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  1. #1
    Join Date
    Aug 2007
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    Georgia
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    1

    Lead Lag Controller

    Just as general discussion, I wanted to find out if lead lag controllers are use any longer in the HVAC industry and if so, on which applications have you used it on. Mainly commercial, server rooms redundancy, etc. Any thoughts?

  2. #2
    Join Date
    Jul 2011
    Location
    East coast USA
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    925
    Quote Originally Posted by wxsosa View Post
    Just as general discussion, I wanted to find out if lead lag controllers are use any longer in the HVAC industry and if so, on which applications have you used it on. Mainly commercial, server rooms redundancy, etc. Any thoughts?
    just installed one last week in a server that has two 8 ton Liebert splits. and will get it on line in the next few days. I'll let you know how it goes..

  3. #3
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
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    7,278
    Quote Originally Posted by wxsosa View Post
    Just as general discussion, I wanted to find out if lead lag controllers are use any longer in the HVAC industry and if so, on which applications have you used it on. Mainly commercial, server rooms redundancy, etc. Any thoughts?
    Of course Lead/Lag is used widely on Pumps, redundant systems, etc.

    Could you further define what it is that you are seeking?

  4. #4
    Join Date
    Oct 2005
    Posts
    318
    If you are looking for a stand-alone controller, I would still use your favorite DDC controller and program the lead-lag, even if the controller never becomes part of a network. If I were a controller manufacturer, I'd sell controllers with a pre-installed lead-lag program for stand-alone use.

  5. #5
    Join Date
    Nov 2007
    Posts
    90
    I agree with tlp261, a small ddc controller is the best way to go. To answer your question, there is the Bard MC3000 Series Master Controller. We have a customer with data sites that uses this controller when their budget does not allow for ddc. The sites are 2 RTU redundant set up. The installer or start-up guy handles the Bard install and setup, so I have not had any experience with them, but I don’t hear any complaints around the office.

  6. #6
    Join Date
    Oct 2003
    Location
    Minnesota
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    1,337
    Quote Originally Posted by wxsosa View Post
    Just as general discussion, I wanted to find out if lead lag controllers are use any longer in the HVAC industry and if so, on which applications have you used it on. Mainly commercial, server rooms redundancy, etc. Any thoughts?
    I, myself, have not spec'd and installed a lead-lag controller ... other than a general purpose programmable DDC controller ... in some years (10-12). But I do see them called for and installed by others on a regular basis, to this day.

    I see them on pumps, boilers, CRU's, wall hangers (such as Bard's), and so forth. Ranging from simple functions to more complex.

    Why?

    <Shrug> I'm not in the mind reading business. Tho, in some instances I do have a clue. i.e. This past summer ran across one, newly installed. Customer (building owner) was having a HVAC system upgrade done. Had a hired engineer from an Architectural firm do the design, spec writing, etc. Among other things the building boilers were being replaced with new high efficiency jobs. In the specs, lead-lag control of boilers was mentioned both in the mechanical section and in the DDC controls section. Left hand wasn't talking to the right, Mech contractor was another company and we were doing controls. End result, new boilers got installed with a standalone lead-lag controller included over on the wall. Mech contractor insisted item was in their section of the spec, so they'd bought it and installed it, and thus wanted to darn well get paid for it. (Poorly written spec book BTW)

    We'd also planned for lead-lag. Had a controller, program loaded, wiring layout etc also done. Wasn't until our installers went down to the boiler room to start doing their thing that they discovered and we found out about that other device.

    In the end, customer just said leave it. Until job was done and everyone paid. Then we were to come back and rip the sucker out and put in our stuff. Which was actually what customer wanted. Since that's how it is in customer's other buildings.

    In other cases, use of such controllers was quite intentional. i.e. Another recent job. Building has numerous server rooms (5), each having twin CRU's. Customer IT department insisted units be standalone and solely under their control. No networking or putting things out there where anyone else might be able to change anything. Okay ... if that's what they want, fine. Mech contractor made it happen. Each server room having twin CRU's and its own, standalone lead-lag controller. Customer's Facility Maintenance Department had fought this. Wanted monitoring and control on their standard DDC control network. But lost that battle. They did however amend the spec's to include provisions for us to install sensors and monitors to independently watch what the heck was going on. i.e. Our stuff monitors space temps, discharge temps, proof of air flow, fan status, etc. With suitable alarming, provisions for emailing/texting alarms, keeping trends and histories, etc. Probably a good thing as just recently I was over there on other business when Facility Maintenance folks noticed disturbing trend data showing up and went to investigate. Found a problem and corrected it before standalone lead lag unit ever sounded an alarm.

    In yet other cases I see things like another customer does. Their building has a lot of DDC controls. But not everything is on the system yet. BIG building. A lot of stuff. In house maintenance folks, little by little, as budget money can be spared add stuff of their own. Just go buy whatever, stick it in themselves. One of those Bean Counter things. Building Maint Engineer wants two pumps running solely on manual control to get DDC controls. The Powers-That-Be in upper management say "No, not right now, that's a capital investment. Submit paperwork, if approved you'll get it in due time. Maybe in 3 to 5 years. After we do the cost-benefit analysis, hire consultant to do design study, ... yadda-yadda-yadda." As with the way such things work in large organizations, not much Building Maint Engineer can do to speed up or prioritize the "due process". However, he DOES have control over his own department's operational money. His daily/monthly/yearly standard budget for buying tools, grease, oil, rags, and other consumables and ordinary expenses. So he scrimps here, saves a little there, etc. Comes up with a bit of extra. Goes and buys a simple lead lag controller. Hands it to his own in-house electrician, tells him to put it in. It gets done. Just a simple time based control sometimes, other times a unit that accepts inputs to detect failure or low pressure. Sometimes he even sticks in a simple pressure switch, runs two conductor cable from it to spare input on one of our controllers (we always make sure he has spares available). And since he knows how (we taught him) he sets up and alarms point, with suitable trigger delay, and puts it on his front end.

    He does this with all sorts of stuff. His way of getting around the 'system', the procedures set up by the Bean Counters.

    Then, if and when later they approved and actually act upon his original request for full DDC control. We put it in and hand him his lead-lag controller and/or whatever. Which he'll probably use elsewhere.

    Been going on for years.

    It's an accounting thing. If the total cost, as it'd show up on the books, is below a certain limit, he has to explain to no-one, and accounting just rubber stamps it without blinking or even really looking at it. Normal daily operating expenses. Cost of manpower to actually install, etc hidden in daily work log of the electrician. But if he has to get a "contract" and bid, accounting is all over that especially if its something new and not previously existing (i.e. its not just a repair/replacement of existing stuff).

    <Shrug> Sometimes we help him along. Regularly, in fact. All new installs we do for him we ensure extra unused points (I/O) are included. We also usually manage to sneak in a little extra on the bid amount so that if, for instance, we're installing new controls on that new heat/exchanger and pair of pumps he just got and he just happens to have a couple extra things he wants done at the same time ... it gets included without showing up on the official paperwork that the accountants and upper management will see.

    But ordinarily, I'd never even think of bothering with a specialized, single purpose lead lag controller. I'd simply grab a small general purpose programmable, stick in one of our standard (its on file), tried and true, lead lag programs. Done. Except the wiring which has to be done in either case. Controller can operate standalone. Or can be networked into rest of control network if wanted/desired. Piece of cake. Cost wouldn't be much different. In some cases even cheaper. Some of the more capable and complete, made for the purpose, leag lag controllers can get a little pricey. A lot of components, custom firmware on a chip, etc. Can be cheaper for me to just use a general purpose programmable which already has all the IO needed, and stick in a program. And if later customer wants to change sequence of operation, its just a program change in most cases. Easily and quickly done.
    A site where I stash some stuff that might be interesting to some folks.
    http://cid-0554c074ec47c396.office.l...e.aspx/.Public

  7. #7
    Join Date
    Jan 2010
    Location
    Whitehorse, yukon
    Posts
    15
    tekmar makes a simple but great lead lag controller to use on boilers and system pumps.

  8. #8
    Join Date
    Apr 2005
    Location
    Boulder,CO.
    Posts
    547
    It's been a long time since I used one but do you mean an Alternating Relay?

  9. #9
    Join Date
    Mar 2007
    Posts
    20

    Confused lead lag controller w/ autochangeover

    I have checked out several lead/lag controllers availible, but I am looking for one that is similar to the liebert ac4, but more geared to being installed with any brand and cost less than the liebert controller. It does need to have auto change over in case of an alarm.

    Thanks

  10. #10
    Join Date
    Aug 2009
    Posts
    2,459
    Quote Originally Posted by flippurr View Post
    I have checked out several lead/lag controllers availible, but I am looking for one that is similar to the liebert ac4, but more geared to being installed with any brand and cost less than the liebert controller. It does need to have auto change over in case of an alarm.

    Thanks
    I don't know your costs for such a unit (and prices can't be posted in this forum anyway).

    But I looked at the Liebert AC4 on the web just now and if anything it seemed more expensive than generic "freely-programmable" controllers you seem to be seeking.

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