G2 Simulation General Requirements
The simulation program shall be a computer-based program for the analysis of energy consumption in buildings (a program such as, but not limited to, DOE-2, BLAST, or EnergyPlus). The simulation program shall include calculation methodologies for the building components being modeled. For components that cannot be modeled by the simulation program, the exceptional calculation methods requirements in Section G2.5 shall be used.
- 8760 hours per year.
- Hourly variations in occupancy, lighting power, miscellaneous equipment power, thermostat set points, and IIVA C system operation, defined separately for each day of the week and holidays.
- Thermal mass effects.
- Ten or more thermal zones.
- Part-load performance curves for mechanical equipment.
- Capacity and efficiency correction curves for mechanical heating and mechanical cooling equipment.
- Air economizers with integrated control.
- Baseline building design characteristics specified in Section G3.
The simulation program shall have the ability to either directly determine the proposed building performance and baseline building performance or produce hourly reports of energy use by an energy source suitable for determining the proposed building performance and baseline building performance using a separate calculation engine.
The simulation program shall be capable of performing design load calculations to determine required HVAC equipment capacities and air and water flow rates in accordance with generally accepted engineering standards and handbooks (for example, ASHRAE Handbook—Fundamentals) for both the proposed design and baseline building design.
The simulation program shall perform the simulation using hourly values of climatic data, such as temperature and humidity from representative climatic data, for the site in which the proposed design is to be located. For cities or urban regions with several climatic data entries, and for locations where weather data are not available, the designer shall select available weather data that best represent the climate at the construction site. The selected weather data shall be approved by the rating authority.
Site-recovered energy shall not be considered purchased energy and shall be subtracted from the proposed design energy consumption prior to calculating the proposed building performance. On-site renewable energy generated by systems included on the building permit that is used by the building shall be subtracted from the proposed design energy consumption prior to calculating the proposed building performance.
The design energy cost and baseline energy cost shall be determined using either actual rates for purchased energy or state average energy prices published by DOE's Energy Information Administration (EIA) for commercial building customers, but rates from different sources may not be mixed in the same project. Where on-site renewable energy or site-recovered energy is used, the baseline building design shall be based on the energy source used as the backup energy source, or the baseline system energy source in that category if no backup energy source has been specified.
When the simulation program does not model a design, material, or device of the proposed design, an exceptional calculation method shall be used as approved by the rating authority. Where there are multiple designs, materials, or devices that the simulation program does not model, each shall be calculated separately and exceptional savings determined for each. At no time shall the total exceptional savings constitute more than half of the difference between the baseline building performance and the proposed building performance. All applications for approval of an exceptional method shall include the following:
- Step-by-step documentation of the exceptional calculation method performed, detailed enough to reproduce the results.
- Copies of all spreadsheets used to perform the calculations.
- A sensitivity analysis of energy consumption when each of the input parameters is varied from half to double the value assumed.
- The calculations shall be performed on a time-step basis consistent with the simulation program used.
- The performance rating calculated with and without the exceptional calculation method.