HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumFeedback SensorsThere are two basic types of input sensors: analog and digital. Thesimplest form of digital input information is an on or off condition, possiblymonitored through a single dry contact. The contact allows the controllerto identify a true or false condition. This can be used to identifysuch conditions as fan or compressor failure. With analog sensors, analogto digital conversion is needed to allow the computer to interpret thedata.Sensor trends that have been growing include the sensor bus andwireless sensors. These are related concepts since they both rely to somedegree on communication.Both of these trends are driven by the desire to reduce cost. The sensorbus brings networking communication technology to input devices.The concept is to reduce both the cost of both the labor and wire used toinstall sensors. This would allow greater ease and flexibility of installationas well as cost savings. It would also simplify relocating sensors thatare not providing the right information on actual zone conditions.About a third of all zone sensors are installed in the wrong location.Yet most are never moved due to the labor and difficulty involvedin moving wires through walls to move the sensor. A sensor bus orwireless sensors would simplify the installation and relocation process.In a sensor bus, all sensors would be on a communication network andany controller would request these points.Wireless sensors are another concept. Wireless sensors have beenintroduced that use either infrared or radio communication. The costsavings are even greater than with the sensor bus, since wiring can beeliminated all together. It is easy to move sensors, replace failed sensorsand redefine a sensor to any given controller or loop.Some wireless sensors require a clear line of sight for the accuratetransmission of sensor data. With any type of radio based sensor ornetwork interference is important. Interference that changes or interruptscommunication of the current sensor information cannot be allowedto affect the control loop.Software/FirmwareFirmware is a term used to identify anything that the average useror technician cannot change. As programmed logic, Firmware is resident©2001 by The Fairmont Press, Inc. All rights reserved.