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Wind Power Applications
The wind is a free, clean, and inexhaustible energy source. It has served humankind well for many centuries by propelling ships and driving wind turbines to grind grain and pump water. Denmark was the first country to use wind for generation of electricity. The Danes were using a 23-m diameter wind turbine in 1890 to generate electricity. By 1910, several hundred units with capacities of 5 to 25 kW were in operation in Denmark (Johnson, 1985). By about 1925, commercial wind-electric plants using two- and three-bladed propellers appeared on the American market. The most common brands were Win- charger (200 to 1200 W) and Jacobs (1.5 to 3 kW). These were used on farms to charge storage batteries which were then used to operate radios, lights, and small appliances with voltage ratings of 12, 32, or 110 volts. A good selection of 32-VDC appliances was developed by the industry to meet this demand.
In addition to home wind-electric generation, a number of utilities around the world have built larger wind turbines to supply power to their customers. The largest wind turbine built before the late 1970s was a 1250-kW machine built on Grandpa’s Knob, near Rutland, Vermont, in 1941. This turbine, called the Smith-Putnam machine, had a tower that was 34 m high and a rotor 53 m in diameter. The rotor turned an ac synchronous generator that produced 1250 kW of electrical power at wind speeds above 13 m/s.
After World War II, we entered the era of cheap oil imported from the Middle East. Interest in wind energy died and companies making small turbines folded. The oil embargo of 1973 served as a wakeup call, and oil-importing nations around the world started looking at wind again. The two most important countries in wind power development since then have been the U.S. and Denmark (Brower et al., 1993).
The U.S. immediately started to develop utility-scale turbines. It was understood that large turbines had the potential for producing cheaper electricity than smaller turbines, so that was a reasonable decision. The strategy of getting large turbines in place was poorly chosen, however. The Department of Energy decided that only large aerospace companies had the manufacturing and engineering capability to build utility-scale turbines. This meant that small companies with good ideas would not have the revenue stream necessary for survival. The problem with the aerospace firms was that they had no desire to manufacture utility-scale wind turbines. They gladly took the government’s money to build test turbines, but when the money ran out, they were looking for other research projects. The government funded a number of test turbines, from the 100 kW MOD-0 to the 2500 kW MOD-2. These ran for brief periods of time, a few years at most. Once it was obvious that a particular design would never be cost competitive, the turbine was quickly salvaged.
Denmark, on the other hand, established a plan whereby a landowner could buy a turbine and sell the electricity to the local utility at a price where there was at least some hope of making money. The early turbines were larger than what a farmer would need for himself, but not what we would consider utility scale. This provided a revenue stream for small companies. They could try new ideas and learn from their mistakes. Many people jumped into this new market. In 1986, there were 25 wind turbine manufacturers in Denmark. The Danish market gave them a base from which they could also sell to other countries. It was said that Denmark led the world in exports of two products: wind turbines and butter cookies! There has been consolidation in the Danish industry since 1986, but some of the com- panies have grown large. Vestas, for example, has more installed wind turbine capacity worldwide than any other manufacturer.
Prices have dropped substantially since 1973, as performance has improved. It is now commonplace for wind power plants (collections of utility-scale turbines) to be able to sell electricity for under four cents per kilowatt hour.
Total installed worldwide capacity at the start of 1999 was almost 10,000 MW, according to the trade magazine Wind Power Monthly (1999). The countries with installed capacity until end of 2009 are shown in Table 1.
| # | Nation | 2005 | 2006 | 2007 | 2008 | 2009 |
|---|---|---|---|---|---|---|
| - | European Union | 40,722 | 48,122 | 56,614 | 65,255 | 74,767 |
| 1 | United States | 9,149 | 11,603 | 16,819 | 25,170 | 35,159 |
| 2 | Germany | 18,428 | 20,622 | 22,247 | 23,903 | 25,777 |
| 3 | China | 1,266 | 2,599 | 5,912 | 12,210 | 25,104 |
| 4 | Spain | 10,028 | 11,630 | 15,145 | 16,740 | 19,149 |
| 5 | India | 4,430 | 6,270 | 7,850 | 9,587 | 10,925 |
| 6 | Italy | 1,718 | 2,123 | 2,726 | 3,537 | 4,850 |
| 7 | France | 779 | 1,589 | 2,477 | 3,426 | 4,410 |
| 8 | United Kingdom | 1,353 | 1,963 | 2,389 | 3,288 | 4,070 |
| 9 | Portugal | 1,022 | 1,716 | 2,130 | 2,862 | 3,535 |
| 10 | Denmark | 3,132 | 3,140 | 3,129 | 3,164 | 3,465 |
| 11 | Canada | 683 | 1,460 | 1,846 | 2,369 | 3,319 |
| 12 | Netherlands | 1,236 | 1,571 | 1,759 | 2,237 | 2,229 |
| 13 | Japan | 1,040 | 1,309 | 1,528 | 1,880 | 2,056 |
| 14 | Australia | 579 | 817 | 817 | 1,494 | 1,712 |
| 15 | Sweden | 509 | 571 | 831 | 1,067 | 1,560 |
Applications
There are perhaps four distinct categories of wind power which should be discussed. These are:
- Small, non-grid connected
- Small, grid connected
- Large, non-grid connected
- Large, grid connected
By small, we mean a size appropriate for an individual to own, up to a few tens of kilowatts. Large refers to utility scale.
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Small, Non-Grid Connected
If one wants electricity in a location not serviced by a utility, one of the options is a wind turbine, with batteries to level out supply and demand. This might be a vacation home, a remote antenna and transmitter site, or a Third-World village. The costs will be high, on the order of $0.50/kWh, but if the total energy usage is small, this might be acceptable. The alternatives, photovoltaics, microhydro, and diesel generators, are not cheap either, so a careful economic study needs to be done for each situation.
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Small, Grid Connected
The small, grid connected turbine is usually not economically feasible. The cost of wind-generated elec- tricity is less because the utility is used for storage rather than a battery bank, but is still not competitive. In order for the small, grid connected turbine to have any hope of financial breakeven, the turbine owner needs to get something close to the retail price for the wind-generated electricity. One way this is done is for the owner to have an arrangement with the utility called net metering. With this system, the meter runs backward when the turbine is generating more than the owner is consuming at the moment. The owner pays a monthly charge for the wires to his home, but it is conceivable that the utility will sometimes write a check to the owner at the end of the month, rather than the other way around. The utilities do not like this arrangement. They want to buy at wholesale and sell at retail. They feel it is unfair to be used as a storage system without remuneration. For most of the twentieth century, utilities simply refused to connect the grid to wind turbines.
The utility had the right to generate electricity in a given service territory, and they would not tolerate competition. Then a law was passed that utilities had to hook up wind turbines and pay them the avoided cost for energy. Unless the state mandated net metering, the utility typically required the installation of a second meter, one measuring energy consumption by the home and the other energy production by the turbine. The owner would pay the regular retail rate, and the utility would pay their estimate of avoided cost, usually the fuel cost of some base load generator. The owner might pay $0.08 to $0.15 per kWh, and receive $0.02 per kWh for the wind-generated electricity. This was far from enough to eco- nomically justify a wind turbine, and had the effect of killing the small wind turbine business.
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Large, Non-Grid Connected
These machines would be installed on islands or in native villages in the far north where it is virtually impossible to connect to a large grid. Such places are typically supplied by diesel generators, and have a substantial cost just for the imported fuel. One or more wind turbines would be installed in parallel with the diesel generators, and act as fuel savers when the wind was blowing.
This concept has been studied carefully and appears to be quite feasible technically. One would expect the market to develop after a few turbines have been shown to work for an extended period in hostile environments. It would be helpful if the diesel maintenance companies would also carry a line of wind turbines so the people in remote locations would not need to teach another group of maintenance people about the realities of life at places far away from the nearest hardware store.
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Large, Grid Connected
We might ask if the utilities should be forced to buy wind-generated electricity from these small machines at a premium price which reflects their environmental value. Many have argued this over the years. A better question might be whether the small or the large turbines will result in a lower net cost to society. Given that we want the environmental benefits of wind generation, should we get the electricity from the wind with many thousands of individually owned small turbines, or should we use a much smaller number of utility-scale machines?
If we could make the argument that a dollar spent on wind turbines is a dollar not spent on hospitals, schools, and the like, then it follows that wind turbines should be as efficient as possible. Economies of scale and costs of operation and maintenance are such that the small, grid connected turbine will always need to receive substantially more per kilowatt hour than the utility-scale turbines in order to break even. There is obviously a niche market for turbines that are not connected to the grid, but small, grid connected turbines will probably not develop a thriving market. Most of the action will be from the utility-scale machines.
Sizes of these turbines have been increasing rapidly. Turbines with ratings near 1 MW are now common, with prototypes of 2 MW and more being tested. This is still small compared to the needs of a utility, so clusters of turbines are placed together to form wind power plants with total ratings of 10 to 100 MW.
SOURCE: Saifur Rahman Virginia Tech
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KNX Architecture
Building Control technology as provided by KNX is a specialized form of automated process control, dedicated to the needs of home and building applications. One premise for KNX is to furnish a radically decentralized, distributed approach; hence the term network.
The KNX Device Network results from the formal merger of the 3 leading systems for Home and Building Automation (EIB, EHS, BatiBus) into the specification of the new KNX Association. The common specification of the “KNX” system provides, besides powerful runtime characteristics, an enhanced “toolkit” of services and mechanisms for network management.
On the KNX Device Network, all the devices come to life to form distributed applications in the true sense of the word. Even on the level of the applications themselves, tight interaction is possible, wherever there is a need or benefit. All march to the beat of powerful Interworking models with standardized Datapoint Types and “Functional Block” objects, modelling logical device channels.
The mainstay of S-(“System”) Mode is the centralized free binding and parameterisation (typically with the PC-based ETS tool). It is joined by E (“Easy”)-mode device profiles, which can be configured according to a structured binding principle, through simple manipulations – without the need for a PC tool. These configuration modes share common run-time Interworking, allowing the creation of a comprehensive and multi-domain home and building communication system.
The available Twisted Pair and Powerline communication media are completed with Radio Frequency (868 MHz band).
KNX explicitly encompasses a methodology and PC tools for Project Engineering, i.e. for linking a series of individual devices into a functioning installation, and integrating different KNX media and configuration modes. This is embodied in the vendor-independent Engineering Tool Software (ETS) suites for Windows.
Elements of the KNX Architecture
KNX specifies many mechanisms and ingredients to bring the network into operation, while enabling manufacturers to choose the most adapted configuration for their market. Figure 1 below shows an overview of the KNX model, bringing the emphasis on the various open choices. Rather than a formal protocol description, the following details the components or bricks that may be chosen to implement in the devices and other components a full operational system.
As essential ingredients of KNX, we find in a rather top-down view.
- Interworking and (Distributed) Application Models for the various tasks of Home and Building Automation; this is after all the main purpose of the system.
- Schemes for Configuration and Management, to properly manage all resources on the network, and to permit the logical linking or binding of parts of a distributed application, which run in different nodes. KNX structures these in a comprehensive set of Configuration Modes.
- Communication System, with a set of physical communication media, a message protocol and corresponding models for the communication stack in each node; this Communication System has to support all network communication requirements for the Configuration and Management of an installation, as well as to host Distributed Applications on it. This is typified by the KNX Common Kernel.
- Concrete Device Models, summarized in Profiles for the effective realization and combination of the elements above when developing actual products or devices, which will be mounted and linked in an installation.
Applications, Interworking and Binding
Central to KNX’ application concepts is the idea of Datapoints: they represent the process and control variables in the system, as explained in the section Application Models. These Datapoints may be inputs, outputs, parameters, diagnostic data,…The standardized containers for these Datapoints are Group Objects and Interface Object Properties.
The Communication System and Protocol are expected to offer a reduced instruction set to read and write (set and get) Datapoint values: any further application semantics is mapped to the data format and the bindings, making KNX primarily “data driven”.
In order to achieve Interworking, the Datapoints have to implement Standardized Datapoint Types, themselves grouped into Functional Blocks. These Functional Blocks and Datapoint Types are related to applications fields, but some of them are of general use and named functions of common interest (such as date and time).
Datapoints may be accessed through unicast or multicast mechanisms, which decouple communication and application aspects and permits a smooth integration between implementation alternatives. The Interworking section below zooms in on these aspects. To logically link (the Datapoints of) applications across the network, KNX has three underlying binding schemes: one for free, one for structured and one for tagged binding. How these may be combined with various addressing mechanisms is described below.
Basic Configuration Schemes
Roughly speaking, there are two levels at which an installation has to be configured. First of all, there is the level of the network topology and the individual nodes or devices.
In a way, this first level is a precondition or “bootstrap” phase, prior to the configuration of the Distributed Applications, i.e. binding and parameter setting.
Configuration may be achieved through a combination of local manipulations on the devices (e.g. pushing a button, setting a codewheel, or using a locally connected configuration tool), and active Network Management communication over the bus (peer-to-peer as well as more centralized master- slave schemes are defined).
As described in the corresponding section below, a KNX Configuration Mode:
- picks out a certain scheme for configuration and binding
- maps it to a particular choice of address scheme
- completes all this with a choice of management procedures and matching resource realizations.
Some modes require more active management over the bus, whereas some others are mainly oriented towards local configuration.
Network Management and Resources
To accommodate all active configuration needs of the system, and maintain unity in diversity, KNX is equipped with a powerful toolkit for network management. One can put these instruments to good use throughout the lifecycle of an installation: for initial set-up, for integration of multi-mode installations, for subsequent diagnostics and maintenance, as well as for later extension and reconfiguration. Network Management in KNX specifies a set of mechanisms to discover, set or retrieve configuration data actively via the network. It proposes Procedures (i.e. message sequences) to access values of the different network resources within the devices, as well as identifiers and formats for these resources – all of this in order to enable a proper Interworking of all KNX network devices. These resources may be addresses, communication parameters, application parameters, or complex sets of data like binding tables or even the entire executable application program.
The network management basically makes use of the services offered by the application layer. Each device implementing a given configuration mode (see below) has to implement the services and resources specified in the relevant “profile” (set of specifications, see below).
For managing the devices, these services are used within procedures. The different configuration modes make use of an identified set of procedures, which are described in the “configuration management” part. As indicated above, and further demonstrated in the Configuration Modes section below, KNX supports a broad spectrum of solutions here, ranging from centralized and semi- centralised “master-slave” versions, over entirely peer-to-peer to strictly local configuration styles.
However, mechanisms and Resources are not enough. Solid Network Management has to abide by a set of consistency rules, global ones as well as within and among profiles, and general Good Citizenship. For example, some of these rules govern the selection of the (numerical value of) the address when binding Datapoints.
But now, we first turn our attention to how the Communication System’s messaging solutions for applications as well as management, beginning with the physical transmission media.
Communication: Physical Layers
The KNX system offers the choice for the manufacturers, depending on his market requirements and habits, to choose between several physical layers, or to combine them. With the availability of routers, and combined with the powerful Interworking, multi-media, and also multi-vendor configurations can be built.
The different media are :
- TP 1 (basic medium inherited from EIB) providing a solution for twisted pair cabling, using a SELV network and supply system. Main characteristics are: data and power transmission with one pair (devices with limited power consumption may be fed by the bus), and asynchronous character oriented data transfer and half duplex bi-directional communication. TP 1 transmission rate is 9600 bit/s.
TP1 implements a CSMA/CA collision avoidance. All topologies may be used and mixed ( line, star, tree, ….) - PL 110 (also inherited from EIB) enables communication over the mains supply network. Main characteristics are: spread frequency shift keying signalling, asynchronous transmission of data packets and half duplex bi-directional communication. PL 110 uses the central frequency 110 kHZ and has a data rate of 1200 bit/s.
PL110 implements CSMA and is compliant to EN 50065-1 (in the frequency band without standard access medium protocol). - RF enables communication via radio signals in the 868,3 MHz band for Short Range Devices. Main characteristics are: Frequency Shift Keying, maximum duty cycle of 1%, 32 768 cps, Manchester data encoding.
- Beyond these Device Network media, KNX has unified service- and integration solutions for IP-enabled (1) media like Ethernet (IEEE 802.2), Bluetooth, WiFi/Wireless LAN (IEEE 802.11), “FireWire” (IEEE 1394) etc., as explained in the KNXnet/IP section below.
Communication: Common Kernel and Message Protocol
The Communication System must tend to the needs of the Application Models, Configuration and Network Management. On top of the Physical Layers and their particular Data Link Layer, a Common Kernel model is shared by all the devices of the KNX Network; in order to answer all requirements, it includes a 7 Layers OSI model compliant communication system.
- Data Link Layer General, above Data Link Layer per medium, provides the medium access control and the logical link control.
- Network Layer provides a segment wise acknowledged telegram; it also controls the hop count of a frame. Network Layer is of interest mainly for nodes with routing functionality.
- Transport Layer (TL) enables 4 types communication relationship between communication points: one-to-many connectionless (multicast), one-to-all connectionless (broadcast), one-to-one connectionless, one-to-one connection-oriented. For freely bound models (see below), TL also separates (“indirects”) the network multicast address from the internal representation.
- Session and presentation Layers are empty.
- Application Layer offers a large “toolkit” variety of application services to the application process. These services are different depending on the type of communication used at transport layer. Services related to point-to-point communication and broadcast mainly serve to the network management, whereas services related to multicast are intended for runtime operation.
Remember KNX does not fix the choice of microprocessor. Since in addition, KNX covers an extensive range of configuration and device models, the precise requirements governing a particular implementation are established in detailed Profiles, in line with the Configuration Modes. Within these boundaries, the KNX developer is encouraged to find the optimal solution to accommodate his implementation requirements! This is expounded in later sections.
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The Benefits of VFDs In HVAC Systems
One of the most successful energy management tools ever applied to building HVAC systems is the variable frequency drive (VFD). For more than 20 years, VFDs have successfully been installed on fan and pump motors in a range of variable load applications. Energy savings vary from 35 to 50 percent over conventional constant speed applications, resulting in a return on investment of six months to two years.
While the number of applications suitable for early generation drives was limited based on the horsepower of the motor, today’s drives can be installed in practically any HVAC application found in commercial and institutional buildings. Systems can be operated at higher voltages than those used by earlier generations, resulting in off the shelf systems for motors up to 500 horsepower.
Early generation systems also suffered from low power factor. Low power factor robs the facility of electrical distribution capacity and can result in cost penalties imposed by electrical utility companies. Today’s systems operate at a nearly constant power factor over the entire speed range of the motor.
Another problem that has been corrected by today’s systems is operational noise. As the output frequency of the drives decreased in response to the load, vibrations induced in the motor laminations generated noise that was easily transmitted through the motor mounts to the building interior. Today’s drives operate at higher frequencies, resulting in the associated noise being above the audible range.
And VFDs continue to evolve. From numerous system benefits to an increasing range of available applications, VFDs are proving to be ever more useful and powerful.
The Heart of VFDs
Most conventional building HVAC applications are designed to operate fans and pumps at a constant speed. Building loads, however, are anything but constant. In a conventional system, some form of mechanical throttling can be used to reduce water or air flow in the system. The drive motor, however, continues to operate at full speed, using nearly the same amount of energy regardless of the heating or cooling load on the system. While mechanical throttling can provide a good level of control, it is not very efficient. VFDs offer an effective and efficient alternative.
Three factors work together to improve operating efficiency with VFDs:
1. Operating at less than full load. Building systems are sized for peak load conditions. In typical applications, peak load conditions occur between 1 and 5 percent of the annual operating hours. This means that pump and fan motors are using more energy than necessary 95 to 99 percent of their operating hours.
2. Oversized system designs. Designing for peak load oversizes the system for most operating hours. This condition is further compounded by the practice of oversizing the system design to allow for underestimated and unexpected loads as well as future loads that might result from changes in how the building space is used.
3. Motor energy use is a function of speed. The most commonly used motor in building HVAC systems is the induction motor. With induction motors, the power drawn by the motor varies with the cube of the motor’s speed. This means that if the motor can be slowed by 25 percent of its normal operating speed, its energy use is reduced by nearly 60 percent. At a 50 percent reduction in speed, energy use is reduced by nearly 90 percent.
The installation of a VFD in an HVAC application addresses the inefficiencies introduced by the first two factors, while producing the energy savings made possible by the third. The VFD accomplishes this by converting 60 cycle line current to direct current, then to an output that varies in voltage and frequency based on the load placed on the system. As the system load decreases, the VFD’s controller reduces the motor’s operating speed so that the flow rate through the system meets but does not exceed the load requirements.
VFD Benefits
The most significant benefit to using a VFD is energy savings. By matching system capacity to the actual load throughout the entire year, major savings in system motor energy use are achieved.
Another benefit of the units is reduced wear and tear on the motors. When an induction motor is started, it draws a much higher current than during normal operation. This inrush current can be three to ten times the full-load operating current for the motor, generating both heat and stress in the motor’s windings and other components. In motors that start and stop frequently, this contributes to early motor failures.
In contrast, when a motor connected to a VFD is started, the VFD applies a very low frequency and low voltage to the motor. Both are gradually ramped up at a controlled rate to normal operating conditions, extending motor life.
VFDs also provide more precise levels of control of applications. For example, high-rise buildings use a booster pump system on the domestic water supply to maintain adequate water pressure at all levels within the building. Conventional pump controls in this type of application can maintain the pressure within a certain range, but a VFD-based system can maintain more precise control over a wider range of flow rates, while reducing energy requirements and pump wear.
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SOURCE: facilitiesnet
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