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  1. #1

    Cold Weather = Bad Day's

    First I'm glad to have found a group of guys and gals that enjoy controls as much as I do. I hope to be helpful in the future. Very brief background. I worked with ALC for 2 different contractors for a total of 12 years with the product. Last year I made a move and am working with the Talon line of controls.

    In the recent cold weather we have had several jobs that have frozen up coils. Not to anyones surprise every one of them have been on jobs that we are integrating the RTU's. I really think the owners are getting the raw end of the integration deal, at least in my cases. Here's why. In my experience the equipment suppliers tend to supply, but not want to control or deal with the controls. They have overworked techs that have to learn many different equipment types and different control systems. It takes YEARS to get good at one system, let alone 3 or 4. As you guys know we are limited on what we can do though whatever interface we are provided from the equipment manufacture. I'm getting tired of telling the customers that I monitor but don't control, and ill try to set up an alarm to warn them before it happens again.

    What if anything do you guys do? Maybe it is as simple as having good equipment reps. Now I need to go to a meeting in the morning for another frozen coil..... just getting sick of being dragged thought the mud for other contractors not doing their job.

    CD

  2. #2
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    Aug 2009
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    Who is the manufacturer of these rooftops? What mode are they [likely] in when they are freezing the coils?

  3. #3
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    i assume you are just integrating these controls and dont have much to do with the actual installation.

    if i am doing the installation, i usually make sure safetys are hardwired to the equipment.
    a freeze stat for instance should be hardwired and interlocked with the fan.
    i don't feel we should count on the programming and controllers to do safety.
    i use aux contacts into my controllers for alarming and possibly some other processes like driving the coil to full heat on freeze stat trip.

    i want the safetys to operate independently of the ddc. i'm a coward that way.

    if your not doing the install then there is not much you can do.

    now trying to explain that to a po'd owner is a totally different story.
    you dont want to slam the contractor because they are most likely the ones who are paying you, but you want to be fair to the building owner. its a tough road. just make sure you followed the spec and can't be blamed.
    unfortunatley this has become a CYA buisness as much as it is technical buisness.
    IV IV IX

    use your head for something other than a hat rack.......Gerry

  4. #4
    Join Date
    Jan 2007
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    In the last two years, I have had to integrate more factory LON enabled RTUs than in the past 15 years. The worst thing is, the factory start-up guys seem to know very little about how their factory supplied control systems work. They are quick to point you to the on-line manuals you probably already found, but the manuals seem to be lacking usually. Most of them have been McQuay, AAON, Carrier and Trane RTUs.

    On one Carrier job in particular, I talked to three different Carrier techs at three different times after having many integration problems. I got three totally different explanations on how to tie in and control their RTU to meet the engineers sequence, and even then, the engineer was not very happy with the end result. The owner is not impressed either.

    I have come to the conclusion that factory mounted controls suck for the integrator as well as the building owner.

  5. #5
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    Go after your reps, I'd even give the customers the reps name and number. Somebody overlooked something here and the building owners shouldn't have to pay.

    I agree with viceman on having other safeties in place as well.

    Tuncos - I've had a few of the same experiences, one of the best was a Carrier rep telling me they met the LON spec on the RTU profile when I had to use a SNVT switch for occupancy.
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
    BIG Government = More Dependents
    "Any 'standard' would be great if it didn't get bastardised by corporate self interest." MatrixTransform
    http://threedevilskennel.com/ - not my website.
    Versatile Hunting Dog Federation - www.vhdf.org/


  6. #6
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    I'm blown away by this. I used to write firmware for an RTU manufacturer. There were two things that we would optimize for in every product- Self-Preservation of the unit and Efficiency. In that order, mind you.

    If the manufacturer's own controls allow their equipment to be damaged then there is zero reason to ever use their controls.

    You need to name the manufacturer because they need to be shamed for this screw up.

    Seriously.

    If the coils can be allowed to freeze while under the control of the factory hardware then this entire thread should be dedicated to calling the manufacturer on the floor for failing it's #1 requirement, cause no harm to the unit.

    So who made this suicidal piece of garbage? And is the building owner going to sue them for a free on site patch job?

  7. #7
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    Quote Originally Posted by crab master View Post
    I've had a few of the same experiences, one of the best was a Carrier rep telling me they met the LON spec on the RTU profile when I had to use a SNVT switch for occupancy.
    Yep, had that same discussion after not being able to get the proper enum occ point to do anything.

    Another fun item I've had is a RTU where we were supposed to control the LON DAT SP based on VAV terminal load. They said the only way to get a direct SP signal to perform that function was for Carrier to add a card to accept a 0-10 vdc signal.

  8. #8
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    I Always recommend a Hard Wired Low Limit (Freeze Stat) installed in any unit with a water coil even if it has Glycol.

    I do a lot of programming and I don't trust myself to always get the low Temp shutdown function correct in software. As said i other posts, cover your hiney, install a "Freeze Stat" as a safety. Your customers will thank you and the Equipment guys should too unless they charge the customer to fix/replace frozen/busted coils on brand new units.

    Safeties are just that SAFETIES ! Would you do Steam Boiler Safety Shut down's in Software ??....I would guess not. Then why do the OEM's try to do it with Package units. Seems negligent to me.

    My 2 cents.
    If sense were so common everyone would have it !

    All opinions expressed are my own. Any advice provided is based on personal experience, generally accepted fact or publicly available information. As such, it is worth exactly what you paid for it, not a penny more not a penny less !!

  9. #9
    Join Date
    Mar 2008
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    Sounds like you are having problems working with a system you are not the rep for. This is a huge problem in our business and until there is truly an open protocol that cannot be made proprietary, this will always be a problem.

    We always hardwire shutdown and alarm through the ddc panel.

  10. #10
    Thanks for all the replies guys. After a 14 hour day here is the results of what i know now.

    Trane Intellapack with roughly 20 hot water vav boxes. The Trane unit has been a problem from day one on this project. This morning when i got there I have record of the unit running 100% fan speed at 100% heat with the OA dampers 100% open and a discharge temperature of about 20 degrees.

    Trane service showed up and reset the modulating gas heater and skated right out of there. Then the mechanical said there is not much we can do SEE YA!

    Me and a Co worker spent a lot of time watching the unit. Here is what we came up with and had to call Trane and the Mechanical back to the site. The unit would go into hvacMrngWarmup. When i came out of warm up and went to hvacCool the OA damper would go to 100% and never shut no matter how cold the supply temp got. Minimum OA position was set for 6%. The OA flow meter (internal to the unit) froze up (its -15 degrees here) so it was reading 0 OA CFM. Apparently, according to the Trane rep the unit should shut down the OA damper and go to 100% return when the supply temp drops below 50 degrees. When physically opening up the unit to look at the OA damper it was still open maybe an inch when the unit was off..... NEVER could have been mechanically checked.

    I agree with the Freezestat ideas you all have 100%. The only thing I will argue briefly is a freezestat in a RTU at these temperatures will trip when the unit is off for unoccupied or whatever and you will never get it restarted without bypassing the freezestat. The unit needs to start the fan not stop it in these situations to circulate warm air, but should still shutdown when discharge continues to fall. The safety we have in place on this project is the discharge temperature on every VAV box is fed back to a less than and overrides the unit to hvacOff (at Tranes request as of today)

    From my understanding per the Trane guy there is not a freezestat hardwired shutdown contact on the unit, nor a software point to write too other than the hvacOff . Sorry enough ranting for one night..... ill see what tomorrow brings.

    Sorry the graphic is goofed up.... i corrected it after the capture...... there is not an extra return bypass duct...... need to talk to my tech about that.

    Last note: building flooded 1" of water on floor 2 and wrecked a bunch of tile, carpet, computers, drywall ect.... this is going to be a bad deal..... i can feel myself being blamed already, even though i was the only one there all day....
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  11. #11
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    Quote Originally Posted by Control Doctor View Post
    Thanks for all the replies guys. After a 14 hour day here is the results of what i know now.)
    First off, welcome to the wonderful world of Systems Integration and working with other people's messes. From hardware to software.

    Fun isn't it? BTDT, many a time.

    Sometimes it gets old to tell one's customer, "Yeah, I agree, its not right. But it is what it is. I didn't design it or install it. You bought it and okayed it."

    Or words to the same effect. Happens all the time. Someone installed and commissioned something improperly. Or what was bought and installed does not perform to the customer's expectations. A combination of the two. Etc.

    <Shrug> Business as normal. I just make sure that prior to finger pointing I make DAMN sure I'm right, can prove it beyond any shadow of doubt, and offer suggestions for a fix.

    When doing systems integration, or any controls work, customers typically look at you as the top of the food chain. That is, you're the one who last touched the "system", and supposedly are the one who actually understands how everything works (may or may not be true but it's their perception more times than not, after all if yah don't understand the stuff how are you supposedly integrating it?), etc. You're typically the last of the trades still on site, and everyone else has declared their stuff working properly, so .... you're the first suspect in any failure events. And the customer is all too familiar with the old finger pointing game where this contractor claims it is someone else's problem. And pretty tired of it.

    I consider all this as just part of normal business in my world. Expected. Nothing to get upset about.

    I just make sure I'm darn good at troubleshooting, carry everything I need to do that, have all the docs I need (I typically have complete sets of the plans and specs on my hard drive, as well as PDFs or whatever of the manuals and cut sheets for most everything I have to deal with whether its something we installed or someone else.) Then I investigate the problem thoroughly, show the customer my proof and evidence of anything I assert. Or, if I don't know, say that explicitly. I have resorted to telling a customer that I don't KNOW ... but this is how we might find out for sure. i.e. Recommended bringing in an independent balancer, or whatever.

    Anyway, as concerns your RTU problems.

    I've seen this sort of issue before with RTUs bought with their own installed control systems (and other types of equipment). Went through the usual, of telling the factory that their control scheme was faulty, and their insistence that (1) either their system had no faults, and/or (2) its running properly IAW what was spec'd and ordered so tough nuts ... yah got what yah asked for. It'll cost yah extra to fix it.

    End fix was sometimes done by the factory or their reps IF the customer started playing hard ball about it, and had the leverage to do so.

    Other times we ended up providing the fix. I've had cases where customer got so upset with lack of adequate response from a manufacturer that they've had us essentially rip the controls out completely and start again using our own stuff and custom programs. Other times we've made intermediate fixes. i.e. Installed some additional hardware/safeties/overrides. Or added external program controls that's override the normal program under certain conditions. Etc.

    Obviously on shutdown that OAD should close completely.

    It would seem that the control program is looking for some minimum OA flow in CFM? Regardless of DAT? Probably should be corrected.

    Personally, I'd install a hardware type Freezestat, and any relays needed and have it close OADs on freeze, open RADs, and open the heating valve (if there is one).

    We do that as a matter of routine. All hardware. Just in case of control program fault or controller failure, or program aborts, or whatever. Within the program we'd make, we typically modulate heating for DAT when the unit is running, but when unit is off we switch to a temp sensor located somewhere inside the box near any coil(s) and have it maintain 50'F or so in that area.

    For gas units, we typically wire a time delay to bypass the freeze lockout on startup for 5 minutes or so.

    <Shrug> Mainly I wanted to say, get used to it. This sort of thing happens routinely in our world.
    Last edited by osiyo; 01-05-2010 at 12:31 PM.
    A site where I stash some stuff that might be interesting to some folks.
    http://cid-0554c074ec47c396.office.l...e.aspx/.Public

  12. #12
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    Put the freeze stat in the supply duct inside the building downstream a ways in order to prevent nuisance trips. Not only that but -15 deg why don't they have some glycol in this loop?
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
    BIG Government = More Dependents
    "Any 'standard' would be great if it didn't get bastardised by corporate self interest." MatrixTransform
    http://threedevilskennel.com/ - not my website.
    Versatile Hunting Dog Federation - www.vhdf.org/


  13. #13
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    Are you controlling the Train through a gbas board?

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