20
Operation:
When the fan output is off (Terminal G), the static pressure control loop and the by-pass damper is fully
opened to 10 Vdc output. This will minimize the air pressure related noise during initial fan start-up. Please
note that the fan is always on during occupied periods and that it will cycle on demand with the heating and
cooling staged only during unoccupied periods.
When the fan output is on (Terminal G), the static pressure control loop is enabled and the by-pass damper
will modulate to maintain the desired static pressure set point according to the static pressure input reading
at the RTU thermostat. The current static pressure value can be read at the RTU thermostat at any time by
using the manual scroll function and displaying the pressure prompt.
4) Wireless Communication Overview
The Viconics VZ7200F5x00W and VZ7656B1000W thermostats, Viconics Wireless Gateway (VWG) and
Jace-driver and other related wireless thermostat family (VT7xxxXxxxxW) networkable devices operate
using ZigBee/IEEE 802.15.4 physical layer for communication.
General characteristics of the wireless physical communication layer are:
·
Wireless physical layer of 2.4GHz with a data rates of 250 kbps
·
Yields high throughput and low latency
·
Automatic multiple topologies configuration: star, peer-to-peer, mesh
·
Fully handshake protocol for transfer reliability
·
Range: 30 feet / 10M typical (up to 100 feet / 30 M based on environment)
IEEE 802.15.4 along with ZigBee’s Network and Application Support Layer provide:
·
Low cost installation deployment
·
Ease of implementation
· Reliable
data
transfer
·
Short range operation
·
Very low power consumption
·
Appropriate levels of security
The main network coordinator for the wireless the IEEE 802.15.4/ZigBee network can be either:
•
The VZ76xx RTU thermostat for
(SA)
Stand-Alone applications: Where zoning system(s) are self
sufficient for communication and no external communication is required. In this layout, the VZ76xx RTU
thermostat acts as the network coordinator.
•
The Viconics Wireless Gateway (VWG / Jace-Driver for
(NS)
Networked Systems applications: Where
zoning system(s) (more than one can be installed in a typical building application) are required to
communicate with the Viconics VWG / Jace-Driver set. In this layout, the Viconics VWG / Jace-Driver
acts as the network coordinator.
Many network specific features of the IEEE 802.15.4 standard are not covered in detail in this paper.
However, these are necessary for the efficient operation of a ZigBee network. The features of the network
physical layer include receiver energy detection, link quality indication and clear channel assessment. Both
contention-based and contention-free channel access methods are supported with a maximum packet size
of 128 bytes, which includes a variable payload up to 104 bytes. Also employed are 64-bit IEEE and 16-bit
short addressing, supporting over 65,000 nodes per network. All the properties of the physical layer are
used and employed by the Viconics mesh network but are hidden to the user for ease of configuration and
commissioning of the network database.
