Page 2 of 4 FirstFirst 1234 LastLast
Results 14 to 26 of 48
  1. #14
    Join Date
    Jul 2015
    Posts
    15
    Post Likes
    Thread Starter
    Logic does dictate that something's changed. Logic also dictates the contractor's priorities are to minimize costs, and pretend the problem isn't there.

    I too think the problem is floor wide. The maintenance contractors keep looking for problems in my apartment, and I keep trying to explain that what Im having are symptoms of a bigger problem. Theyre looking in the wrong place.

    They use the term FHU to refer to the big unit on the roof. My guess is that they mean FAHU (Fresh air handling unit). I did ask them, but the workers have no clue what it stands for.

    They did block the fresh air supply and that didnt change the environment. I asked them to do some more experimentation, but one of their experts told me theres no need because only about 10% of fresh is mixed in with the apartment air, and that the FCU is mostly circulating indoor air.

    Not sure if it helps*to know that in every apartment only supply air runs in ducts. Return has no ducts.

    I also suspect the chilled water is the problem, but cant quite explain how. They checked the water temperature on every floor of the return water supply, and its perfectly fine according to specs (44-46 F).

    Each floor uses its own chilled water loop, and each apartment has its own chilled water valve. They did experiment in my apartment by closing the valve to reduce the flow to 60% of its maximum. They had very little effect on humidity.

    I understand that the water flow speed could affect heat removal, but that doesnt seem to be a problem at all since all the apartments and the corridor are cool, and temperature readings are accurate.

    The thread you linked to is really interesting. Who would have thought reducing water flow would increase heat removal. Do you think it would have the same effect on condensation?

    Quote Originally Posted by BBeerme View Post
    It appears the key is that the problem is floor wide, and not just your apartment.

    So logic would dictate that readings would be taken from each floor and compared to each other. Logic would also say that something changed.

    You said "both levels are controlled by the same FHU". What does FHU stand for?

    You said there is a fresh air supply? Has this been completely blocked off to see if there are any changes to the environment? Somehow, I would guess that this has been tried, but you never know. At a minimum, you want to eliminate [or confirm] the obvious first.

    After the fresh air, what else is common? Seems to me it would be the chilled water. So what has changed? I would be comparing the supply and return temps for the chilled water loop on each floor.

    Let's try thinking just a bit outside the box. Could it be a balance problem, flow's not to design anymore? What if your floor is getting too much water flow? I know that sounds odd, but check out this thread. Only the people here could give me the correct answer to a problem I found [and corrected] many years ago.

    http://hvac-talk.com/vbb/showthread....ed-to-This-Day

    So if each floor uses its own common loop, how are the flows controlled in those loops? Could have been a simple mistake by someone adjusting a valve. Or replacing a valve or circulation pump. Or a strainer restricted; or too fine of a mesh of screen inserted.

    Just because the water is cold, doesn't mean the system will work well. Maybe some food for thought.

  2. #15
    Join Date
    Jul 2015
    Posts
    15
    Post Likes
    Thread Starter
    Quote Originally Posted by Wingmans10 View Post
    RH should drop the longer the unit is cooling. The cold coil will condense the moisture in the air, resulting in condensation. Slowing the fan speed down will aid in humidity removal.


    What is your supply air temperature/RH, return air temperature/RH, entering supply water temperature , leaving supply water temperature.

    To clarify, does every apartment have there own individual unit or is there a central unit serving the individual floors?

    As for identifying the "fuzzy stuff", I would bring in a professional or take a sample that can be sent to a lab. They can better explain what is dangerous or not and what are considered safe levels of growth.
    I'm running the fan on low to help condensation, but it's having little effect. Your comment makes sense that RH should drop the longer unit is cooling, but my understanding is that water should condense anytime chilled water runs through the coil, regardless of room temperature. Am I missing something?

    Every apartment has an individual FCU. The building has 7 floors, and there are two individual big units serving levels 1-4 and 5-7 respectively.

    Supply air is ~50 F / 45% RH. Haven't measure return air since I think it's the same as indoor air (74 F / 80-85% RH). Entering water supply is 46 F and leaving at 48 F or so.

    I am getting a professional to identify the fuzzy stuff. The contractor said they took it to the lab and came back as dust. For reference, here's a picture of one of the supply vents. Would you say that's dust or mold forming?

    Name:  Apartment Supply Vent.jpg
Views: 894
Size:  58.6 KB

  3. #16
    Join Date
    Apr 2015
    Location
    San Diego, CA
    Posts
    39
    Post Likes
    I think the following information would be helpful to know:
    -Your apartments unit information(make,model, serial) to pull up design specs
    -The fresh air CFM, temperature & RH entering your unit.
    -mixed air temperature & RH entering your unit.
    -Supply air CFM
    -apartment size
    With enough info, I think we should be able to make a better assessment of the issue and hand.

    2 degree temperature differential doesn't seem like much on the CW supply/return. You have a decent discharge air temperature and supply water temperature that would lead me to believe the low water temperature split is due to higher than design water flow.

    I'm also curious as to how they are conditioning the fresh outside air. Is it a large 100% outside air mechanical cooling unit? A swamp cooler? Just a large supply air fan?

  4. #17
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    26,563
    Post Likes
    That's a huge piece of information right there.

    Check and compare the supply and return temps on a system on the floor that is operating fine.

    It's very likely all you have is a balance problem.



    Quote Originally Posted by curious_owner View Post
    I'm running the fan on low to help condensation, but it's having little effect. Your comment makes sense that RH should drop the longer unit is cooling, but my understanding is that water should condense anytime chilled water runs through the coil, regardless of room temperature. Am I missing something?

    Every apartment has an individual FCU. The building has 7 floors, and there are two individual big units serving levels 1-4 and 5-7 respectively.

    Supply air is ~50 F / 45% RH. Haven't measure return air since I think it's the same as indoor air (74 F / 80-85% RH). Entering water supply is 46 F and leaving at 48 F or so.

    I am getting a professional to identify the fuzzy stuff. The contractor said they took it to the lab and came back as dust. For reference, here's a picture of one of the supply vents. Would you say that's dust or mold forming?

    Name:  Apartment Supply Vent.jpg
Views: 894
Size:  58.6 KB

  5. #18
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    26,563
    Post Likes
    10% of humid air is plenty of load on the system to create the problems you are seeing. But how it would be affecting one floor and not the other is a bit puzzling. Just as with having too much water flow can reduce the cooling effect, so can weird things happen when you have too much air flow.

    It all depends on how the duct work was put together. For example, it is not the least bit uncommon to find NEGATIVE pressure in a supply duct. It happens right after a 90* bend. Measured down stream of the 90 on the inside of the 90.

    So, if someone changed out pulleys and increased the air flow, and depending on how the system was ducted, that could cause the problems you are seeing. And it's not the least bit uncommon. Maybe when the system was put together it was commissioned with all of the proper water and air flows. Maybe the blower motor in your FHU was drawing 70% of the rated amps. So some maintenance guy comes along and changes out the pulley. And adjusts the pulley so the motor is now drawing 93% of the rated amps. And he thinks he just did everyone a favor.

    Bottom line, I think the key is in finding the original prints. They will contain all of the proper design flows. Once the water and air are balanced to design, I'll bet your problems go away.

    If you [or whoever] can't get the original specs, start with the water. Compare the flows of one floor to another. That could lead you in the correct direction.





    Quote Originally Posted by curious_owner View Post
    Logic does dictate that something's changed. Logic also dictates the contractor's priorities are to minimize costs, and pretend the problem isn't there.

    I too think the problem is floor wide. The maintenance contractors keep looking for problems in my apartment, and I keep trying to explain that what I’m having are symptoms of a bigger problem. They’re looking in the wrong place.

    They use the term FHU to refer to the big unit on the roof. My guess is that they mean FAHU (Fresh air handling unit). I did ask them, but the workers have no clue what it stands for.

    They did block the fresh air supply and that didn’t change the environment. I asked them to do some more experimentation, but one of their experts told me there’s no need because only about 10% of fresh is mixed in with the apartment air, and that the FCU is mostly circulating indoor air.

    Not sure if it helps*to know that in every apartment only supply air runs in ducts. Return has no ducts.

    I also suspect the chilled water is the problem, but can’t quite explain how. They checked the water temperature on every floor of the return water supply, and it’s perfectly fine according to specs (44-46 F).

    Each floor uses its own chilled water loop, and each apartment has its own chilled water valve. They did experiment in my apartment by closing the valve to reduce the flow to 60% of its maximum. They had very little effect on humidity.

    I understand that the water flow speed could affect heat removal, but that doesn’t seem to be a problem at all since all the apartments and the corridor are cool, and temperature readings are accurate.

    The thread you linked to is really interesting. Who would have thought reducing water flow would increase heat removal. Do you think it would have the same effect on condensation?

  6. #19
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    4,434
    Post Likes
    What about renting a infrared camera for a day and see if something shows up with it, maybe leaks behind walls?
    UA Local 32 retired as of Jan 2020

  7. Likes kamersoutdoor liked this post.
  8. #20
    Join Date
    Jul 2015
    Posts
    15
    Post Likes
    Thread Starter
    Quote Originally Posted by Wingmans10 View Post
    I think the following information would be helpful to know:
    -Your apartments unit information(make,model, serial) to pull up design specs
    -The fresh air CFM, temperature & RH entering your unit.
    -mixed air temperature & RH entering your unit.
    -Supply air CFM
    -apartment size
    With enough info, I think we should be able to make a better assessment of the issue and hand.

    2 degree temperature differential doesn't seem like much on the CW supply/return. You have a decent discharge air temperature and supply water temperature that would lead me to believe the low water temperature split is due to higher than design water flow.

    I'm also curious as to how they are conditioning the fresh outside air. Is it a large 100% outside air mechanical cooling unit? A swamp cooler? Just a large supply air fan?
    Unfortunately, it's going to be difficult to get most of this information without a struggle. I have some of it if that helps:

    - Fresh air temperature is 114 F / 45-50% RH. I don't know the CFM, but they said that temperature and RH are ideal.
    - I haven't checked mixed air temperature and RH. Would it be any different than the indoor readings I have?
    - Apartment size is 850.00 sq.ft.
    - I'm not sure how to get CFM information without resorting to building design specs to be honest.
    - I'm going to check what conditioning unit they have. It didn't occur to me to ask them because I don't know much about HVAC systems, and didn't see how that would be relevant given that the fresh air supply entering my apartment is within the correct range.

    What should the water temperature split be? Is it expected to be much higher?

  9. #21
    Join Date
    Jul 2015
    Posts
    15
    Post Likes
    Thread Starter
    Quote Originally Posted by BBeerme View Post
    That's a huge piece of information right there.

    Check and compare the supply and return temps on a system on the floor that is operating fine.

    It's very likely all you have is a balance problem.
    What do you expect the chilled water temperature to be for supply and return? Are you expecting a bigger difference between the two temperatures?

    When I told them I suspect the chilled water isn't chilled enough, the contractor said that the way they made sure that chilled water system is fine was by measuring the water return temperature, which they expect to be 46-50 F. Is that wrong?

  10. #22
    Join Date
    Jul 2015
    Posts
    15
    Post Likes
    Thread Starter
    Quote Originally Posted by BBeerme View Post
    10% of humid air is plenty of load on the system to create the problems you are seeing. But how it would be affecting one floor and not the other is a bit puzzling. Just as with having too much water flow can reduce the cooling effect, so can weird things happen when you have too much air flow.

    It all depends on how the duct work was put together. For example, it is not the least bit uncommon to find NEGATIVE pressure in a supply duct. It happens right after a 90* bend. Measured down stream of the 90 on the inside of the 90.

    So, if someone changed out pulleys and increased the air flow, and depending on how the system was ducted, that could cause the problems you are seeing. And it's not the least bit uncommon. Maybe when the system was put together it was commissioned with all of the proper water and air flows. Maybe the blower motor in your FHU was drawing 70% of the rated amps. So some maintenance guy comes along and changes out the pulley. And adjusts the pulley so the motor is now drawing 93% of the rated amps. And he thinks he just did everyone a favor.

    Bottom line, I think the key is in finding the original prints. They will contain all of the proper design flows. Once the water and air are balanced to design, I'll bet your problems go away.

    If you [or whoever] can't get the original specs, start with the water. Compare the flows of one floor to another. That could lead you in the correct direction.
    The 10% fresh air coming into my unit is already treated, and it's at 74 F / 45-50% RH. Would that cause a heavy load on my FCU?

    Your comments about air flow make perfect sense. From what I understand though, since floors 1-4 are handled by the same FHU (and ducted identically), if they changed the flow it would affect all floors, not just mine. How would it be possible for my floor to be affected, but not the other ones?

    I'll go hunting for some more information about water flow and temperatures on my floor and others, and see if it's identical.

  11. #23
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    26,563
    Post Likes
    For the water to only be picking up 2*F of heat, that is not enough work. The engineers could have designed any number they wanted, but in the absence of the design specs, I would start with a difference of 10*F. But keep in mind virtually all of my experience in this area is larger commercial and industrial equipment. Still, 2*F is the obvious place to start.

    Tell that contractor to measure the difference in the apartments that do not have a problem.

    Remember, especially in the absence of the original design specs, the best thing you got going right now is you have other floors that do not have a problem. That is your base line. What is different between the readings on those floors compared with the readings on your floor.


    Quote Originally Posted by curious_owner View Post
    What do you expect the chilled water temperature to be for supply and return? Are you expecting a bigger difference between the two temperatures?

    When I told them I suspect the chilled water isn't chilled enough, the contractor said that the way they made sure that chilled water system is fine was by measuring the water return temperature, which they expect to be 46-50 F. Is that wrong?

  12. #24
    Join Date
    Jul 2015
    Posts
    15
    Post Likes
    Thread Starter
    Quote Originally Posted by BBeerme View Post
    For the water to only be picking up 2*F of heat, that is not enough work. The engineers could have designed any number they wanted, but in the absence of the design specs, I would start with a difference of 10*F. But keep in mind virtually all of my experience in this area is larger commercial and industrial equipment. Still, 2*F is the obvious place to start.

    Tell that contractor to measure the difference in the apartments that do not have a problem.

    Remember, especially in the absence of the original design specs, the best thing you got going right now is you have other floors that do not have a problem. That is your base line. What is different between the readings on those floors compared with the readings on your floor.
    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?)

  13. #25
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    26,563
    Post Likes
    That's probably not the source of the problem. I think we've narrowed it down to the chilled water loop. Could just be one balance valve for the loop on your floor got opened all the way up.

    Typically, even though the original engineer could have designed anything, each floor will have it's own loop. And if each floor is typical with one another, then each loop will have pretty much the same water flow. So, finding each of those four balance valves would be a good place to start.

    Then you plug on a flow meter to the circuit setter. You then look at the pressure drop on the meter and use a sort of circular slide rule and compare that to the setting of the circuit setter, and you know exactly how much water is flowing at that point in the system. Although anything could be in your system, images of a B&G circuit setter and flow meter below.



    Quote Originally Posted by curious_owner View Post
    The 10% fresh air coming into my unit is already treated, and it's at 74 F / 45-50% RH. Would that cause a heavy load on my FCU?

    Your comments about air flow make perfect sense. From what I understand though, since floors 1-4 are handled by the same FHU (and ducted identically), if they changed the flow it would affect all floors, not just mine. How would it be possible for my floor to be affected, but not the other ones?

    I'll go hunting for some more information about water flow and temperatures on my floor and others, and see if it's identical.
    Attached Images Attached Images   

  14. #26
    Join Date
    Jul 2005
    Posts
    7,075
    Post Likes
    Quote Originally Posted by curious_owner View Post
    Maintenance contractor said that all apartments are completely separated from each other.

    I went around the neighbors and asked if they either cook too much or something, and none of them seem to do anything to raise humidity levels. Also, if the neighbors were the cause, I'd guess that my humidity levels won't be affected by the outdoor humidity.

    The thermostat has 3 fan settings. I didn't need to open the unit.
    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.

Page 2 of 4 FirstFirst 1234 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Contracting Business
HPAC Engineering
EC&M
CONTRACTOR