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House Performance

A computer simulation program called TRNSYS was employed to evaluate the performance of the various systems used in and on the house before it was built. This enabled the team to make significant design decisions based on more than industry rules-of-thumb and historical designs. Individual simulations were run for each of the following systems to project the energy performance of each:

  • Solar Thermal
  • Photovoltaic
  • Heating/Ventilating/Air Conditioning
  • Lighting (programs other than TRNSYS used for lighting simulation)

TRNSYS has a modular structure, in which the user specifies the building components and the manner in which they are connected. This structure is illustrated in Figures 5 through 7. It can also perform simulations at timesteps less than one hour and model solar thermal and photovoltaic systems. This gives TRNSYS tremendous flexibility and is the primary reason why it was chosen over other building energy simulation programs, such as Energy-10, DOE-2, etc.

A detailed simulation report was submitted as part of the Solar Decathlon competition. It documented the parameters and inputs to the simulation, as well as the assumptions, improvisations, and rationalizations used to model the systems listed above. The report also discusses the parametric studies that were performed to aid in the design decision-making process. Figures 1 through 3 summarize the major findings of the simulations. Energy (kWh)

Energy Collected by Solar Thermal System

Figure 1: Energy Collected by Solar Thermal System

Useful PV Output

Figure 2: Useful PV Output

Conditioning Simulation Summary

Figure 3: Space Conditioning Simulation Summary


A classic example of how a simulation can be used to aid in even the architectural design process is illustrated in the orientation of the three primary roof surfaces upon which the photovoltaic modules are installed. Typically, solar houses stick out like a sore thumb due to their "cheese wedge" shape, which is intended to maximize Southern exposure. Our design seeks to change the "solar paradigm" by achieving both superior energy performance and architectural appeal. Figure 4 shows how well the performance of our design matches up with more "optimal" and traditional designs with roof slopes closer to latitude.

Monthly Effect of Tilt and Azimuth on Entire PV Array

Figure 4: Monthly Effect of Tilt and Azimuth on Entire PV Array