Honda and UC Davis mash together our two biggest carbon emitters, the house and the car.
All the big boys are into smart homes these days; GE, Bosch, and Google all make the thermostats, heat pumps, sensors and equipment needed to run these marvels. Honda makes cars, not gadgets, so they could pick and choose their technologies, and have built a home on the campus of UC Davis that deals with our biggest problem: CO2 from our buildings and cars. I have expressed a preference for dumb homes, worrying about cost and complexity, but this one hits a smart balance.
Passive Solar Design
For one thing, they paid attention to the basics. The best way to reduce your cooling costs is to keep the heat out in the first place, so they carefully studied the sun angles and shading, using passive solar design. The house is built from FSC certified lumber, metal roofs, to a very high standard, according to Green Building Advisor:
Double stud wall construction. Above-grade exterior walls are made from two 2x4 stud walls on 24-in. centers designed to eliminate thermal bridging except at the fire blocking. The 9 1/2-in. wall cavities are insulated with cellulose (R-31).
Triple-glazed windows. The argon-filled casements are manufactured by Alpen.
A truss roof with a vented roof deck. The roof is insulated to R-60 with cellulose.
Insulated slab. Rigid foam under the concrete slab has an R-value of 10.
Airtightness. The house tested at 2.0 air changes per hour at a pressure difference of 50 pascals.
They used clever materials like pozzolan infused concrete, along with post-tensioning, to reduce the carbon footprint of their concrete slab.
Concrete accounts for approximately 5% of global, man-made CO2 emissions. This large CO2 footprint is a result of producing cement – the concrete’s “glue” – by heating limestone to more than one thousand degrees Celsius. This heating requires the burning of fossil fuels, while the chemical reaction itself also releases CO2. A naturally-occurring substance called pozzolan was infused into the Honda Smart Home’s concrete to replace half of the cement typically needed. A technique called post-tensioning, which uses steel cables to compress the concrete slab, was also used to reduce the amount of concrete and steel needed.
Indeed, the post-tensioning reduced the thickness of the slab from the normal 10" down to 3-1/2" and uses a lot less reinforcing stee.
Complex ground source heat pumps cool and heat the house and its water
The house has an extremely complicated heat recovery system where gray water goes into tanks in the garden and then then is recovered to be put through heat pumps to heat and cool the house through radiant floors and ceilings. It seems total overkill for the mild Sacramento climate and the well insulated and carefully designed and shaded house; radiant floors are not particularly useful in these circumstances. They are very expensive and respond slowly. As Alex Wilson has noted, a radiant floors are “a great heating system for lousy houses.” That is not what we have in this house.
However there is a lot of other things going on here, with the integration of domestic hot water and the use of radiant cooling. Running everything out of one heat pump theoretically reduces the hardware costs, and predictive software deals with the thermal lag issue by adjusting the temperature in advance. The tanks only go down 20' so there was a lot less drilling than conventional piping for ground source heat pumps.
UC Davis " will evaluate the performance of the system to determine its adaptability to mainstream use." Read Martin Holladay at Green Building Advisor and I think you will come to your own conclusion about whether they make sense. And please, especially in California where there is real geothermal, stop calling it that, it is a ground source heat pump.
I want the lighting. At Fast Company, Ben Schiller sort of sneers at it, but this one of the great benefits of LED lighting, its ability to change color temperature.
Honda worked with researchers from the California Lighting Technology Center at UC Davis to explore new circadian color control logic. Mimicking the natural shifts in daylight that occur from morning to night, the circadian-friendly lighting design allows occupants to select lighting scenes that complement occupants’ circadian rhythms and support nighttime vision. The amber hallway night lights, for example, provide enough light to navigate through the home in darkness without depleting a photopigment in the human eye called rhodopsin that helps humans see in low-light conditions. This allows occupants to move about safely and return to sleep quickly and easily.
Home Energy Management
The real story of this house is the energy management system. 9.5 kW of photovoltaics on the roof are connected to a 10kWh battery array in the garage, which "leverages the battery to balance, shift and buffer loads to minimize the home’s impact to the electric grid."
Honda’s HEMS is also capable of improving grid reliability by automatically responding to demand response signals and providing other grid services. If the electricity grid is overloaded, for example, Honda Smart Home is capable of shedding its load and even supplying power back to the grid. This type of smart grid connectivity will enable the mass deployment of electric vehicles and renewable energy without sacrificing grid reliability.
It also lets Honda look at the re-use of older batteries, giving them a second life in the home after they can no longer take a full fast charge needed for a car.
The most important feature of this house is how the car and the house work together; what a difference it makes. The house on its own saves the equivalent of 13,100 pounds of CO2 per year, but roll in the electric car and " CO2 savings rise to more than 23,500 pounds per year versus a comparable home and vehicle"
This is where the idea of the smart house makes sense for the average homeowner and builder. Who cares if your fridge is talking to your washing machine; what matters is that your house is talking to your car and working together with it to make them both net zero energy and net zero carbon, dealing with our two biggest sources of CO2, the house and the car.
With the exception of the crazy heat pump and radiant floor system, the Honda Smart Home doesn't rely on gizmo green but has good design, lots of insulation and great windows. it is doing the important stuff and it is doing it well. More power to them.
It is a nicely designed 2,000 square foot house; here's the project team:
Lim Chang Rohling & Associates, Pasadena,
Monley Cronin, Woodland,
MAK Design+Build, Davis,
Davis Energy Group, Davis,
Kitchen appears to have a Bosch induction range with a pop-up exhaust hood. Surprisingly, there is no Heat or energy recovery ventilator; instead there is a sophisticated bathroom exhaust system and a mechanical damper on an air inlet.
More at Honda Smart Home