BCHP Screening Tool Development

GARD Analytics developed the BCHP Screening Tool software program for analysis of building cooling, heating and power generation systems.  This development effort pulled together information on thermally activated technologies, on-site power generation, and integrated science research for energy and economic analysis of integrated systems featuring combined cooling, heating, and power.  It builds upon a proven building load model and climate data with the inclusion of current information on generating, absorption, and desiccant equipment, thermal storage technologies, and electric and gas utility tariffs.  The tool provides users with a way to compare the economic feasibility of different integrated energy system concepts for a wide range of commercial applications across the U.S.  The target audiences for the screening tool are design and design-related professionals including:

  • Architecture and engineering firms
  • Heating, ventilating and air conditioning equipment manufacturers
  • Power generation equipment manufacturers
  • Energy service companies
  • Marketing personnel at utility companies.

The premium price expected in the market for integrated energy systems compared to typically specified systems in commercial buildings can only be justified when factors such as the annual energy costs are reduced to a point where the life-cycle cost or simple payback is acceptable.  With complex building systems that include the use of waste heat recovery, such as BCHP systems, the only way to accurately estimate the annual energy cost savings is with a sophisticated building energy simulation program like DOE-2.  Unfortunately, DOE-2 is very complex to use and not directly usable by the targeted users.  This project provided a software program that insulates the user from the complexities of DOE-2 yet allows a great deal of flexibility.

The BCHP Screening Tool performs the economic analysis for various system configurations based on annual energy results calculated from the DOE-2 building energy simulation program and detailed utility rate descriptions.  The tool includes equipment performance for:

  • On-site electrical generation equipment such as engine generators, microturbines, turbines and fuel cells.
  • Heating, ventilating and air conditioning equipment including those that are thermally active technologies.

The waste heat recovered from building sited fuel cells, microturbines, gas turbines and engine generators will offset the electrical and fuel needs of the chillers, boilers, service water heaters and humidity control equipment typically found in commercial buildings.  Thermally activated technologies such as absorption chillers and regenerative desiccant dehumidifiers can reduce the primary energy used in a building for providing cooling.

The program user interface was developed entirely by GARD Analytics using Visual Basic and the simulation engine DOE-2 was modified to better model desiccants and generators using FORTRAN.  The desiccant modifications allowed the use of the add-on (pre-conditioner) desiccant unit in DOE-2 to access user modifiable curve-fits of off-design condition performance.

As part of this project, curve fitting of performance data was done for a variety of HVAC equipment including unitary and central plan equipment.  The database of curve-fit coefficients that was developed by GARD includes numerous unitary and chiller models by Carrier and Trane.  The database includes:

  • Part load performance
  • Capacity as a function of temperature curvefit coefficients
  • Sensible capacity as a function of temperature curvefit coefficients
  • Efficiency (energy input ratio) as a function of temperature curvefit coefficients
  • Equipment and installation costs.

The utility rate database covers over 200 TMY2 cities across the country with detailed data on each utility rate including multiple blocks, time-of-use, ratchets and taxes.  As many as 20 commercial rates were entered into the database for each electric and gas utility.