August 2006
  
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The not so obvious benefits of wireless control networks

These benefits come from the flexibility provided by being able to sense without the need for connecting wires.

Paul Ehrlich, P.E. Building Intelligence Group
Contributing Editor

As published in August Issue
 

There has been a lot written about the many benefits of using wireless technology for building control systems. New products on the market make a strong case on the benefit of cost reduction in wiring, by many accounts reducing system installation costs by as much as 50%. While these are very real benefits there is also a series of less tangible benefits from using wireless technology. These benefits come from the flexibility provided by being able to sense without the need for connecting wires. Space sensors can not only be located where they will work best, but can be installed once wall finishes and furniture is in place. If an additional sensor is required, it is easy to add or to relocate an existing sensor.

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Even the construction process is greatly simplified allowing the controls contractor significant savings by requiring fewer trips to the jobsite. In order to understand these benefits, we need to look deeper into the construction process. The typical design and installation of terminal units (VAV, Fan Coils, etc.) for a new construction project follows a number of familiar steps. Letís take a look at these for a traditional wired installation and for a wireless installation:                                                         

Wired                                                                 Wireless

1.      System Design: The first stage of installing a control network is design.  During the design process the location of all zone sensors must be identified.  This is typically done by the design team.  Unfortunately, it is often necessary to locate sensors on the plans without detailed information about how the space will be utilized.   

This often results in sensors being mounted behind cabinets, on columns, exterior walls, in the path of bright sunlight,  or behind a stray coffee pot.  Moves after construction is complete are expensive and require not only running of wires through completed walls, but patching existing surfaces.

Sensor locations on plans are only a recommendation.  Final sensor locations can be determined once all of the furniture and wall finishes are complete.

2.      Equipment Rough In: The controls contractorís electrician need to show up at the project site at the point where partitions are framed but not yet sheathed.  At this time, they run in the sensor cable either within the wall framing or in many areas, using a conduit drop.  Wiring is left roughed in and not connected. 

Roughed in wiring requires a close level of coordination with other construction trades.  Since the controls contractor electrician is not always on the job site this can be a problem.  Also, on many projects, there is a need to have temporary heating or cooling.  In order to provide this, a temporary sensor has to be mounted at the terminal unit. 

No rough in required.  Temporary heat or cooling can be easily accommodated with a wall or unit mounted sensor. The terminal units can be installed by the mechanical contractor.  Controls can be factory mounted or field mounted by the controls contractor at any time.  If a wired controls communications network is used, it needs to be roughed in above the ceiling, however this communications can also be wireless, combining factory mounting of controllers and wireless communications means that the controls contractor does not need to be at the job site until it is time to do startup.

3.      Sensor Installation: Once the wall sheathing and final finish is completed, the zone sensors can be installed.  This installation requires the removal of any temporary sensors, and installation of the permanent sensors.  Note:  Temporary sensors will often be damaged by paint and other construction debris and typically canít be used for final installation. 

The installation of the final sensors is required to finish the building and receive a certificate of occupancy which requires final dry-walling, paint, paper, etc. to be completed.  Again this is a coordination challenge that may require multiple trips to the jobsite to install sensors.  Unfortunately, once the sensors are installed, they can be easily damaged by moving crews locating furniture and other material into the building.  Damaged sensors may result in controller damage and require replacement at the ownerís expense.

The wireless sensors can be brought to the project site near to project completion.  They can be mounted in the most optimal location onto any surface.  In many cases, they are mounted to cubicle partitions, walls or columns, making sure to place them out of sunlight or other problem areas. 

The end result of using wireless sensor and control networks are in additional cost reductions for the controls contractor, but it additional flexibility and ultimately better control for the owner and occupants.

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