Porch House

The house is designed to be nearly thermally autonomous, allowing the occupants to open and close the house and deploy shades as needed. When the weather turns cloudy or becomes cool under clear night skies, the glass panels can slide closed and the floors are gently warmed. Natural cross-ventilation is afforded by operable windows placed in strategic locations. The skylights and large window walls flood the interior with daylight, relying on a minimal use of electric light for the evening hours.

The heavy thermal mass of the cast-in-place concrete, coupled with strategic insulation, sets the tone for how the house behaves, feels and performs. The thermal mass helps to insulate against highly fluctuating outside temperatures and to find some degree of thermal equilibrium, staying cooler than outside during during hot days and warmer during cooler evenings. The roof reduces the heat island effect from solar radiation by using a highly reflective waterproofing membrane. Shading devices, including deep overhangs in the southwest façade and automated exterior venetian blinds control heat gain due to direct sunlight.

Airtight construction methods reduce air infiltration and potential heat gain or heat loss due to air leaks. Spectrally-selective glazing provides low solar heat gain coefficients with high visual transmission, maintaining the view towards the ocean. The process of designing the house included a range of performance simulations using research-grade software. Hour-by-hour thermal comfort analysis and load analysis revealed patters of performance, guiding the mechanical strategies and operational protocols.

Thermal autonomy to reduce energy usage is coupled with renewable energy generation by photovoltaic and solar hot water panels, reducing peak loads on all electric energy use. Thermal comfort and energy performance simulations were based on current climate data but also look ahead to the effects of climate change.

In analyzing the performance of the house, the factors associated with increased HVAC demand were priorities for improvement. Results from elimination parametrics showed that cooling loads came mainly from solar gain through the glass. To control this, possibilities included choosing a better performing glass or adding a controlled shading device that deploys only when needed (either when the interior temperature is too hot or when the sun is hitting the window).

Using elimination parametric analysis results, further studies focused on envelope requirements (insulation, glazing) helped select the optimal construction assemblies to achieve maximum comfort. In this, we used a sensitivity analysis, parametrically modifying the thickness of the insulation in each part of the envelope. This allowed us to identify the reasonable R value on the roof and in the walls that would optimize the building performance.

We then compared the heating and cooling loads in each case, observing how both curves reach a point of diminishing returns where adding more insulation has minimal impact.  This identified the sweet spot for specification.

Studies revealed that the house needs some heating during the winter season,  particularly during nighttime hours. For this, a gentle radiant heating system was proposed. Radiant systems, as they are usually installed consist of a set of piping that is set into a 1.5 to 2” lightweight concrete layer or composite wood. The piping supplies hot water that heats up the surface and provides gentle heating primarily through radiation. The same principle can be used to cool the house as long as the cooling loads are moderate. Cooling is less effective than heating; we cannot lower the temperature of the floor too much since the floor quickly goes from delightfully cool to uncomfortable. The lower range of the floor temperature is controlled to ensure that the house is always comfortable. Restricting the minimum cooling temperature also ensures that the floor never gets cold enough to condense moisture. In the summer there may be times, particularly after unoccupied times, when the chilled floors will not cool the house fast enough. For those times we proposed an additional air system based on a mini-split multizone system that instantly can deliver both cool and warm air in a separate zones of the house.

From the initial work on the Porch House, renewable energy was assumed as part of the design.  The questions was, where should the photovoltaics be located on this steeply sloping site?  On-site photographs were taken with a fish-eye lens from a number of potential locations, each looking straight up at the sky, with the fisheye capturing the 360 degrees of the horizon and all vertical trees, landforms and buildings that surround the site. These photographs were then overlaid with the sun path calculated for the latitude and longitude of the site.  This allowed the design team to identify issues such as when the PV array will be shaded depending on its location on the roof, or when direct sun will most likely be blocked by the trees on site or surrounding buildings, for example.

In addition, sun studies using shading masks analyzed the efficacy of the proposed overhang in the southwest facing façade. When the sun is positioned inside the gray area, the overhang would block direct solar radiation. The goal was to allow solar heat gain inside the building to achieve passive heating of the concrete floor slab and walls during the winter while blocking it and provide shade during the warmer summer months.