Honda's open source smart home: the template for new builds?

Honda’s decision to open source its smart home blueprint sounds altruistic, but the Japanese industrial giant’s ulterior motive is found at the heart of the home. The Home Energy Management System (HEMS) is a solar panel array and power storage unit, which can potentially be synced with other smart home ecosystems. HEMS represents Honda’s move into the smart home, and potentially the heart of millions of homes around the globe ‘ a lucrative venture in HEMS sales to third parties.

The open source move simply is about maximizing the number of homes that Honda’s system could be installed in. HEMS also has the potential to be retrofitted to existing homes; a much larger market than the amount of new builds that are constructed each year. An API would allow systems such as Apple’s HomeKit, Google’s Nest or the smaller players in the market to control HEMS or let HEMS control them. This feature puts a product such as HEMS in a very strong market position, and it won’t be long before rival systems begin to appear.

So Honda seems to have a head start on the competition, as we haven’t found an equivalent integrated system. But Honda’s approach will be dictated by its potential buyers. This is a system that can be easily built into new homes, which would no doubt comply with government energy efficiency regulations. As such, large construction companies whose entire business is building homes look to be the most receptive customers to HEMS, and you won’t find much political opposition, given that homes and vehicles are responsible for 40-50% of the average US consumer’s carbon emissions.

But this system doesn’t make much sense for older homes. Solar panels don’t produce enough energy for older homes, which use far more energy in their HVAC systems than a passive home. Put simply, an old home will waste more energy through its poor energy efficiency than HEMS will supply – especially if you are using the system to fuel an electric vehicle as Honda does in the prototype. The cost of adding a HEMS system to a home would also hinder sales to older homes, as the cost savings made through the solar panels may never reconcile the purchase price ‘ and Honda has yet to announce pricing.

The prototype smart home, built at the University of California’s Davis campus, is a passive home ‘ a design which prioritizes low energy consumption. HEMS is an integral part of the system, so Honda’s approach is very different to other smart home projects. It’s building a smart home from the ground up, instead of adding smart tech to a dumb home.

Passive homes are airtight and use ventilation systems to bring fresh air into the home without adversely affecting the internal temperature. A large concrete slab, a fundamental component of a passive home, is used to further regulate the temperature so that energy is not spent cooling the house in the day and heating it at night. The concrete acts as a thermal mass, and contains water pipes that are used to change its temperature. The home is heavily insulated too, and uses as many low-carbon materials as possible.

Honda says its prototype home will use 75% of the energy used by the average house, meaning that over the course of a year it will produce a surplus of 2.6 megawatt-hours, offsetting 5,942kg of carbon emissions, as opposed to consuming 13.3 megawatt hours like the equivalent normal home.

Honda claims the panels can generate 9.5kW of electricity per day. The average US home uses 903kWh per month, roughly 30kWh per day. The HEMS system is not something that could be installed with any success in a home that was not designed to be very thermally efficient, but the passive design of the Honda home means that the house is capable of drawing a very small net amount of power from the grid over the course of a year.

Honda uses solar panels fitted on the roof to power both the home and the accompanying Fit electric vehicle (Fit EV). However, this power generation is constrained by seasonal variations in the solar panels’ performance, so the home will still need to be connected to the main electrical grid to both draw power when the home generates a deficit but also to transfer spare capacity to the grid when there is a surplus ‘ such as on the sunniest days in summer.

The home is aligned north-south, and positioned so that the south-facing roof can optimize the solar energy, as well as large south-facing windows to make the most of the low sun’s energy in winter. External shades and roof overhangs built over the windows will reduce the solar heat that gets into the house in the summer, and Honda says this means no additional air conditioning loads are required in the summer. Ceiling fans can be used to quickly cool the home down if needed.

HEMS does have the capacity to store 10kWh of electricity in a lithium-ion battery that Honda have installed in the garage. The battery is key to this system of balancing the supply and demand of electricity, and could not work properly without it. What looks like a small server rack and display screen accompanies the battery inside a clear glass enclosure, which Honda have no doubt designed to show off its concept but which could easily be hidden from sight. The HEMS system can be controlled via a smartphone.

HEMS will generate 278 channels of data that are stored locally at a refresh rate of 1 minute. Every 12 hours, the data is uploaded to the cloud where it can be analyzed. HEMS can also check to see if any of its sensors are offline and inform the owner to take action.

The solar panel and battery use DC current, but the electricity that comes from the grid is AC. As such, HEMS acts as an interchange between the two incompatible forms, although the conversion from AC to DC is not perfectly efficient, so some power is lost in the transfer.

When the Fit EV is at home, the solar panels will prioritize charging the car. When it is away, the panels will store their output in the HEMS battery, and at night, when the home’s occupants have gone to bed, the stored battery power will charge the car. Basically, the home produces and stores energy in the daylight, and consumes it after sunset.

HEMS will also monitor the performance of the local grid, and Honda claims it is able to boost its output to the grid to supply power to the local community as needed, as well as share excess power for community use ‘ reducing the draw on the national grid. The idea behind this mechanism is to reduce carbon emissions by only consuming electricity when the carbon footprint of the main grid is low, something that HEMS is able to measure and adapt to. The home therefore buys (consumes) electricity when the grid is under-stressed (low-carbon footprint) and sells (provides) electricity to the grid when the grid is over-stressed (high-carbon footprint). This model should reduce the overall carbon footprint of the home significantly.

The HVAC system inside the home uses a ground source heat pump, effectively a boiler that harnesses the ambient heat from the ground, which is reversible and can be used for both cooling and heating. The home’s under-floor radiant system distributes the required temperature water around the home by warming or cooling the thermal mass that is the concrete slab.

This system also allows ‘waste heat’ from say the shower to be used in a process called drain water heat recovery, which combines the heat from the wasted gray water with the cold fresh water ‘ raising the temperature of the fresh water so that less electricity is used to heat the next load of hot water.

The water usage of the house is also tightly controlled. One of the largest sources of water consumption in California is found in the garden, when home owners water their lawns. This house has a xeriscaped (zero-water) design, that uses indigenous species that don’t require as much, if any, extra water from the home, and if the owner does need to water the garden, Honda will use the gray water from the house to irrigate the plants, after it’s passed through a simple filter. A rainwater recovery system is also used in the garden, which will also fill a faux river creek under heavy rainfall.

Smart LED lighting will mimic the circadian pattern of the sun, with brighter lighting in the day and warmer lighting at night. Amber pathway lights have also been installed to guide the occupants at night, without having to turn on the overhead lights ‘ a key cause of falls, as amber light doesn’t interrupt the dark-adapted eyesight but white light can knock it out of use for up to ten minutes.

If such a design takes off, the impact on the electrical grid will be transformative, driving the need for investment in decentralizing the grid and investing in the various smart grid initiatives. However, there have been stark warnings about introducing more devices to the smart grid that echo the security concerns of adding more things to IoT networks. A link to the US Center for the Study of the Presidency and Congress report can be found in the Around the Web section of this newsletter.