When we launched the Honda Smart Home in 2013 as a “living laboratory,” we knew we were literally breaking new ground with a bevy of environmental technologies, some of them very experimental. Now that we have multiple years of data from the 230+ sensors built into the home along with feedback from three sets of unique occupants, we’ve learned a great deal about how these systems perform in real-world situations. So let me share with you the top five things we’ve learned about the zero-net energy Honda Smart Home.

1. Radiant Geothermal Borehole Heat Exchangers – Good, But Limited Capacity

In the ground beneath Honda Smart Home’s backyard, eight 20-foot deep boreholes allow a geothermal heat pump to harness the ground’s relatively stable thermal sink to heat and cool the home’s floors and ceiling throughout the year. These borehole heat exchangers have been working pretty well. However, their actual capacity is a bit lower than we expected. The dry bores – 2’ diameter by 20’ deep with 250’ of tubing inside – only have a capacity of about 0.2 tons each. Combined with the wet bores, our total capacity is about 1.8 tons, which is below our design target. In retrospect, drilling ten or twelve boreholes would have helped us achieve our desired capacity.

2. Energy Recovery – Free Hot Water

Conventional homes waste a lot of energy by heating water for showering and then sending that water immediately down the drain. Using a drain-heat-recovery unit whenever an occupant is showering, combined with a desuperheater to recover energy from summertime cooling, we’re able to produce more than 30% of our hot water for free. Imagine the energy savings multiplied by 11 million homes in California. That’s a lot of free hot water.

3. Heating and Cooling of Floors – Long Delays

We installed a system to efficiently heat and cool the home’s floors through a system built into the Smart Home’s foundation. This system has not performed as well as expected. The long time delays to heat or cool the floors, combined with the chilly-floor feeling in the summer, make it fairly impractical and one of the least-preferred systems in our home.

4. Pre-Cooling Systems – Finding the Right Balance

Our home does not have a traditional air conditioning system. Instead, we use a few different methods to keep the home a comfortable temperature, especially when occupants come home in the evening. After several iterations, we have settled on pre-cooling the house on summer nights using a combination of a whole-house fan, which pulls outside air into the house through a filter, and individual bath fans, which are typically found in bathrooms but are strategically deployed throughout the Smart Home. Together these fans consume a bit more energy than just a whole house fan but provide a better pressure balance and noise performance.

5. Control Systems – Using More Energy than the Systems they Control?

We have a lot of control systems running in the house for HVAC, lighting, and energy. Last year those loads totaled 1412kWh, which is more than our actual LED lights consumed (they consumed 1121kWh). We anticipated that these systems would use a lot energy, but now we are able to quantify how much. The key point is that “smart” systems need to pay attention to stand-by loads.

What’s Next

These are just some of the top takeaways, but really we’re learning new things about the home everyday. Technology development is never a straight line: there are stops and starts, breakthroughs and setbacks. We’ve seen our share of both, but of course that’s what is to be expected in a living laboratory. Overall, the Honda Smart Home continues to provide us a unique opportunity to do real-world experiments and gradually improve our approach to designing zero-carbon homes of the future.

If you’d like to check out the latest data sets collected from the operation of the Smart Home, click on the “Downloads” tab above.

