Hello, some very informative posts on this site. I'm new and would appreciate any advice.
The issue: SUPPLY air is reading high humidity around 70%. Even when the space is empty after hours overnight.
The location:
I'm the owner of a 2700 sq ft gym that holds cardio classes.
The workout space is about 1800 sq ft, it has two 4-ton Trane units.
Already investigated:
The units do a good job of cooling the space, even when full.
The units have economizers. We already closed those to test that outside air is not causing the issue.
I have the engineering specs attached here. We haven't done a Test and Balance yet.
We have dehum with reheat coils. But the thing is, the supply air is humid even when no people are present and not as humid outside
Serial number: THC048E3REA1LD0B0A1A0B00AA000C0000000000
The commercial HVAC company I work with has a lot of experience. But they can't figure out, why is the Supply air so humid??
It's causing the mirrors to fog up even when no people are inside the space.
Is this a common problem? Any advice on next steps to investigate or resolve would be great thanks!
So they are getting high humidity in the supply duct with or without the ac circuits running?
What is the temp and dew point of the space during all these times.
Off my head, 8 tons of cooling for a space of 1800 sqft empty is gross. Now I understand this is a gym and fills with lots of people and they make a lot heat.
But empty, the unit(s) cant run but for a few minutes to reach temp.
Let me go back and look at the design sheet and see what setup was engineered
So they are getting high humidity in the supply duct with or without the ac circuits running?
What is the temp and dew point of the space during all these times.
Off my head, 8 tons of cooling for a space of 1800 sqft empty is gross. Now I understand this is a gym and fills with lots of people and they make a lot heat.
But empty, the unit(s) cant run but for a few minutes to reach temp.
Let me go back and look at the design sheet and see what setup was engineered
Sent from my iPhone using Tapatalk
Yes, when the AC units are running, the air coming out of the duct will be high humidity.
When the AC is off, we didn't measure the air inside the duct.
That's true, I think when empty it reaches set point quickly.
During the day we set the thermostat to 65 (I know that's low, but it hasn't frozen). At night we set it to 80.
Attached are graphs of temperature, humidity, dew point over a week. The spikes are when class is happening and 20 ppl are running around. The lows are in between class or overnight.
So the temp ranges from 62 to 72 and dew point ranges from 50 to 66.
(Not sure how accurate the sensor is, it's a Govee from Amazon)
Membership Chair/ARP Committee / Professional Member*
Join Date
Sep 2002
Location
I try to stay as far away from myself as I can.
Posts
37,825
Post Likes
Likes (Given)
441
Likes (Received)
11527
Dislikes (Given)
5
Dislikes (Received)
27
AC units cool and dehumidify the air. They remove moisture from the air by operating the cooling coil below the dew-point of the air moving through the cooling coil. The air leaving the cooling coil is always close to being able to hold all the moisture that it is able to hold at that temperature.
RH% is the amount of moisture in the air As Compared to 100% of what the could hold At That Temperature - expressed as a percentage. In an air conditioning circumstance All the air leaving the cooling coil is at a much high RH% than it was before it went through the cooling coil.
What is the return air RH%? Please post that number.
PHM
------
Originally Posted by FitSA
Hello, some very informative posts on this site. I'm new and would appreciate any advice.
The issue: SUPPLY air is reading high humidity around 70%. Even when the space is empty after hours overnight.
The location:
I'm the owner of a 2700 sq ft gym that holds cardio classes.
The workout space is about 1800 sq ft, it has two 4-ton Trane units.
Already investigated:
The units do a good job of cooling the space, even when full.
The units have economizers. We already closed those to test that outside air is not causing the issue.
I have the engineering specs attached here. We haven't done a Test and Balance yet.
We have dehum with reheat coils. But the thing is, the supply air is humid even when no people are present and not as humid outside
Serial number: THC048E3REA1LD0B0A1A0B00AA000C0000000000
The commercial HVAC company I work with has a lot of experience. But they can't figure out, why is the Supply air so humid??
It's causing the mirrors to fog up even when no people are inside the space.
Is this a common problem? Any advice on next steps to investigate or resolve would be great thanks!
-Joe
PHM
--------
When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
AC units cool and dehumidify the air. They remove moisture from the air by operating the cooling coil below the dew-point of the air moving through the cooling coil. The air leaving the cooling coil is always close to being able to hold all the moisture that it is able to hold at that temperature.
RH% is the amount of moisture in the air As Compared to 100% of what the could hold At That Temperature - expressed as a percentage. In an air conditioning circumstance All the air leaving the cooling coil is at a much high RH% than it was before it went through the cooling coil.
What is the return air RH%? Please post that number.
PHM
------
Sure, attached are the Supply RH numbers, I don't know if I have Return Air RH. I'll try to get those next time I'm on site.
Your cooling coil is producing 50^F dew point air occasionally. Would be better to have a colder cooling coil provided <48^F whenever the cooling coil is cooling. This would suggest less air flow which would allow the cooling coil to remove more moisture and less sensible cooling.
Go back to your equipment manufacturer for assistance.
Just a couple farther adjustment. As others have stated, do not be confused by high %RH while cooling and right after cooling cycle ends. At the end of the cooling cycle, normal to see spike in %RH as the moisture on the cooling coil evaporates.
Keep us posted on advice from manufacturer. Hoping you can find simple way to adjust the fan speed to get more moisture removed while cooling.
Regards Teddy Bear
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
When is the humidity problem? Always? When people are there? At night?
Sent from my iPhone using Tapatalk
The humidity seems to remain high both when people are in the workout room and after hours at night when no one is there. It's also tends to be more humid in the workout room when it is humid outside. San Antonio is frequently at 90% humidity during summer and fall.
Your cooling coil is producing 50^F dew point air occasionally. Would be better to have a colder cooling coil provided <48^F whenever the cooling coil is cooling. This would suggest less air flow which would allow the cooling coil to remove more moisture and less sensible cooling.
Go back to your equipment manufacturer for assistance.
Just a couple farther adjustment. As others have stated, do not be confused by high %RH while cooling and right after cooling cycle ends. At the end of the cooling cycle, normal to see spike in %RH as the moisture on the cooling coil evaporates.
Keep us posted on advice from manufacturer. Hoping you can find simple way to adjust the fan speed to get more moisture removed while cooling.
Regards Teddy Bear
Yes the fan is on "Auto" and we are aiming for 50% RH although 40% RH would be nice.
So slowing down the fan speed will potentially allow the unit to remove more moisture?
Wish the units were a 2 stage. I'll try and get info about other ways to decrease fan speed.
90+% with ac on isnt unusual. 70% may be too low, in other words, coils not cold enough to really pull moisture out air,
too much airflow over coil, refrigerant charge low, or air leaks could also be pulling moisture into building (air would be hotter and more humid going into coil )
AC units cool and dehumidify the air. They remove moisture from the air by operating the cooling coil below the dew-point of the air moving through the cooling coil. The air leaving the cooling coil is always close to being able to hold all the moisture that it is able to hold at that temperature.
RH% is the amount of moisture in the air As Compared to 100% of what the could hold At That Temperature - expressed as a percentage. In an air conditioning circumstance All the air leaving the cooling coil is at a much high RH% than it was before it went through the cooling coil.
What is the return air RH%? Please post that number.
PHM
------
That is the best decription of relative humidity that I have ever read.
Thanks PHM
Can someone please explain to me -
Why is there never enough time to do it right the first time, but plenty of time to do it twice?
AC units cool and dehumidify the air. They remove moisture from the air by operating the cooling coil below the dew-point of the air moving through the cooling coil. The air leaving the cooling coil is always close to being able to hold all the moisture that it is able to hold at that temperature.
RH% is the amount of moisture in the air As Compared to 100% of what the could hold At That Temperature - expressed as a percentage. In an air conditioning circumstance All the air leaving the cooling coil is at a much high RH% than it was before it went through the cooling coil.
What is the return air RH%? Please post that number.
PHM
------
What's the best way to measure RH in the Return Air?
Btw, I think the units might be short cycling. Sometimes they'll only come on for a couple minutes since they reach set point quickly.
Is there a simple way to check for air leaks that would pull in humidity from the outside?
Membership Chair/ARP Committee / Professional Member*
Join Date
Sep 2002
Location
I try to stay as far away from myself as I can.
Posts
37,825
Post Likes
Likes (Given)
441
Likes (Received)
11527
Dislikes (Given)
5
Dislikes (Received)
27
1. Any sort of psychrometer would be close enough for your purposes.
2. There is at least a part of your problem. Units remove zero moisture from the air when they are not running. Units don't remove very much moisture from the air for the first 10-15 minutes of operation.
How many units are there in total? Start staging them on temperature. Set one at a degree or two below the desired space temperature. Stage the others on at sequentially higher temperatures. With the goal of keeping at least unit one running as long as possible.
3. Pressurizing the building would be easier. But on a calm day I guess a smoke candle could be used at all the joints in the structure of the units. That's all I can think of right this second but there are lots of smart guys on this forum who will likely be along directly.
PHM
--------
Originally Posted by FitSA
What's the best way to measure RH in the Return Air?
Btw, I think the units might be short cycling. Sometimes they'll only come on for a couple minutes since they reach set point quickly.
Is there a simple way to check for air leaks that would pull in humidity from the outside?
Thanks.
PHM
--------
When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
Got it, I'll place my psychrometer at the return grill to get a reading.
I reached out to the original mechanical engineer a few times, he wasn't much help. Finally recommended a separate dehumidifier to me, I'll try a floor model dehum and see if that helps.
Part of the problem is that the installer and the mech engineer are completely separate and don't communicate.
It was installed 5 years ago, and I didn't know that the installer didn't wire the units properly in the first place.
I've had 5 HVAC companies take a look since then, I even had Trane technicians investigate multiple times. Trane didn't notice the incorrect wiring, my most recent local HVAC company finally figured out the wiring.
1. Any sort of psychrometer would be close enough for your purposes.
2. There is at least a part of your problem. Units remove zero moisture from the air when they are not running. Units don't remove very much moisture from the air for the first 10-15 minutes of operation.
How many units are there in total? Start staging them on temperature. Set one at a degree or two below the desired space temperature. Stage the others on at sequentially higher temperatures. With the goal of keeping at least unit one running as long as possible.
3. Pressurizing the building would be easier. But on a calm day I guess a smoke candle could be used at all the joints in the structure of the units. That's all I can think of right this second but there are lots of smart guys on this forum who will likely be along directly.
PHM
--------
Awesome thanks,
1. I'll use my psychrometer to take a reading
2. There are 2 units. I can try the staging temperature. I'm wondering if there's a thermostat setting to tell them to stay on for at least a certain amount of time? I'll read through the manual again.
3. I can try the smoke candle thing also. It's definitely more humid in the space on days when it's hot and humid outside.
Reply
Originally Posted by jbhenergy
