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Old 06-28-2022, 06:22 PM   #1
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DIY AC duct efficiency improvement project?

Has anyone done the AC duct efficiency improvement projects described in a number of YouTube videos? They're copying the RV Airflow idea, building it out of duct board rather than paying for the custom-molded styrofoam. If you have done it yourself, was there an improvement?

I looked in the plenum of the 15K BTU Coleman Mach AC in my Mini-Lite. It looks to me like Rockwood did a pretty good job of isolating the return air flow from the cold air output, and sealing the obvious big gaps in the output plenum.

What I don't know is whether adding the baffles to the outflow improves the efficiency of pushing the air down the ducts. Even if it does, it's not worth the cost to me of paying RV Airflow for their kit. It would be cheap for me to do it myself using 1/2" insulation sheathing and the project would be interesting, but I don't want to waste my time if it doesn't accomplish anything.

The insulation board insert would block the air dump outlets, but I really never use those.
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Old 06-28-2022, 07:23 PM   #2
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Originally Posted by chriscowles View Post
Has anyone done the AC duct efficiency improvement projects described in a number of YouTube videos? They're copying the RV Airflow idea, building it out of duct board rather than paying for the custom-molded styrofoam. If you have done it yourself, was there an improvement?



I looked in the plenum of the 15K BTU Coleman Mach AC in my Mini-Lite. It looks to me like Rockwood did a pretty good job of isolating the return air flow from the cold air output, and sealing the obvious big gaps in the output plenum.



What I don't know is whether adding the baffles to the outflow improves the efficiency of pushing the air down the ducts. Even if it does, it's not worth the cost to me of paying RV Airflow for their kit. It would be cheap for me to do it myself using 1/2" insulation sheathing and the project would be interesting, but I don't want to waste my time if it doesn't accomplish anything.



The insulation board insert would block the air dump outlets, but I really never use those.
Never heard of it. My Rockwood has a ceiling made of 8 in Styrofoam that s channeled out for each vent in the ceiling.
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Old 06-28-2022, 08:20 PM   #3
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... Rockwood has a ceiling made of 8 in Styrofoam that s channeled out for each vent in the ceiling.
We all have the same, in that respect.

The RV Airflow system is a custom-molded polystyrene foam insert for the inside of the AC plenum. Installation includes removal of the baffle that makes the air dump vents work. The purported result is more efficient delivery of cold air to the ducts and a larger intake surface area for the return.

YouTube videos show measured improvements. I'm not skeptical about it working. I am skeptical about the value. The kit costs close to $200.

What I'm asking about is DIY substitutes for the commercial kit. Materials are 1/10th the cost of the kit. What I don't know is if the result justifies the effort, specifically in a Rockwood.

Most YouTubers don't do anything to improve the return air surface area. Only one emulated the scooped-out intake that does that. I think that's critical to the improvement.
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Old 06-29-2022, 10:18 AM   #4
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Originally Posted by chriscowles View Post
Has anyone done the AC duct efficiency improvement projects described in a number of YouTube videos? They're copying the RV Airflow idea, building it out of duct board rather than paying for the custom-molded styrofoam. If you have done it yourself, was there an improvement?

I looked in the plenum of the 15K BTU Coleman Mach AC in my Mini-Lite. It looks to me like Rockwood did a pretty good job of isolating the return air flow from the cold air output, and sealing the obvious big gaps in the output plenum.

What I don't know is whether adding the baffles to the outflow improves the efficiency of pushing the air down the ducts. Even if it does, it's not worth the cost to me of paying RV Airflow for their kit. It would be cheap for me to do it myself using 1/2" insulation sheathing and the project would be interesting, but I don't want to waste my time if it doesn't accomplish anything.

The insulation board insert would block the air dump outlets, but I really never use those.
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Old 06-29-2022, 11:12 AM   #5
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Thanks
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Old 06-29-2022, 11:50 AM   #6
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We accomplished similar by just using foil tape, and installing that strategically (at the unit as well as at each of the ceiling registers). Prevents warm air from mixing with cold, prevents air loss, etc. That and installing a mirrored tint to the windows made dramatic improvements in the temp inside the trailer. We used to see temp at the registers about 6 degrees cooler than the return. Now we see about 18 degrees cooler.
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Old 06-29-2022, 02:02 PM   #7
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Looks to me that the guy on the YouTube video nailed it. Blocking off the return air better and putting in the V-shaped structure to direct the cold air into the ducts should drastically improve cooling.
Our a/c started tripping off the 20 amp dedicated a/c breaker on the coach inside panel when we started it up in early June. So it goes off to the repair place Friday to be figured out.
I had done a lot of tape work previously to block off some of the obvious waste and ill-fitting joints so I guess I will have to redo that first if we get a new a/c. But then I will follow the DIYer's directions and put in the V shape.
Thanks for the link to his video.
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Old 06-29-2022, 03:45 PM   #8
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User Rustynuts on the Jayco Owners forum has 3D printed one for his own. He said his designs are on Thingiverse:

https://www.thingiverse.com/browningm37/designs

He added, "They really make a difference but make sure to clean up the entry point of the duct work. A few people have had fitment issues but it was because the AC unit was installed crooked and that can be fixed by loosening the 4 bolts and straightening it and tightening back down. This can all be done from the inside."
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Old 06-29-2022, 04:29 PM   #9
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I sprang for the RV air kit. in hindsight should have done the DIY though.



One thing that helps a LOT is to foil tape up the supply plenum properly and especially the supply/return divider, mine was not placed properly and was not sealed.


From an HVAC engineering (me) perspective both methods have merit. I guess I was just lazy, it did make quite a difference. Most noticeable is the reduced return air noise, slight increase in airflow. However you don't get more capacity, just more air flow. Remember air temperature changes in reverse to air flow (more CFM is less delta T).
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Old 06-29-2022, 07:07 PM   #10
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... However you don't get more capacity, just more air flow. Remember air temperature changes in reverse to air flow (more CFM is less delta T).
That makes sense, since the evaporator has a physical limit on the total heat it can transfer under ideal conditions. I think there's still an opportunity for an increase in the absolute amount of heat transferred to the room, if the evaporator is more capable than the volume of air that previously was flowing through it. The increased air flow may improve total heat transferred, though not necessarily in direct proportion to the increase in flow. Increased flow may also add to the perceived improvement, just as ceiling fans do.

I'm hoping to benefit from some noise reduction as well, but I'm not expecting much.
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Old 06-29-2022, 07:09 PM   #11
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User Rustynuts on the Jayco Owners forum has 3D printed one for his own. He said his designs are on Thingiverse:

https://www.thingiverse.com/browningm37/designs

He added, "They really make a difference but make sure to clean up the entry point of the duct work. A few people have had fitment issues but it was because the AC unit was installed crooked and that can be fixed by loosening the 4 bolts and straightening it and tightening back down. This can all be done from the inside."
How do I find somebody with a 3D printer? It's definitely not something I'm going to buy myself. Is there a network of people who do that commercially?
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Old 06-29-2022, 07:23 PM   #12
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Somewhat related, this enhancement to the grate in front of the compressor coils may improve heat transfer under severe conditions, but I don't think the effect will be as great as the interior changes.
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Old 06-29-2022, 11:40 PM   #13
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So, first off, just to set the record straight…a Rockwood roof is not 8 inches thick (I wish!)…it’s only a mere 4 inches. Walls are 1.25 inches thick, ugh

I did the DIY modification to my 15k BTU Coleman. Took pieces of foam and cut/shaped it into a curve, then covered it in foil tape…sealed up any gaps in the ceiling opening and fitted that thing in snug and level with the duct openings. Really gave it my best effort and spent several hours making the foam block. Only mistake I made was the a/c plenum is slightly offset…my v shaped curve foam block was centered. Oh well, shouldn’t make much difference…other than possibly slight increase in airflow on the one side. Anywho, the results? Minimal I say. I didn’t notice much increase in airflow, if at all really, and noise is about the same. I think the culprit on airflow is the foam channels in the ceiling cause inherent airflow drag. I did this a/c mod on my old trailer and didn’t do a V curve…only flat foam board sealing off the plenum duct side. That yielded significant decrease in noise and increase in airflow on that Coleman 13.5….but less vents and metal ducting (not a Rockwood). That air conditioning cycled on and off respectively on even the hottest of days in my region (98-100f). Was very satisfied.

Being somewhat disappointed with the modification to the a/c plenum on my Rockwood…the next thing I did was remove the roof top a/c cover and wrap the air conditioner compressor in reflectix bubblewrap, including the cold line to the evaporator. I left the hot line to the condenser alone for obvious reasons. This has maybe made a small difference in efficiency? I mean, it can’t hurt! If you look at your home a/c the compressor is covered with an insulating blanket and the lines are foam wrapped.

Would love to see someone do a CFM comparison without and with the RV Airflow system installed.
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Old 06-30-2022, 09:50 AM   #14
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I did the mod. I started with the RV airflow product but it didn't fit right. I created a new plenum and directed it to both duct channels. It did make an improvement and quited the ac a bit. I would recommend doing it. Although it was a tedious mod that took several hours but the outcome was worth it to me. One caviat i noticed was in the duct work on each duct end register, Manufacturing did not make the end smooth, they sprayed expanding foam and therefore it created air turbulence so i cut it smooth and round then placed aluminum duct tape that made a difference as well. The key here is too elliminate any air turbulence in the plenum and duct work.
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Old 06-30-2022, 11:23 AM   #15
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How do I find somebody with a 3D printer? It's definitely not something I'm going to buy myself. Is there a network of people who do that commercially?
As around to your friends. I have at least 2 people in my close friends network with them.

Or, I've heard that you can sometimes rent time from a 3D printer at the local library. I've never looked into it, though.
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Old 06-30-2022, 11:37 AM   #16
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You cleaned up duct ends like this??
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Old 06-30-2022, 11:43 AM   #17
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As around to your friends. I have at least 2 people in my close friends network with them.

Or, I've heard that you can sometimes rent time from a 3D printer at the local library. I've never looked into it, though.
There are also companies online who will print and ship it.
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Old 06-30-2022, 04:54 PM   #18
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So, first off, just to set the record straight…a Rockwood roof is not 8 inches thick (I wish!)…it’s only a mere 4 inches. ...
Thank you for correcting my error. I know it's 4" and don't know why I wrote otherwise.
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Old 06-30-2022, 05:09 PM   #19
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You cleaned up duct ends like this??
On the topic of duct ends, how do I remove the cover without breaking it? Unrelated to this project, I broke a vane in one when I hit it with something. Now it won't stay open. I can swap it with the one in the bathroom because we usually keep that one closed. But I don't want to break the good one taking it out.
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Old 06-30-2022, 06:52 PM   #20
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While I did not read everything word for word here but I was recently looking at the ac styrofoam thing for the $200 and a YouTube channel I follow just so happen to get one to try. He had already sealed the vents better,the return and sealed the dump valve with foil tape and reflectix. He got a little gain by adding the wedge thing but not nearly what was claimed. What he found was by just sealing the vent, divider, output and return did okay but by selling the dump valve is what made the most difference. He found that while the foam thing does work really by just diy sealing the dump valve does 90% what the 200$ kit did.
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