Environment / Green
Smart home energy savings – update for 2010
Dec 14th
Here’s an updated graph showing the ongoing reduction in energy for our smart home. Driven mainly by continual improvement in the algorithms that control the heating, air conditioning and lighting the overall consumption of gas and electricity has continued to decline throughout 2010. It appears however that I am approaching the limit as to what is possible as the trend lines are beginning to flatten out. Going forward I’ll continue to try to improve the algorithms but I’ll also be on the lookout for any parasitic power-consuming devices and I’ll be dealing with them using techniques like the smart power strip I mentioned here.
A smart power strip
Dec 9th
Recently I added a smart power strip to the TV/Amplifier setup in the living room. My main aim was convenience – to make it easier to turn everything off all at once. But I also wanted to see how much power I could save by eliminating the parasitic power drain that a TV, amplifier and two DVD players have when in the ‘off’ state.
The power strip I bought is the one featured to the right here and to date I’m pretty happy with how it’s working. The power strip has one ‘blue’ outlet that senses when a single device goes on or off and then several ‘green’ outlets that switch accordingly. Initially I plugged the amplifier into the sensing output and everything else into the green outlets. That worked great and when the amplifier goes off so does the TV, the DVD player and the DVD changer. Since the amplifier is a Denon -CI model I can also control it remotely and since everything else switches on and off with it I can remotely shut down the whole stack from my home automation software.
The only problem with that approach is that in the ‘off’ mode the Denon -CI still consumes about 5W whereas the TV consumes 0W when off. The TV is one of the earliest HD TVs, a Panasonic Tau CRT TV so it’s fairly power hungry when on but it has a ‘real’ on/off switch so when it’s off there is no power draw at all. [Until recently the picture on that CRT beat nearly every flat panel TV on the market, but with recent LED LCD TVs I think I may finally be willing to part with it. It's old technology, but still an awesome HD picture.] So now I have to chose between remote power-off control and a 5W constant draw or no remote control and 0W consumption.
When I purchased the smart power strip I was concerned that it might itself have a phantom power drain equivalent to one of the other devices but it appears to be relatively harmless consuming hardly any current for itself.
The one adjustment you need to make on the smart power strip is to set the sensitivity so it can turn on and off at the right point.
Overall, definitely a recommended buy on this one.
Passive Air Conditioning to reduce Energy Consumption
Jul 26th
photo credit: dynamosquito
Technology to heat or cool buildings naturally and without expending huge quantities of energy has existed for thousands of years. In Iran this ‘badgir’ has a natural cooling system made with mud bricks and Adobe. It uses the air circulation between two towers passing through a dome refreshed by the flow of water into an underground channel named Qanat.
By contrast, typical American home construction affords few opportunities to use nature to help heat or cool the spaces we live in. Homes here are built with thin walls making them poor insulators and although modern homes are well insulated with fiberglass insulation in the walls and roof spaces that is done primarily to keep the heat in; it provides little thermal inertia and has the unintended consequence of trapping heat in the house during summer months when there is plenty of sunlight streaming through large windows but no way out. Worse still, in modern construction, windows and doors are kept tightly closed and the building itself is built so tight that it needs a fan to bring in outside air regularly to improve the air quality in the building. That fan uses energy and runs on a dumb timer, sucking in potentially cold air in winter and hot air in the summer.
Having already reduced my total electricity consumption by over 40% and made inroads in how much gas we use for heating I’ve recently begun to look at how we can reduce the amount of cooling needed to keep our house comfortable in the summer.
In a location where there is a significant variation between daytime and night time temperatures there ought to be an opportunity to heat or cool a house naturally using free energy from the environment. Here near Seattle for several months each year we have just such an environment as you can see on the graph to the right (click to enlarge). The nighttime lows are currently below 70°F and the daytime highs are well above 70°F.
Since we already have a fan connected up that’s forcing external air into the house why not connect that fan to the home automation system and dispense with the dumb timer that was driving it. Now the house has control of that fan it can change the time of day when fresh air is brought into the house to use warmer air in winter (around 3PM) and cooler air in summer (around 3AM). It can also use this fan in conjunction with the air conditioning system. For example, it knows you are upstairs and that it’s too warm up there tonight, the air conditioning has been running but it’s now past midnight and although it’s still 72 inside it’s dropped below 70 outside. In this situation it can simply open the external damper, turn on the fan and turn off the air conditioning. Cool air flows in and the compressor is idle.
All this seems like a good theory but because I’ve only had it installed for a few days it’s too early to say how well it will work.
But what about houses with no circulation fan? Could we simply use doors and windows to improve comfort and reduce costs by telling the occupants when to open and close them? Today for example I was up early and it was cool outside so I opened up all the doors to the deck. The graph below shows what happened: a much bigger temperature drop than the day before even though it’s a much warmer day today overall. What I failed to do today, however, was to close them at the right time so the early gains in ‘coolness’ were soon offset by the rapidly rising outdoor temperature and before lunch it was already warmer inside than the day before. But what if the house calculated what to do and told you so that you could do an optimum adjustment to doors and windows to achieve free cooling?
My home automation system tracks the temperature in each zone in the house using an Aprilaire communicating thermostat with RS485. It can display graphs for any variable or collection of variables using the ASP.NET charting control. These graphs and experiments like the one this morning are helping me understand the dynamics of our house and figure out the best ways to achieve passive cooling (or heating).
Home Automation Heating and Cooling (HVAC) Features
Jul 7th
Now that summer is finally upon us in this part of the world I thought I might make a list of the many ways in which my home automation system monitors and controls the heating and cooling systems (HVAC) in our house. It does this to reduce energy consumption and to provide a more comfortable environment for the occupants.
1. Reduced heating/cooling when the house isn’t occupied
The house automatically drops back to a lower (or higher in the case of the air-conditioning set-point) setting whenever a zone in the house is unoccupied for a set period.
2. Further reduction in heating/cooling when the house isn’t occupied in the case of a vacation
If the house is totally unoccupied for the majority of the day (i.e. excluding brief visits from cleaners and pet sitters) it will automatically flip into an even lower power consumption mode using less heating and no cooling at all.
3. Heat-point / cool-point variation by time of day (for each zone)
Instead of aiming for a single fixed temperature for a 24 hour period the house has target temperatures for different times of day – at night for example it lowers the heat-point substantially, during the evening it lowers it subtly in preparation for nighttime (except if we have visitors (which it knows)). On hot summer evenings it will cool the bedrooms in advance of bedtime (as shown in the graph here) but during the night it will allow the temperature to creep up slightly. Each zone has it’s own target temperatures curve because what’s right for the bedrooms isn’t right for the kitchen.
4. Optimum start in the morning
A traditional thermostat with a timer typically simply slams the thermostat up to 68F at, say, 5AM every morning to get the house to the right temperature by the time we wake up. My smart house instead follows an ‘optimum start’ routine whereby it gradually increases the set-point every five minutes along a predefined curve that matches the house’s thermal characteristics for heating (which varies according to the outside temperature). This means it heats the house for the absolute minimum duration necessary to arrive at the correct temperature by the desired time of day. A traditional thermostat by contrast may have been holding the house at 68 for an hour or more before it was really necessary.
5. No heating of cooling at all if the weather forecast says it’s not needed
If the house is going to get warm all on its own today because it’s forecast to be a hot sunny day then the house will automatically skip all heating in the morning even if it means the house will be a few degrees cooler than desired for an hour or so in the morning. When it’s sunny and the forecast is for a hot day there’s no point heating just to increase comfort for such a short period and besides when it’s sunny outside people don’t feel as cold anyway. This also means that the house will not need as much cooling later should it be a really hot day.
Another example of this can be seen in the graph above where the house decided to stop cooling the upper floor because the forecast indicated that it would soon be cool enough outside to not require any A/C and it would be cheaper and more effective to just suck in air from outside.
6. Manual override and the subtle shift back to computer control
There are unfortunately many people in the world who don’t understand thermostats let alone thermodynamics. For some there is a perception that the higher you set it, the faster it will get warm. Rather than try to reason with such people, or offend them with rude alerts or announcements over the speakers to explain how thermostats work, my home takes a more subtle approach: you can set the thermostat to whatever value you like but within an hour it will have taken back control and the set point will be back to where it should be.
7. Thermostats are part of the occupancy sensing network in the house
If you adjust a thermostat that counts as an occupancy trigger in the room in which the thermostat is located. In order to have the densest possible network of occupancy sensors any device that receives input is treated as an occupancy sensor, so thermostats, light switches, TV remotes all act as occupancy sensors just like the more traditional door sensors, motion sensors, floor sensors etc.
8. The house refuses to attempt to cool the entire world – Close the doors!
If the house is in cooling mode and external doors are left open it will wait for 5 minutes, then issue a verbal warning over the speakers, and then if the doors are still left open it will simply stop trying to cool that zone until the doors are closed.
9. The house logs what happened in each zone and can explain why it made changes
Any complex system will have unexpected behaviors, but unlike other home automation systems this one keeps a detailed individual log for each zone and in that log you can see what happened and equally importantly why it happened because the house leaves a trail including explanations as to what it was doing and why.
| yesterday at 12:00 AM | 14.04% on today |
| last Monday at 9:16 PM | Temperature 67°F [64°F < |65.3°F| < 68°F] |
| last Monday at 7:05 PM | Heatpoint changed to 55 because warm outside (Outside ave=57.2°F now=65.0°F |
| last Monday at 6:38 PM | Temperature 68°F [64°F < |65.0°F| < 68°F] |
| last Monday at 3:01 PM | Heatpoint changed at thermostat to 66°F |
| last Monday at 3:01 PM | Heating (Off) |
10. The house makes graphs for each zone
These graphs show how the temperature varied and what changes it was making to the set points during the course of the day
These cooling and heating features together with all of the other home automation features directed at energy saving mean that our total electricity consumption is down 40% from where it was five years ago and comfort has if anything improved along with convenience – it’s very rare now that we ever need to adjust a thermostat.
11. Future improvements
Although the house can tell if we are home or away, or if we have visitors for the evening or visitors stopping over all without being told, it still can’t figure out when we will get home. But that’s about to change, the house now knows where we are when we aren’t at home (more about that later) and it will soon be able to predict a return time. Armed with that I hope to improve it so it can have the house ready for our return after we’ve been away without having to explicitly tell it anything!
12. A more detailed example
Click the image on the right to enlarge it. You’ll see a detailed example of how the house manages the cool point to achieve optimum comfort with minimal energy consumption.
Is a 24hr energy consumption graph really useful?
May 28th
I’m somewhat surprised to see how much effort and excitement Google and Microsoft are putting into the ability to show graphs of home energy consumption minute-by-minute from a smart meter. I’ve had that ability in my house for several years now (not directly measured but a close enough proxy based on knowing which devices are currently on or off). My conclusion after staring at the graph on and off for several years now is that it’s really not that interesting!
Here’s one of my 24 hour graphs showing the peak, minimum and average electricity consumption in five minute intervals during the day. Fascinating huh? So what are you going to do with it?
The fact of the matter is that you still need to take a shower and the fridge still needs to stay cool – those peaks really aren’t interesting. If you do want to see how much energy any device is using you can get one of the many Wattage Monitoring Products
It turns out that the real problem here is the base-load rather than the occasional short-lived peak. Some of that base load is unavoidable but one of the top controllable loads is lights that stay on for hours at a time, so, in your quest to reduce energy consumption, start with them. Replacing them with compact fluorescents or LED lights is an obvious step, but not without drawbacks (lack of dimming, harsher white light, flickering, …). A better solution is to have a smart home; one that can turn lights off when people aren’t in a room, or can lower the brightness according to the time of day. That’s what my home automation system does and it has produced some fairly dramatic energy savings as a result: over the past 5 years it now uses 40% less electricity than it used to! Unfortunately most home automation systems aren’t smart enough to do this – they will happily plunge you into darkness because you sat still for too long in one room. After years of refinement (both software and hardware) my own system can now accurately assess which rooms are occupied and very rarely does it make a mistake that results in darkness when there should be light. As I mentioned earlier it also prolongs bulb life by running them at less than 100% saving more energy and dramatically reducing how often you need to go up a ladder to change those high-up lights.
This then is really the graph you want to pay attention to and it’s something you can make yourself using the utility bills you get every month. I also think that the energy companies could do more to promote green-envy: simply show people how much less energy their neighbors are using! Shame them into action. Rank them … “you are #1 in your street for energy conservation”. I know some places have started to do something like this but it needs to be widespread.