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An Example Of KNX Project Design

An Example Of KNX Project Design

It is basically possible to design a residential building according to criteria similar to those of a functional building and with that to plan the same functionality. The building installations usually seen up to now have for years been based on the distribution and switching of electrical energy. This method is long outdated. Private clients still tend to derive their requirements and expectations regarding electrical installations from their experiences with familiar installation technology.
But in terms of:

  • comfort
  • possibilities for flexible room usage
  • centralised and decentralised controls
  • security
  • the intelligent linking of systems across different building disciplines
  • communication possibilities
  • environmental considerations as well as
  • a reduction in the energy and operating costs,

modern installations have changed dramatically.

During a consultation, the private client is largely unaware of the range of possibilities and opportunities for future extension that are offered by an EIB installation. This information must be passed onto him as clearly as possible without overloading him with unnecessary details. He must be told that it is easily possible to expand or complete his EIB installation at a later date. Good and comprehensive consultation is the best foundation for follow-on contracts for the completion and extension of carefully planned EIB systems.

Incomplete or inadequate consultation can quickly turn an initially satisfied customer into a very unsatisfied customer, if he later learns that his investment in a bus installation cannot be fully exploited.  It must be made clear however, that the answers themselves do not define the installation. They only serve to analyse the customer’s requirements as a basis for determining the feasibility.

Some of the questions hint at technical solutions that will only be available on the market in the months or years to come. They do however play a role in the suggested solutions, as it is possible to take them into consideration for implementation at a later date (preparatory cabling). Completion of this questionnaire essentially represents the specifications. An offer can then be made on the basis of this document, using the “ZVEH calculation aid”. Project design begins once the contract is awarded.

KNX Project

Fig.1 - KNX Project

Writing the specifications based on a given example

The answers marked in the questionnaire yield the following basic requirements on the EIB project:

  • The private customer is building a one-family house with garden and garage on a remote site.
  • There are distinct demands on security.
  • Value is placed on ways to save energy and costs.
  • Particular demands have been made regarding comfort.
  • Some of the wishes cannot yet be technically realised, which means that a system planned with foresight is extremely important for follow-on contracts.
  • Subsequent extensions to the system and functionality must be taken into consideration.
  • A few of the possibilities mentioned in the questionnaire are viewed as critical; further information and more detailed explanations could extend the project and offer approaches to a service contract.

The system requirements essentially comprise the following:

  • Within the house, switching points should be located near the doors as well as in the sleeping and seating areas.
  • Lighting control with movement detectors should also be planned for the garden and access paths.
  • Security lighting should be incorporated.
  • The simulation of an “occupied house” by adjustable sequences is required.
  • The lighting control should be integrated into the Home-Assistant.
  • Switchable sockets should be provided for the exterior areas, kitchen, workroom and bedrooms.
  • Sockets must have child-protection.
  • For the simulation of an “occupied house”, switchable sockets should be planned for lights.
  • The switching status of the sockets should be represented in the HomeAssistant.
Room heating
  • Single room temperature control should be included, which in addition to manual intervention also allows monitoring and control via a HomeAssistant.
  • The radiators should be switched off when the windows are open.
  • Remote control and remote signalling should be possible for the heating system.
  • Reporting to a customer services department should be planned for a later date.
Heating system
  • The heating system should be adapted to the requirements in a way that saves energy and costs. It should also be possible to monitor it from a central position; i.e. it should be connected to the EIB and integrated into the HomeAssistant.
Hot water supply
  • The hot water supply should be investigated separately, as a combination of gas, electricity and perhaps at a later date solar energy must be taken into account.
Blinds and shutters
  • The blinds should be motorised and must react accordingly in adverse weather conditions.
  • In addition to manual operating possibilities located near to the windows, it should also be possible to control and monitor them from a central position.
  • In rooms subject to dazzling sunlight, it should also be possible to adjust the angle of the slats.
  • The open or closed status should be centrally displayed.
  • They should be incorporated into a security system.
  • In addition to manual operating possibilities, awnings installed on the patio should be automatically retracted in strong wind or rain. It should also be possible to use them to influence the temperature of the shaded room.
  • They should also be used to simulate an “occupied house” and allow the possibility of control from a central position.
Window monitoring
  • The closed status of the windows should be monitored and displayed centrally.
  • Any tampering should be detected and incorporated into a security system.
  • Motor-driven operation should be included as a possibility for use at a later date.
Door and gate monitoring
  • The closed status of the house doors and garden gates is to be incorporated into a security system. Additional visual monitoring is also desired.
Monitoring the supply lines
  • For extra safety, the water and gas supplies should be monitored and integrated into a security system. As this is not yet on the market, a provisional installation must be planned.
Meter monitoring
  • As a prerequisite for measures to save energy and costs, the meter readings and running costs should be displayed. The installation should be designed for the future implementation of remote meter reading.
House appliances
  • Regarding new purchases, interest lies in the use of devices with a bus connection. It is therefore necessary to plan, at least provisionally, the corresponding number of communication sockets.
Garden system
  • In the garden and along the path to the house there should be lighting and movement detectors and these should be integrated into a general security system.
  • It should be possible to operate a sprinkler system depending on the dampness of the ground.
Security equipment
  • Measures should be included to increase security. This must include interior and exterior lighting, the windows, blinds and the entrance doors.
  • Monitoring at the HomeAssistant with remote signalling possibilities should be planned.
  • It should be possible to trigger emergency and help calls, quickly and easily.
Central operating and control unit
  • A device, which is capable of receiving television signals in addition to allowing the simple operation and control of the household installations, should be fitted in the kitchen (HomeAssistant).

There is also interest in the following extensions, planned for the future:

  • Cultivation of a winter garden with shadowing and utilisation of the heat energy that is produced in the transitional period.
  • Lighting in the living area.
  • Isolation of the bedrooms to avoid electromagnetic fields.
  • Connection to service stations for the various devices.
  • Construction of a garden pond with the ability to monitor the circulating pump and maintain a constant level.
  • Installation of a solar panel and integration into the existing hot water supply.

An example of designing a project

Although in comparison with a large functional building, we are dealing with a much clearer installation here, a  installation should be planned. This has as much to do with the variety of functions desired as well as with the high probability of later expansion. A separate line should be provided for each floor to ensure simple and clear structuring. Because this example deals with a new project, the project design is carried out with ETS 3. The result is an extensive set of detailed lists. For projects where there is a high probability of expansion or modification within subsequent years, other documents should be provided in addition to the lists.

Results of the project design stage form the foundation for all subsequent steps of the installation, commissioning and maintenance, and with that of course for all future expansion. Reference is made to the documents or wiring diagrams in accordance with the standards of the EN 61082 or DIN 40719 series, in particular to the bus devices and bus lines with physical and group addresses that are marked on the ground plan (see Fig. 1). The logic diagram indicates the bus devices and their physical addresses as well as allocation to the lines. If the complexity of the project demands, it may also be necessary to draw up a functional diagram. This saves a considerable amount of time during subsequent expansions or modifications.

If you also draw the parameter block for each of the bus devices, you are left with an excellent and very clear set of documents. The HomeAssistant necessary to implement this example system demands exact adherence to the rules of ETS 3 and to the design guidelines. Of particular importance is the entry of room structure, completion of the key fields and the addition of extra groups (so-called single actuator groups).

Adherence to these guidelines is important because the terms and names for the rooms and devices are derived from this data and appear in the operating menus of the HomeAssistant, allowing the end user to recognise his own individual system. The database created with ETS 3 is transferred into the HomeAssistant using the HomeAssistant Tool Software (HTS), which is included in the scope of supply.

SOURCE: Project Engineering for EIB Installations


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Power transformer

Power transformer

In a real transformer, some power is dissipated in the form of heat. A portion of these power losses occur in the conductor windings due to electrical resistance and are referred to as copper losses. However, so-called iron losses from the transformer core are also important. The latter result from the rapid change of direction of the magnetic field, which means that the microscopic iron particles must continually realign themselves technically, their magnetic moment—in the direction of the field (or flux). Just as with the flow of charge, this realignment encounters friction on the microscopic level and therefore dissipates energy, which becomes tangible as heating of the material.
Taking account of both iron and copper losses, the efficiency (or ratio of electrical power out to electrical power in) of real transformers can be in the high 90% range. Still, even a small percentage of losses in a large transformer corresponds to a sig- nificant amount of heat that must be dealt with. In the case of small transformers inside typical household adaptors for low-voltage d.c. appliances, we know that they are warm to the touch. Yet they transfer such small quantities of power that the heat is easily dissipated into the ambient air . By contrast, suppose a 10MVA transformer at a distribution substation operates at an efficiency of 99%: A 1% loss here corresponds to a staggering 100 kW.
In general, smaller transformers like those on distribution poles are passively cooled by simply radiating heat away to their surroundings, sometimes assisted by radiator vanes that maximize the available surface area for removing the heat.

Large transformers like those at substations or power plants require the heat to be removed from the core and windings by active cooling, generally through circulat- ing oil that simultaneously functions as an electrical insulator.

The capacity limit of a transformer is dictated by the rate of heat dissipation. Thus, as is true for power lines, the ability to load a transformer depends in part on ambient conditions including temperature, wind, and rain. For example, if a transformer appears to be reaching its thermal limit on a hot day, one way to salvage the situation is to hose down its exterior with cold water—a procedure that is not “by the book,” but has been reported to work in emergencies. When transformers are operated near their capacity limit, the key variable to monitor is the internal or oil temperature. This task is complicated by the problem that the temperature may not be uniform throughout the inside of the transformer, and damage can be done by just a local hot spot. Under extreme heat, the oil can break down, sustain an electric arc, or even burn, and a transformer may explode.
A cooling and insulating fluid for transformers has to meet criteria similar to those for other high-voltage equipment, such as circuit breakers and capacitors: it must conduct heat but not electricity; it must not be chemically reactive; and it must not be easily ionized, which would allow arcs to form. Mineral oil meets these criteria fairly well, since the long, nonpolar molecules do not readily break apart under an electric field.

Another class of compounds that performs very well and has been in widespread use for transformers and other equipment is polychlorinated biphenyls, commonly known as PCBs. Because PCBs and the dioxins that contaminate them were found to be carcinogenic and ecologically toxic and persistent, they are no longer manufactured in the United States; the installation of new PCB-containing utility equipment has been banned since 1977.11 However, much of the extant hardware predates this phase-out and is therefore subject to careful maintenance and disposal procedures (somewhat analogous to asbestos in buildings).

Introduced in the 1960s, sulfur hexafluoride (SF6) is another very effective arc-extinguishing fluid for high-voltage equipment. SF6 has the advantage of being reasonably nontoxic as well as chemically inert, and it has a superior ability to with- stand electric fields without ionizing. While the size of transformers and capacitors is constrained by other factors, circuit breakers can be made much smaller with SF6 than traditional oil-filled breakers. However, it turns out that SF6 absorbs thermal infrared radiation and thus acts as a greenhouse gas when it escapes into the atmos- phere; it is included among regulated substances in the Kyoto Protocol on global climate change. SF6 in the atmosphere also appears to form another compound by the name of trifluoromethyl sulfur pentafluoride (SF5CF3), an even more potent greenhouse gas whose atmospheric concentration is rapidly increasing.

Transformer fan

Transformer fan

Heat from core losses and copper losses must be dissipated to the environment. In dry type transformers, cooling is accomplished simply by circulating air around and through the coil and core assembly, either by natural convection or by forced air flow from fans. This cooling method is usually limited to low-voltage indoor transformers (5 kV and below) having a three-phase rating below 1500 KVA. At higher voltages, oil is required to insulate the windings, which prevents the use of air for cooling the core and coils directly. At higher KVA ratings, the losses are just too high for direct air cooling to be effective. In outdoor environments, direct air cooling would introduce unacceptable amounts of dirt and moisture into the windings.
Transformers come in various cooling classes, as defined by the industry standards. In recent years, there have been attempts to align the designa- tions that apply to transformers manufactured in North America with the IEC cooling-class designations. Table below gives the IEC designations and the earlier designations that are used in this book. All of the IEC designations use four letters. In some respects, the IEC designations are more descriptive than the North American designations because IEC makes a distinction between forced-oil/air cooled (OFAF) and directed-flow-air cooled (ODAF). Some people find using the four-letter designations somewhat awkward, and this book uses the earlier designations throughout.
In small oil-filled distribution transformers, the surface of the tank is sufficient for transferring heat from the oil to the air. Ribs are added to the tanks of some distribution transformers to increase the surface area of the tank and to improve heat transfer. Large distribution transformers and small power transformers generally require radiator banks to provide cooling. Regardless of whether the tank surface, ribs, or radiators are used, transformers that trans-fer heat from oil to air through natural convection are all cooling class OA transformers.

Radiators used on OA transformers generally have round cooling tubes or flat fins with large cross section areas in order to allow oil to flow by natural convection with minimal resistance. Hot oil from the core and coils rises to the top of the tank above the inlet to the radiator. Cool oil from the radiator sinks to the bottom of the radiator through the outlet and into the bottom of the core and coils. This process is called thermo-siphoning and the oil velocity is relatively slow throughout the transformer and radiators. For this reason, OA transformers have relatively large temperature gradients between the bot- tom oil and the top oil, and relatively large temperature gradients between the winding temperatures and the top oil temperature. Likewise, the air circulates through the radiator through natural convection, or is aided by the wind.

Designations and descriptions of the cooling classes used in power transformers
Previous designationIEC designationDescription
Oil-air cooled (self-cooled)
Forced-air cooled
Oil-air cooled (self-cooled), followed by two stages of forced-air cooling (fans)
.OA/FA/FOA.ONAN/ONAF/OFAFOil-air cooled (self-cooled), followed by one stage of forced-air cooling (fans), followed by 1 stage of forced oil (oil pumps)
Oil-air cooled (self-cooled), followed by one stage of directed oil flow pumps (with fans)
. OA/FOA/FOA.ONAF/ODAF/ODAFOil-air cooled (self-cooled), followed by two stages of directed oil flow pumps (with fans)
Forced oil/air cooled (with fans) rating only—no self-cooled rating
Forced oil / water cooled rating only (oil / water heat exchanger with oil and wa- ter pumps)—no self-cooled rating
Forced oil / air cooled rating    only    with    di- rected oil flow pumps and fans—no self-cooled rating
Forced oil / water cooled rating only (oil / water heat exchanger with directed oil flow pumps and water pumps)— no self-cooled rating

As the transformer losses increase, the number and size of the radiators that are required to cool the oil must increase. Eventually, a point is reached where wind and natural convection are not adequate to remove the heat and air must be forced through the radiators by motor-driven fans. Transformers that have forced air cooling are cooling class FA transformers. FA transform- ers require auxiliary power to run the fan motors, however, and one of the advantages of OA transformers is that they require no auxiliary power for cooling equipment. Since additional cooling is not usually needed until the transformer is heavily loaded, the fans on most FA transformers are turned off until temperatures exceed some threshold value, so under light load the transformer is cooled by natural convection only. These transformers are cool- ing class OA/FA transformers.

Some transformers are cooled by natural convection below temperature T1, turn on one stage of fans at a higher temperature T2 and turn on a second stage of fans at an even higher temperature T3. These transformers are cooling class OA/FA/FA transformers. The direction of air flow in forced-air units is either horizontally outward or vertically upward. The vertical flow pattern has the advantage of being in the same direction as the natural air convection, so the two air flows will reinforce each other.

Although the cooling capacity is greatly increased by the use of forced air, increasing the loading to take advantage of the increased capacity will increase the temperature gradients within the transformer. A point is reached where the internal temperature gradients limit the ability to increase load any further. The solution is to increase the oil velocity by pumping oil as well as forcing air through the radiators. The usual pump placement is at the bottom of the radiators, forcing oil from the radiator outlets into the bottom of he transformer tank in the same direction as natural circulation but at a much higher velocity. Such transformers are cooling class FOA transformers. By directing the flow of oil within the transformer windings, greater cooling effi- ciency can be achieved. In recognition of this fact, the calculation of hot-spot temperatures is modified slightly for directed-flow cooling class transformers.

As in forced-air designs, forced-oil cooling can be combined with OA cooling (OA/FOA) or in two stages (OA/FOA/FOA). A transformer having a stage of fans and a stage of oil pumps that are switched on at different temperatures would be a cooling class OA/FA/FOA transformer.
The radiator design on FOA transformers can differ substantially with the radiator design on FA transformers. Since the oil is pumped under consid- erable pressure, the resistance to oil flow is of secondary importance so the radiator tubes can be designed to maximize surface area at the expense of cross section area. FOA radiators are sometimes called coolers instead, and tend to resemble automotive radiators with very narrow spaces between the cooling tubes and flat fins in the spaces between the cooling tubes to provide additional surface area. The comparison of the two types is illustrated in picture left (OA/FA type) and right (FOA type).

OA/FA radiator construction

OA/FA radiator construction. The large radiator tubes minimize restric- tion of oil flow under natural convection. The fan is shown mounted at the bottom with air flow directed upward.

FOA cooler construction

FOA cooler construction. The oil is forced through narrow tubes from top to bottom by means of oil pumps. The cooling fans direct air horizontally outward.

Cooling equipment requires maintenance in order to run efficiently and provide for a long transformer life. There is the obvious need to main- tain the fans, pumps, and electrical supply equipment. The oil coolers them- selves must be kept clean as well, especially FOA-type coolers. Many transformers have overheated under moderate loads because the cooling fins were clogged with insect and bird nests, dust, pollen, and other debris. For generator step-up transformers, where the load is nearly at nameplate rating continuously, steam-cleaning the coolers once every year is a good mainte- nance practice.


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