31 Jul Good Design Makes Net Zero Houses Easy

A very energy efficient house means you only need a small solar PV system to go net zero on annual energy usage. This was a major theme on Tuesday this week during the first of three Green by Design sessions presented by Austin Energy Green Building (AEGB). Heidi Kasper and Lee Doar, architects with AEGB, presented a great overview of green building features to make this possible.   The primary things to accomplish with good design include minimizing heat gain in the summer, maximizing heat gain in winter and minimizing the amount of conditioned space. After that you consider highly efficient systems for the building envelope.

Orientation & Layout

The position and configuration of a well-designed house is strongly influenced by the sun’s path across the sky, seasonal wind patterns and the physical features (trees, elevation changes, etc.) of the site. In Central Texas typically this means the long axis of the house runs east/west with deep overhangs on the south and no windows on the west. This minimizes heating from walls and windows in the summer. Low windows on the east and south allow for solar heating in winter.  Appropriate placement of windows on the long south and north walls also allows you to take advantage of south/southeast winds in the spring and fall for cross-ventilation. In truth, these ideas have been with us for millennia since we’ve only had air conditioning for a relatively short time.

Minimizing the amount of conditioned space is key, so it’s important to carefully consider the question: How much space do we really need? For instance, some people like to entertain large groups of people. However, this only really happens a handful of times a year, so in many cases the best place for these gatherings is outside rather than inside. In general, designing indoor spaces that are multi-use   with furniture you can rearrange is great.

Inside the Envelope

A well-designed building envelope and the equipment within it also have a major impact on energy efficiency. Here’s a breakdown of about how much energy can be saved annually compared to an average 2,000 square-foot house in Austin:

• You save about 1,000 kWh/year with a light-colored, reflective roof, well-insulated attic and walls, and good windows.
• You save about 2,800 kWh/year on hot water with solar, or heat pump water heating, short pipe runs (<20 feet), high-efficiency washer and low-flow showerheads.
• You save about 400 kWh/year on lighting and controls with things like LEDs and motion detectors.
• You save about 1,100 kWh/year with very efficient appliances. For the best of the best, check with the Consortium for Energy Efficiency.
• You can save hundreds more kWh/year with energy management tools like occupancy sensors, smart thermostats and smart power strips.

Of course, all these considerations can be part of your remodeling projects, too. It’s not just for new construction. And, a big caveat, the number and behavior of occupants can have a significant impact on the house’s performance. An AEGB five-star-rated house can quickly become an energy hog if you don’t have a five-star lifestyle.

As I sat there on Tuesday taking it all in, it struck me that approaching home design from this perspective really puts a person more in touch with the natural world and how energy is used. This is a really fantastic series. I’d definitely recommend checking out the two remaining sessions (Green by Design course registration).