser power
psychro.js Psychrometric functions (humidity ratio, wet bulb, BPF/ADP)
database_module.js Weather data access
classes.js Data classes (StageState, StagePair, SystemProperties)
data/
stations.json U.S. weather station design conditions
Tbins_new.json Temperature bin hours by station
shared/ CSS stylesheets
docs/ PDF documentation (user manual, enhancement plan)
methods/ Engineering methods pages describing the calculations
- User Manual — Detailed guide to the calculator's features and inputs
- Quick Start — Step-by-step instructions for running a comparison
- Engineering Methods — Description of the calculation methods
- Revision History — Version changelog
- Architecture — Code structure, calculation flow, and module communication
- All calculations run client-side in the browser using ES modules — no server required.
- Charts are rendered with Google Charts.
- Weather data covers U.S. cities with ASHRAE design conditions and TMY3 temperature bin distributions.
- The calculator was originally developed as a Classic ASP application at Pacific Northwest National Laboratory (PNNL) and has been ported to client-side JavaScript.
- PNNL-24130: RTU Comparison Calculator User Manual
- PNNL-23239 Rev 1: Advanced Rooftop Unit Control Retrofit — Enhancement Plan
This project is licensed under CC BY-NC 4.0. You are free to share and adapt the material for non-commercial purposes with appropriate attribution. See the LICENSE file for details.
This calculator is provided as a demonstration tool for preliminary analysis. Its output should not be used for final purchasing decisions.