Extremely noisy A/C unit in loft with visible ducts


  #1  
Old 07-10-17, 12:55 AM
J
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Extremely noisy A/C unit in loft with visible ducts

We just had our Heat Pump and AC replaced with a larger unit. It looks the same but it is supposed to be 3 ton instead of 2 (I think). The main duct comes out of the room where the air-mover is in a huge duct. Immediately off of that duct is a vent for the kitchen. Then the duct comes to flat end but has two smaller ducts on either side that supply the rest of the loft.

It is unbearably loud. And it's not rattling or fan noise because we have it in it's own room that is heavily insulated. It's just the air rushing through the vents, I believe. My thought is that the first vent should not be where it is. It's is entirely too forceful and it is super loud. Trying to close the vent a little makes it really loud.

My second thought is that there should be some sort of Y split in the vents so the air doesn't just hit a stop and then force itself down either side.Name:  ductwork-basic.jpg
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Would eliminating the kitchen duct and adding a Y help with the noise? Any suggestions would be great. Thanks.
 
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Old 07-12-17, 05:32 PM
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Corrections

As it turns out, my partner gave me some bad information. We started with a 3.5 ton unit, but upgraded to a 5 ton unit.

I will attach the ductwork diagram (superimposed on my loft floorplan) so it makes better sense.

Our loft is about 1500 sq. ft with exposed brick walls and 14-15' ceilings that are exposed beam. We have beautiful arched glass and metal doors that were handmade, but do not seal very well at all. Though I plan to caulk the edges, there are places between the brick and the door frame that you can see light through. Our roof has a membrane, but we also have 4 skylights that we cover with car shades in the summer.

In the back of our loft, the two bathrooms sit under the utility room. The utility room houses just the AC and the water heater. There is plenty of wasted space in this room and you have to crawl through a service door (about 2ft x 2ft to get into it). The wall that surrounds it (in red on the diagram) is the only interior wall that goes floor to ceiling.

We have a diagonal wall that is about 8' tall that runs through our place but does not go to the top of the 14-15 foot ceilings. The ducts currently hang down about 1 1/2 feel. They are not sealed or taped at all. There are visible gaps near every vent or junction.

The return vent is located in a makeshift closet that has shelves in front of half of it, but about 2 feet away.

Removing the filter does not solve the noise problem.

The small flexible duct that feeds the bathroom (VENT G) is super loud and way too powerful. We keep the vent closed and it's still too loud and too much air makes it through.

VENT A is also too strong and way too noisy. We can't even close VENT A because it is too loud. And it blows directly into the kitchen..coldest room in the house.

Most of the noise seems to be coming from around VENT A

There is no noticable difference in noise when the intake is blocked or the closet is accentally closed so I don't think it's the return.

Any suggestions would be greatly appreciated. Here are the specs and diagram:

New unit installing in June 2016
MAKE: Trane
MODEL: 4twr4060e100b, TAM4AOC60S51ED
SEER: 14
BTUH COOLING: 5 ton
BTUH HEATING: 8kw
CFM:2000

We live in Atlanta, GA if that helps.
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Thanks again for your help. Sorry for the misinformation.
 
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Old 07-12-17, 07:03 PM
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We started with a 3.5 ton unit, but upgraded to a 5 ton unit.
The problem now is you upgraded to a bigger unit with a lot more airflow but didn't increase the main duct size.

Why was such a large increase made in the cooling system ?
I'm not sure what to recommend as far as the ductwork. It depends largely on what you can get to and what will fit there.
 
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Old 07-12-17, 07:07 PM
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j,
12 x 8=400 cfm, 14 x 8=490 cfm, 16 x 8=580 cfm's. What is the height of your trunk line. Is all 8" high or higher. If it is all 8" it sounds like you have way to much unit for your duct work. You cannot just increase unit size with small duct work. It's only capable of handling so much air velocity.

You should measure all your ductwork to see the total cfm value. Even though you split you still have a very small main supply. You could have come off the plenum with different trunks.

I have a 2 ton unit with a 20 x 8 main trunk to handle about 1100 cfm's then decreased as needed.

You could possibly try adjusting your blower speed to see if it makes a difference.

It sounds like your trying to run a pressure filled fire hose into a 1/2" pipe. Too much.
You can try googling DUCT SIZING CHARTS to see the different values.

Just my thoughts. Hope this helps a little.
 
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Old 07-12-17, 07:26 PM
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There isn't a single peace of duct there that's correctly sized. It will all have to be replaced to support the 2000 CFM your now needing to move.
 
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Old 07-14-17, 11:10 AM
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Well, fortunately enough, the ductwork could not be easier to access. It hangs just above a half-wall that runs through the loft. It is completely exposed and could be removed in less than 5 minutes. It's held up with less than a dozen straps and you wouldn't even need a ladder (though we have several, inlcluding a nice rolling ladder that's super easy to move).

Thanks for the reply, We are going to start looking for someone to install new ducts. I appreciate the help.
 
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Old 07-14-17, 11:14 AM
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Thanks for the reply. I tried to look up duct sizing and it appears there are 3 models. All of which sound like they have been carefully engineered for people in the industry. Which is totally reasonable, but way outside the scope of my understanding. I will call someone to replace the ducts. I appreciate your help. Thanks.
 
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Old 07-14-17, 11:41 AM
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http://www.virginiaair.com/index.php...sidential-duct.

The site above will show the size ducts you need to move the amount of air you have. This is for informational purposes if interested.
 
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Old 07-14-17, 12:04 PM
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Just for kicks, who suggested such a drastic increase in unit capacity? Why was such a suggestion made?
Did this person explain that a bigger unit isn't really an "upgrade"?
 
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Old 07-15-17, 01:43 AM
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Roughneck,

It was July of last year during a heat wave in Atlanta, GA that our AC went out. There are no windows in my loft and it's not well insulated.

When the AC went out, it was roughly 99 degrees and since my office is located at the back of my loft, the temp was over 100. Since the exposed brick walls were great at storing heat from the day, there was literally not a minute of relief the entire time. At that point, you could have sold me a million ton AC unit and so long as you could get it installed quickly, I wouldn't have complained.

We managed to get an AC guy to come out and install this unit after 5 days of being unable to function at all. He suggested that our previous unit was underpowered due to the 1600 sq. ft layout, the position of the unit and the fact that we have 4 large unventilated skylights that literally bake anything under them during the summer, and likely his availability to get us a unit of any size at that time. He was working about 18 hours a day 7 days a week and said that he hadn't had so many AC units to install in his 15 years of doing this as he did that summer.

He managed to get us AC that for the first time actually cools the entire place in a matter of a couple of days...including removal of the old heatpump/ac and installation of the new heatpump and AC and he charged us about 3 grand less than four other quotes we got for work they could not deliver on for a month.

We are happy with how cool the unit stays now (we keep it around 69 year round), but we just want to eliminate the noise. Sounds like new ducts will be the deal.
 
 

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