Odd Maxxair Deluxe airflow problem

[thejingles]

I'm partially through my build and installed my ceiling panels not to long ago. I trimmed and fit the Maxxair Deluxe garnish, inserted it into the matching cut-out in the ceiling, and figured that was that with the fan.

I've noticed a strange problem, though. With the garnish installed, the air from the fan (when blowing into the van) is no longer directed down. Most of it instead wraps around with the garnish and is directed out from the fan along the ceiling. Hold your hand directly under the fan and you barely feel anything, but hold your hands up near the ceiling and you feel all of the airflow. Remove the garnish and the air flows down again.

Has anyone dealt with this and/or found a solution? I'm trying to figure out how to install some louvers or something to direct the airflow, but I thought I might try here first.

Thanks for the help.

 

[sparkplug]

I'm slightly confused how that could happen unless you trimmed the 'garnish' too short so that air is getting into the top of it.

I fitted mine yesterday (will go out and check the airflow now after your post!) and you can see from the (bad) photo below that the garnish goes up the sides of the fan unit so that the top of the garnish is above the lowest point of the fan.

Could you post a pic of yours to see if it sheds any light on what might be going on? I just can't think how that could be happening.

 

[Timo27]

Ive just fitted one ill check it later and report back.

 

[gs850gx]

Is there a good path for air to exit the van? Not much happens when everything is closed up. However, I have noticed the airflow you describe as well and believe it has to do with back pressure.

 

[thejingles]

Tried it with windows open and closed - same result - so it doesn't seem to be a back pressure issue. Here is an illustration of what's happening. The inside of the garnish is tall enough to keep air from flowing around it. There are small gaps at the front on back of the garnish lip due to the curvature of the roof, but I checked and the air is not flowing out of those.

One of my thoughts is that this might be happening because of how low-profile the ceiling is (the panels are attached directly to the roof ribs through threaded rivets.) The image on the far right is another solution I am considering in lieu of the louvers - to fab a sort of "extension" ring around the ceiling opening that effectively increases the length of the garnish to give it more time/space to direct airflow. Dry fitting like this ( garnish detached from the ceiling and slid down an inch or two) does seem to help a little.

 

[sparkplug]

Thanks for the pictures - they help a lot, however there's one detail which I'd like to check which I can't quite see from the middle pic.

The only way I can see that the air would come out sideways is if it was passing between the garnish and the roof, not bending around the outside of the garnish as your picture suggests.

Forgive my attempt at showing what I'm getting at from an old pic when I was installing mine and some rough pic editing.

My theory is that you currently have a gap at the top of the garnish and that air is getting in here and passing round the outside of it. The red indicates where the top of the garnish would be if my assumption is correct.

The way mine is fitted, the garnish goes higher up past the plastic of the fan frame... again, a pic should explain this better than my words. Green is the garnish in this one with the air passing on the other side of it....

Does that make sense? I think you maybe just cut the garnish too short. You could test this by taping some card to it and see how it affects airflow.

 

[thejingles]

Does that make sense? I think you maybe just cut the garnish too short. You could test this by taping some card to it and see how it affects airflow.

That makes sense, but it's not the case. The garnish is cut to a length such that it fit's all the way around that outer rim of the fan, overlapping by an inch or two. In that third picture, with the garnish extended out a bit, it is still overlapping the fan edge. The air is definitely not coming out from between the ceiling and the garnish.

 

[sparkplug]

OK - well, so much for my theory then!

I'm stumped.

Let us know how you get on and if / how you manage to fix it.

 

[BrennWagon]

Is there a good path for air to exit the van? Not much happens when everything is closed up. However, I have noticed the airflow you describe as well and believe it has to do with back pressure.

This is an excellent point and would apply to wether the fan is set to intake or exhaust. If the air has nowhere to flow, then it will move along the path of least resistance, IE along the roofline. An opening of roughly equal square inches will give the air a much better path. People with floor vents and or a second fan on the opposite end of the van Won’t have these issues with everything open

 

[autostaretx]

If you open a door, does the flow pattern change?
(this is the "exit vent" test)

--dick (whose MaxxFan blows straight down, as expected (i don't recall feeling any appreciable side-flow))

 

[hein]

Interesting observation. Can you tape some telltales (strings) to the fan to show and confirm the change in airflow? Maybe time to design an improved interior bezel.

All the best,
Hein
DIYvan
541 490 5098

 

[thejingles]

Interesting observation. Can you tape some telltales (strings) to the fan to show and confirm the change in airflow?

Thank you for the idea. Turns out it is the effect of back pressure, but seemingly the opposite of what you would expect. With the front windows closed, the fan blows more or less straight down. With the windows open it blows out along the ceiling. Adding or removing the garnish makes no difference (tough to see in the fourth picture with the streamers moving, but rest assured they were moving out like in the second picture.)

It is not a windy day, so I'm not getting low pressure outside the van nor am I getting excess wind coming in through the windows. I'm stumped as to why, but that's what's happening.

 

[autostaretx]

Interesting observation. Can you tape some telltales (strings) to the fan to show and confirm the change in airflow?

What a great idea!
So i head out to my Sprinter, tape a bunch of newsprint tell-tales to it ....
and turn on the fan ....



... it would'a helped if it'd remembered that my fan only blows *out*, not in.

In theory, with the lid closed it's supposed to *circulate* the air.
With the lid shut, the tell-tale pattern was,(shall we charitably say?) "ambiguous":




--dick (too little coffee...)

 

[billintomahawk]

A burning stick of incense making smoke really shows up air patterns. Mine doesn't blow straight down. It ventilates rather than blows but I'll check it again in the morning. In general the unit underwhelmed me but it doesn't leak.

I mostly use it when cooking to get moisture and odors out. It doesn't blow a steady stream of air on me sitting below it.

It's an odd duck.

bill in tomahawk

 

[sprint2freedom]

This thread may be of interest to the OP:

MaxxFan Modification

www.promasterforum.com

 

[thejingles]

This thread may be of interest to the OP:

MaxxFan Modification

www.promasterforum.com

Thanks for the link. Definitely an interesting wrinkle. Seems like I need to figure out which takes priority for me, intake or exhaust, because I definitely don't want to be fiddling with flipping the fan blade all the time. Like the OP in the link I really like intake for sleeping, but exhaust is better in most cases for managing ambient temperature.

It's looking like we'll have some sunny, warm days coming up next week. I'll try to test how much the exhaust efficacy is affected by flipping the blades and report back. A additional option would be to leave the Maxxair as-is and install a separate 12V fan somewhere on the walls to move air around while sleeping.

 

[autostaretx]

We (ok: i) went cheap and have the exhaust-only fan.
It is possible to convert it to bi-directional (snip two wires, install DPDT reversing switch).
So far, we rarely use the fan under power ... simply opening the lid and letting "chimney effect" happen has been adequate.
So we could flip the blades to give ourselves "enthusiastic breeze" (inward) and "casual" exhaust.

A different blade-shape would provide more balanced CFM, but the compromises involved would probably make it noisier.

--dick

 

[sprint2freedom]

A additional option would be to leave the Maxxair as-is and install a separate 12V fan somewhere on the walls to move air around while sleeping.

I have three Caframo Ultimate fans mounted in various spots to distribute air. They're inexpensive(ish), use very little power, move a ton of air, have two speeds, are compact, and can be pointed in any direction. The lack of a guard means you can put your fingers in the propeller-like flexible plastic blades which gives a brief little sting without breaking the skin, but also means the airflow is far superior to anything similarly sized.

Their only downfall is that they can be kind of noisy, especially if mounted to something that can resonate. But I prefer tolerating a little fan noise in comfort to sweating in silence. I typically don't sleep with any of them on, but I've discovered the best way to do this is to turn on the farthest one from bed. This introduces enough swirling motion in the otherwise still air to greatly improve comfort without having air blowing directly on my sleeping face.