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The lesson that the team gained from the daylighting design of ElementHouse was to use the windows wisely. All the windows are designed at various heights and with various shapes for different activities. For instance, the horizontal window in the kitchen was placed right above the kitchen counter and at eye level height. This location and height provided just the right balance of daylighting and wide view. The size of the window was minimized in such a way that daylight penetration was not negatively impacted. Openings were placed mainly on the south and north sides of the house with minimum east and west openings. Horizontal windows were placed on the north side of the house to help evenly distribute daylight. Vertical windows on the south side prevented excess solar beam radiation from directly entering the house and provided an excellent method for diffusing the beam radiation throughout the house. They also extended the indoor life out by creating a physical and visual connection with the outdoor.41383
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The interaction between engineering and architectural teams yielded several initial design variations for ElementHouse. While the window and door opening area was reduced to minimize heat losses, the shape of the house was also modified to minimize external surface area in order to reduce the area for heat transfer and energy usage for space conditioning. With EnergyPlus, the team was able to compare how geometric parameters area affected the house performance. Table 1 shows the way the team reduced the surface area and window area gradually until the final design was reached.
Energy simulation also helped to decide window construction. Multiple window constructions were modelled and quadruple pane windows were found to be ideal for competition purposes because of their notable increase in thermal insulation and resulting decrease in heating and cooling requirements. However, due to sponsorship availability, double-pane windows and triple-pane doors were used in the actual house, leading to a predicted performance that was lower than optimal. During the time of the Solar Decathlon in October, this variation had less impact than what the simulation predicted for the annual extremes.
One issue that caused great uncertainty during the design was the assumptions for water heating energy and internal loads. Because of the pursuit of custom appliances and heat pump water heaters, the future electrical usage of the house was unclear even at advanced stages in the design. For instance, initial assumptions for internal loads proved to be underestimated when compared to actual measured values on prototypes, leading to higher overall energy usage projected in later designs despite having a highly insulated and passive-oriented envelope and openings. It was also found that increased controlled ventilation could have a cooling effect and help compensate such an increase in internal loads.
4.2. Electric lighting and control
The selection and design of the electrical lighting system were coupled with the opening design. The team considered dimmable fluorescent lighting systems to provide additional lighting only when daylighting was incapable of providing all lighting required. Florescent lights were mounted on the ceiling with indirect light fixtures along the perimeter of each module. They were grouped independently in the three house modules and controlled respec-tively by three daylight sensors. Lights within each module were further pided into subgroup based on their distance from the windows, which enhanced the even lighting distribution and saved energy at the same time (Fig. 18).
In addition to numerical simulation, laboratory experiments with various lighting systems were conducted in order to deter-mine the most appropriate option for the lighting need. Light emitting diode (LED), compact fluorescent, and incandescent bulbs were tested in similar settings. It was concluded that LEDs would provide desired levels required for task lighting applications with minimum power. Also, the light distribution from indirect lighting obtained from fluorescent bulbs was more uniform than direct lighting. Thus, a combination of indirect lighting with super T8 dimmable fluorescent bulbs and LEDs for task lighting was chosen. The selected super T8 fluorescent lamps rank among the ones with highest luminous efficacies on the market. LEDs are becoming more popular in the market and their luminous efficacy is expected to increase.