Upgrading Metasys N2 to BACnet
Technology pressures are pushing organizations to upgrade older controllers and systems from Metasys N2 to BACnet. One of the issues that is faced by technicians and engineers is making devices from different manufacturers talk to each other. The sharing of data is a critical part of creating an efficient energy management system.
Johnson Controls tried to get the N2 communications protocol to become the industry standard which would allow for cross device communications. Unfortunately for Johnson Controls the communication protocol that seems to claimed the title of the industry standard is BACnet.
Most controls manufacturers will use some form of BACnet within their devices and Johnson Controls ended production of newer N2 controllers around 2014. The GX9100 and HVAC Pro software used to program those devices hasn’t been updated since the 1990’s.
Replacing older Metasys N2 devices with newer BACnet controllers
There is still a significant number of N2 networks still in service that are running the older devices. As those devices begin to fail the decision must be made to either install an identical replacement or upgrade to a newer device. Organizations may not be able to afford the expense of switching an entire network from Metasys N2 to BACnet all at once.
Older N2 devices are becoming harder to find and are usually only available from the repair shop. It has been my experience that the cost of a repaired N2 device is higher than a newer generation controller. Many newer controllers have the capability of communicating on an N2 network.
There are two options for switching from Metasys N2 to BACnet. The first option is running new communications cabling for the BACnet devices that will be added and installing another supervisory device. This option is the most expensive but will get the best results the soonest.
A gradual change over an extended period of time may be the more economical solution by using newer BACnet devices that have the capability of being switched to communicate on an N2 network. Once the older N2 devices are replaced, the network can be switched to communicate BACnet.
Video demonstration of switching FEC to communicate N2
Problems associated with adding newer devices to an N2 trunk
There are issues that may develop within the system due to adding newer BACnet devices to an older N2 network. The communication changes made at Metasys 8.0 and newer seemed to dramatically impact how N2 worked. We experienced a significant slowdown in the N2 networks we still have in service once we upgraded to that version.
The communications changes made within Metasys 8.0 and newer caused instability in one of our critical buildings. We had controller issues that caused us to replace the DX9100’s with a newer device and switching it to communicate on the N2 trunk.
It has been our experience that adding enough newer devices to an older N2 network can cause the network to become unstable. We ended up adding an additional NCE and running new cable and switched those devices back to communicating BACnet due to the N2 trunk crashing.
There are several factors that can impact the point where the N2 trunk becomes unreliable. The size of the trunk, the version of Metasys and the amount of data being shared across the devices will all impact the reliability.
Newer devices becoming better
The newer versions of controllers seem to do a better job and working on an N2 network but we haven’t been able to identify a specific point where the N2 becomes unstable. It varies from one building network to another.
Pulling control points from a newer generation device into Metasys is another issue to consider. When you write a control program in CCT you have the ability to create a PRN file that will make pulling control points into the system a little easier, or does it?
Every PRN file I’ve used has always had issues and requires editing. Something as simple as the occupancy point of a VAV will come into as an analog value instead. Pulling some points into Metasys manually seems to work better since you can control how the system sees them.
As older devices have failed we continue to replace them with newer devices and simply switch communication to work on N2. Pulling the points into Metasys manually becomes easier because we have others within the system to reference in order to get it working smoothly.
Making the transition from Metasys N2 to BACnet isn’t easy but is a necessary step in keeping your overall system relevant with the newer technologies.
Pingback: Technology upgrades strategy is important for BAS Systems - System Control Tech