Three years ago my aunt and uncle built an amazing house using many different energy saving tactics. Here is our first guest post, by my uncle Bob Sanderson, describing their house, what they do to save energy and some recommendations on how to reduce your energy usage.
Our 3-year-old house in a San Francisco suburb is situated on a steep, south-facing hillside. In the summer, afternoon temperatures are in the 85 – 95º range, dropping to 55 – 65º overnight. Most of the house is in direct sunlight throughout the day.
The architects designed a number of passive heating and cooling features into the house in order to deal with these conditions, while keeping energy consumption to a minimum.
These features include:
- PV and solar hot water systems
- A living roof
- High R value insulation throughout
- A high volume of natural air circulation
- Low-E glass
- Semi-opaque exterior shades
- Big-time thermal mass
Most of the thermal mass is generated by thick, reinforced concrete in the walls and foundation, plus double-layered sheetrock. The thermal mass contributes the most to keeping the house warm in the winter and cool on summer days. The exterior shades block sunlight from coming through floor-to-ceiling glass doors.
On a summer afternoon the interior of the house is 10 – 15º cooler than the outside temperature without the use of air-conditioning.
The house has radiant heating and forced air AC. It is outfitted with “smart” thermostats that control both heating and cooling. However, due to the daily 10 – 15º drop in the outside temperature during the sunset hour, the thermostats don’t react quickly enough to be effective at conserving energy. Therefore, when we do need AC, we turn it on manually, then turn it off at sunset. We also open doors and windows.
In the winter, the radiant heating warms the floors (and air) — it doesn’t “heat” them. The thermal mass then retains the warmth. Thus, it is quite energy-efficient to keep the thermostats set at a constant temperature 24/7.
We were able to incorporate all of these passive heating and cooling features because we were building a new house.
To get these benefits in an existing house, you should install as much insulation as you can, convert to low-E glass windows, and put in an attic exhaust fan if the house’s air circulation is good. If you have windows and doors that get a lot of direct sunlight, the exterior shades will contribute a lot to your comfort and to reducing your energy consumption.