January 21, 2006
Building Cooling Electric Demand Could Be Shifted Toward Mornings
Buildings could be pre-cooled in the mornings.
Engineers have developed a method for "precooling" small office buildings and reducing energy consumption during times of peak demand, promising not only to save money but also to help prevent power failures during hot summer days.
The method has been shown to reduce the cooling-related demand for electricity in small office buildings by 30 percent during hours of peak power consumption in California's sweltering summer climate. Small office buildings represent the majority of commercial structures, so reducing the electricity demand for air conditioning in those buildings could help California prevent power-capacity problems like those that plagued the state in 2000 and 2001, said James Braun, a Purdue University professor of mechanical engineering.
The results focus on California because the research was funded by the California Energy Commission, but the same demand-saving approach could be tailored to buildings in any state.
"California officials are especially concerned about capacity problems in the summertime," said Braun, whose research is based at Purdue's Ray W. Herrick Laboratories.
A building's physical mass could get cooled down in the morning and therefore help keep the building cooler later in the day.
Findings will be detailed in three papers to be presented on Monday (Jan. 23) during the Winter Meeting of the American Society of Heating, Refrigerating and Air-Conditioning Engineers in Chicago. Two of the papers were written by Braun and doctoral student Kyoung-Ho Lee. The other paper was written by researchers at the Lawrence Berkeley National Laboratory, a U.S. Department of Energy laboratory managed by the University of California.
The method works by running air conditioning at cooler-than-normal settings in the morning and then raising the thermostat to warmer-than-normal settings in the afternoon, when energy consumption escalates during hot summer months. Because the building's mass has been cooled down, it does not require as much energy for air conditioning during the hottest time of day, when electricity is most expensive and in highest demand.
Better ways could be found to do this where humans are less affected by temperature changes. A building could get constructed (or upgraded) to contain a large mass (made out of lead perhaps?) that gets cooled at night more than the air does. The air conditioner could cool it down way below normal room temperature (say close to freezing or even below). Granted the method reported here requires only an upgrade to the thermostat electronics. But it has drawbacks and limits on what it can achieve. Demand could get shifted for more hours or even days if a high density mass was cooled in the summer. Also using solar or wind energy such a mass could get heated in the winter whenever the wind blew or the sun shined.
Basically they shift demand from the afternoon to the morning.
Precooling structures so that it takes less power to cool buildings during times of peak demand is not a new concept. But researchers have developed a "control algorithm," or software that determines the best strategy for changing thermostat settings in a given building in order to save the most money. Research has shown that using a thermal mass control strategy improperly can actually result in higher energy costs. Factors such as a building's construction, the design of its air-conditioning system, number of windows, whether the floors are carpeted, and other information must be carefully considered to determine how to best use the method.
"The idea is to set the thermostat at 70 degrees Fahrenheit for the morning hours, and then you start adjusting that temperature upwards with a maximum temperature of around 78 during the afternoon hours, " Braun said. "When the thermostat settings are adjusted in an optimal fashion, the result is a 25 percent to 30 percent reduction in peak electrical demand for air conditioning.
But currently there is little incentive for most businesses to shift a portion of their electricity demand from afternoon to morning. What is needed are utility rate structure changes to implement dynamic pricing so that current price comes closer to the marginal price. That'd make electricity much more expensive during peak times but cheaper during low usage times.
"If you couple this reduction in demand with a utility rate structure that charges more during critical peak periods, utility costs will drop. Without such a change in peak rates, though, the actual impact on operating costs is relatively small, with about $50 in annual savings per 1,000 square feet of building space.
"A good incentive for reducing peak demand would be to impose a higher peak demand charge for the critical peak-pricing periods, and if customers reduce their consumption during these times, they are rewarded with lower energy costs for the rest of the time."
Some of the technology developments needed to allow demand shifting are pretty low tech. It is easy to develop a computer program that will vary the thermostat setting as a function of the time or day and not much harder to develop software and a communications system to broadcast marginal prices so that companies could adjust their demand as a function of current electric prices. The bigger obstacle is at the policy level, not the technological level.
If public utilities were to more widely implement dynamic pricing of electricity then businesses would pretty quickly implement lower tech methods of adjusting demand. At the same time, incentives would then come into existence to develop better technologies for shifting demand. For example, the value of better battery technologies would increase and therefore dynamic pricing would accelerate the development of better battery technologies.
An acceleration of battery technology development in response to dynamic electric pricing would eventually accelerate the shift toward hybrid and pure electric cars. Increased demand for electric power storage technologies would increase investment to develop such technologies.
The deployment of technologies and business practices that allow rapid demand adjustment in response to dynamic pricing would be bullish for both solar and wind electric power. Businesses would treat rises in electric prices that happen when the sun isn't shining or the wind isn't blowing as reason to shift business activity (or accumulation of energy in batteries or cool or heat in previously mentioned building masses) toward the times when the sun does shine and the wind does blow. To put it another way: if demand can be made more dynamic by market forces then the inconstancy of solar and wind power would pose less of a problem for their wider spread adoption. Greater market forces in electric power distribution would accelerate energy technology development and deployment.
This is a surprise? Operators of zone HVAC systems with circulating salt water have operated air conditioning during off-business hours for years. I doubt however that building material is ever "pre-cooled" significantly enough to form the basis for this system. Rather, cool air is dehumidified more efficiently in the cool morning than between 9 and 5. As the morning progresses, building inhabitants enjoy dry heat, which is quite comfortable at 78 F. Indeed, typists make fewer errors at such temperatures *, and 68 F is a signicantly less efficient environment. Perspiration makes the air perceptively hotter as the day goes on, and notably less efficient to breathe. But the air should be circulated anyway to avoid 'sick-building' syndrome, and remove excess CO2.
Install lead in buildings? You'd be better off creating ice blocks with the AC during off peak hours. Ice has one of the highest heat capacities around, meaning it takes a long time to put at room temperature. Adding salt lowers the freezing point more. The ice can also dehumidify air in its own right. Humidity accounts for between 15 and 30% of the work performed by an AC to produce a reduction in air temperature.
* Take a look at the latest Business Week. It reports how schools are tying to reduce thermostatic temperatures by extremes, and charging employees for the privilege of using a coffee percolator. Talk about market responsive government!
In SoCal humidity is not much of an issue. We get mostly pretty dry heat.
Lead versus water: I am curious to know what materials can store cool or heat most cost effectively.
Thanks for the excellent links on phase change materials. The second link points out that in some climates which have cool nights and hot days in summer (e.g. much of California) phase change materials have the potential to totally eliminate the need for air conditioning. I like it!
I've also previously read about designs that would take summer heat and store for winter release. I'd imagine such designs could basically transport winter coolness into summer as well. I think E-P might once have said something about such designs. Though I can't remember what he said.
It is obvious that these engineers have never been around women in an office. Women seem to not handle cool temperatures in an office or at least they complain the loudest and the longest.
Put such a system in place and the women would bring electric space heaters to work, and there goes your savings. And make no mistake about it, office temperatures are controlled by the women not the men.
jimcrack's solution is the only one that would work.
i've read about using circulated slush (water + ice) in pipes for cooling, similar to what jimcrack mentions. freezing/melting water is a very convenient phase change to store thermal energy.
i suspect they cost more than standard hvac. there probably is a misalignment of motives between builders and occupants of new buildings, such that there's not much incentive for builders to go through the extra time and uncertainty of using technologies they are unfamiliar with. so in addition to pricing real time power according to marginal cost, as RP suggests, maybe there should also be some serious cost impact for building permits based on the efficiency/expected energy use of the building.
If there is so much dry heat in California, so much the better. Swamp coolers can cool the air via adding moisture, and can be conjoined with independent room fans to spot cool people where they are sitting.
You have a water crisis out there, but why not aggressively pursue water energy substituting water use and home water recovery, and kill 2 birds with one stone? Recovery, particularly of brown and gray water is cost effective even in New York City, where gobs of money were already spent on a new aquaduct system up the Hudson. In time, the deterioration of sewage and water lines in the boroughs, combined with the endorsement of sink garbage disposals for food waste (to save fuel costs of carting), will make recovery a very attractive proposition.
We should see a thread here devoted exclusively to water issues.
Back to fusion..
The European Fusion Power Plant Conceptual Study has just been published.
"...investigating four different concepts for a fusion power plant: All four models have an electric power of about 1500 megawatts and are of the "tokamak" type like ITER. ...each based on different extrapolations of present day plasma physics and technology ..."
"Accordingly, different electricity prices are expected with the four power plant models: Model A entails the highest cost of electricity, followed by models B and C; avant garde model D costs the least. Even B and C would, however, be competitive with power production costs of 5 to 10 cents per kilowatt hour. "
In order for fusion to fully replace fossil fuels either fossil fuels have got to get a lot more expensive or fusion has got to come in at 1 or 2 pennies (in US dollars) per kwh.
So much of the debate about electric energy sources takes place at the level of comparing costs of generating electricity. But most energy is not used as electricity. Well, electricity has got to get a lot cheaper for it to displace biomass or coal.
Though with really excellent battery technology I suspect electricity could displace gasoline due to efficiencies in how it would get used.
I'm increasingly curious about figuring out at what prices each energy source can displace other energy sources. For example, even if solar was to fall to the price of other electric sources it isn't there all the time. So it'd have to fall even further to make solar plus storage cost competitive even at night and in winters. Similarly, corn has to be cheaper than natural gas in dollars per BTUs by enough to make the handling of corn worth the hassle.
So I want to know what the cross-over points are for competitiveness. Granted, those cross-over points aren't single points for all applications. But, say, for 50% displacement what are the cross-over points for nuclear fission or wind or solar against coal or oil for major purposes? Some major purposes: heating, moving cars around.
Barrier to Conservation: Fixed Customer Charges
In the US, it is suggested that the unavoidable customer charges in the electrical billing system are a barrier to electrical conservation and green house gas mitigation. The customer charge is fixed and is independent of the actual electricity consumption used. In trying to maximize their benefit from the unavoidable fixed customer charge, smaller electricity users are inclined to conserve less. The paper referenced explains the policy requirements and the change in the electrical rate required, along with its impacts. The results indicate that removing the fixed charges and increasing the electrical rate can be economical for the US, the electrical companies and the households and environmentally beneficial. The increased rate penalizes smaller users less and encourages smaller and larger users alike to conserve responsibly.
For more on this, see this article:
J. M. Pearce and Paul J. Harris, "Reducing greenhouse gas emissions by inducing energy conservation and distributed generation from elimination of electric utility customer charges", Energy Policy, 35, pp. 6514-6525, 2007.[http://www.sciencedirect.com/science/article/B6V2W-4R008R9-2/2/1e692cc89cae024a6a4492e736848941]