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  1. #1
    Join Date
    Oct 2003
    Location
    South Carolina
    Posts
    1,241

    Confused

    Went to a hair salon today where my employer changed out an old 5-ton gas pack for a new one back in mid-April. The tenant in the space is complaining of high humidity in her space since the new unit was installed. She had PERGO type wood flooring installed at some point in the past and the floor boards are now buckling severly and paper products are becoming limp, curling and wrinkling all throughout the space.
    They're also complaining that the cookies they leave out for snacking are getting very soggy. They are very NOT HAPPY about this!
    In the space today I found that the floor is indeed buckling way too much.

    We put some data-loggers in the space from last Wednesday afternoon until about noon today.
    The graphs from the loggers show some severe swings in humidity and temperature throughout the period. Values are as follows.

    Front of space/reception area:
    Temp Min 69.20 deg. F Temp Max 78.68 deg F
    RH% Min 54.8 %RH RH% Max 80.06 %RH

    Rear of space/Wash Station-Hair drying area
    Temp Min 69.59 deg F Temp Max 79.36 deg F
    RH% Min 52.31 %RH RH% Max 78.18 %RH

    Above Drop Ceiling next to Front Return Grille
    Temp Min 69.79 deg F Temp Max 79.95 deg F
    RH% Min 52.72 %RH RH% Max 76.38 %RH

    If you can imagine the graphs as a saw toothed wave, the Temperature and Humidity readings are moving in opposite directions during the 24 hr periods of the days. When the temp decreases, the humidity rises. And, when the temp rises, the humidity decreases.

    I took our balometer and checked airflow volumes between supplies and returns and found one problem. There are 859 cfm's of air coming from all the supply grilles and only 596 cfm's of air through the return grilles. The supplies are all 6" round runs with a 6' flex run to the lay-in grilles. They average about 72 cfm each.

    There are two 24x24 lay-in return filter grilles for 20x20x1 filters with a 14" flex run each to the return plenum under the unit. There were 1" pleated filters in the grilles with 2" pleated filters in the RTU. I removed the 1" filters from the grilles. I still don't have enough return airflow.

    I checked on my Ductulator and found that the return plenum needs to be 15" x 20" and that is what it is into the unit. With two 14" return runs to the plenum, there should be plenty of return air.

    I have opened the sheave on the blower motor as far as I dare to slow the blower and give the evap coil a bit more ability to collect the latent heat from the air. I helped another tech a few days ago and we found the set-screw on the adjustable sheave had worked loose and spun itself shut running the blower too fast and drawing moisture off of the evap. coil. We do not have a tachometer so I can't reference the fan curve to see what is happening with the blower.

    I checked the ductwork and did not find any leakage anywhere I could look. Unfortunately, it's a bit higher off the floor than I can reach even with a ladder, it was a visual inspection mostly.
    Where the plenums joins the bottom of the RTU, both are well sealed. I probed around with a small wire and met resistance all around the perimeter, no openings.
    There is a fresh-air intake on the return panel of the unit, it has been completely closed.

    I do not find any problems with the refrigeration circuit of this unit. It's a CARRIER 48TFD006A511, Serial# 1604G20288. My ODA was 92 deg. F and my pressures were 265 psig high and 82 psig low. My return temp was 77 deg F and the supply was 58 deg F. These were taken at the unit, across the coil. On the grilles inside I only got an 11 deg F Delta-T. All the ductwork is insulated. I didn't take SH and SC as I felt they were not necessary for this problem. The unit is removing as much moisture from the air as it can, good pee-stream from the condensate drain and, it is removing a fair amount of heat from the space as the air from the condenser coil was rather warm. Hands-on measurement, didn't use the thermometer. I am concerned about the 82 psig suction pressure with the 77 deg F return air temp. The pressure seems a bit high for that temp. This unit has a metered header leading into the evap coil, no restrictions there. There were no leaks of outside air into the unit that I could find except for the screw slots on the fresh-air damper on the return panel. Those slots are 1/4" wide and about 3-4" long, with a gasket behind them. Shouldn't be enough infiltration to be a concern.

    The tenant is past becoming upset about this and has told me that she is going to call her landlord and tell them she is leaving the space if the problem is not corrected. According to the tenant, there have been 8 seperate service techs out there to work on this problem and I'm No. 9. She's very unhappy with the service she is getting and the fact that her expensive new floor is coming apart and also causing people to trip from the pressure ridges.

    My biggest concern is, where is all this extra latent heat coming from and how can I get rid of it? And, why were there no problems with the old unit and this one is nothing but a problem? The old one was replaced due to a lightning strike and the new one has been hit twice since install, I've been told. The old one was a CARRIER also so, keep the derogatory comments to yourself please. I've only been on this one twice and I thought I had it the last time. I was wrong!

    I apologize for the length of this read. I figured giving all the info I had would be helpful to those who can help me. I appreciate all attempts to help me solve this problem. THANK YOU!!

  2. #2
    Join Date
    Aug 2004
    Location
    DFW
    Posts
    147
    with balometers you will hardly find two the same. I would not worry to much about your return being slightly lower due to infiltration of outside air @ your outdoor air intake. even fully shut you are pulling outside air.I am more worried about your 800+ cfm. you should be up around 2000cfm and you will have to be more specific on your temp/hum charting.

    what is the weather like?

    [Edited by svc on 08-02-2004 at 10:07 PM]

  3. #3
    Join Date
    Dec 2002
    Posts
    9,871
    4 TON? If so, the cfms top limit should be 1600 cfm and the bottom should be 1280 cfm.

    [Edited by rob10 on 08-02-2004 at 09:35 PM]

  4. #4
    Join Date
    Feb 2004
    Posts
    534
    Hey maybe i can help here, you are on the right track about the blower I have had that same problem adjusted airflow and humidity problem went away (adjusted sheaves). Is this unit short cycling at all on temp? Is the space temp dropping to fast? Do you know how long it takes the space to pull down say from 78f to 70f . Also I wonder about those 2- 14 inch return grills sounds like you have enough return air did you make sure the flex is not kinked going back to unit. Where are you pulling the return air from I'm concerned about the 77 deg return, also i see this unit is going off at night is this causing floor to buckle?? and one more thing why the hell would you put wood floors in a hair salon that with all the water and crap in the salon should have went with tile.. JMO

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    What kind of metering device does this unit have? If it's a piston, I'm thinking maybe it's just slightly not seated properly? I actually had this problem once. Just slapping the gauges on, everything looked normal (this is before I really understood the value of superheat/subcooling), but in the heat of the day the tenant complained of sub-par cooling. Sure, the unit still cooled, but not like it should, and when I'd visit the apartment in the hot afternoon, the air was somewhat cool, but sticky.

    I took apart piston after pumpdown and found it ever so slightly not seating correctly due to just a minute amount of trash. Cleaned it up, reassembled, restored charge, got great cooling and a really happy tenant.

    I'm a bit surprised as thoroughly as you've gone over this system and ductwork that you skipped superheat and subcooling. Had I done that on the apartment unit I would've found the problem in a heartbeat. As it was I made a good stab and got lucky. Since I've learned the value of these readings, just feeling things isn't good enough for me anymore. I still do it, but go by the line, "trust, but verify" when it comes to my senses.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Join Date
    Oct 2003
    Location
    South Carolina
    Posts
    1,241

    Thumbs up Thanks for the replies!!

    svc, I have opened the sheave on the blower motor in an effort to reduce the amount of latent heat in the space. I knew this would cause a corresponding decrease in overall cfm of airflow but, my main concern is removing the excess latent heat. Weather here in Columbia, SC has been mostly rainy for much of the last several weeks/months. This is the only unit of ours, that I know about, that is having such difficulty keeping the RH at a reasonable level in the space.
    I did consider posting the graphs in this thread but decided it wouldn't show very well as the lines on the graphs are rather thin and light and they would, most likely, have gotten lost through the process of scanning and posting.

    rob10, this is a 5 ton RTU so I am aware that my airflow should be about 2000 cfm with a minimum of no less than maybe 1600 cfm. When I came to this job last week, we found the sheave had closed itself from a loose setscrew on the adjusting half and caused the blower to run so fast that it pulled condensate off of the evap coil. I thought this was the problem the tenant was complaining about when we were told her printer paper was curling instead of laying flat as paper should.

    service guy, as near as I can tell, the unit is not short cycling. The thermostat is set at about 73 deg F for cooling and seems to maintain that temp, at the thermostat that is. Space temp does not seem to be dropping too fast but, the scale on the data-loggers I used were set for hourly measurements. The trend seems to be about 12 hours between lowest and highest temp readings. Lowest for one was about 69 deg F and highest was 74 deg F.
    I did look at the return flex runs and they are not kinked and are resonably supported from the grille to the plenum. The grille in the front of the space, however, is pulling about twice the cfm's as the grille in the rear of the space. I can't get to the flex easily enough to see if the liner has fallen in the rear flex.
    All of the return is pulled through two return filter grilles in the drop ceiling in the space with no filters in them. I removed them earlier, there are filters in the RTU already.
    As for wood floors in a hair salon, I am very aware of the latent heat load in these type establishments. I, too, would have used VCT for the floor. I think the tenant may have been trying to "put on airs" as I have heard situations like this described, know what I mean?
    Most of the heat load will be staff, customers, hair dryers, hair wash stations, pedicure and manicure station, some electronic equipment, picture windows at the front of the space, tinted, and some incandescent lights in the ceiling. Not many of those though, mostly flourescent lighting.

    shophound, this unit is one of those CARRIERS where the metering orifices are in the liquid line header at the evaporator. 7 or 8 circuits each with their own fixed orifice. No seating problem there, it can't move.
    I agree about the importance of SH and SC measurements but, as I said, I felt they weren't necessary here. I'm more than confident the charge is correct and that there are no restrictions or bypassing in the refrigerant circuit. I will be honest, the majority of the time I do use SH and SC measurements. I'll be going back to this unit probably in the near future so I'll get them just to be absolutely sure. I also just remembered, I lost my clamp thermometer just recently so I couldn't get an SC or SH reading to save my life, I had to do it the old schooler's way today. I'll have a replacement soon though.
    I know it is removing the latent heat but, it isn't removing enough. I'm wondering if this unit is being subjected to an increasing latent heat load throughout the day or is it something else?

    Again, I appreciate your responses. Thank You!!

  7. #7
    Join Date
    Jan 2002
    Posts
    1,895
    5 tons with under 1000 cfm and what looks like a slightly higher than normal suction pressure doesn't add up. The combination of multiple techs and 2 sets of pleated filters would really get me thinking someone had screwed with the charge.

    Does the humidity drop at night ? and the temp remain stable all day long ? If they have a gas fired water heater might want to check the venting on it.

  8. #8
    Join Date
    Feb 2002
    Posts
    211

    you need to find why cfm is so low.
    static pressure profile of the unit would help.

    or have test and balance stop by and check out the cfm problem.



  9. #9
    Join Date
    Aug 2002
    Location
    manitowoc wisconsin
    Posts
    4,943
    I think I would start over.Speed the blower back up to 2000 cfm & take your sh/sc readings.
    Take your time & do it right!

  10. #10
    Join Date
    Jun 2004
    Location
    Richmond Virginia
    Posts
    1,078
    If you are starting at the unit with a 20 degree split but only ending up with 11 degrees at the vents, you have some severe duct loss/gains. Since you are short on the return air measurements, start with checking the return for duct leaks. Is this unit a downflow? The horizontal access panels can be removed for you to look down the duct from the roof and you can check the seal at the roof and make sure that it is sealed OK. I had a customer complain of high humidity after a remodel and found the HVAC contractor the general hired set these same units on curbs with 3" hanging open on the return end. The same curb is used on multiple tonnages and you must shove the unit all the way forward at the return end. If you have this, both the supply and return will be leaking at the roof. If there is a dent in the middle of the unit, supply can go back into return but that would make your suction pressure and temperature lower. I don't know how you are maintaining that suction pressure at those CFM's! You're at half of the minimum you should be at, that is if you are catching it all.

  11. #11

    Air Flow

    I agree with the others get the air flow as close to 2000 cfm also can you trend the data in 5 min intervals. you need to know what the humidity in the space is, the supply air temperature, and the space temperature. then compare the space temperature and humidity on a psychrometric chart and see if your supply air temperature is getting below the dew point on the chart. If not you have equipment problems if it is getting below the dew point check for outside infiltration. also tell them to shut the door.


  12. #12
    Join Date
    Jul 2004
    Posts
    49
    Get the airflow back up and recheck system SH. Also, is the fan cycling with temp or is fan running continuously? Could be putting removed moisture right back into area after mechanical shuts down, causes spikes in RH as system cycles.

  13. #13
    Join Date
    Nov 2001
    Location
    Seattle, WA
    Posts
    7,763
    To me, it's all in the basics. Get back on the roof and set the system up the way it is designed to be, airflow, temp drop, RA ari temps, SA temps, pressures, amp draw, etc, etc. Once that is established go into the space and measure for the same airflow and, especially, compare the supply temps and the return air temp to what you had on the roof. If they are different, there is your problem.

    BTW, do your installers install a new thermostat and, if so, have they configured it correctly? Is there a hole in the wall behind it setting off the thermostat too soon or too late?

    Record all the normal basics and tell us what they are. That will point to what your problem is.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

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