As you know, Sustainability is paramount to the goal of the SURE HOUSE. That is why we are striving to achieve the most stringent energy efficient building standard in existence today – the Passive House standard.
While the term “passive” is used often in the sustainable building industry, for instance when describing the utilization of passive solar gains for heat, in this instance a Passive House describes a building that has been designed from its very inception to reduce heating and cooling energy demand to the point that conventional HVAC systems are unnecessary. This standard, created in Germany in the 1980s, has been growing in popularity in the United States over the past decade and has been shown to reduce home energy use by up to 90%. The standard has three main requirements in order to maintain simplicity:
1. Specific Heating Demand: < 15 kWh/m²a or 4.75 kBtu/ft²-yr
Specific Cooling Demand: < 15 kWh/m²a or 4.75 kBtu/ft²-yr
2. Primary Energy Use: < 120 kWh/m²a
3. Air Tightness: 0.6 Air Changes per Hour at pressure (50 pascals)
The combination of these criteria require a building with an exceptionally efficient envelope designed to reduce energy loss to such a point that a minimal amount of energy is required to heat or cool the space. To achieve this, the SURE HOUSE is employing four main strategies in its construction that set it apart from a typical home.
2. Intelligent Detail Design
3. Control of Solar Gains
4. Energy Recovery Ventilation
One of the main tenants that the Passive House idea was built on was the need for unusually high amounts of insulation in building assemblies. The concept is simple: put in the upfront cost to have thicker walls, roofs and floors and reduce heat flow into or out of the house, reducing conditioning costs. In the SURE HOUSE, R-Values of 10 h ft² F/Btu greater than NJ code are being used for the entire shell, reducing heat losses and lowering yearly space conditioning energy demands. A higher degree of interior comfort is achieved with this strategy as well, reducing the existence of drafts and uncomfortable indoor surface temperatures. This simple design change is by far the easiest and cheapest way to reduce energy demands.
Intelligent Detail Design
The weakest point in any building envelope will always be at the connection details – the corners of the building as well as any seams where two different materials must be connected such as window frames. These areas have such a high potential for energy loss for two reasons: air leakage and a condition known as “thermal bridging”. The concept of thermal bridging is relatively simple but equally as foreign to most builders today. Put simply, a thermal bridge is a break in insulation where heat can flow more easily from the inside of a space to the outside through a material with a higher conductivity (or lower thermal resistance). This material acts as a heat sink and can reduce the thermal performance of an assembly immensely as well as pose a risk of condensation and mold growth.
Energy Recovery Ventilation
When designing a home with the required air-tightness of a Passive House, it is very possible to encounter issues with indoor air quality because of a lack of ventilation to the space. Therefore mechanical ventilation must be added, which gives the designer the ability to control the flow of air into and out of the house unlike a traditional home where air flows freely. To take full advantage of this control, the use of an ERV (Energy Recovery Ventilation) system is advised. The basic idea behind an ERV is that if you mix the outgoing stream of conditioned (but stale) air with the incoming stream of fresh (but unconditioned) air, you can recover a certain amount of the energy used to condition the outgoing air. In the winter this means using the warmer indoor air to heat the cooler incoming air and the opposite in the summer. The ERV used in the SURE HOUSE has a nominal efficiency of 92%, meaning that almost all of the energy put into a space can be recovered just by using that air to condition the incoming air before it is sent to the heating or cooling system. While this technology is becoming more popular in the U.S., it is still unheard of by most builders. A greater integration of ERVs into typical home construction could have an immense effect on home energy use across the United States.
With regard to thermal performance, the most efficient house is a completely opaque box with no windows or breaks in insulation. This is counterintuitive though because windows are often one of the first things considered when designing an efficient home, but the reality is that windows will always be less thermally resistant (have a lower R-Value) than walls and therefore will always contribute to greater heat losses than a wall of the same area. So why does every building have windows? The answer is obvious. No one wants to live in a house with no sunlight or access to immediate fresh air. Luckily, with enough forethought, windows can provide enough benefit to combat the losses they cause. This benefit can come in the form of ventilation during the summer but more importantly as solar gains during the winter.
While it is easy to design a house to harvest as much solar energy as possible, what is just as important is keeping these solar gains from heating the home when they are unwanted. This requires an intelligent shading design that is adapted to the location and climate of the home to prevent unnecessary cooling. For an automated, motorized shading system, these means reacting to the heat of the sun to block radiation when unwanted. In the case of the SURE HOUSE however, a stationary shading strategy is being used, requiring a great deal of analysis to ensure that we are getting enough shading in the summer and not shading too much in the winter. The combination of our shutter and louver system helps to keep out the high summer sun as well as the lower afternoon and morning rays that can often have a great effect on indoor temperature. Without intelligent shading, a highly glazed home can quickly become a greenhouse oven.