ATF: Bighorn - Whisper Quiet ducting design issue

[avvidclif]

The airflow does not cause the air to come out the ducts. Pressurizing the ducts does. The job of the AC is to pressurize the duct, either one or 2 units. The ducts relieve the pressure and you feel it as airflow. If the ducts are not properly sealed the pressure cannot build up to force air out the ducts.

My 2 cents: The AC system and ductwork was properly designed to work correctly. What the design engineer did not plan for was 3 sided ducts that are not sealed correctly in assembly, pipes running thru the ducts and not sealed, etc. All of those bleed off pressure that should be forcing air out the ducts. Someone with a temp gun needs to measure the ceiling temp with the AC running. You should be able to follow the cool air down the duct by looking at ceiling temp. If all of the ceiling is about the same, somethings leaking and you are cooling the attic.

 

[TravelTiger]

Clif, I am sure you are right about how an AC system should work. I don't know how the RV system can be a completely sealed system though, too many pieces put together too quickly and with lots of angles.

What I have done:

sealed the duct run in both the supply and return ducts just past the last vent at the rear of the coach.

sealed the duct run in both the supply and return ducts just past the last vent at the front of the coach.

added blocks to stop the rear (living) AC from going to the front of the coach, in both the supply and return ducts, just past the vent into the kitchen.

added blocks to stop the front (bedroom) AC from going to the rear of the coach, the supply duct just past the vent into the bathroom (the return duct stops when it gets to the bathroom vent fan, so essentially the same place.)

The air speed coming out of the 3 living room vents (from closest to furthest) has now increased from 24 to 33mph, from 18 to 27mph, and from 14 to 23mph. So more/faster air is making the coach cool better, I believe. (Still cloudy here so hard to test.)

Short of getting a tech out to remove the ACs and look in there, I don't know what else we can do.


EDIT: I still have not added the new vent covers. Put one up just now, and I'm not sure I like that they are slightly different color than the OEM return vents. That means buying return vents that match, or painting them and living with the slight shape/vent difference. :-/

 

[AAdams]

I guess we are fortunate. Our BH3750FL has 2 supply and returns in each of the rooms ( Living room, kitchen, bedroom ) and one return in the bathroom. We are in Florida and it is 92 outside and 72 inside.

You may want to block the air return for the furnace that runs to the basement, since cold air drops you may be losing a lot of cold air through it. Our return is in the steps to the living room and I will be taking out the drawer and stilling a pillow in the area to block the cold air from cooling the basement and putting the drawer back in ( Haven't done this yet ). We also have less cubic footage to cool since the bedroom is raised in the rear, which may play a small part on us cooling down.

 

[mlpeloquin]

Clif, I am sure you are right about how an AC system should work. I don't know how the RV system can be a completely sealed system though, too many pieces put together too quickly and with lots of angles.

What I have done:

sealed the duct run in both the supply and return ducts just past the last vent at the rear of the coach.

sealed the duct run in both the supply and return ducts just past the last vent at the front of the coach.

added blocks to stop the rear (living) AC from going to the front of the coach, in both the supply and return ducts, just past the vent into the kitchen.

added blocks to stop the front (bedroom) AC from going to the rear of the coach, the supply duct just past the vent into the bathroom (the return duct stops when it gets to the bathroom vent fan, so essentially the same place.)

The air speed coming out of the 3 living room vents (from closest to furthest) has now increased from 24 to 33mph, from 18 to 27mph, and from 14 to 23mph. So more/faster air is making the coach cool better, I believe. (Still cloudy here so hard to test.)

Short of getting a tech out to remove the ACs and look in there, I don't know what else we can do.


EDIT: I still have not added the new vent covers. Put one up just now, and I'm not sure I like that they are slightly different color than the OEM return vents. That means buying return vents that match, or painting them and living with the slight shape/vent difference. :-/

Clif is correct. You have block off leaky vent runs. By doing so, you have allowed more pressure to build in the remaining runs. The remaining runs may also be leaky as well, but at least they are not leaking so much that it is robbing you of the air pressure required to send cold air into your rig. Someone might want to call the AC manufacture and ask just how much air the AC blower pushes in cubic feet. Then measure the air flow coming out each vent. This should tell you how much air is leaking out of the system. You would be supplied just how much air will leak out of a few small cracks and defeat an AC or furnace system. With this knolage of air flow loss, you can approach Heartland about fixing the (not proven yet) defective vent system in some fifth wheels. Root cause may be an assembly problem or a few defective preassembled vent system. Until someone gets the data, you may not get very far.

 

[Gary521]

The system puts out about 350cfm for each air conditioner at high speed. I am not an AC guru but that does not sound like a lot of air volume ( a fantastic fan puts out about 900 cfm for comparison ). My system does not have a common duct on the output side due to the shape of the bathroom. Thus, the living room and the bedroom out feed ducts are similar to what TravelTiger modified the ducts to do. There are three out feed ports on each AC. The center port has less flow on each AC system. End of run, pretty good

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TravelTiger, I would be a bit concerned about blocking the return side. This may restrict some flow to the front AC.

 

[Bohemian]

Another thing to consider.
A leak on the intake side can be just as effective at keeping the unit hot.

 

[mlpeloquin]

http://www.omega.com/googlebase/product.html?pn=HHF-309&gclid=CNiDxsTJ38wCFRRgfgodfgEABw

To measure the cubic feet per minute. Place at output of each duct. Add all and anything less than the rated cfm, is your duct air loss. Note if the reading is within the meters +/- accuracy then your fine.

 

[avvidclif]

Be interesting since the Dometic AC's put out 300/350 CFM (min-max) each.

 

[RVFun4Us]

THAT is strange. I was on board with you until the bathroom...I have a 2016 3270 built 2/16, and the bathroom vent is definitely a supply....which side of the coach are your supply vents on...mine are off doorside. My bathroom supply vent runs right between the shower skylight and the vent fan. Both intrude into the ductwork.



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Frostking makes a heavy foil/foam stick on duct insulation. I used this to insulate the interior bottom of the ductwork. It can also be used to stick a small flap on the top of the ductwork to route the airflow a bit. Keep in mind that airflow direction changes depending on which ac is in play.

Celt.

We might be talking the same thing. I interpret "supply" as the input side of the system which is on the door-side. I interpret "return" as the output side of the system which is on the off-door side. My filters are all in the door-side or input vents. So the output is coming into the bathroom, pretty good airflow in fact like many others have said. And the middle output vent both upstairs and downstairs seems to be the weakest air flow which somebody said is because they are right below the AC unit. I think our units are the same, just terminology issues.

 

[TravelTiger]

The output (blow) and input (suck) sides as I've blocked them are the same length. This applies to both bed and bath. The input side of the bedroom air does have one less vent, as there is not an input vent in the bath. My bath has an output vent only, and it has very strong flow.

I have 4 output vents and 4 input vents for the living room AC, 3 output vents and 2 input vents for the bedroom AC. The bedroom has not problem keeping the space cold.

The living room as of today is doing much better.

As I said, there's no interior access to where the ducts connect to the boxed area the AC sits over. You'd have to pull the roof AC to get to it.


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[TravelTiger]

Another test, old vs new vents. Though the volume of air coming out was not significantly different, 2-3mph less for the old vent, the angle of the air was. New vents pushed air lower into the room.

old vent (above)

new vent(above)


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[SNOKING]

Another test, old vs new vents. Though the volume of air coming out was not significantly different, 2-3mph less for the old vent, the angle of the air was. New vents pushed air lower into the room.

old vent

new vent


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Did you reverse the pictures, our new 2017 BH3575 has registers like you labeled old? Chris

 

[Toy1Ton]

so are the new vents Worth buying?

 

[TravelTiger]

Did you reverse the pictures, our new 2017 BH3575 has registers like you labeled old? Chris

The first pic is the original vents that came in our 2016.

The new vent is:

http://www.dwincorp.com/products.php?product_id=11

At first I only bought for the outflow, but realized they are different color than the original. So we'll need to buy additional vents/filters for the inflow side... Or live with them being different. I am considering painting them to match.

 

[TravelTiger]

so are the new vents Worth buying?

The jury is still out on that. I think they are going to help some, but are they worth the money spent? I'm not sure yet.

 

[NHCelt]

We might be talking the same thing. I interpret "supply" as the input side of the system which is on the door-side. I interpret "return" as the output side of the system which is on the off-door side. My filters are all in the door-side or input vents. So the output is coming into the bathroom, pretty good airflow in fact like many others have said. And the middle output vent both upstairs and downstairs seems to be the weakest air flow which somebody said is because they are right below the AC unit. I think our units are the same, just terminology issues.

I'm with ya now).... We have the same. When both ac's are running the bathroom is some kind of cool.

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[TravelTiger]

I'm with ya now).... We have the same. When both ac's are running the bathroom is some kind of cool.

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Consider one of these for the bath. It can be adjusted. It doesn't seal completely but can limit the airflow.

 

[Bones]

Consider one of these for the bath. It can be adjusted. It doesn't seal completely but can limit the airflow.

I like that

 

[SNOKING]

Maybe we need to go by industry standard terms. There appears to be some confusion! Chris

http://www.energyvanguard.com/blog-...he-Lingo-Air-Conditioning-Terminology-Tidbits

Supply - The side of the duct system that pushes conditioned air back into the house. Supply vents have cool air coming out of them when the AC is on.

Return - The side of the duct system that pulls air from the house back to the air handler to be conditioned again. You can identify return vents by taking a piece of tissue and seeing if it gets pulled in or blown out when you hold it in front of the grille or register.

 

[dlw930]

Consider one of these for the bath. It can be adjusted. It doesn't seal completely but can limit the airflow.

Erika,

Are these a D&W product also? Do you know the model no.?