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A Brief Comparison of Distributed Versus Centralised Intelligence in Whole House Control Systems (28/11/2003)

By Bob Farinelli

While I suggest that professional custom installers do not get their clients tangled up in yarn over hardware and software discussions, they should still consider the technology behind the feature set, when making a recommendation. There are some definite trade-offs worth noting on distributed versus centralized intelligence in whole house control systems.

Sophisticated systems installed in today's homes provide user interfaces in each room that can control the lights, the thermostat, and the security panel, as well as the whole house audio/video distribution system. The overall system architecture is generally configured with either distributed intelligence or with centralized intelligence.

Distributed intelligence means that the processing horsepower is located in a user interface such as a keypad or touchscreen control panel, and the central 'hub' is a simple switch matrix. The control panel executes the complex functions and the hub serves as a signal router.

Centralized intelligence means that all of the processing horsepower is located in a master control unit (MCU). Each user interface is dumb, which means that it sends simple instructions (token commands) that are interpreted by the MCU which then executes complex functions and routings.

How do system integrators decide which type of system they should be promoting? It depends on many factors, and clearly there are pros and cons to both. Not all systems fit the stereotypes I describe, but these are good general rules of thumb based on today's technology.

Distributed Intelligence Pros

* Each control panel's appearance, labelling, programming and macros can be custom configured per room.

* The control panels can be customized or cloned from room to room. (To clone a panel means copying the same configuration from one to another).

* There is more flexibility and there are probably more features available than centralized systems.

* Overall system responsiveness is optimised because there are no screen updates or command code interpretation / service routines in cue waiting to be processed by an MCU.

* There are usually more options in choosing control panel hardware (including third party suppliers).

* In-room local control of source equipment and TVs is easily facilitated.

* Individual components are more likely to be reprogrammable or upgradeable.

* Redundancy - if one panel goes down it does not bring the rest of the house down.

* Individual subsystems can continue to operate on a stand alone basis if there is a fault in either a control panel or a subsystem.

* System troubleshooting can be simplified because the installer can isolate subsystem components.

Distributed Intelligence Cons

* It takes longer to program individual panels than one master system unit, although cloning routines can minimize programming time.

* Hardware costs are usually higher.

* There may be cable distance limitations due to higher signal data rates transmitted by the control panels to the MCU.

* System integration complexities may be higher if custom programming is implemented.

* Changes to the software configuration after the fact (like adding a new piece of source equipment) may require reprogramming each control panel.

* More electronics means more potential for component failures.

Centralized intelligence Pros

* Minimal programming time.

* Lower cost to manufacturer.

* Fewer installation complexities.

* May be able to have longer cable run lengths because lower data rates are used.

* Changes to programming of the system only need to be done once.

* Low data rate token passing commands from dumb user interfaces may be more immune to noise ingress.

Centralized Intelligence Cons

* Lack of flexibility in room to room programming configurations.

* A fault at the main unit will bring the entire system down.

* No local control of source equipment.

* May not be as responsive because one processor has to do all the work in managing multiple requests from dumb control panels.

* Limited control options to choose from - usually proprietary control schemes prevent third party controllers to be used.

* May not be upgradeable without replacing an expensive central unit.

* More difficult to troubleshoot.

There are a lot of factors to consider. If you boil this all down you can characterize these system's key positive attributes as follows: Distributed control systems are more flexible and more fault tolerant. Centralized control systems are less expensive and take less time to set up.

Which one is best?

That depends on the installer and the client. In either case remember this basic rule of thumb: When you pull the plug on the system controller you should still be able to turn on some lights, heat the house, talk on the phone, arm the security system and watch the Weather Channel. Any dealer that installs large systems that cannot support this basic level of functionality (when the control system is down) should be prepared for 24-7 service calls.

As whole house control systems become more prevalent in today's new homes, a few well placed light switches wired with Romex, stand alone security panels, thermostats, rabbit ears and an RJ-31X telephone system bypass jack will always come in handy.

Bob Farinelli is the President and Chief Technology Officer of ELAN Home Systems. This article appears courtesy of ELAN Home Systems.

www.elanhomesystems.com