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  1. #1
    Join Date
    Oct 2005
    Location
    Oregon
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    96
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    Multiple package units, one stat.

    Hello people, I've got a question concerning multiple packaged heat pumps supplying a large area using one thermostat.
    The customer is requesting that only 4 thermostats be used to control 16 rooftop package heat pumps. This is going to take care of a very large open space with no drop ceiling.
    My question is, what is the best way to control 4 systems with one thermostat? My first thought was to utilize a series of relays with time delays on each system for staging.
    Any suggestions would be helpful.

  2. #2
    Join Date
    Jun 2011
    Location
    Central Indiana
    Posts
    619
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    I have a larger music performance/music shop that has a pretty extreme load swing. When they are just using the space as a show room, the load is low but when they pack the place with 300 people and a live band, the need a lot more. They have 3 units and I just set up a 3 heat 3 cool Honeywell programable with some relays to control the staging. I think it wouldn't be too hard to add an extra "stage" with a time delay. The easiest way I have found is to build a control center with all your relays and transformer and mount that indoors that way your wiring isn't a mess. All of the connections can be made in the box and then a wire to each unit and one to the stat. Looks nice and performs nice.
    The only true knowledge is the pursuit of knowledge

  3. #3
    Join Date
    Oct 2002
    Location
    Plano, TX
    Posts
    2,417
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    Done this. Use one relay for each function, Y-O-G-W. 4 pole relay. A pole for each RTU. Room Stat, with its own 24 volt transformer, will control relays. Use relays with indicator light and manual push button simplifies troubleshooting.

    Add delay relay after 4psp relay and all at same location. Draw wiring diagram, label parts and post. Will sure help the next tech in fixing.

  4. #4
    Join Date
    Oct 2005
    Location
    Oregon
    Posts
    96
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    Thread Starter
    Thanks for the responses. Well it looks like I'm on the right track.

  5. #5
    Join Date
    Apr 2007
    Location
    Amarillo by mornin'
    Posts
    1,016
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    You might want to run a test rig first. Some one we know did this and when the compressors all fired at the same time it would trip one of the main breakers due to such a high in-rush.
    "It's not that I'm smart, it's that I stay with the problem longer”
    Albert Einstein

  6. #6
    Join Date
    Feb 2014
    Location
    Niagara On The Lake, ON,Canada
    Posts
    42
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    I've done this with relays years ago. It takes a lot of relays and a lot of wiring. If I was doing it now I would look at using a simple programmable logic controller such as Siemens Logo. It can be programmed to read the input from the thermostat and respond with appropriate outputs to the units, including time delays to prevent the problem that was brought up by xarralu.

    Link

    Another option would be an I/O controller.

    Link

  7. #7
    Join Date
    Jul 2003
    Location
    Elizabethtown ,KY
    Posts
    215
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    Another consideration, is staggering start times. I don't know what size of equipment you're dealing with, but if fairly large, there may be "Demand" surcharges attached to your client's electrical bill if too large an inrush current is measured.
    " Go sell crazy somewhere else,we're all stocked up here.

  8. #8
    Join Date
    Jan 2014
    Location
    Arizona
    Posts
    111
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    I do this often and You can use a Bard MC4000 controller to stage all 4 package units. It's a 4 stage controller. Do it all the time and Don't matter what units either. Also don't have to remove transformer in units either. It Can take one or multiple sensors and can average temps. It's easy to install and works good. If you need more info key me know. Now has optional remote communication board for remote internet access..

  9. #9
    Join Date
    Oct 2005
    Location
    Oregon
    Posts
    96
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    Thread Starter
    It looks like the MC4000 might work.
    The Logo controller is nice because you can have it do what ever you want but I haven't programmed before so it is a bit difficult. I've downloaded the demo software for Logo and looked over the examples but I need more time to learn it. Thanks for the input
    Last edited by napoleon-dynomite; 02-09-2014 at 03:20 PM. Reason: correction

  10. #10
    Join Date
    Jan 2014
    Location
    Arizona
    Posts
    111
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    Did a 4 unit install last Thursday on a MC.. I missed the part about 16 units but re-read the post my bad on that. We done this for 20 units on Tridium jace and NDIO modules. It was easy to do. Sorry I missed the 16 units.

  11. #11
    Join Date
    Jan 2014
    Location
    Arizona
    Posts
    111
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    I guess you could add 4 N.O relays per stage in parallel on the mc4000 and have each stage in the mc400 bring on 4 units at a time. Just a thought FWIW. May not help you.

  12. #12
    Join Date
    Aug 2010
    Posts
    4,337
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    Do you want them soft zoned or just work all together?

    A drawing of layout would be a good start. A setup that is manifolded into one big duct is different from a setup with each cluster supplying different segments of room.

  13. #13
    Join Date
    May 2004
    Location
    Salt Lake City/Tooele
    Posts
    5,362
    Post Likes
    I work on these BARD controllers a lot. Many oil and natural gas remote sites have multiple modules married together to create a large work, sleep, or storage facility. Each module has a BARD or similar exterior wall mounted package unit and we utilize the MC4000 to marry up all the BARD units to operate on a single thermostat or usually a remote sensor or two. Being remote and sometimes used as storage for slurry and other drilling liquids, the communication card is used to send out temperature alarms. Many of these remote sites are no longer manned, and simply an oil pump or natural gas well head is operating away and if they loose cooling or heating in a control room it can become catastrophic, thus remote alarm and communication is essential.

    Great device, never thought about utilizing it for something other than multiple module units. This thread has got me thinking that this would make a great replacement for the hard to find and nearly obsolete H/W W7100 discharge air controller.

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