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Thread: DDC Stories

  1. #1
    Join Date
    Jan 2007
    Location
    U.S.A.
    Posts
    209

    Post DDC Stories

    Just found this web-site last month, it's full of great information. I'm sure there are lots of good tales about controls here, too, that most normal people would never understand. Let me share one:

    I had a small project a few years ago at a rural hospital where we tied in our DDC controller to the T-stat interface on a high-end AAON RTU with a VFD. We directly control the VFD via duct pressure.

    Anyway, the redneck maintenance guy said he did not trust my controls, so he was going to install a traditional thermostat and several toggle switches so when my controls die, he could just flip some switches and be good as new. He also decided to install a potentiometer on the VFD so he could manually adjust it, too.

    Well, while pulling his thermostat cable, he brushed his metal fish-tape across the open, energized VFD and sent sparks everywhere. His new VFD was now burnt toast and he had to order a new one for about a thousand bucks.

    Five years later, my controller is still going strong, without ever having a hiccup

  2. #2
    Join Date
    Jan 2002
    Location
    Fort Worth\Dallas, Texas
    Posts
    1,706
    Welcome to the forum Time Until Next Change Of State.

    I see you have have some Honeywell Xl500 background as well as Tridium.

    Just curious, on your new jobs are you going completly Tridium, or are you still installing SymmetrE systems as well?

  3. #3
    Join Date
    Jan 2007
    Location
    U.S.A.
    Posts
    209
    Thanks for the welcome. I first got heavily involved with DDC when the XL5000 was first released in the early 90's. Even though I came from a heavy electronics background, I was amazed at all the acronyms involved in DDC, such as tuncos, utml, etc.

    Our high end jobs are pretty much all Tridium now. We have quite a few installed SymmetrE sites out there that are constantly expanding and upgrading, so I'm going to have to stay involved with that for quite awhile.

    I like SymmetrE, but I have way more JACE projects and feel more comfortable with them, especially since AX came out. Then there's the XL15B, it's OK for small sites that don't expect much. I'm sure looking forward to it being updated to Tridium.

    Are you more of a SymmetrE or WEBs guy?

  4. #4
    Join Date
    Jan 2002
    Location
    Fort Worth\Dallas, Texas
    Posts
    1,706
    I have just done my first AX job. I have many SymmetrE sites that I will continue to maintain, but I have no desire to ever do another new job with SymmetrE.

    AX is so much better than SymmetrE.

  5. #5
    Join Date
    Feb 2007
    Location
    Sacramento, CA
    Posts
    67

    Confused Idiot Not Savant

    Ok, want another story? I was involved in putting in a controls system (Siemens System 600) for a new chiller in a large southern California town. It was for the city there and the city employee who was in charge wanted to have chilled water storage. So after running his calculations on what he needed he had a service station gasoline storage tank cleaned, sealed & installed. The sequence he insisted on resulted in chiller starting and stopping every 20 minutes. The tank was a thermal capacitor. During the summer it would run out of cold water in 20 minutes, the chiller would start and cool down tank water in another 20 minutes and then the chiller would shut off and the tank would run out of chilled water again. Then of course repeat the cycle. When confronted about the sequence problem he insisted it was my problem. Oh yes, the city employee who had designed all of this (and there are additional horrors I'm not including here) was originally a welder who worked his way up into management.

  6. #6
    Join Date
    Jun 2006
    Location
    Des Moines
    Posts
    286
    I was called in a cold weekend to a State building that had an AHU that wasn't running.
    As soon as I entered the mechanical room, I could detect the scent of a burnt board. I checked the DDC board and sure as shootin', alot of traces were just smoked, caps with the top blown off and busted diodes. I started testing and found 120 vac coming in on a wire that we (the DDC panel) was sending out 30 vdc (it was a DI).

    Found, at the low temp, that the starter safety circuit wires (120v) were ties to the DDC wires, bypassing the LTD. I carefully questioned the building engineer and he admitted that he thought the LTD was bad (he was correct) and had attempted to bypass it.
    Keeping it as simple as I could, I said-
    "Dude, never, ever, ever hook big wires to little wires." LOLOLOLOL.
    Dingman from Iowa~
    "A lie gets halfway around the world before the truth has a chance to get its pants on."
    - Sir Winston Churchill (1874-1965)

    The Dingman's webpage, featuring the Ding_Z

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