Results 1 to 11 of 11
  1. #1
    Join Date
    Jul 2014
    Posts
    306
    Post Likes

    30RBA with High DT

    Doing an efficiency check out on a 106Ton Carrier 30RBA110 - 10 years old.
    Put in data loggers on the electrical feed and pressure sensors on the main supply & return ports (measure the evap. pressure drop to determin flow). The single B&G constant volume CHWP (2.5BB) is 5HP with a capacity of 254gpm (about 60ft head).

    Took spot readings on the CH supply/return temps and the pump pressures and amp draw.

    1) getting an average 14.7F difference between the leaving and entering temps - readings from the operator display (verified with a water draw temp test). Issue: the chiller is 10F design.

    2) getting average 9.9 amps on the CV CHWP draw - very constant. Calculating about 4.5HP. Flows should be close to design capacity (254gpm). However getting approx. 12 feet of head (?). Could be impeller issue. No idea what the flow is out of the pump.

    3) getting an average 1.2 psi drop across the evaporator (validated with calibrated Dwyer digital pressure gauges). Using the Carrier Performance Head-GPM data, that yields about 140gpm. Getting lots of flow from opened pressure ports - shower time - so no restrictions. That low dP seems to be real.

    I'm thinking we've got a crummy impeller that's resulting in low flow. Never seen a delta T over the design spec. That sounds like a symptom of low flow.

    Need to get an accurate GPM # to determine the actual Tons (then kW/Ton).

    Any insights would be appreciated.

  2. #2
    Join Date
    Sep 2002
    Posts
    26,316
    Post Likes
    What do the pump strainers look like?

    PHM
    --------


    Quote Originally Posted by tridiumtech View Post
    Doing an efficiency check out on a 106Ton Carrier 30RBA110 - 10 years old.
    Put in data loggers on the electrical feed and pressure sensors on the main supply & return ports (measure the evap. pressure drop to determin flow). The single B&G constant volume CHWP (2.5BB) is 5HP with a capacity of 254gpm (about 60ft head).

    Took spot readings on the CH supply/return temps and the pump pressures and amp draw.

    1) getting an average 14.7F difference between the leaving and entering temps - readings from the operator display (verified with a water draw temp test). Issue: the chiller is 10F design.

    2) getting average 9.9 amps on the CV CHWP draw - very constant. Calculating about 4.5HP. Flows should be close to design capacity (254gpm). However getting approx. 12 feet of head (?). Could be impeller issue. No idea what the flow is out of the pump.

    3) getting an average 1.2 psi drop across the evaporator (validated with calibrated Dwyer digital pressure gauges). Using the Carrier Performance Head-GPM data, that yields about 140gpm. Getting lots of flow from opened pressure ports - shower time - so no restrictions. That low dP seems to be real.

    I'm thinking we've got a crummy impeller that's resulting in low flow. Never seen a delta T over the design spec. That sounds like a symptom of low flow.

    Need to get an accurate GPM # to determine the actual Tons (then kW/Ton).

    Any insights would be appreciated.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. #3
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    3,517
    Post Likes
    When I measure pressure drop across a vessel, I don't care how accurate my gauges are. I always use one gauge, moved from one side to the other.

    Also a high pressure at a port does not prove no restriction. In fact it may be a symptom that one does exist. Downstream of the port.
    In honor of RichardL: "Ain't 'None' of us as smart as 'All' of us".

  4. #4
    Join Date
    Sep 2002
    Posts
    26,316
    Post Likes
    I have a manifold with two ball valves and a single gauge.

    Actually several as I have one for oil pressures too. <g>

    PHM
    -------


    Quote Originally Posted by Nuclrchiller View Post
    When I measure pressure drop across a vessel, I don't care how accurate my gauges are. I always use one gauge, moved from one side to the other.

    Also a high pressure at a port does not prove no restriction. In fact it may be a symptom that one does exist. Downstream of the port.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    3,517
    Post Likes
    Quote Originally Posted by Poodle Head Mikey View Post
    I have a manifold with two ball valves and a single gauge.

    Actually several as I have one for oil pressures too. <g>

    PHM
    -------
    Nice!

    I like to see an installation with a permanent setup like that, too.
    In honor of RichardL: "Ain't 'None' of us as smart as 'All' of us".

  6. #6
    Join Date
    Jul 2014
    Posts
    306
    Post Likes
    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    I have a manifold with two ball valves and a single gauge.

    Actually several as I have one for oil pressures too. <g>

    PHM
    -------
    Cool! - I'm off to my plumbing store. Now I can pressure spot trend that 2nd chiller. Thanks for that PHM.
    And I'll look into the strainer, etc.

    Back to the ~15F temp drop across the evap. barrel. It's a 10F design. How high of a delta F can you get?
    That outdoor 30RBA is basically putting out 45F and the return is coming back at 60F. The weather is a 'boat
    anchor' on the condenser and the AHU coils - we're in Okinawa climate (similar to Miami conditions).
    Avg. Conditions: 92F DBT, 83F WBT, 68% RH, 80F DPT (you wear a bandana working those conditions;
    very wet shirt, underwear, etc. when you get home ;-)

    When you see the dT 5F greater than the design dT what are the obvious 'red flags' to consider?
    Low flow should be one. Maybe also a charge issue?

  7. #7
    Join Date
    Nov 2011
    Location
    East Side
    Posts
    6,700
    Post Likes
    you have to verify flow before you can do anything else.....get that right, then see what it's doing.

    a lot of the troubleshooting process is eliminating possibilities until you're left with the real problem.

  8. #8
    Join Date
    Jul 2014
    Posts
    306
    Post Likes
    Thread Starter
    Took some air-side measurement to estimate the water flow.

    1) Hobo temp/Humidity loggers to determine the delta enthalpy (h) across the cooling coil.
    2) VelociCalc probe to determine the supply CFM.
    3) Estimate the cooling load (btuh): 4.5 x CFM x delta h
    4) Estimate the GPM: (cooling load)/(500 x dT)

    Estimate GPM came out to 146 gpm. Close to the 136 gpm estimate from the evap. pressure drop.
    We can now look the HVAC staff 'in the eye' and tell them they've got a low flow issue.

    In regards to the prelim. 'walkthrough' tour, when I looked at the cooling coil I noticed a large pool of
    condensate water on the internal floor. Many times its the result of clog condensate lines. When I
    looked at the pre-coil (MAT) temp/RH trends (80F, 88%RH, 41Btu/lb) the conditions were close
    to the outside air (87F, 80%RH, 45Btu/lb) - found the manual OAD at 100%. Walkthrough tours are
    part tech, part art (experience).

    The AHU controls are very simple - the HVAC staff manually sets the OAD at 100% in the winter & min.
    position in the summer - they forgot to set it for summer conditions. All the reason to have a
    controls-based actuator on the OAD - especially in very humid environments. A 'low-cost' standalone
    controls option: 2-position actuator wired to the CHWP status or CH status. Major energy waste.

  9. #9
    Join Date
    May 2012
    Location
    California
    Posts
    685
    Post Likes
    Close discharge valve on the pump with it running and the diff between suction and discharge should be 25.97 psid if your design is 60 ft hd that will prove your pump is functioning to its design.

    Sent from my SM-G960U using Tapatalk

  10. #10
    Join Date
    May 2018
    Location
    VA/DC
    Posts
    248
    Post Likes
    pump design is 254, and you're getting 140 gpm. as someone said did you check the strainers? All of them. What is the design gpm of the chiller. Now carrier run on a very large range. im expecting a 230 gpm range for design.
    I bet you get 14 deg TD without all the compressors on.

    Its not a charge issue.

    you are right in saying there is a flow issue. Are you contracted to diagnose that issue yet? or is it the engineers responsibility. I'm going to get this building is falling apart mechanically?

  11. #11
    Join Date
    Jul 2014
    Posts
    306
    Post Likes
    Thread Starter
    Got the HVAC mech. guys to check the strainers (they were told to check them) - after they cleaned them the pressure drop across the evap. barrel went up and the flow is back at design. Still getting 15F temp delta.

    Put in a data logger in the return duct: 79F, 66%RM. The facility is a dining hall - kitchen exhaust system is making the bldg. very negative (pulling in humid Okinawa air); also the dishwashing room is next to the dining spaces - both doors are open and there's to huge portable fans exhausting hot, humid air into the dining spaces. No wonder that AHU cooling coil is 'sweating'.
    Issue with conditioning the dish washing room.

    I sort of 'broke the rules' - should of done a full walk though tour & sample temp/hum in the beginning - just focused on the outdoor chiller and mech. room (CHWP & single AHU). (trying to keep CH efficiency evaluation time short). Other lesson: trust but verify (in regards someone saying 'we checked the strainers').

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •