Zero Energy Certified



Certification StatusZero Energy Certified
Version of LBC3.1
LocationDavis, CA, USA
Project AreaHouse: 1,944 SF, Garage: 477 SF
Start of OccupancyOctober 2014
Owner OccupiedNo
Occupancy TypeSingle Family Residence
Number of Occupants4


OwnerAmerican Honda Motor Co., Inc
Project ManagerMichael Koenig
General ContractorMonley Cronin
ArchitectLim Chang Rohling
MEP EngineerDavis Energy Group
Lighting DesignUC Davis California Lighting Technology Center
Interior DesignMak Design + Build
PlumbingGary Klein
HVAC DesignUCD Western Cooling Efficiency Center
ConcreteSyar Concrete
Key SubcontractorsAP Plumbing and Fire, Country Bear Electric
Photo Courtesy of American Honda Motor Co., Inc


Wall R value and section specificationR31. Double stud 9.25” cavity, dense pack cellulose
Roof R value and section specificationR60. Loose fill cellulose, vented roof deck
Floor R value and section specificationR10. Viega underslab insulation for hydronic installations
WindowsAll windows Alpen triple pane. U values = 0.11 ~ 0.20, SHGC = 0.10 ~ 0.32
Air infiltration rate and sealing protocol1.9 (ACH-50). Sealing consisted of conventional caulk sealant, plus application of a prototype aerosolized sealant system (UC Davis)


The passive design strategy optimized the orientation of fenestration for daylighting (north clerestory windows) as well as the southern windows’ overhangs; note that the roof overhang is optimized for 2F windows, as well as the additional awnings applied over the lower windows on the South side. Also, although the shades are primarily provided for privacy, the 2F West window shade will automatically lower at noon for heat gain, but will open again at sunset for a nice view of the mountains.


Bosch TW025 water/water heat pump with hydronic distribution. The ground source heat pump uses a novel helical-coil exchanger design for high performance and moderate cost; primarily “dry” bores are used for source side exchange, but wetted bores are also in use for data comparison.


Depending on need, we ventilate the house using up to 5 bath fans (Panasonic FV-13VKS3), and/or the whole house fan (Motor: GE/ Regal-Beloit 1 hp ECM 2.3, Blower: Morrison 12-10 forward curve centrifugal blower) pressurizing the house with filtered air distributed by registers into the great room. This is used to take advantage of diurnal temperature swings (to pre-cool the house on summer nights) and also to provide 62.2 ventilation. This is also used to moderate excessive solar gain in the house during shoulder seasons so mechanical cooling is not required.


Bosch TW025 (same unit as heating/cooling) with desuperheater, stored in Triangle Tube Smart SME 80 tank. We also use a PowerPipe R3-72 Drain Heat Recovery unit to pre-heat incoming makeup water during showers.


100% LED with occupancy sensor and daylight sensor. 5 scenes per room (depending on time of day) with wall-button override, and novel “sleep” setting for bedrooms. Lutron Ecosystem control.


Real time energy performance, as well as 24 hour history are presented to the occupants on the home screen of the control tablet.

Photo Courtesy of American Honda Motor Co., Inc


36 – Suniva Optima 265W = 9.54kW nameplate PV Inverter is Honda proprietary equipment, integrated with the Home Energy Management System, 10kW bi-directional capability. Location is a dedicated Equipment Room in the garage with auxiliary cooling available.


Actual energy use during performance period10,634 kWh
Actual energy produced during performance period11,236 kWh
Net Energy Use-602 kWh
EUI18.7 kBTU/sf/yr


This home was imagined as a demonstration of a Zero Carbon future, including not just the home but also the daily transportation.  The purpose was to engage society in a discussion to try to move forward to a future of renewable energy and electrified vehicles; it was therefore conceived as a package including the home, vehicle, and energy management system.  In order to bring as much societal value as possible, we also wanted to highlight discussions of sustainability beyond energy.  So while energy is clearly a focus, we also tried to demonstrate sustainability of the materials themselves, water use, waste, and occupant health.

The project was developed by Honda, led by the Environmental Business Development Office (EBDO) within American Honda Motor Co., Inc.

Photo Courtesy of American Honda Motor Co., Inc


The name “Honda Smart Home” refers to the Smart design and use of energy.  We therefore began with a holistic, integrated design process considering all aspects of sustainability.  As with most “real-life” projects, our site required specific layout features in order to make full use of solar access, while providing for access to the garage.  To make full use of solar energy, our roof form is biased towards southern exposure with minimal roof penetrations to disrupt panel layout; and the North side is designed for natural daylighting.  Every detail of design was similarly considered, which meant continuous discussion among the architect, HVAC designer, mechanical engineers, certification members, and EBDO leadership.


The basic viewpoint for the project was to first build the home as efficiently as possible:  the envelope, HVAC system, lighting, appliances, and MELs.  Then to allow the occupants to live without sacrificing quality-of-life.  Of course, they are aware that they are living in a demonstration home, and that their usage data will be recorded; but the intent is not to try to coerce specific behavior.  If the occupants need to run laundry or wash dishes, then the home should respond as requested, but if this would cause hardship for the electrical grid, then the HEMS machine will seamlessly step in to allow them to continue their daily routine, but also provide value to the grid.

We therefore do not control any of the appliances with the HEMS machine.  In extreme cases, we can use the thermal mass of the home to slightly shift the HVAC run times, but in general we only actively control the vehicle charging to minimize CO2 (and use the stationary battery to provide grid support).

The home is oriented for maximum winter sun collection, but with careful design of the roof overhangs and addition of awnings to shade the South windows from summer sun.  The home also takes advantage of the cool summer evenings by pre-cooling using only fresh air, and throughout the year ventilates primarily at times of day when the outdoor temperatures are preferable (note that this climate has low summer humidity which allows for this pre-cooling strategy).  We are also able to track vented air from the central vacuum, range hood, or bath fans so that we do not over-ventilate on days that have supplemental sources of fresh air.  We use a passive heat exchanger to recover heat from greywater, then further remove heat (mechanically) from that greywater as it percolates through our wetted boreholes.  And of course, the windows provide excellent natural daylighting for most of the day (the lighting system uses daylight sensors to reduce consumption when enough light comes from the windows).

Photo Courtesy of American Honda Motor Co., Inc


The home is continually being updated with new features and controls, and our occupants have always been very flexible and accommodating.  In some cases, as we develop new HVAC controls, we have had to work with them to fine-tune the system to their preferences (for example, the blower settings for pre-cooling and the zoning for the hydronic distribution).

The occupants have been very positive on the home’s overall layout and open plan, and the lighting.


One of the most impactful issues we had was with our original strategy to use the whole house fan to pressurize the house, and open the clerestory windows to allow the cool air to flush the home on summer nights.  The third-party motors used to actuate the windows were intrusively loud, and did not reliably lock the windows when closed.  The fan itself was also too loud to operate when occupants were sleeping.  Using the bath fans to pull cool air into the house (through a dedicated outside air damper, and through a filter) resulted in an uncomfortable depressurization, and limited effectiveness.  Ultimately, we replaced the whole house fan with a quieter version, and now use it combined with the bath fans to exhaust the warm air while keeping the clerestory windows closed (balanced ventilation).


There were no issues.  All of our systems were permitted and installed using the “typical” process, without any request for variance.  At the time of installation, there was some question regarding the use of a stationary battery, but ultimately the utility determined that the system could be interconnected using the same process as a typical solar system.

Photo Courtesy of American Honda Motor Co., Inc


Although our HVAC system is an elegant design, it required substantial development and engineering.  A turn-key solution for a water to water heat pump with integrated Heating, Cooling, and Hot Water functions, as well as thermostatic control would be welcome.


There are a lot of specific lessons to be learned in areas ranging from the door latch hardware, to the thermal modeling, to the solar gains, to the use of polished concrete!  The public is invited to reach out to us at to discuss any of these topics with the project leader.  We post all of our monitoring data, as well as videos, specs, and drawings to