For a more thorough analysis of this subject, there are some studies currently underway and other useful info around the web, but I'm not sure if they make this point well enough. Try this link or Google "daylight saving energy" for more info.
Based on some of the information about peak electrical demand in California (see my other posts about some data that came out of UC-Davis) I'm not convinced that daylight saving actually saves energy as much as it used to. When previous studies were done, central air conditioning was not nearly as common as it is today (many of the studies date back to the 1970s). I believe that central air is a large contributor to the peak demand when people return home from work in the afternoon, even more so when they use a programmable thermostat to set the temperature higher while they are at work. Without a programmable thermostat, the overall energy usage is much higher, because the A/C unit runs more during the day. However, a programmable thermostat changes the setpoint around the time you get home, effectively turning on the A/C for an extended period right at that time, increasing demand a lot, even though the overall usage throughout the day is lower.
Daylight saving effectively gets everyone home from work one hour earlier (as far as where the sun is in the sky) and therefore closer to the hottest part of the day. At this point, more energy is needed to cool the home to a comfortable temperature, while if people returned home an hour later (without daylight saving) the house wouldn't be as hot because the sun is lower in the sky. Of course the evening lighting load will be greater, because the sun goes down, but certainly that's a smaller load (overall) than the A/C unit.
This is an idea that may sound completely backward, but consider it for a moment. Assume for a moment that it is true that programmable thermostats cause most A/C units in California to turn on at about the same time each summer afternoon (within an hour or two of each other) and then they run for an extended period of time to cool the buildings. Now what if, instead of using demand response controls to disable some of those A/C units to reduce peak demand, you instead use a demand response control to turn some of those A/C units on earlier, cooling some of the homes earlier than others, so they won't need it later when all the other units kick on. It's the exact opposite of a typical demand response system, but in terms of reducing peak demand, it may be exactly the right thing to do.
I really think that new studies will show that daylight saving is no longer helping our energy usage (especially on the basis of peak demand) as much as it used to (if at all).
Thursday, December 11, 2008
Tuesday, December 2, 2008
Hotel room Energy Savings
There seems to be a lot of interest in saving energy in hotel rooms and timeshare resorts lately. After hearing what some of these places spend on electricity (hundreds of thousands of dollars per year) it's no wonder. I think there's a lot of energy to be saved there, given how often people leave the A/C running full blast even when they leave the room for the whole day.
Whether it's a standard window air conditioner like you'd pick up at Home Depot, or a PTAC (packaged terminal air conditioner, I think) unit, they use a lot of power. When running, they're probably 2 kW at a minimum, and if you're out of the hotel room most of the day, that's a lot of kWh. I understand that in Europe, a lot of hotels have occupancy (presence or absence) sensors in the rooms or "key card switches" at the entry of the rooms to enable the power in the room. It seems that there aren't any cost-effective technologies to detect the presence of a non-moving person in a room, so when people go to sleep at night an occupancy detector isn't an ideal solution.
The key card switch seems to be pretty popular, however. When you enter your hotel room, using a magnetic stripe key, there is a slot near the entry door to "store" the card. When you insert the card into the slot, a switch is activated to enable the power and A/C in the room. In a new hotel, it's pretty easy to wire for this, though the extra wiring may be expensive. In a retrofit, however, a wireless device like the illumra key card switch is really slick - just sitck it on the wall, and it sends radio messages to the receiver installed in the PTAC (at a minimum) and on the lights and television, too.
I've intentionally stayed away from discussing specific illumra products in this blog, rather focusing on energy savings, green solutions, and other general topics. I'll generally keep to this policy, only occasionally linking to illumra.com, because the energy problems we face are much bigger than any product or company can hope to fix on their own. (See the "full disclosure" in my first post - I work for a company making energy saving products, so I'm at least a little biased.) Everyone has something to contribute to the solution, and I expect to cover a lot of them. Even within the battery free wireless space there are a lot of players, and if you want to see some of them, take a look at the EnOcean Alliance for more information. There are a lot of very cool products out there, but a little due diligence is important before installing any new technology. Analysis, even a quick back-of-the-envelope calculation or even a very rough "guestimate" should be used to justify any energy saving measure.
As an example of this, one of the features some people have requested for hotel key card switch control is the use of a window sensor to disable the A/C when the window is open. This is nothing new, it's used in a few places in Europe I know of. However, the incremental cost of adding the window sensor may (or may not) result in a significant return on investment compared to just using the hotel key switch alone. After all, if only one or two windows are opened regularly in a 1000-room hotel, even if the A/C is running, the cost savings of having the A/C turn off automatically (when the window opens) may be pretty small. On the other hand, if you're in a tropical area near the beach and people open windows regularly, the cost of the extra sensor may be paid off very quickly.
In the end, a lot of little changes will add up to a big change over time. I've been more careful to shut down my computers or put them to sleep when not in use, and noticed a few dollars difference in my last electric bill. Not much, I admit, but maybe I can find a few more places in the house to use compact fluorescents. Once the dimmable ones aren't prohibitively expensive, I may be able to try them in a few more fixtures, too. I'm glad I live in a dry climate, as my evaporative air conditioner ("swamp cooler") is a lot less expensive to operate than central air would be.
Whether it's a standard window air conditioner like you'd pick up at Home Depot, or a PTAC (packaged terminal air conditioner, I think) unit, they use a lot of power. When running, they're probably 2 kW at a minimum, and if you're out of the hotel room most of the day, that's a lot of kWh. I understand that in Europe, a lot of hotels have occupancy (presence or absence) sensors in the rooms or "key card switches" at the entry of the rooms to enable the power in the room. It seems that there aren't any cost-effective technologies to detect the presence of a non-moving person in a room, so when people go to sleep at night an occupancy detector isn't an ideal solution.
The key card switch seems to be pretty popular, however. When you enter your hotel room, using a magnetic stripe key, there is a slot near the entry door to "store" the card. When you insert the card into the slot, a switch is activated to enable the power and A/C in the room. In a new hotel, it's pretty easy to wire for this, though the extra wiring may be expensive. In a retrofit, however, a wireless device like the illumra key card switch is really slick - just sitck it on the wall, and it sends radio messages to the receiver installed in the PTAC (at a minimum) and on the lights and television, too.
I've intentionally stayed away from discussing specific illumra products in this blog, rather focusing on energy savings, green solutions, and other general topics. I'll generally keep to this policy, only occasionally linking to illumra.com, because the energy problems we face are much bigger than any product or company can hope to fix on their own. (See the "full disclosure" in my first post - I work for a company making energy saving products, so I'm at least a little biased.) Everyone has something to contribute to the solution, and I expect to cover a lot of them. Even within the battery free wireless space there are a lot of players, and if you want to see some of them, take a look at the EnOcean Alliance for more information. There are a lot of very cool products out there, but a little due diligence is important before installing any new technology. Analysis, even a quick back-of-the-envelope calculation or even a very rough "guestimate" should be used to justify any energy saving measure.
As an example of this, one of the features some people have requested for hotel key card switch control is the use of a window sensor to disable the A/C when the window is open. This is nothing new, it's used in a few places in Europe I know of. However, the incremental cost of adding the window sensor may (or may not) result in a significant return on investment compared to just using the hotel key switch alone. After all, if only one or two windows are opened regularly in a 1000-room hotel, even if the A/C is running, the cost savings of having the A/C turn off automatically (when the window opens) may be pretty small. On the other hand, if you're in a tropical area near the beach and people open windows regularly, the cost of the extra sensor may be paid off very quickly.
In the end, a lot of little changes will add up to a big change over time. I've been more careful to shut down my computers or put them to sleep when not in use, and noticed a few dollars difference in my last electric bill. Not much, I admit, but maybe I can find a few more places in the house to use compact fluorescents. Once the dimmable ones aren't prohibitively expensive, I may be able to try them in a few more fixtures, too. I'm glad I live in a dry climate, as my evaporative air conditioner ("swamp cooler") is a lot less expensive to operate than central air would be.
Thursday, November 27, 2008
Demand Response Systems to help the power grid
I recently read that California is stepping up (or planning to increase) their billing rates for electrical usage during peak hours. There's a fascinating graph (from a study done by UC Davis) showing the amount of power consumed by residential and commercial customers during a typical day. The sum of the two graphs actually looks pretty sinusoidal, with peak demand occurring between 4pm and 7pm. The peak of the commercial/industrial graph is a little sooner, the residential one is a bit later.
In many parts of the country, consumers receive a credit on their utility bill if they install a remote-controlled shutoff device to their air conditioner. Given that the A/C unit on most homes is the largest electrical load in use (particularly during the daytime) it is a good candidate for saving electricity and reducing peak demand on the electrical grid.
There's a downside to this method of demand reduction (not just the fact that your house will get a bit warmer for a while) as it defers, rather than eliminates, the electrical demand. Once the utility allows the A/C unit to turn back on, it will then operate for a longer time to bring the temperature of the house back down. In the end, you only shift the demand, you don't eliminate it.
A better (but more complex) solution
A better method would be to raise the temperature setpoint a few degrees for several hours, assuming that the outdoor temperature will begin dropping, reducing the cooling load later. If discomfort of someone in the residence is an issue, it seems that reversing the logic might actually serve the purpose better: a few hours in advance of peak demand, commanding a longer cooling cycle (to pre-cool the house a few degrees) would reduce the demand that will occur later in the day. Unfortunately, this doesn't prevent the electrical usage, it again shifts it. However, shifting it earlier, rather than later, may be a better solution.
Another study by UC Davis (and supported by others) indicates that decreasing the level of lighting by 15% is imperceptible to people in a building. While that is probably true, I don't think the answer is as simple as dimming the lights. I haven't made measurements to be sure, but I suspect that decreasing the level of a dimmable fluorescent light by 15% results in a power savings less than 15% (probably 5 to 10) so the lighting efficacy is reduced. (Efficacy is the efficiency of a light source in terms of light produced per watt of power consumed - usually specified in lumens/Watt.) Even if a reduced light level is perceived, dimming the lights in a building is certainly preferable to a rolling blackout.
Dimming incandescent bulbs to save energy has another side effect (in most cases). Incandescent dimming is usually accomplished by chopping off part of the electrical power waveform. In other words, the power is turned off for a fraction of every power line cycle. This phase-cut method of dimming places a nasty load (along with lots of electrical harmonics) on the power grid. Dimming a large percentage of a building load in this manner would probably cause power quality problems.
Load Shedding on-demand
Demand response - an action taken by a customer of an electric utility in response to a request by the utility during a period of high demand - is likely to become more important to protect the integrity of the power grid in certain areas. A demand response that eliminates, rather than defers, power consumption is more useful than simply shutting off A/C units for a while. Some critical technologies to make this possible: building-wide lighting and HVAC control systems, dimmable fluorescent ballasts, per-fixture control when dimmable ballasts are not an option (allowing a subset of light fixtures to be turned off), and communication methods to get the demand message from the utility to the fixtures.
I've been experimenting with a dimmable (0-10 V controlled) fluorescent ballast, and I hope to have some efficiency vs. dim level information in the future. I've noticed a small shift in color temperature as the bulbs are dimmed, but nothing even close to the color shift that occurs when dimming incandescents.
In many parts of the country, consumers receive a credit on their utility bill if they install a remote-controlled shutoff device to their air conditioner. Given that the A/C unit on most homes is the largest electrical load in use (particularly during the daytime) it is a good candidate for saving electricity and reducing peak demand on the electrical grid.
There's a downside to this method of demand reduction (not just the fact that your house will get a bit warmer for a while) as it defers, rather than eliminates, the electrical demand. Once the utility allows the A/C unit to turn back on, it will then operate for a longer time to bring the temperature of the house back down. In the end, you only shift the demand, you don't eliminate it.
A better (but more complex) solution
A better method would be to raise the temperature setpoint a few degrees for several hours, assuming that the outdoor temperature will begin dropping, reducing the cooling load later. If discomfort of someone in the residence is an issue, it seems that reversing the logic might actually serve the purpose better: a few hours in advance of peak demand, commanding a longer cooling cycle (to pre-cool the house a few degrees) would reduce the demand that will occur later in the day. Unfortunately, this doesn't prevent the electrical usage, it again shifts it. However, shifting it earlier, rather than later, may be a better solution.
Another study by UC Davis (and supported by others) indicates that decreasing the level of lighting by 15% is imperceptible to people in a building. While that is probably true, I don't think the answer is as simple as dimming the lights. I haven't made measurements to be sure, but I suspect that decreasing the level of a dimmable fluorescent light by 15% results in a power savings less than 15% (probably 5 to 10) so the lighting efficacy is reduced. (Efficacy is the efficiency of a light source in terms of light produced per watt of power consumed - usually specified in lumens/Watt.) Even if a reduced light level is perceived, dimming the lights in a building is certainly preferable to a rolling blackout.
Dimming incandescent bulbs to save energy has another side effect (in most cases). Incandescent dimming is usually accomplished by chopping off part of the electrical power waveform. In other words, the power is turned off for a fraction of every power line cycle. This phase-cut method of dimming places a nasty load (along with lots of electrical harmonics) on the power grid. Dimming a large percentage of a building load in this manner would probably cause power quality problems.
Load Shedding on-demand
Demand response - an action taken by a customer of an electric utility in response to a request by the utility during a period of high demand - is likely to become more important to protect the integrity of the power grid in certain areas. A demand response that eliminates, rather than defers, power consumption is more useful than simply shutting off A/C units for a while. Some critical technologies to make this possible: building-wide lighting and HVAC control systems, dimmable fluorescent ballasts, per-fixture control when dimmable ballasts are not an option (allowing a subset of light fixtures to be turned off), and communication methods to get the demand message from the utility to the fixtures.
I've been experimenting with a dimmable (0-10 V controlled) fluorescent ballast, and I hope to have some efficiency vs. dim level information in the future. I've noticed a small shift in color temperature as the bulbs are dimmed, but nothing even close to the color shift that occurs when dimming incandescents.
Tuesday, November 4, 2008
Measure the payback time: Green Speedometer
With the constant fluctuations of the price of energy in various forms, combined with fluctuations in the cost of renewable alternative sources of energy (for example, the price for 1 kW worth of solar panels) it's hard to keep track of how fast an installed system will pay for itself.
What I'd like to see is a web page that dynamically monitors these factors, and perhaps by entering your postal code it calculates your location (for an estimate of the number of sun days per year, the local electrical rate, and all other applicable factors) and creates a graph or even just a "speedometer" to show how long until the system is paid for.
Perhaps along with this, and estimate of the number of tons of CO2 that will be saved as well, though I'd prefer that the calculation include the impact of producing the solar cells (or whatever) in the calculation.
What I'd like to see is a web page that dynamically monitors these factors, and perhaps by entering your postal code it calculates your location (for an estimate of the number of sun days per year, the local electrical rate, and all other applicable factors) and creates a graph or even just a "speedometer" to show how long until the system is paid for.
Perhaps along with this, and estimate of the number of tons of CO2 that will be saved as well, though I'd prefer that the calculation include the impact of producing the solar cells (or whatever) in the calculation.
Friday, October 17, 2008
When "green" isn't
I recently attended (and presented at) an open source conference. One of the presentations was fascinating, covering all kinds of automation devices for home lighting, security, and automation. The presentation is here:
http://2008.utosc.com/presentation/51/
He uses Control4 wall-mounted dimmers to control the lights throughout his house, and motion detectors dim the lights on (gently) when you walk into a room or down a hall. The part I found fascinating, however, is that if you try to use his system to save energy, there isn't too much to be saved, because each wall box dimmer consumes a few watts of power, even when off. With a house full of these, that could be over 100 watts of standby power, added to whatever the central controller requires (maybe a few hundred watts if it's a PC). This means that you're burning between 3 and 10 kWh every day just to run the automation systems. He specifically pointed this out during the presentation so we would not try to save energy by burning just as much energy.
Referring back to the system in my kitchen that I described in my first post, since I'm using older generation Watt Stoppers, only one of them is drawing power, and it provides the DC supply to the illumra room controller and the other relays. If all the Watt Stoppers were powered by 120VAC, there would be a lot more standby power being used. I think it's only 2 or 3 watts, so it would probably be a wash to swap it out for 120VAC powered illumra single-channel room controllers, as they draw about 1 watt each. If I had single switches rather than three in one spot, then the power savings of the single-channel illumra receivers would be more compelling, compared to watt stoppers and the 3-channel room controller. Maybe I'll try out a one-channel unit somewhere else in the house.
http://2008.utosc.com/presentation/51/
He uses Control4 wall-mounted dimmers to control the lights throughout his house, and motion detectors dim the lights on (gently) when you walk into a room or down a hall. The part I found fascinating, however, is that if you try to use his system to save energy, there isn't too much to be saved, because each wall box dimmer consumes a few watts of power, even when off. With a house full of these, that could be over 100 watts of standby power, added to whatever the central controller requires (maybe a few hundred watts if it's a PC). This means that you're burning between 3 and 10 kWh every day just to run the automation systems. He specifically pointed this out during the presentation so we would not try to save energy by burning just as much energy.
Referring back to the system in my kitchen that I described in my first post, since I'm using older generation Watt Stoppers, only one of them is drawing power, and it provides the DC supply to the illumra room controller and the other relays. If all the Watt Stoppers were powered by 120VAC, there would be a lot more standby power being used. I think it's only 2 or 3 watts, so it would probably be a wash to swap it out for 120VAC powered illumra single-channel room controllers, as they draw about 1 watt each. If I had single switches rather than three in one spot, then the power savings of the single-channel illumra receivers would be more compelling, compared to watt stoppers and the 3-channel room controller. Maybe I'll try out a one-channel unit somewhere else in the house.
Thursday, October 16, 2008
Introduction
Green Solutions - Why should you care?
Full disclosure first: I work for a company making energy saving devices, so of course I'm interested in you saving energy, money, and everything else that goes along with it.
I'm writing this blog to share some of my thoughts on green technologies that I have purchased, designed, or thought about building. I'm sure I'll figure out some other interesting things to include later as well.
To answer the title question of this post, there are many angles to "green" technologies. A few of them, in intentionally random order, are:
First off, my three children are ages 9, 7, and 4, so while they're pretty well trained at turning off the lights, they forget to do so at least once a day. I decided to set up one of the devices I worked on at the office to try to save a little energy. It's a "room controller" from illumra. It connects to Watt Stopper power packs to control the lights in the room.
I use a wireless switch, mounted on the wall, to turn on the lights, and a motion detector mounted in the opposite corner of the room. The motion detector connects to another room controller, which transmits the status of the motion detector back to the main room controller. If no motion is detected in the room for 15 minutes, the lights turn off. If you move during the 15 second period after the lights turn off, they will come back on.
I bought a batch of Honeywell motion detectors off of ebay for a good price, but I had to set them to the highest sensitivity (and I installed the non-"pet-immune" lenses) so even small motion will be detected. If I were building a security system, I probably wouldn't want the occupancy detection to be so sensitive, because it would cause false alarms, but in "vacancy" detection, it's better to err on the side of falsely detecting someone in the room, rather than the other way around.
I haven't calculated the energy savings, but the main light fixtures in the kitchen (there are two) each have 4 fluorescent tubes (high-efficiency T8) with electronic ballasts. That's about 256 watts, I guess, so if the sensors turn off the lights for an extra 1 hour a day, that's about 1.8 kWh of savings per week, or about 21 cents a week in electrical savings. If the other can lights are on, and perhaps the ceiling fan, too, the savings could exceed that. If I used incandescents the savings would be higher, too. That's not a very compelling savings by itself, though, even with the longer lifetime of the bulbs factored in. I guess in a commercial building or a warehouse, the savings could be a lot more.
Full disclosure first: I work for a company making energy saving devices, so of course I'm interested in you saving energy, money, and everything else that goes along with it.
I'm writing this blog to share some of my thoughts on green technologies that I have purchased, designed, or thought about building. I'm sure I'll figure out some other interesting things to include later as well.
To answer the title question of this post, there are many angles to "green" technologies. A few of them, in intentionally random order, are:
- You want to do your part to "save the planet."
- You want to save money on your energy bills.
- You want everyone else to know you're trying to save the planet.
- You think it's cool to try out new things.
- Energy independence sounds nice in case there's a disaster (solar panels on your roof?).
- You don't think our way of life is sustainable (we'll run out of "stuff").
First off, my three children are ages 9, 7, and 4, so while they're pretty well trained at turning off the lights, they forget to do so at least once a day. I decided to set up one of the devices I worked on at the office to try to save a little energy. It's a "room controller" from illumra. It connects to Watt Stopper power packs to control the lights in the room.
I use a wireless switch, mounted on the wall, to turn on the lights, and a motion detector mounted in the opposite corner of the room. The motion detector connects to another room controller, which transmits the status of the motion detector back to the main room controller. If no motion is detected in the room for 15 minutes, the lights turn off. If you move during the 15 second period after the lights turn off, they will come back on.
I bought a batch of Honeywell motion detectors off of ebay for a good price, but I had to set them to the highest sensitivity (and I installed the non-"pet-immune" lenses) so even small motion will be detected. If I were building a security system, I probably wouldn't want the occupancy detection to be so sensitive, because it would cause false alarms, but in "vacancy" detection, it's better to err on the side of falsely detecting someone in the room, rather than the other way around.
I haven't calculated the energy savings, but the main light fixtures in the kitchen (there are two) each have 4 fluorescent tubes (high-efficiency T8) with electronic ballasts. That's about 256 watts, I guess, so if the sensors turn off the lights for an extra 1 hour a day, that's about 1.8 kWh of savings per week, or about 21 cents a week in electrical savings. If the other can lights are on, and perhaps the ceiling fan, too, the savings could exceed that. If I used incandescents the savings would be higher, too. That's not a very compelling savings by itself, though, even with the longer lifetime of the bulbs factored in. I guess in a commercial building or a warehouse, the savings could be a lot more.
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