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Don't do this.... (ME)

Tom R.
Tom R. Member Posts: 139
Powers and Honeywell used to have a low temp. cutout/alarm (DPDT) that had a huge long bulb to string criss-cross across the face of the HX. (Freezstat) The claim was that if any two feet of the bulb went below the setpoint, the switch would trip. We used them successfully on hot water coils in 100% OA units with variable flow. But why not just use an aquastat in the idle boilers energized by OAT below freezing(or the above mentioned device)?


  • Frozen Broken heat exchangers


    I was recently invited to bid on a pair of frozen/broken copper fin tube heat exchangers on some rather large (5,000,000) btuH boilers.

    The mechanical room serves a large apartment complex. It is on the top (6) floor of a parking garage. There were 4 of these 5 mil fire breathing dragons, piped primary/secondary. The building engineer kept trying to say that it was the Tekmar multi stage boiler control that caused the boilers to freeze and break. I contend that it was the DESIGN that caused the problem, and I backed it up with simple calculations.

    Essentially, even at design conditions, only 2 of the fire breathing dragons were necessary to maintain proper supply temepratures to the building. Consequently, when design conditions raised their ugly head, two of the 4 boilers were not moving any water through their heat exchangers, and they froze and broke due to cold air spilling down the flue gas breach.

    The mechancial room is not heated, other than standby heat from the appliances within, and I'm not so sure that even with the space heated, the exchangers would not have frozen and broken. The size of the room is minimal in comparison to the equipt installed, and consequently, there are HUGE holes everywhere for combustion air requirements, none of which are dampered. Again. I don't think dampering would have kept the cold air from spilling down the vents and freezing the HXers.

    In any case, the damage is done and I've been commissioned to straighten it out. My crews are going to get some serious lessons in the use of ropes, cables, come alongs and aerial materials handling. Each heat exchanger weighs in at 1,000 pounds each. I will take some pictures during the extraction/replacement process.

    But the problem/potential for a frozen broken heat exchanger still exists. So I contacted the maker of the boiler and ask them if they have a freeze protection kit for their boilers, "No, why would you want to do that?"


    So, being the father of invention, I came up with my own using tekmar 2 stage set point controllers. THe sensor will be located in the inside of the heat exchanger using a long immersion well. If the fluid temperatures drop below 40 degrees F, stage one turns on the boilers circulator and sends some heated water into the heat exchanger. If the heat exchanger falls to 35 degrees F, an audible/visual alarm activates via stage 2 to notify maintenance/security that there is a REAL potential of having to spend another $20K on frozen/broken heat exchangers...

    I have about three jobs where I did DHW ectomies and isolated the boilers using P/S piping methods exactly like this, and I'm going to make the required changes to provide proper freeze protection. In most cases, where the physical plant is properly sized, and not grossly oversized as it was in this case, it probably wouldn't even be an issue, unless there was a mechanical failure (relay, pump, flow switch etc).

    So, to avoid being fiddle faddled by the fickle finger of fate, cover your butt with electronic freeze protection.

    The heat exchanger you save may be your own...

    Don't do it without proper protection.

    Live, learn, share and teach.

  • lchmb
    lchmb Member Posts: 2,997
    and that

    And that just goes to show why having a professional do the job is the best place to start. Sound's like you have all aspect's covered!! Can't wait to see the pic's of those beasts..
  • Keith_8
    Keith_8 Member Posts: 399
    lesson learned

    Thanks for sharing. We installed a couple of Camus boilers coupled with 650 gallon storage tanks for domestic hot water. They have direct vent,sealed combustion. If the boiler failed what would keep it from experiencing the same senerio?

    Mark, In your case. Wouldn't a motorized damper on the breaching and combustion louvers stop the cold drafts? Are the combustion louvers sized for all of the burners firing at once? Probably not they would be huge.

    Seems like a shame to burn fuel to keep the exchangers from popping.


    Have you had any experience with tempered, ducted combustion air sealed directly to the burner? Seems like a more cost effective way to supply air.

  • Constantin
    Constantin Member Posts: 3,796
    Let me ask a dense question...

    ... given that the units installed are 100% oversized even under design load conditions, wouldn't it make more sense to extract 2 units and use the scrap for beer money? :-)

    But seriously, these guys need 100% redundancy for their heating needs? Sounds like a great opportunity for a small fleet of modulating boilers to cover the lower end of the spectrum, i.e. everything below 5MMBTU...
  • Guy_6
    Guy_6 Member Posts: 450

    I find it interesting that some European control manufacturers build in freeze protection. The sensors are already in place, as is the logic board-just a few lines of code and the boiler is protected.
  • Brad White_36
    Brad White_36 Member Posts: 30
    Maybe another dumb-a question

    Are there at least vent dampers? Not that it would help in such a small room but to minimize the reverse heat exchanger effect.

    Also with your P/S, it seems to be piped in series such that the earlier firing boilers will heat the return water to the downstream boilers. May not be a big deal, just curious. The alternative being to pipe all boilers to a sub-header and enter the secondary via a single pair of closelyspacedtees.

    My concern (if you can call it that) is short-cycling second-stage boilers because of pre-warming them. Certainly if condensing you want the same cold water into each.

    Constantin's point questioning redundancy need as well as opportunity for mod-cons (sealed combustion!) have much merit.

    I hope this Owner appreciates what you are doing from him. As always, thanks for sharing.
  • jwade55_3
    jwade55_3 Member Posts: 166
    Just had this feature save a job.

    Was doing a walk thru, going over the controls, boiler operation, etc. on a project with 4 Munchkins serving a church. While the installing contractor, architect, and engineer and I are standing in the boiler room, with no heat demand present, two of the boilers pumps start, then the burners light. Everyone looks at me like I have six heads. Little bit of investigation later, I notice the water temp in the other boilers are dropping, It was the freeze protection brining the boilers on. Now the question WHY?

    Turns out the boiler room was under a VERY strong negative pressure, drawing 18deg air into the boiler thru the exhaust, (the intakes were not connected to the boilers yet). This could have been a disaster, as the boilers were not going to be actually fired until the next day, the old scorched air system was still heating the church, nice feature.

  • Beer money...

    Con, I guarantee you that our beer fund will be full in short order. 2,000 lbs of scrap copper...

    As for redundancy, this is a high class complex, and the owner must have told the mech eng that he wanted extreme redundancy, or would that be redundant redundancy... In any case, they've got it.

    The area manager asked my if they needed to replace the two heat exchangers, and my initial reaction was, "No, but...If you were driving around out in the country with one head light out, and the other head light went out..." to which he replied, "Fix'em both..."

  • Motorized dampers on breaching...

    Keith, as I stated, that would be a great idea IF someone made them that big. In order to apply that type of device to an appliance of this category (CSD1) it would need ALL kinds of approvals first. The side of the damper would look like alphabet soup. Ul, CSA, AGA GAMA, IAPMO, UPC, and who knows who...

  • Brad White_36
    Brad White_36 Member Posts: 30
    Excellent reminder of cause and effect, J.

    Another reason to never exhaust a boiler room but to keep them under positive pressure to control that sort of thing.

    Good catch; imagine if they were vented but not yet powered?...

    Sounds like a nice job, that church.
  • No, no vent dampers...

    I proposed doing just that and interlocking them into the individual boilers. At a cost of $5,000 each installed, and 5 of them required (DHW too), he said it was out of the question.

    C/A was done via leaving random cinder blocks out of the cinder block walls low, and the whole soffit is a screened vent for high air, so dampering existing is out of the question. I was proposing to block off all existing air and cut dampers through the wall to serve each individual appliance. No go...

    As for pipng methodology, you are correct, this is a series parallel arrangement. In as much as the appliances are 82%ers, I don't think it makes that much difference to thermal performance. You and I think alike. If it were mod con, there'd be one set of take offs for the secondary input side to assure lowest EWT to the applainces. This is not my design :-)

    Given the time of design/install, it was typical.

    As for base laoding with modcons, there is no more room at the inn... Maybe next time. When this system was conceived and installed (10 years ago) there weren't any decently sized modcons on the market. Missed opportunity.

    The boilers are 2 stage, 2:1. When tehy are running on low burn, their combustion numbers suck due to all the excess air being drawn through the combustion process. On paper and in theory, it looks good and makes sense. In reality, it sucks. If I were the king of all things hydronic, these boilers would not exist unless they were handling LARGE single loads, like snowmelt or DHW, and you could be assured that they would only fire at full rate, and not short cycle. Maybe in my next life...

  • Constantin
    Constantin Member Posts: 3,796
    I agree...

    ... were I a contractor facing this sort of system, I'd use combined pri-sec to ensure that all condensing boilers get to condense, see the same water temps, etc. The right Tekmar control would then allow staging/cycling, etc. to ensure that all of them log the same number of cycles, burntime, etc.

    [EDIT] I can't help but think that ripping out two units and replacing them with four Vertomats or whatever would provide the same redundancy as the current setup. Like you said, Mark, if only we could have our way more often...
  • jwade55_3
    jwade55_3 Member Posts: 166

    Thanks Brad,

    Turns out that the church steeple, is directly above the boiler room location, during the remodel some walls were removed, causing the steeple to act as a chimney, nice warm boiler room, COLD steeple, you get the idea. We were lucky that the engineer is inquisitive, he wanted to see the workings of the boilers, but couldn't be there the following day.

    The project was very fun, an old church, hall, and school that had been at one time steam, someone removed it sometime in the 80's, went completly scorched air? New pastor, generous donation from a member, and now they will be heated by steel panelel rads,and some baseboard :( (Access issues) We were able to use some of the existing/partialy removed steam piping as chases. The engineer orginally wanted to just replace the furnaces with Fan coils, fortunately the pastor wanted Hw heat. The contractor is like a proud papa, I'll post some pics in the future.

  • Yeah but...

    and theres a butt in every crowd...

    On a recent snowmelt system we installed the M399's in, I was standing next to a remote, firing 399, with no call for heat. Same scenario, cold air dumping freely into the vestibule due to the leaky jacket. Boiler fired to protect the appliance. Only problem was, the slab distribution pump was connected in parallel to the boiler primary pump, so it started sending energy out to the dry, but extremely large and cold snowmelt system. The boiler ran for 2 hours before it shut down. At $1.50 per therm, I figure it wastes about $6.00 per hour. So, it wasted $12.00 for what??...

    The system was filled with glycol, so it was not necessary to have internal freeze protection. HTP needs to release the code that provides freeze protection so that it can be over ridden by competent Vision contractors. If they do not, they are going to lose a lot of business to their johnny come recently competitor that DOES allow the installing contractor access to this access code in their identical controller.

    Wake up and smell the coffee boys. The competition is knocking on the door HARD...

  • Mad Dog_2
    Mad Dog_2 Member Posts: 4,813
    THey are VERY lucky you were the next contractor they called

    or I'm CERTAIN history would have repeated it UGLY self. Good call ME. I was apprentice to a salty ol' Navy man who taught me several nice rigging knots that I use today...clove hitch, barrell hitch, bowline on the bight. Mad Dog

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • jwade55_3
    jwade55_3 Member Posts: 166

    I agree completly! I'd like to be able to select circulation operation, for a set amount of time, or circulator then burner.

  • ttekushan_2
    ttekushan_2 Member Posts: 57
    last ditch freeze protection

    Have any of you encountered these Sarco "Freezeton" temp operated drain valves? My local dealer tells me he usually sells them to protect steam coils that are used to heat incoming air. In this case they are often installed in conjuction with a vacuum breaker so that all the water can drain.

    Apparently they are suitable for all kinds of freeze protection uses. This would be one of those "last-ditch-break-glass-in-case-of-emergency" sort of deals.

    Just a thought.

  • Adam_18
    Adam_18 Member Posts: 1

    Mark , do they have any hydronic unit heaters in the mechanical room ? , how about eskimo traps around the openings for combustion air ?. Here in Edmonton the winters can be brutally cold , the standard practise here is to put a couple of hydronic unit heaters in a mechanical room and eskimo traps on in the intakes for combustion air . Dont laugh that is what there called , the combustion air is piped from an opening near the ceiling to about 18 inches above the ground and then a metal piece shaped a C is fastened around the combustion air and to the floor . The space between the combustion air duct and the C [sorry best way I can explain it] must have the proper free area required for the appliance and the C extends up about 36 inches above the ground .In effect you create a cold trap that keeps the colder air from flooding a room but allows adequate combustion air in when required .
  • S Ebels
    S Ebels Member Posts: 2,322
    I gotta ask

    Maybe this is like the little boy in the fairy tale pointing out that the emperor has no new clothes on but........... Why was there no antifreeze in the system?

    Another possibility might be to install an immersion type electric element in the header or hx itself, depending on configuration, which would be energized by a water temp sensor.
  • Maine Doug_28
    Maine Doug_28 Member Posts: 10
    Since the

    mechanical room is on the top, have you looked into using a helicopter to take out the scrap? A couple of thousand pounds in one lift, carried to your waiting trailer. Then with the roof open, they can install correctly dampered combustion inlets.
  • Dick_3
    Dick_3 Member Posts: 60
  • adayton_2
    adayton_2 Member Posts: 130
    Eskimo trap pictures

    yes please Adam. :-)..Sounds like a great creative solution. Only then you got to put a BIG RED "DANGER" sign on it Warning service persons and passerbys to keep a u hands OFF....lol.

    As for the original thread of frozen xchangers, Mark, How about something in the control strategy that would fire two sets of the monsters in a continuously rotating schedule, lets say 30 or so minutes each fire. This would tend to keep each set "warm" AND would excersize each set in a rotating redundancy excersizing pattern. Reliablility wise, should any one SET "fail" the other set would still provide full service while the alarum bells would send appropriate alerts to service persons for repairs...

  • S Ebels
    S Ebels Member Posts: 2,322
    I've done the same thing

    We set a 55 gallon barrel in the mech room of a small commercial job and ran the 12" round combustion air duct down inside of it. The twelve inch was suspended about 15" from the bottom of the barrel and the top of the barrel was off of course.
  • rich pickering
    rich pickering Member Posts: 277

    > We set a 55 gallon barrel in the mech room of a

    > small commercial job and ran the 12" round

    > combustion air duct down inside of it. The twelve

    > inch was suspended about 15" from the bottom of

    > the barrel and the top of the barrel was off of

    > course.

  • rich pickering
    rich pickering Member Posts: 277

    > We set a 55 gallon barrel in the mech room of a

    > small commercial job and ran the 12" round

    > combustion air duct down inside of it. The twelve

    > inch was suspended about 15" from the bottom of

    > the barrel and the top of the barrel was off of

    > course.

  • rich pickering
    rich pickering Member Posts: 277

    > We set a 55 gallon barrel in the mech room of a

    > small commercial job and ran the 12" round

    > combustion air duct down inside of it. The twelve

    > inch was suspended about 15" from the bottom of

    > the barrel and the top of the barrel was off of

    > course.

  • I asked the same thing...

    then I realized that there is potable hot water (DHW) and the make up for the hydronic system that are all being exposed as well. I pointed that out to the regional director and he said he'd get it insulated and heat taped.

    Other than the fact that they're letting the great out of doors in, (which is normal in a small setting like this with lots of fire power) it doesn't really need aunty frieze.

    If there were a telephone line or cable TV line nearby, I'd offer to "baby sit" his physical plant for him because there ain't no one on property that understand hydronics any way...Mentioned it to the RM. He said he'd think about it... :)

    I also considered the possibility of putting in a small pony pump to warm the boiler if needed instead of firing the 2 horse beast they have on their now. Just another thing to go wrong. Besides, them pumps needs exercise every once in a while anywho..

    I have 1/2" taps to work with. Not sure I could find an element small enough for electric heat. Maybe I could run some of that single core heat tape through all the tubes, there must be a dozen tubes in that thing. In one side, and out the other. Big ol' red wire nuts to make the final connection.. Yeah, that's the ticket:-)

    Over heard this conversation at a local wholesale supply house counter the other day, "License?? We don't need no stinkin' licenses!!"

    Travel safe out there.

  • rich pickering
    rich pickering Member Posts: 277

    And there is always a but...
    We use traps all the time. I have a boiler room serving an arena with 3 fin tube boilers, 1.4 mill each, each one individually vented. Combustion and relief air. Piped P/S.Everything is fine until it gets to -23f or -30c. Now there is massive downdrafting, but the hx are protected by baffles and glycol.

    Turns out that at -23, the path of least resistance for air is down the vents, not back up the trap of the combustion air. So the vents on the boilers that are off become combustion air ducts and when the boiler fires, it can't establish draft.

    The solution was to bring in additional combustion air from the arena using a fan to maintain positive pressure in the boiler room.

    Since then, I've seen the same problem in two other boiler rooms.

    Hotsy pressure washers want NO other appliance in the same room if it uses air and the outside air temp may drop below freezing.
  • Thanks Dawg...

    My pappy was a Naval man. His rope work use to AMAZE me and anyone else standing near him. He could climb a flag pole in nothing flat with two ropes. And get to the bottom in about 1 second flat.

    I'll be borrowing some of this strengths on THIS job, I guarantee you. Hope to do him proud.

    Your rigging jobs continue to amaze me. I think about that bakery job all the time. Now THAT took some extra cribbing...

  • Eskimo traps and heaters...

    I've used that trick in 5 gallon buckets, and flexible metal pipes for higher ones. It works great. Actually found the idea in a government book on combustion air alternatives. Can't remember which agency, but it was official.

    As for heaters, there are two after the fact electric heaters that kick out about 9000 watts total, that's like a fart in a wind tunnel in that room...


  • Alfred...

    These boilers are 2 stage. It has a tekmar 8 stage boiler control/reset on it. It does rotate boilers, once they shut down. That means it has to get above WWSD before this happens. During a long deep cold spell, that could be for a week at a time, or more. If the control decides that only two boilers are necessary, then the other two sit there idled. If one of the other firing boilers fail, the control WILL bring on other boilers, but if the HXer is already froze up it won't/can't fire because the flow switch isn't made.

    TO be quite honest, I don't think they ever tried. They didn't know they had a problem until it DID warm up outside. Remember, these boilers are massive in comparison to the real time loads that they are seeing for the majority of the time. To be quite honest with you, the plumbing contractor who put this in was supposed to call me to do the controls. Guess they found someone else to do the work for less money. Not really sure I'd have done anything differently then what WAS done. It never crossed my mind that it could get that cold in these boiler rooms.

  • Tom...

    THanks for the info. I am familair with the coil freeze stat with which you reference. THe whole goal and intent of piping boilers in a P/S manner is to avoid unneccessary standby heat loss. Using a OSA system to start the boiler pumps would majorly compound the heat losses of the boiler coils. My method will also lose heat, but not nearly as much as having the boiler pumps run full time.

    I'm not sure the sensor bulb has the ability to resist long term exposure to the high temperatures (+350) and flue gas byproducts.

    Thanks for the suggestions in any case.

  • Tom R.
    Tom R. Member Posts: 139

    OK, Mark. I figured that any outfit that would install 4 boilers when they needed three (2 on line, 1 standby) wouldn't mind preserving them by increasing their fuel budget some. Can you tie all 4 boilers together into a common stack, or pair them (#1&2;#3&4) to preclude exposing the coils to low temps? I never did like boilers on roofs...or chillers, for that matter. Seems unnatural to keep them anywhere but the basement, where they belong...near the coal bin.
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