CHP Capacity Optimizer

CHP Capacity Optimizer logo

Selecting the proper installed capacity for cooling, heating, and power (CHP) equipment is critical to the economic viability of distributed energy/CHP projects. Poorly matched installed capacities can cause an otherwise profitable project to incur a life-cycle economic loss. To enhance the likelihood of a positive economic outcome, the CHP Capacity Optimizer has been developed to provide guidance on the proper installed capacities for distributed energy (DE) prime movers and absorption chillers in commercial applications.

Generally, CHP systems are not the sole source of electricity and thermal resource for a facility. In most cases, these systems are merely alternatives to utility grid-supplied electricity, electric chillers, and electric or gas-fired on-site water heating. As a result, CHP systems are characteristic of the classic �make-or-buy� decision, and economic viability is relative to grid-based electricity and on-site boiler heating. Using load data from a building simulation program such as EnergyPlus, the CHP Capacity Optimizer simulates both a CHP system and a traditional non-CHP approach (i.e., electricity solely from the grid, heating from on-site boilers) to form a relative economic savings resulting from installing a CHP system. Through the use of a nonlinear optimization algorithm, the installed equipment capacities that maximize the relative economic savings are determined. Screen Shots


CHP, cogeneration, capacity optimization, distributed generation


Operation simulation validated against results from EnergyPlus. Optimization results compared with independent, third-party optimization tools.

Expertise Required

The user should be familiar with building simulation tools, utility tariffs, and CHP equipment efficiency parameters.


Unknown, software is available as a free download from the web.


Energy system developers, energy service companies, building owners who wish to consider installation of an on-site cooling, heating, and power system.


The CHP Capacity Optimizer requires hourly building heating, cooling, and non-cooling electrical loads for a one-year period. It also requires the relevant utility electricity cost structure (i.e., tariff) and price of on-site primary fuel. Data needs on CHP equipment are efficiencies, minimum operating levels, and capital and operating costs. The user must also specify the period of evaluation (up to 16 years), discount rate, and income tax rate. Optional inputs include annual escalation rates, and specific hourly operating schedules.


Output includes the optimal capacities for prime mover and absorption chiller (if applicable), summary of hourly operation, annual costs with and without a CHP system, and life-cycle net present value cost savings from the CHP system. In addition, the tool provides a graphical representation of the overall solution space and detailed hourly calculation results.

Computer Platform

Windows-based PC

Programming Language

Microsoft Excel spreadsheet with Visual Basic automation (macros).


The tool provides an efficient means to determine the capacities of prime mover and absorption chiller that maximize economic benefit on a life-cycle basis. Utilizing hourly load data readily available from building simulation tools such as EnergyPlus, the software requires a minimal amount of input data to characterize and evaluate an on-site cogeneration system. Existing in spreadsheet form, the computations underlying the tool are available to the user in spreadsheet cells. The automation within the tool via Visual Basic macros permit numerically intensive calculations to be done with ease. User�s manual available.


Multi-unit prime movers limited to two identical units at this time. User must provide equipment efficiency parameters (i.e., no equipment libraries). Due to the computational intensity, optimization calculation can take several minutes on slower PCs.



Oak Ridge National Laboratory


MS 6070
P O Box 2008
Oak Ridge, Tennessee 37830-6070
United States


+1 (865) 574-0578




Software and users manual available at no charge from the contact web site or from DOE's web site