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HVAC control w/ AMX

2nd Rick2nd Rick Junior MemberPosts: 6
I am a little confused with the best approach to use to control the AMX branded VST or Aprilaire branded version of the communicating t-stat system.

At the least, I am looking to define the difference in the various approaches,

Does anyone have any experiences to share as to why I may want to use one approach over the others.
Hereare the ways to communicate to the system that I can see:

1) Mini-verters for ICS Net-to-RS-422 (adds @$200 msrp per stat, plus the components to add the req'd ICS Net ports)

2) Hard wiring right into the A+, A-, B+, B- terminals on the VST-DIST (or Aprilaire 8818) distribution panel and communicating directly to the system in RS-422. (no additional cost, needs 1 port)

3) Aprilaire 8811 protocol adapter which is an RS-232-to-RS-422 adapter (adds @$175 msrp for the system, needs 1 port) I have pretty much determined that this is for lesser control systems like Elan and Vantage that cannot communicate directly w/ RS-422.

I have seen the RS-422 module listed in the InConcert section. The reason I am curious is because the MiniVerter method adds so much extra cost between the MiniVerters themse;ves (or integrated VST 'stats) and also the additional ICSNet card, frame, and power that I may not otherwise need.

I am assuming that it adds some significant benefit for the additional cost.

Price is obviously somewhat important, because if I do not need mini-verters or a protocol adapter, I might be able to squeeze in more temp/humidity sensors or an extra zone.

BTW, this will be used with NI-3000 controller on a new installation...


  • Reese JacobsReese Jacobs Junior Member Posts: 347
    HVAC control w/ AMX

    I don't think there is a right answer or a wrong answer. There are some pros and cons to both approaches and I have used both methods. Here are some thoughts.

    Prior to the ViewStat (with MiniVerter option), I used the OPStat thermostats which were the predecessors to the VST. The miniverter was not an option for this thermostat model and I always wired my OPStats back to a distribution panel with communication cards and then connected the panel to the RS422 port on the Netlinx system. As a result, this is an approach that is familiar to me and has always proven to be quite reliable.

    The distribution panel option is one I use frequently with the VST thermostats as well. The panel provides a common location for wiring runs from the thermostats to be terminated and also provides for a common power supply. It is then a relatively simple matter to connect the distribution panel to the RS422 port and control the thermostats using the AMX module (there are some guidelines to follow for thermostat addressing in this implementation that are different from the miniverter implementation). I like this approach - it is simple yet elegant, is supported by an AMX module, requires a single RS422 connection to Netlinx, provides a common power supply, is less expensive than the miniverter approach overall, and the approach works reliably. The distribution panel is however limited to 8 thermostats so system design and control where more than 8 thermostats are used requires additional planning and implementation steps including equipment. The miniverter approach is more flexible when dealing with large numbers of thermostats.

    The miniverter approach also works well. The biggest cons I note for this approach are the following (this is based on my experience):

    - The miniverters are relatively expensive
    - Installation of the thermostat in the wall with the miniverter can be interesting (we have installed them together using the chassis as well as separately to save space)
    - I have had some reliability issues with the miniverters

    That said, using the miniverter does provide you with a quick method of determining if a thermostat is online (communicating) by examining the device tree (we use this for remote system maintenance). However, the miniverter can show up in the online tree but still not be controlling the thermostat. Down the road, with Duet, it seems the direction is that VSTs with miniverters will be automatically recognized by Netlinx and the proper module loaded for control automatically. Perhaps there are some advantages in this area - I can't say for sure. I am speculating that there will be IP based thermostat replacements by this time which is why I am not overly concerned about Duet and its impact on the current VST/miniverter product.

    In summary, both approaches are reasonable. The RS422/distribution panel approach does offer a lower cost and control is as reliable as using the miniverter approach. I am hard pressed to think of any tremendous advantages with the miniverter approach that would cause me to recommend that approach in all cases. The miniverter approach might support large installations more easily since multiple distribution panels and RS422 connections would not be required (more than 8 thermostat installations).

  • DHawthorneDHawthorne Old Timer Posts: 4,584
    I use these thermostats all the time. I have found several installations where reporting from the first thermostat on the buss (ID 1) is completely lost when hooked up directly to the 422 buss with the NetLinx. Subsequently, I always use the protocol adapter to convert it to 232 - it's simply more reliable. I have no idea why this should make a difference, since I haven't seen it on every job.

    I've never used the miniverters - it just seemed too costly a solution.
  • Spire_JeffSpire_Jeff Formerly Caffeinated Programmer Posts: 1,917
    I have never used the minisverters. I have used the adapter back in my Elan days without problems (except the older model thermostats had issues). I have been using the 422 communications and have not had any problems with thermostats dropping of the bus. I have had problems with what I think is a nail through one of my longest runs, but other than that everything is fine.

    One thing to note on the 422 implementation, I am not sure if it has been fixed, but I had to manually slow transmissions of changes that affected all thermostats in order for the changes to take place. I'm not sure if the comm module didn't utilize the bus or if it just couldn't queue commands for 10 stats, but slowling it down made everything work fine.

  • ericmedleyericmedley Senior Member - 4000+ posts Posts: 4,177
    One little issue to be careful about when using the Miniverter - ICSNet stuff...

    I've been burned (literally) several times by this. The miniverter gets power from the 24 volt line coming off the furnace controller. (it has to. it makes sense)

    However, if you have a ham-handed HVAC person dinking around with the wiring, they can zap your miniverter and quite a few other components connected to your system. (like a ME260 master...)

    The client at that house had a brilliant idea. He suggested we put an interupt switch in the 24 volt line that will isolate the minverter from the power when it's being serviced.

    I've used all three methods you mentioned to control several zones of HVAC at houses and have had good luck with all of them. Since I'm kind of a control freak, I like to get each stat separately, (serial) if possible. ISCNet works fine with the module too.

    It's a pretty stable setup either way. I'd say it's more of a choice of location and wireing available.

    my 2 cents for the day.

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