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  1. #1
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114

    Chilled water, Air Handlers, warm supply

    I have an account with A Chiller, 42F water, and a half dozen air handlers. 250ton system in all.
    My issue, high supply air temperatures?
    62-65F return 74-78F
    chilled water 42 out, 50 in.
    Several areas are warm, and im having trouble dialing them in.
    return 78
    supply 62

    My splits all look like that, anywhere from 10-15F splits. I pulled the strainers on the main AH's, they were dirty, problem still not solved.

    pump 312gpm, 350gpm setpoint. I can up the gpm to 350, if thats the issue.

    Typically what should your supply temperatures be on a chilled water coil with 42-45F water?
    Yes, the fans are on drives, 1.7" static setpoint. Ones low at 1inch, ones right on in the troubled areas.

    -Im considering a fire damper issue in adjacent zones, creating negative static in my warm zones, or partially shut supply damper, I verified airflow, return and supply in my warm zones, and yes the VAV's are wide open. The boilers off.
    -Or is my supply air temp to warm?
    -bypass valve issues, 3 way valve issues?

    I have to get this fixed asap, or Im in quicksand.. Any help by someone familiar with chilled water systems would be appreciated.

  2. #2
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    1,002
    what is the temperature drop at the coils supply and return water. whats the temp outside. Do you have Outside air open? 74 return air is good 78 is warm. when did this start to happen? any recent work, could you have some coils air bound?

  3. #3
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    10% outside air, 100 ambient. I purged the coils. I'm getting a water in/out today at the coils. I need to really inspect all the fire dampers, especially return, since it feels like its starving and possibly drawing in excess return in my zones in question. My theory is I have a main return fire damper in another branch area shut, so its making my zones negative pressure, basically raised return static in my zones.
    Back at it.

  4. #4
    Join Date
    Mar 2011
    Location
    North Carolina Piedmont Area
    Posts
    455
    I wonder if you have a low water flow issue at the chiller. Has this system worked properly in the past? Normally a chiller is rated at 2.5 GPM per ton on the chiller barrel. This would equate to 625 GPM of chilled water flow for a 250 ton system.
    What is the Brand and model number of the chiller? Verify maximum water flow and minimum water flow per design of chiller.

    I would look at the water side first and verify that you have full water flow based on demand.
    Have you checked for a main bypass valve for minimum water flow and is it closed based on your demand. How about checking the circuit setter and verifying its position based on maximum water flow per design of your system.
    Is the chiller running part loaded, or is it fully loaded.
    Do you have an air separator at the chilled water pump and have you verified that the air has been purged?


    Trouble shooting is not part of the repair...........Understand the symptoms and you will find a a solution.

  5. #5
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    RTAC 250 Trane. The setpoints 350 gpms, but it has not run more than 290 while I have been there. I can get it to 350gpm.
    I do have an air separator, but didnt have access to shut down the pump to purge it. Thats on the list tomorrow. Also to check the drain on the separator to see what comes out. The strainers had some grooved piping machined parts in them. I am considering checking the suction diffuser as bad as the strainers were.
    I checked the bypass valves at the coils, and they were 100% open to the coils. I actuated them to verify. I didnt see circuit setters. The piping is probably 2.5".
    The chiller is fully loaded circuit 1, problem im looking at on circuit 2 tomorrow. I think 2 is shutting down under low load conditions, on high oil temp. Regardless, I will purge the separator and up the gpm first thing and see what happens.

  6. #6
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    2,145
    As alcomech asked, has this system worked properly in the past?

  7. #7
    Join Date
    Mar 2011
    Location
    North Carolina Piedmont Area
    Posts
    455
    Quote Originally Posted by B1978 View Post
    RTAC 250 Trane. The setpoints 350 gpms, but it has not run more than 290 while I have been there. I can get it to 350gpm.
    I do have an air separator, but didnt have access to shut down the pump to purge it. Thats on the list tomorrow. Also to check the drain on the separator to see what comes out. The strainers had some grooved piping machined parts in them. I am considering checking the suction diffuser as bad as the strainers were.
    I checked the bypass valves at the coils, and they were 100% open to the coils. I actuated them to verify. I didnt see circuit setters. The piping is probably 2.5".
    The chiller is fully loaded circuit 1, problem im looking at on circuit 2 tomorrow. I think 2 is shutting down under low load conditions, on high oil temp. Regardless, I will purge the separator and up the GPM first thing and see what happens.
    There is definitely some questions here as to the set up and the control of water flow for the 250 ton chiller. This may not be your overall problem, however I have to ask what was the original design. It will be necessary to identify the piping arrangement which you have in place which is important to both the building requirements and most important to the chiller itself.

    Do you have in place in primary pump system with a single loop and 1 or maybe two pumps
    or do you have a primary and secondary pump system where you have a primary dedicated chiller pump and in addition a secondary circulating pump which maintains chilled water flow to the building and air handlers based on demand.
    There are many other flow necessities for this type of system but for now lets just identify what you actually have.

    You have indicated that the water flow is only set for 350 GPM which leads me to believe that you have a Variable Water Flow system. This raises an eyebrow for the lack of a better word. Again minimum flow is 259 GPM and maximum flow is 929 GPM. This brings up the question what is controlling your water flow. Why is it that you have a building under a full load as you previously stated but are clearly running part loaded well below 40 percent of the chiller design. What controls the pump. It is not unusual for the pressure transducer (if this is what you have) to be located down stream with in the building it self, and have you located it?

    These are just some simple points to shed some light as you clearly have a water flow concern or better put, why are you running so very little water through this unit when the building is at full demand?

    As for the air separator it is not required to turn off the pump in order to purge the air. This is the air separator's function- to remove air while the system is running. However there are many installations which have been overlooked. In order to do this, it must have a High Capacity air vent which vents there air out by itself. Other wise the air will remain in the system. Its OK to blow down the tank just to see what kind of trash you may have.

    If the strainers or suction diffusers have not been checked or cleaned in sometime than you will definitely want to check and clean them.

    You indicated that you checked the by-pass valve at the coils which are 100% so you are saying the bypass is fully closed and are flowing 100% to the chilled water coil. Is this correct? If so than you have a full demand for cooling.


    Troubleshooting is not part of the repair...............understand the symptoms and you will find a solution.

  8. #8
    Join Date
    Dec 2003
    Posts
    2,432
    Are the coils piped correctly? Counterflow. Your coldest water, should be with your coldest air.

  9. #9
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    Excellent questions, I found one circuit on the chiller down, I got it working 100% now, so we are 100% capacity again. The main system piping goes from the building, to the air separator, and expansion tank, make up water into the top of the air separator, then the inlet of the pump, through the chiller, out to the 6 air handlers, with bypass valves and then back.
    I verified the bypass valves are 100% open to the air handlers.
    Today I shut down the pump and chiller, cleaned the suction diffuser strainer, it was partly fouled. Started it and had to purge the air separator 15 times to remove air before it felt like most of the air was removed from the piping. The hoffman air vent on the top of the separator was clogged, I cleaned it, but removed it to purge air. I purged air at both high points at the Chiller as well. Basically, ran the pump for a half hour, purged and repeated. The separator is on the inlet side of the pump which pulls air in, unless the pumps off. I understand the check valve in the hoffman valve, mine leaks.
    Flow, its on a vfd, the controls are not functioning, so its in hand at 44HZ to match its 350gpm setpoint, which the contrtols claim is the setpoint.
    I can let it rip at 60HZ and i may see 600gpm. I can try it at full speed tomorrow.
    I'm unsure of the history of when it last worked as designed.
    I think my transducer is after the chiller, before the building, regardless I can locate it.
    A controls upgrade is in the works.
    So my checklist is down to 4 A/H strainers, flow, and air in the system as far as I can tell.
    The strainers on the main AH's are a job and a half.
    One more thing, the piping hits the main building first, then goes underground and back up to my 2nd building.
    supply temps are the same on all the AH's
    Back to flow and purging air tomorrow. I should force more air from the piping and coils with increased flow.

    so 250x2.5= 625gpm
    That may be 60hz on my vfd.
    I need to get it to work off the controls again.

    The coils are labeled in and out, I better verify they did pipe them correctly, excellent point.
    I think I have air in the system, and low flow. Crossing my fingers after purging so much air that it runs like a different system tomorrow.
    I will re-purge my air handlers as well.

  10. #10
    Join Date
    Mar 2011
    Location
    North Carolina Piedmont Area
    Posts
    455
    Glad to hear its under control now.

  11. #11
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,725
    3 way valves on the ahu's? Why is there a VFD on the pump?

  12. #12
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    Think about the valves on the AHU's, one air handler is shut down, the water bypasses the coil. Winter time, they have a heating coil as well. The pump needs a vfd to react to changing load conditions, valves bypassing etc.

  13. #13
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,725
    Quote Originally Posted by B1978 View Post
    Think about the valves on the AHU's, one air handler is shut down, the water bypasses the coil. Winter time, they have a heating coil as well. The pump needs a vfd to react to changing load conditions, valves bypassing etc.
    And where is the valve bypassing to? Are they 3 ways ?

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