Automation

February 20th, 2012, Published in Articles: Vector

Information from Siemens

In the future, smart buildings will adjust their electricity consumption to fluctuating supplies of solar and wind power automatically. A recent study demonstrates the technical feasibility of this approach. 

Wind facilities now account for roughly 7% of all the electricity generated in Germany, with almost 2% obtained from solar generation. Over the last few years, wind parks in the North Sea have been shut down repeatedly due to strong winds that threatened to overload the local grid. In other cases, surplus electricity has been exported to neighbouring countries despite the fact that it was not really needed. This can sometimes reduce prices to such an extent that suppliers begin losing money, especially since they still have to pay transmission fees. Conversely, whenever winds are weak, so-called peaking plant must be switched on, which makes electricity more expensive.

According to the German Energy Agency, some 3600 km of new power lines will have to be built by 2020 in Germany alone to transport electricity to end-users. But even that won’t be enough, as grids will have to become more intelligent to create greater transparency and ensure more flexible pricing models and better electricity distribution.

Also being discussed are electricity storage units that store surplus electricity when winds blow and the sun shines, and then return it to the grid in the absence of wind and sunshine. In addition, electric vehicles might be used in the future as a giant energy pool consisting of innumerable batteries. Indeed, the batteries in 2-million electric vehicles would have an energy content of roughly 40 GWh – the combined capacity of all German pumped storage units.

Fig. 1: Future buildings will adjust their power consumption to
supplies of  renewable energy autonomously by adjusting heating and cooling systems and using electric cars for energy storage.

Consumption follows production

A new potential solution to this energy puzzle is emerging – one that could be implemented by introducing a sophisticated software package. Known as “load shifting”, the idea is to manage electricity users, or loads, in buildings in such a way that they are mainly allowed to occur only when windmills and photovoltaic modules are generating surplus power, i.e. when electricity is cheap. Conversely, as much electrical equipment as possible would be powered down at night or when winds are weak. This amounts to a paradigm shift, since these days the operation of gas and coal-fired power plants is geared toward energy consumption behavior in households, factories, and offices. But in the future, the situation would be reversed. Buildings would alter their power demand in line with current energy supplies. Consumption would follow production.

Working with specialists from Siemens Building Technologies, researchers at the Technical University of Munich (TUM) have found that a range of equipment in all kinds of buildings can be switched on and off in a relatively simple manner. The team spent several months collecting data from building management centers on everything from ventilation system and water pump activity to temperatures in offices and conference rooms. They examined questions such as “How long does it take for an office made of lightweight materials to heat up after you turn off the air conditioning system?” According to TUM research assistant Timm Rössel, the key question was how long you can turn off certain equipment without affecting comfort in a room or office. German building standards stipulate that office temperatures should not fall below 21°C if comfort is to be maintained. Rössel and his team analysed four different building types for their study: office and administrative buildings; hospitals; indoor swimming pools, and schools.

They found that load shift potential was particularly high in office buildings. For example, ventilation systems in offices with normal occupancy can be shut down completely for as long as half an hour without causing rooms to become stuffy – and this can be done several times a day. The same goes for ventilation systems in underground garages. The researchers also examined how often and, more importantly, how fast elevators travel in office buildings.

They determined that elevator speed could be cut back several hours every day outside the morning and evening rushes, thereby reducing electricity consumption by around 10%. They also found that elevator users were not annoyed by the slower speed.

Fig. 2: In the future, building management systems will take
into account hundreds of parameters in real time to alter power
demand in response to power availability.

There is also plenty room for improvement in buildings equipped with a service water system for toilet flushing. The pumps that fill the system’s tanks could be started with a delay of as much as 12 hours without any danger of the tanks running empty. And in hospitals, energy-saving efforts can focus on sterilisation equipment for surgical utensils. In buildings equipped with indoor swimming pools, the greatest load shift potential lies in the compressors used in dehumidification systems, which can actually be shut down for several hours. The same is true of ozone and UV units used for water purification.

The results of the study indicate that large buildings have an overall load shift potential that pays off. Siemens is now developing software tools with TUM that can be used to manage building control systems.

A new regulation that went into effect this year in Germany requires energy suppliers to offer variable electricity rates that change throughout the day in line with supply and demand. Although the system still does not allow for extremely short-term price fluctuations, experts believe that in the near future we will be seeing electricity prices that change every hour or even every 15 minutes. In this scenario, building management systems would shut down or ramp down certain types of equipment when demand for electricity is high and power is therefore more expensive. Price alerts would enable building management systems to turn on pumps and fans primarily when solar and wind power are flooding the grid and prices are falling.
 
Several hundred parameters and measurement values are fed into modern building management systems today, including office temperatures and fan output figures. All of this data will have to be linked together by load shifting software. TUM researchers are now using building simulations to refine the corresponding calculation specifications.

The goal is to make buildings intelligent and to determine how quickly they cool down, how much heat they require, and when they can shut down certain devices to conserve electricity.

Load shedding solutions

The USA faces a situation in which power plants and infrastructures which, in some cases, are outdated and are being pushed to the limits of their capacity. This is a problem particularly on hot days when millions of Americans turn on air conditioners. To prevent supply bottlenecks, power companies shut down specific end-users – i.e. they shed loads. For example, private customers who agree to turn off their air conditioners on several hot days throughout the year are rewarded with lower electricity rates. The same is done for industrial companies and refrigerated warehouses. As more precise weather forecasts make short-term alerts possible, power companies are able to inform such end-users of the outages by e-mail or phone timeously. Some 80% of all load-shedding customers are directly informed in this manner. This may sound complicated, but a nationwide call center service is a lot cheaper than building new power plants or grid components.

As part of its strategy to automate load management operations, Siemens has acquired load management software company SureGrid. Its central computer in Austin, Texas, can, for example, accept an order from a power company for a required amount of electricity and then distribute this total among all participating buildings in a region automatically. This solves the problem of insufficient reliability. When a power company requests load shedding via e-mail, there’s no guarantee that customers will remember to turn off their air conditioners the following day. The energy supplier therefore needs to play it safe by planning for more load shedding than is actually needed. Automation, on the other hand, will make load management calculations more reliable and secure in the future.

At the moment, energy suppliers must use weather forecasts to estimate roughly one day in advance when and for how long they need to shed electricity loads. Suppliers therefore create a “buffer” by asking customers to shut down appliances for several hours – in most cases longer than is actually necessary.

Automation will allow power companies to react right before a bottleneck occurs, which would reduce the duration of a load shedding event. The US energy market differs greatly from that of Europe in that, in the case of the former, emphasis is placed on supply shortages, whereas Europe focuses on fluctuating electrical output from wind and solar facilities. Nevertheless, the USA is also taking an initial important step toward greater building intelligence and smart power consumption through its automated load management systems. The next step would be to implement the type of building management technology the TUM project seeks to develop.

Contact Keshin Govender, Siemens, Tel 011 652-2412, keshin.govender@siemens.com

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