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  1. #27
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    It's certainly possible. You've got enough information to bone up on the correct terminology so that when you talk to whoever, you'll know if they know what they are talking about. And if they've ever done this stuff before.

    I'll bet dollars to doughnuts they do not know where the balance valves are. And quite possibly do not even know what to do with them.

    Remember, even though I was able to fix that other problem in that other thread I posted, years of techs and other contractors came before me that didn't have a clue what they were looking at. And even then it took me decades to find out the real reason why the system acted the way it did. Thanks to the folks here.


    Quote Originally Posted by curious_owner View Post
    That's an excellent question. Since I took the maintenance contractor's word about the chilled water system being fine, it didn't occur to me to find out what's it like on other floors. I'll have them compare other floors as well.

    If the chilled water isn't picking up enough heat, would that have such as a massive effect on condensation? (Of course it affects condensation, but would the effect be so huge?)

  2. #28
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    I agree that a 10 degree water side temperature differential is a good start/average split on a CW coil. As for the Fresh air, 114 degrees down to 74 degrees with no change to RH seems off to me. Not that it is impossible (just add humidity controls, humidifier & reheat to your fresh air unit)but I would expect a change.

    We have established that we are bringing in fresh air, are we exhausting any simultaneously?

  3. #29
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    Quote Originally Posted by BBeerme View Post
    It's certainly possible. You've got enough information to bone up on the correct terminology so that when you talk to whoever, you'll know if they know what they are talking about. And if they've ever done this stuff before.

    I'll bet dollars to doughnuts they do not know where the balance valves are. And quite possibly do not even know what to do with them.

    Remember, even though I was able to fix that other problem in that other thread I posted, years of techs and other contractors came before me that didn't have a clue what they were looking at. And even then it took me decades to find out the real reason why the system acted the way it did. Thanks to the folks here.
    Do you think a weak (read moldy) chilled water pipe insulation has an effect on RH? The pipe leaks in the corridor sometimes, but they said that's due to the weakened insulation, and it won't affect humidity.

    I bet the word balancing didn't enter the vocabulary until I mentioned it. Let's see if they find the valves.

    Thank you very much for your insight. I'll update this thread if I get any more information, or hopefully close the case.

  4. #30
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    Quote Originally Posted by hvacrmedic View Post
    Humidy levels indoors will always be affected by humidity levels outdoors unless the structure is air tight like a foamed house. Your structure is obviously not air tight and is likely quite the opposite. The most likely cause of the higher RH is a plumbing leak. A small drip can have a very large effect on indoor RH. 1 drop per second is about 5 gallons per day. The leak could be overhead in the upstairs neighbor's plumbing. In the summer multi-story structures have a negative stack effect, which means air will come in through cracks in the upper levels and air will go out of cracks in the lower levels. Infiltration up high and exfiltration down low. That would account for the difference in RH levels overall between floors. That's just a guess with the limited data. I wouldn't mind investigating a call like that in person. Sounds like a good challenge.
    Thank you, that is a good point. Haven't thought about looking at plumbing because there are no obvious signs (wet walls, concentrated mold growth, stagnant smell, etc.) and I don't have access to the building's plumbing.

    It's a good observation that we've completely ignored since we've been focused on A/C parts.

  5. #31
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    Anything is possible at this point. But didn't you say you were pulling out 7 liters of water a day from a dehumidifier when it gets very humid outside? If the humidity problem is the same in every apartment on your floor, that's a lot of water.

    Ideally, they will have the original prints in their maintenance shop. Or they could find out who did the original engineering and order another set from them. First you put everything back the way it was originally intended to be. Chilled water and the air flows, including the fresh air.

    Good Luck !!


    Quote Originally Posted by curious_owner View Post
    Do you think a weak (read moldy) chilled water pipe insulation has an effect on RH? The pipe leaks in the corridor sometimes, but they said that's due to the weakened insulation, and it won't affect humidity.

    I bet the word balancing didn't enter the vocabulary until I mentioned it. Let's see if they find the valves.

    Thank you very much for your insight. I'll update this thread if I get any more information, or hopefully close the case.

  6. #32
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    I have to admit I did not read through all three pages of responses but something struck me. You said you live in an arid climate. By any chance does the system have a "HUMIDIFER" installed in it. Ask the building maintenance guys. then have them turn off the water supply to the humidifier if you have one and see if your problem get better

  7. Likes kamersoutdoor liked this post.
  8. #33
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    Quote Originally Posted by Answer-Man View Post
    I have to admit I did not read through all three pages of responses but something struck me. You said you live in an arid climate. By any chance does the system have a "HUMIDIFER" installed in it. Ask the building maintenance guys. then have them turn off the water supply to the humidifier if you have one and see if your problem get better
    That is good insight. The building and the apartments are not humidity-controlled at all. There's no humidifier or dehumidifier, and the drying of air is apparently just a side effect of air conditioning.

  9. #34
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    Thread Starter

    Updates

    So in the past few days, the maintenance contractor sent their most senior project manager/mechanical engineer. I let him know the observations from this thread about the chilled water temperature difference, and he agreed that this is the most likely problem.

    After they looked on the roof, they found these problems:
    - Chilled water temperature difference: The return water is just too cold, so it's not picking up enough heat. The difference between supply and return chilled water is around 2-3 °F.
    - Heat recovery wheel on the roof wasn't spinning properly
    - The slope of the drain pipe in the FAHU is not done properly, so the condensed water is filling up the FAHU after a while. (They said they fixed the drain pipe, but that still didn't fix the problem.)

    The chilled water temperature difference both makes sense and makes no sense to me. If it's not picking up enough heat, how come my air conditioning is just fine. The indoor air temperature is perfect. That should mean that it's able to condense water regardless of whether it's picking up enough heat or not, right?

    I don't know the effect of the heat recovery wheel. My understanding is that it's supposed to raise the temperature of the fresh air stream. But given how hot the fresh air already is, I don't see why the heat exchange would be needed.

    Also, since my floor (which is has high humidity) and the level above me (which don't) are supplied by the same FAHU. So if the heat recovery wheel was a problem, wouldn't it be a problem for both floors?


    P.S. Thank you very much everybody for your help and insights. I really have learned from you in the past one week more than I've learned from the contractor's "engineers" in the past year.

  10. #35
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    The heat recovery wheel is probably intended to avoid dumping that precious [aka expensive] air that has already been conditioned. And it would work in both the heat and cool modes. Another possibility is it may be a wheel to dry desiccant for dehumidification. Either way, at least they found one more thing wrong.

    Regarding another comment you made "That should mean that it's able to condense water regardless of whether it's picking up enough heat or not, right?" Here is your confusion . . . In air conditioning terms, the humidity in the air IS heat. It is just another form of heat.

    It all goes back to how the original engineer engineered the system. For example, unlike the low split example I gave you in that other thread, in your case the air temp may have been reached too fast. So the cooling valve closed. But if the water is moving slower, picking up more heat, there will be more time for the moisture in the air to condense on the coil.

    In the end it looks like the problem, as it is with so many problems like this, was a combination of several things. Some affecting the results more than others, but it was the sum of all to give you the environment you received.

    Sounds like you are finally on a path to get things resolved. Glad we could help.



  11. #36
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    water flow

    Quote Originally Posted by curious_owner View Post
    Done that too. They put a pump/compressor and made sure it's not clogged. They've done the same thing to the drain pipe for good measure.

    Most of the companies who came over said there's nothing left to do in the apartment, and we should start looking in the building. The building's contractor isn't able to find the problem yet, but they agree with the companies that my apartment seems fine.

    Btw, how would bad water flow affect dehum? Is it because the coil won't be cold enough to condense the water that the fan is blowing?
    i would go one step more. have someone come in with a contact thermometer and check the water temp in & out of the coil....the pump may have trash in the impeller , etc. or a partially plugged strainer. see if there is a separator in the system to eliminate that kind of problem......thats what it sounds like to me , low flow through the coil & coil not staying cold enough over its whole surface............
    B[COLOR=a friend is one who knows us , but loves us anyway

  12. #37
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    Tips to Lower Humidity
    1. First and foremost, ventilate. Especially the areas that create moisture, like the kitchen and bathroom. When vent fans are present, make sure to turn them on and/or leave them on longer. Especially in the kitchen, bathroom, and basement. If not, consider having them installed by an electrician.
    2. If you do not have exhaust fans or a ventilation system, you can crack a window for a few minutes to dry the air out, especially in the bathroom areas that tend to hang onto additional moisture for longer periods.
    3. Ensure that exhaust fans in kitchens, bathrooms, and laundry rooms vent to the outside. Installing vents and attic fans can help too.
    4. Increase indoor temperature because warm air can hold more moisture (relative humidity decreases if temperature increases).
    5. Use fans to increase ventilation
    6. Take colder, shorter showers. Use a low flow showerhead or shower under a less powerful stream by not fully opening the tap. (personally, I find showering with the tap partially open just as pleasant)
    7. Becoming mindful of the indoor and outdoor temperature also can ease the concern of proper humidity within the home. What is the current temperature inside versus outdoors?
    8. Are you keeping your home much cooler than the suggested temperature? If that answer is yes, then minor adjustments to the humidity level are easily adjustable.
    9. Run the AC. Since this option is costly other possible measures are preferred.
    10. While cooking, try to cover your food and take full advantage of the exhaust fans in which your home is equipped. Oven and stove-top cooking produce more moisture. Slow cookers contribute less to indoor humidity.
    11. Vent clothes dryers outside.
    12. If there is a humidifier or vaporizer in the home, turn it off for a little while or simply turn it down. Most humidifiers or vaporizers on the market today have a turn dial, or button to adjust the level of vapor or water you would like dispersed into the air. (a no-brainer but added for the sake of completeness)

  13. #38
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    Hi HVAC Members,

    Need your help - being in a similar situation like curious_owner, have decided to use this thread instead of creating a new one. Live in an apartment where the air conditioning is through central cooling (chilled water).

    An upfront honest disclaimer that I am a newbie when it comes to HVAC / IAQ matters and started doing some reading very recently when I encountered increased indoor moisture/RH levels, which lead to a mold / mildew attack on clothing, leather goods, wood related items, shoes, etc. I have managed to clean out and/or dispose off the affected items and thus have not yet identified a re-lapse (been nearly two months).

    Sometime in end September / early to mid October (when the cooler weather started to begin - am living in the Middle East thus desert-ish weather), my wife and I started experiencing that our bedroom felt quite moist / wet (clothing, flooring, etc) - at that time, we were not sure why and continued our normal life - a couple weeks later we identified the mold/mildew (whiteish stuff of clothing/leather goods) which lead to contact a professional duct and HVAC cleaning and disinfection company, who told us that the aircon and its components would need to be cleaned as it was not dehumidifying the air, thus leading to the increased indoor moisture.

    We believed it and agreed to get it done and they took nearly a full day (three units in the apartment) to clean out the ducts, filters, coils, drip trays, etc. However, to no avail, when we ran the aircon, the indoor RH levels were not improving (hovering in the mid to late 60's). Post cleaning, one of the guys stated that the lining in one of the unit's supply ducts was broken and should be replaced, which could also be a source of moisture (is that true?)

    As the weather started to improve, our usage for aircon decreased, however I did not see that the indoor RH levels were any better without the aircon running (which I was assuming was increasing the indoor RH as it was not dehumidifying the air). We contacted another company to conduct an inspection to help identify what would be the rootcause / source of moisture and they concluded the following;

    (a) The aircon was not operating appropriately as they measured the air supply from two different units and found the readings to be (i) 61.88`F and 87%RH and (ii) 67.28`F and 78.6%RH. When the aircon were turned on, they were instead increasing the indoor RH levels instead of decreasing.

    (b) Air infiltration occurring through the windows and door - they found traces of dust / sand in the window seals and found a gap underneath the main door which was resulting in humidity from the corridor to come in (have taken care of that by installing a doorstrip)

    (c) There is a fresh air supply duct coming into the master washroom, in which the air was measured to be 75.38`F and 65.4% RH (this was previously closed but didnt have any such impact on RH and currently is set at 50% opening).

    In my attempt to find an HVAC expert who could help inspect the air con and find out the issue [as recommended in (i)], to be honest, I have not been quite successful but came across one, who visited a few days back and tested one FCU. Before running it, the indoor RH in that room was exactly at 60% and after running it for about 30-40 mins, the RH started increasing and went up somewhere bw 66-68% (supply vent was showing similar readings as mentioned in point (a) (i) above (also this was not the duct which was found to have a broken lining). So their conclusion was that they would need to service all of the air con units and their components (filters, coils, etc) using some chemical and would also need to descale the chilled water pipes.

    So in vain, I ask you experts out here, who are pretty learned in this field;

    (a) Is this diagnosis even correct i.e. servicing of all the parts which would result in the aircon dehumidifying the air? If so, I had previously gotten the HVAC cleaned, what would that have been? (tbh I dont know what exactly they did but they were the most reputable and highly recommended company for duct and hvac cleaning)

    (b) My current indoor temp and RH levels are at follows in the different rooms (i) 74.84`F and 52%RH, (ii) 75.2`F and 48%RH and (iii) 75.38`F and 50%RH - No air con is running since 24 hrs and in rooms (ii) and (iii) the windows are open while in (i) I have a pedestal fan running - thus should such RH levels worry me that there is another source of moisture in the apartment (accuweather is showing humidity to vary between 20% to 30% - I havent taken the hygrometer outside to measure the RH levels in my vicinity)

    (c) Should I contact my building maintenance guys who manage the central air con system and if so, what should I ask them to check or look for?

    I'm sorry if I may not have provided all the relevant information as I am very new to all this and would appreciate all the guidance that you guys can provide me so I can execute that.

    thanks in advance

  14. #39
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    Hi,

    Just an update - I am noticing that with all the windows being shut, with an increase in the outside humidity, the indoor RH levels have already increased - currently at 61%, 64% and 66% in the different rooms with temps ranging between 74.66`F to 77.54`F. (no air con running in any rooms)

    Is that be a clear indication that there is air infiltrations through the windows? If so, I have contacted someone to come and replace/repair the rubber gaskets. How can I ensure / check that post replacing the infiltrations have been taken care off?

    Thanks once again for the help.

    Regards..

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