Cruise control for the home

Drivers and pilots make use of technologies that make their life easier and increase energy savings, why not home owners?

I’ve been thinking a bit lately about the future of energy monitoring and intelligent control systems. We recently installed an energy monitoring system from Powerhouse Dynamics. It is very good at telling us how much energy we’re using for which circuits, and advice about how we can use the appliances on those circuits more efficiently. Although we don’t own one*, Nest has been in the news a lot lately for their intelligent use of occupant behavior history and weather predictions to actively optimize your heating/cooling equipment, and for telling you how much you saved by using their product.

I’m imagining an energy monitor that tracks our energy usage for major appliances and through a combination of active control or user suggestion determines the ideal time to use those appliance to 1) optimize their effectiveness, 2) increase our enjoyment of said appliances and 3) lower our energy usage.

Example 1. Water heater. Nest says the thermostat controls 50% of your home energy usage. For us it’s the water heater because our heating and cooling requirements are so low. Now that Martin Holladay has determined that tankless water heaters are a waste of money, we should be able to make tank style heaters more efficient. Let’s say our monitor knows generally when and how much we tend to use hot water. Similar to the calculations required to heat and cool the house, it could determine the optimal water temperature between 120 or 140 degrees F and when the heat is required. For us, it is mainly needed in the morning when we take showers and a bit in the evening when we do a bit of hand washing of pots and pans that don’t fit in the dish washer. No need to stay at 120 or 140 degrees F 24/7/365.

Example 2. Clothes washer and dryer. Let’s say our monitor energy tracks how often we wash clothes and dry them. Let’s say it understands some correlation between season, outdoor temperature and humidity. It might suggest after a few months of usage and weather data that if we wash our clothes this Sunday rather than Saturday then we can dry them on the drying line versus having to use the dryer because there is a higher chance of rain on Saturday. Or maybe it knows we don’t have a drying line but we have a solar array that can supply the required energy without going to the grid. It could predict the energy savings if we follow the monitor’s advice.

Where to control these appliances? At the circuit box or at the device? Circuit level control seems crude. It seems like it would make more sense to have more intelligent devices, each knowing what factors affect it’s efficiency. But then you end up with lots of appliances with redundant functionality. Plus, you may be missing out on efficiencies across appliances.

Consider if we decide to wash and dry our clothes in the winter when the sun is shining and powering our solar PV system while adding passive heat via our high solar gain windows that face south? Maybe we can lower the set point on the heating thermostat so that we don’t overheat. Or maybe we use the condensing dryer to heat the house instead of the air-source heat pump.

This is one of the scenarios that makes me think that someone is working on a Nest-like appliance for the entire home. It will monitor not only energy and hot water usage, but also every generation, occupant behavior and weather predictions to put the house on auto pilot, or suggestion or cruise control mode. Occupants can override this mode manually whenever required and then compare at the end of each month to see who did better, them or the algorithm. Who knows, maybe the user gets a credit on the system if they out perform the algorithm more than 3 consecutive months.

None of these ideas are new, and I’m guessing most are already being used in large scale commercial operations. But I think the Nest shows us that the future is closer than we think for home owners. We don’t need a lot of intelligent appliances, or a lot of intelligent appliances talking to each other. We don’t even need automated controls, but a simple auto pilot for the home can maximize the efficiency of home appliances and the happiness of the home owner.

* Note to Nest. We don’t currently own a Nest thermostat because our heating and cooling loads are so low, but we would gladly own one if it could use similar logic to control our water heater.

2 Responses to “Cruise control for the home”


  1. 1 Jim Merrithew 27-April-2012 at 5:54 pm

    Hello Larry and Jill,

    This is an interesting proposition and question.

    In many households, there may be a difference in the behaviour and useage of energy by different individuals. This difference could be as simple as one person liking the house warm while another prefers cooler temperatures. This preference would affect the energy consumed for both heating and cooling.

    One occupant may prefer short showers, while another likes to bathe.

    One individual may work from home while another is away much of the day or for several days at a time.

    For your monitoring and controls to work effectively, would you also need to track who is in the house at various times during the day and the week?

    Would it be useful to not only track the current external temperature, but also the projected temperature and weather conditions? For instance, if the morning is sunny and cool but the forecast is for the external temperature to rise by 15 degrees by noon, then you might want to reduce the morning thermostat setting to avoid passive solar overheating later in the day.

    Conversely, on a warmer, sunny morning, if the forecast is that the wind speed will increase, the temperature will drop dramatically and a blizzard will hit by noon, the thermostat setting could be increased to compensate for the projected heat loss. In this case, morning overheating would increase the heat banked by the thermal mass, thereby reducing the chilling effect later in the day.

    – Jim

    • 2 Larry 1-May-2012 at 12:27 pm

      Hello Jim,

      Thanks for your thoughts. I don’t think any thermostat is going to resolve different temperature preferences between individuals. If you choose to live together then there’s an implicit assumption you’ve agreed to tolerate different preferences and agree on an average set point that makes all parties relatively happy.

      As for tracking projected temperatures and conditions, absolutely. Perhaps I am wrong, but I believe the Nest thermostat may already be doing this. If not, then it may only be a few upgrades away.

      If you have a super insulated house, you don’t need a thermal flywheel, and therefore you don’t need to ramp up or down for expected extreme temperature differences. Perhaps the Nest will learn the house’s general rate of heat loss or gain by comparing energy use and outside weather conditions to optimally ramp up or down to anticipate extreme conditions based on the efficiency of the thermal envelop. That might be pretty difficult however, if someone accidentally leaves a window open on a warm spring day and temps plummet below freezing at night. There’s always a limit to our ingenuity.

      There’s a fairly good chance these ideas are already at work in larger commercial buildings where the energy to heat and cool the building is very large. It’s just taking a little time to get own to the residential market.


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