wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

26-6 Industrial Communication Systems
(and their specific profiles), or Modbus are used at this level. As a software interface into BMS software,
OPC [19] has reached importance. Today, also Web technologies are used, for example, for management
and configuration of DDC stations. However, these are still of limited use for machine-tomachine
communication.
One fact that must not be neglected is the long life cycle of a building and its respective services.
When faced with a future extension or change of the system, access to all new data points must be
preserved. In this case, only an open system can guarantee that one does not find oneself tied to the
contractor that originally installed the system. With BACnet• [9,11], KNX• [6,10,19], and LonWorks
[1,5,20], three major, open standards exist in the field of building automation. While these standards
cover multiple application domains, and hence a broad range of applications, also several domainspecific
busses are emerging. These replace the interfaces that were traditionally used to connect field
devices to controllers. Since they are designed for the use in a specific application domain, they often
provide additional functionality, which makes them especially appealing and cost-effective to install.
A prominent example of these application-specific standards is Digital Addressable Lighting Interface
(DALI) [7]. DALI allows control of up to 64 electronic ballasts for fluorescent lamps and intends to
replace the classical 1–10.V interface. Another example is M-Bus [4], which has been designed in Europe
for (remote) meter reading. The Standard Motor Interface (SMI) bus [22] is mainly used for shutters,
protection systems, and sunblinds.
Another trend is the tighter integration of BAS between building service domains. Previously, each
building service domain such as HVAC had its own dedicated control system based on a specific technology.
Other domains might have used different technologies. A set of arriving new functions requires
cross-communication between the BAS domains. It is, for instance, no longer acceptable that presence
detectors from the lighting domains are not accessible for intrusion detection systems. Another example
is constant light control, which can benefit from integration with shading. If two domains are not based
on the same communication technology, the use of gateways is mandatory (e.g., to provide a set of
DALI registers to BACnet). If two domains use the same technology, but different address domains, the
use of proxies is required (e.g., provide network variables of LonWorks domain A to domain B). The
problem with gateways is that the number of translations between systems is of quadratic order. Also,
configuring gateways is challenging, as the mapping between technologies can never be a 1:1 mapping,
and therefore information is always lost. A new trend is to equip those devices, which shall integrate the
singular functions, with network technologies of both domains. For example, the DALI constant light
controller may provide both a LonWorks and BACnet interface for transparent access by the respective
system. The advantage is no extra configuration as the device already knows about its data points and
no loss of information into the other system has to be faced.
It is the task of the project engineer to choose among a variety of applicable protocols as well as
various options regarding network topology and function distribution. One may opt to use a common
protocol throughout the system and only varying the network layer according to the expected traffic
load, or one may choose to interconnect multiple trade-specific and level-specific solutions using
gateways. The project engineer also has the choice between using DDC stations to implement the automation
functions or using intelligent field devices instead. However, these decisions are not entirely
independent and therefore should not be made arbitrarily. For each specific project, related requirements
finally determine which approach is suited best.
26.2.4 applications
Today’s BAS have gone a long way from simple HVAC systems and become more complex. For once,
centralized control has been replaced by distributed controls. Typical zones for building services now
range from entire building wings down to rooms or window axles. A building service might have different
requirements in different zones, for example, room control may have to be considered separately
from corridors or stairwells. This typically results in different designs for rooms and corridors.
© 2011 by Taylor and Francis Group, LLC