# Performance of a Mid-Size Net-Zero Energy Solar House
## 5 Energy Modeling and Discussion  
### Model Setup  
OpenStudio (EnergyPlus) 8.0 software was used to model a residential solar home to test the effects of increasing the insulation value of external wall structures on the energy consumption and demand on the home's HVAC unit. Varying the value of air infiltration in the home was also tested for its effects. The EnergyPlus 8.0 software was used to perform the energy calculations throughout a year-long period on the model using weather data files for both Birmingham, AL, the home's final resting place, and Denver, CO, where the home was placed for the month of October 2017 to compete in the U.S. Department of Energy's Solar Decathlon competition.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{Refrigerator} & Refrigerator Capacity & 15.4 cu. ft. \\ \cline{2-3}  & Freezer Capacity & 7.98 cu. ft. \\ \cline{2-3}  & Total Capacity & 23.3 cu. ft. \\ \cline{2-3}  & Annual Energy Consumption & 544 kWh \\ \hline \multirow{2}{*}{Washer and Dryer (all in one)} & Capacity & 2.3 cu. ft. \\ \cline{2-3}  & Annual Energy Consumption & 120 kWh \\ \hline Dishwasher & Annual Energy Consumption & 225 kWh \\ \hline \multirow{2}{*}{Oven} & Bottom Heating Element Wattage & 1200 W \\ \cline{2-3}  & Upper Heating Element Wattage & 2200 W \\ \hline Microwave & On high power level & 1200 W \\ \hline \hline \end{tabular}
\end{table}
Table 4: Appliances specifications.  
The home was drawn in Sketchup Make using the OpenStudio plug-in. The model was drawn based on the as-built drawings. The building's visual representation in Sketchup was created using the outer dimensions of the house. The model was created having two thermal zones, one an unconditioned crawlspace area, 2 feet tall and the other conditioned area that has 2 bedrooms, 1 shared bathroom, a safe room, and a large open space which contains the living room, kitchen, and dining room. Energyplus does not perform calculations based on computational fluid dynamics and, therefore, the conditioned zone was modeled as one large space with no internal wall structures. Figure 2 shows the plan view of the house.  
The electrical appliance loads matching appliances likely to be used in the actual house were created in the OpenStudio model and set up with schedules that, as accurately as possible, represent patterns in which a four-person household might use them. Schedules for heating and cooling were created using the 74 \({}^{\circ}\)F (23 \({}^{\circ}\)C) maximum and 68 \({}^{\circ}\)F (20 \({}^{\circ}\)C) minimum allowed temperatures for maximum points at the Solar Decathlon competition. A staggered double 2\({}^{\prime\prime}\times 4^{\prime\prime}\) exterior wall construction was modeled with 2\({}^{\prime\prime}\times 6^{\prime\prime}\) bottom and top plates to form the wall frame. Vertical exterior walls were modeled as having from outside-in: cement (Hardie) sliding, with 1\({}^{\prime\prime}\) (R5) rigid foam board, 0.5\({}^{\prime\prime}\) plywood sheathting, respective wood stud structure filled with 1\({}^{\prime\prime}\) closed-cell sprayed foam, and two layers of batt insulation, 2\({}^{\prime\prime}\) and 3\({}^{\prime\prime}\), respectively, and 2\({}^{\prime\prime}\) plywood and gypsum board. The roof and the floor framing were handled in the same manner, but with 2\({}^{\prime\prime}\times 8^{\prime\prime}\) using 5.5\({}^{\prime\prime}\) rigid foam insulation on the outside and 1\({}^{\prime\prime}\) closed-cell-sprayed foam on the inside. Table 5 shows the layering of materials used for the different construction sets used to build the house.  
Figure 2: The plan view of the house.  
The effects of air infiltration were tested using the model with a staggered double 2\({}^{\prime\prime}\)\(\times\) 4\({}^{\prime\prime}\) wall structure and varying the air tightness values ranging from 0.05 CFM/ft\({}^{2}\) to 0.15 CFM/ft\({}^{2}\) with 0.05 CFM/ft\({}^{2}\) increments.