already had a model before the architects got into the project. From this model, they tried to give
orientation in the design. The main areas that were affected by energy simulation were window
placement, insulation thickness, window construction, indoor air quality, as well as the sizing of the
thermal (heating/cooling) and electric (PV) equipment.
When beginning the design of an energy efficient structure, there are several factors which must be realized. As a starting point, the most energy efficient structure would be a fully insulated sphere without any windows, doors or thermal bridges of any kind. Obviously, this structure would in no way be inhabitable. For sake of simplicity, it can be send that any step away from this structure leads to negative effect on the structure thermal efficiency. So, when the building becomes more rectangular, for ease of construction and livability, the building loses some thermal efficiency. Then, in order for the inhabitants to get into the structure, doors must be added. On top of that, windows must be added to make the space more enjoyable. Now, every time a window, door, or corner is added, we are also adding a thermal bridge. While there are ways to limit the effect of the thermal bridges (as mentioned in “Construction Techniques: Advanced Framing” section) it is nearly impossible to rid an entire building of them. If this concept is understood, it is clear that each of these derivations should be as efficient as possible in order to make the structure, as a whole, perform to it’s the best of its ability.
This is where thermal analysis plays an important role in energy efficient structures. In the design of the ELEMENT, energy modeling brought about a substantial design change in the window-to-wall ratios (WTWR) of the house. Originally, the WTWR was around 30% for the entire building, with the WTWR being around 30% on all four elevations. After the change inspired by the thermal analysis, the south façade still had a WTWR of roughly 30%, but the north was reduced to 13%, the east to 5%, and the west to around 1%.
The energy modeling went beyond this aspect of window-to-wall ratios when considering window
openings. . First, the thermal impact needed to be considered; that is, how much heating and
cooling energy would be required. The idea is to minimize these energy requirements as much as
possible. Second, the amount of natural daylight needed to be considered. In other words, properly
placed windows will bring in natural light and therefore will reduce the need for artificial light and
fulfill the aesthetic requirements of the house. From the energy standpoint, energy simulation
shows that it would be better to have as small window area as possible. Windows are energy
holes; although they have some energy benefits, such as relieving some lighting and winter heating
loads, on an annual basis, their net effect is negative, and thus increases the energy requirements.
On the other hand, from the aesthetic and psychological standpoint, there is a strong desire to
want to have plenty of openings from which to view the outdoors and supply natural light.
Screenshot of EnergyPlus’ Computer Model of the Solar House
The design of ELEMENT tried to reconcile both standpoints into one design that has a very low
window to wall ratio but guarantees adequate daylight in all interior spaces. The energy simulation
used to perform the thermal analysis was very dynamic. It is an annual simulation with time steps
every 15 minutes. This means that the energy load is calculated every 15 minutes over the course
of one year while also incorporating day lighting into the calculation.
