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10 story building circulation problems

mikedo
mikedo Member Posts: 174
i have a 10 story building i do mostly plumbing in. they have a 2 pipe system used for both heat and ac. its an open system with a tank on the roof. its always had a few units that dont want to heat or cool. they used to have a steam heat exchanger this fall they installed new boilers with primary secondary piping threw a large floor mounted  exchanger (cant remember the name). now the air does not seem to be self bleeding as well as before. and im having problems getting the units to work mostly on the tenth floor. water is hot up to supply on units that wont circulate but will not pull threw. there are no bleeders except a coin vent on units them selves. also there are no valves to isolate any of the risers. there are valves at each unit. i have removed the coin vent and installed a ball valve with a hose adapter to purge the runs but it does not help.sorry for the long post.   thanks for any help.

Comments

  • JStar
    JStar Member Posts: 2,752
    RE

    When you bleed the radiators, does any water come out?

    What pressure is your boiler filled to when it's cold?
  • mikedo
    mikedo Member Posts: 174
    re

    water is at units i added a ball valve and hose adapter. i close the supply and bleed the return then close the return and bleed the supply. the water and coil get hot but will not circulate when valves are open. pressure on first floor is approx 55lbs its an open system so the higher you go the less pressure maybe 10 at 10th floor. its happening to both old units (carrier) or new ones (mcquay). 
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited November 2011
    Where are the pumps in relationship too...

    The vertical profile of the building (basement or roof) and are the pumps pumping away from the expansion tank connection?



    Can you see the differential in pressure across the pump/circulators?



    Off hand, it sounds as if it is lazy brother in law syndrome...



    Also, how is flow through the FCU's controlled? 2 way valve or 3 way bypass valve, or no valves at all?



    By having the system connected to an open tank, you are essentially maintaining an "open" system. I hope all components within the loop are non ferrous or that a high pH is bing maintained to control O2 attacks...



    Lastly, when you attempt to bleed the system, are the pumps on or OFF? (They should be off)



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • icesailor
    icesailor Member Posts: 7,265
    10 Story Building Pressure:

    I've always wondered about how this works.

    It sounds to me like you don't have enough pressure in the system to keep the water up at the tenth floor. Are the boilers rated for the pressure in the system?

    If it worked before the change, and now it doesn't, maybe the impossible happened. The mechanical engineer/designer made a mistake. Of course, we all know that that couldn't happen.

    If you have fan coils on the top floor, I have had experience with the flow being so slow through them that it seemed that they weren't working. If the fan is turned off, and you feel hot water going into the coil, note how far the heat goes across the coil. If you turn the fan on, and the coil gets cold, the flow is too low. If you can't get a decent flow of water through the coil vent, the pressure on the system on the top floor is too low.

    Something is wrong. Or so it seems to me.

    Here's a thought from me and what I would do. A 10 story building must have a set of plans around. Scale off the plans. Measure the height from the boiler on whatever floor the boiler is on and from the gauge height on the boiler, to the water level on the top floor where the highest radiation is, multiply that by .434 and that will give you the minimum pressure to the highest emitter on the system. Add for the open tank if that is higher. How much water is in the tank?

    In the boiler changes, did they re-pipe and add or replace circulators? Is there any new piping on the primary/secondary where closely spaced tees are very close to ells or tees on the primary side? On smaller systems, I have seen disturbed flow where horizontal flow, had to go to vertical and was so close to a secondary tee that the flow wasn't what was designed.

    If you want to become a hero, figure this one out. The "experts" will tell you that you are wrong, but if it worked before, and plans were followed, there's a mistake somewhere. You need to find it.

    Keep us informed. Post pictures. And remember about purging air. Water takes the path of least resistance. Air will cause greater resistance. If you can't isolate the unit to stop the least resistance, you can't vent or purge.



    Good Luck.
  • mikedo
    mikedo Member Posts: 174
    re

    its an open system. single pump on feed piped to a floor mounted heat exchanger in the basement. must be a 300 gallon open expansion tank on roof. at this time water is not being treated. pressure at 1st floor is about 50lbs and decreases as you get to upper floors.the original units circulate all the time no 2 or 3 way valve. the replacement units get a solenoid and a manual changeover switch. i'm going to get the name of the heat exchanger on monday and try to test some pressures on the feed and returns. the system is copper and steel piping. no plans for the building and no valves on system. the  circulator has not been changed yet .their are two circulators one for backup. im thinking of putting a small pump on at the units that wont circulate to try to get them to work. but their is no room in units pump would have to be small. 
  • icesailor
    icesailor Member Posts: 7,265
    10 story building:

    I still don't understand how you get 50# in the boiler room floor with the open tank on the roof. That makes it 11 stories. Maybe it is on the edge and it must have worked before.

    It sounds like a flow problem. What happens if you put the other back up pump on-line? Does the situation improve? Did you put an infra-red thermometer gun on the supply and returns? What kinds of differential temperatures are you getting?

    Don't accept the fact that the new boilers had no bearing on the situation. If they worked before the boiler changes, and it doesn't work now, don't blame the toilets.

    Where I work, a large local museum put on a huge addition and connected some buildings together and put in two boilers to take care of the whole campus. They were to back up each other. I had nothing to do with the project. One very cold winter day when it was in the teens, the maintenance guy stopped me and asked me if I would look at their problem. That one of the boilers wouldn't stay running and it made one part of the building cold and they were afraid that something bad might happen. They had a service contract with a company, many miles away and they came down once a month to service the boilers. They had this problem with this boiler for a long time and hadn't resolved it. The right hand boiler, when re-set, would go off after establishing flame and going into high fire. I told the guy that I had never seen anything like it but I would see what I could find. It had a 300# fuel pump and a variable pressure actuator that moved the air linkage and opened the air shutter. I found a loose adjustment bolt and the air shutter wasn't opening all the way. I reset it to where the other burner was set and the problem stopped.

    But why did they need both boilers running to heat the buildings? They were designed to run on one boiler, and if both boilers were running, that they ran as alternating lead/lag. It was primary/secondary with back up pumps.  Looking at the piping behind the boilers, I saw what was probably the problem. In the piping.

    It wasn't my customer, I would never be called to work on it, experts far smarter than I had designed and installed it, and it was part of the design that both boilers had to run to heat a pert of the building that one, when running, would never send hot water to.

    It's still that way today. When the right hand boiler is off, there is no heat in the research room. When the left hand boiler is off, there is no heat in the old, small exhibit room. That's normal. I guess.

    If it worked before the change, and doesn't work now, something changed. Be prepared for extreme resistance to the problem. Remember, "They're smart. You're not". That's why they asked you to look at it.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Sounds like the EX brother in law syndrome to me....

    My ex-bro in law was a water skiing bum. All he wanted to do was go for a ride around the lake on water skis. He, like water, was wet, lazy and stupid. Hence, he's an EX brother in law :-)



    The water in your system is essentially wet lazy and stupid, and the system was piped parallel DIRECT return, which means the water is going to follow the path of least resistance back to the pump, which causes the water to move, or go for another ride around the lake...



    You MUST show it where YOU want it to go. You do this by balancing out the flows. Those floors closest to the pump will have their balance valves mostly closed, and those units furthest from the pump will have their valves mostly, if not fully opened. You could do this with the coil isolation valves, but it wouldn't be an exact science as it would be with true "balance" cocks. Besides, if some unknowing first year technician walks in, he's going to open the valves all the way, because that's what his gut tells him to do, then all of your work is for naught.



    Additionally, I suspect that your pumping station is not set up "ideally". In fact, if your 2 pump system was designed for manual change over, and its isolation valves for all pumps are open, and there are no check valves on each individual pump, you may be suffering from small circle jerk syndrome. Again, the water from one pump is running backwards though the OFF pump, thereby causing a short circuit in the system flow. Those units closest to the pumps may see some flow, but the further away you get, the less flow you get.



    I've seen this situation more than once, and all I had to do to correct it was close off one valve on the OFF pump, and suddenly, ZOOOOom, the whole system saw more than adequate flow.



    Turning both pumps on at the same time will result in a doubling of the flow, but not a doubling of the pressure generated. Which brings me to my next point, regarding the optimum pump location in relationship to the expansion tank connection to the system.



    I suspect that your expansion tank piping is simply an extension of the upper distribution system, and if it is, then the pump is not exactly pumping away from the Point of No Pressure Change (PONPC), which means that it is not producing all POSITIVE pressure. When the pump is half way around the loop from the PONPC, it presents its pressure differential as half positive, and half negative pressure. This means that any air in suspension on the very top of the system will see a slight negative pressure condition that will cause it to ballon when it sees negative pressure and become air bound. If you can move the expansion tank connection to the pumps inlets, they will have no option but to present their pressure differential as all POSITIVE pressure, and air binding on upper floors will go away after manual bleeding (with all pumps off of course).



    That, of course, would probably be difficult at best to do, so I would probably approach the owners about eliminating the large open tank on the roof, and opt for a much smaller, diaphragmatic expansion tank and locate it in the basement mechanical room, and make certain that its connection to the system was as close to the pumps inlets as possible. This would also address the open system problems inherent with open tank design.



    Try closing off the OFF pumps isolation first, if it isn't already that way and see what happens. If it clears up, you are done. If not, try turning both pumps ON and see what happens. If that doesn't work, you may have to do balancing valves throughout. Before you do that, it might be a good idea to get a manufacturer rep involved in proper pump sizing. That is tough to do when you don't have drawings, but it can be done.



    Also, using pressure gages on either side of the pump, check them to make certain that their impellers have not been degraded by the excess oxygen in the system.



    I'd suggest a variable speed pump, but I don't think it is going to help you any based on the fact that there are no flow controls on any of the FCU's.



    Check it out and get back to us.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • bob_46
    bob_46 Member Posts: 813
    Open system

    I wouldn't be too quick to suggest closing the system. You mention that this piping serves both heating and cooling. I suspect the system was designed this way to make changeover from heat to cool simple as system water content probably changes quite a bit when you add the chillers to the system thus 300 Gal. tank. As to 50# pressure the tank is on the 11th. floor, the roof. One thing that has changed is the heat-x, it may have a larger pressure drop than the old one. What are you using for a system pump ? I would also do as ME suggests and verify the condition of the impeller. You could dead head the pump and look at the Mfg. curve although the impeller may have been custom cut.
    bob
  • mikedo
    mikedo Member Posts: 174
    re

    ive run both pumps they have check vales also. when running the 2 pumps the condition improved slightly. im waiting for the new pumps to be installed to see if that helps the problem. the problem is the boiler install guys are slow and people want heat know. they boiler install company is installing new gauges on the pumps. they tried to throttle down the return hoping to increase the head pressure that did not work. im going there monday and im going to take some pressure readings.  
  • mikedo
    mikedo Member Posts: 174
    re

    ive run both pumps they have check vales also. when running the 2 pumps the condition improved slightly. im waiting for the new pumps to be installed to see if that helps the problem. the problem is the boiler install guys are slow and people want heat know. they boiler install company is installing new gauges on the pumps. they tried to throttle down the return hoping to increase the head pressure that did not work. im going there monday and im going to take some pressure readings.  
  • icesailor
    icesailor Member Posts: 7,265
    edited November 2011
    Pipe Sizing:

    They didn't happen to reduce the size of the piping going into the boilers from what is going to the system did they?

    My money is a queeb in the new piping connections to the boilers.

    My #1 rule of troubleshooting is "If it was working fine for years and suddenly stopped working, what changed?"  It has never failed me.

    Mark E. is correct in how the flow may go. Someone in the past may have spent a long period of quality time balancing the system. If you weren't there for the initial fire off, and have been called in because it isn't working, you have no idea what someone did while trying to get it to work. If someone doesn't understand how something works, and they start twisting balancing valves, you may really be eating the pickle because it wasn't working after the change and it is now worse,

    A real chance to improve your knowledge base.

    Post some pictures. Something is wrong.
  • mikedo
    mikedo Member Posts: 174
    re

    ive been working in the building for about five years. doing mostly plumbing work and changing some of the fan coil units. the reason i didnt even bid on the boilers is im a small company and its not my area of expertise. i dont want to lose all the work for this building or i would just tell them to get someone else. im not at all impressed by the boiler install company. its just a big pain in the butt for me. building is in bridgeport ct. if anyone is close and feel they have the knowledge to help solve the problem. these people are very nice and great payers.  
  • nice people

    i am glad your customers are nice people, and i wonder if they will ever know about the extra effort you are putting into solving this problem. i don't imagine the boiler installers, or the engineer are paying much attention! --nbc
  • icesailor
    icesailor Member Posts: 7,265
    Low Bid Screw-Ups:

    I second NBC's comment.

    I've been there, I've done that. If you had given them a price to do the boiler change, you would have been considered a cousin of Bernie Madoff and trying to make off with their cash. If you have been working consistently in this building, and the owners are happy with your work, you will make more money than the installers of the boilers will have made.

    Post pictures of the piping near the boilers that is new. There is a mistake. I've seen them and I'm not a mega-boiler/heating expert like Mark E. is. Something changed. Like I said before, if the boiler installers went around changing settings, they probably crashed the system. The fact that you said it worked a small amount better when you ran both pumps show this.

    You need to imagine the system and the flow in your mind. You have diverted flow somewhere. Why did they change the boilers in the first place?

    Post pictures.
  • richardplace
    richardplace Member Posts: 10
    re:circulation problem

    It sounds to me that the "open system" on the roof is the cooling tower for the chillers used for the air conditioning. I would imagine the boilers are in the basement. A two pipe system will allow cooling  or heating not both at the same time.That would require a four pipe system on the main pipe. The pressure setting on the boiler needs to be set to the correct setting to "push" the hot water 10 stories. A 12 pound setting is used in residential systems,look it up and do the math for 10 stories.It does sound like you have an air lock in the units upstairs.You should be able to bleed out the air if the pressure setting is corrected
  • mikedo
    mikedo Member Posts: 174
    re

    the cooling tower water is separate from the heating ac water. the changeover from heat to ac is done by 2 large zone valves in basement. water feeder is on the roof in the exp tank its got a gauge glass to check the level. this tank is also shot and needs to be replaced. some people have suggested going to a closed system would help the circulation but im not sure how that would affect air removal. right now the system should self bleed with all the air rising out the open tank. since new boiler install air does not seem to be bleeding as well as before. the super has been shutting down the pumps twice a day to allow the air to rise but its not helping.
  • mikedo
    mikedo Member Posts: 174
    update

    went to the job on monday and talked to the boiler install guys while going over the piping i saw a valve they installed about 20 feet in the air in a corner.    they had shut it to stop flow into the chillers. i pointed out that 2 2" mains were picked off after the valve. since they are there everyday i asked them to open it to see what happens. on thursday i gave up on them and opened the valve and shut the valevs to the 2 chillers. it was on the supply. now i have solved all the new flow problems imagine that. still have about 4 units that dont want to flow but those are old problems. also the air it trapped in the main is gone. wish i found it a week ago but at least i found it.  
  • good job

    i don't see why the installers gave you no help in closing that valve. perhaps they don't know that it is the building owner who is actually providing their pay-check--maybe not this exact BO-job, but in general that's the case.--nbc
  • icesailor
    icesailor Member Posts: 7,265
    10 Story Problems:

    Good on you. My pride would have killed me if that was me and you found it.

    Those other four units have a solution. Keep looking. Show us some piping pictures.
This discussion has been closed.