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Little round Vents
#11
(08-04-2019, 06:44 AM)tx2sturgis Wrote: I installed one of those round ventline fans in my pickup topper.

They use a cheap 'hobby motor'....with brushes. They do the job but they are noisy, and only have one speed, and one direction.

I modified mine (of course) to have 2 speeds, and better airflow with a coarse plastic screen replacing the fine mesh bug screen.

BTW they are factory installed in Casita campers in the bath/shower.
Sounds affordable that Ventline you mention. I’m looking at all options currently as I have not ordered the vents or fans yet. I’ve thought about using the “chimney effect”, convection, using natural draft on dwelling designs before. A temporary tube going up on a RV might induce some draft on a RV. But to have a lot of natural draft the tube might need to be very wide. But it would use no power. The tubes inducing draft on the Forest Service toilets are big, I think about 12”. But not very tall.
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#12
Natural draft works fine for ventilating sewage holding tanks, but you will find it wont work at all for cooling a living space.

When you need the airflow the most is on warm or hot, and calm or still days or nights.

In other words, when you need ventilation the most, there is no wind to provide it.

Seriously, you will want to have powered ventilation in addition to any passive ventilation you already have or will have.
Wondering about Wandering.
[-] The following 2 users say Thank You to tx2sturgis for this post:
  • heron (08-11-2019), Roadtripp (08-12-2019)
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#13
Agreed, passive ventiation is Ok at best, for some applications.

The mushroom style vents, with or without a fan, work better with a slipstream of air going over them as the downwind side creates a low pressure area that helps suck air from the vent.

As I type, since rain is unlikely in my Locale this time of year, my mushroom vent is removed and I have a 4 inch skylight with two 4.75 inch counter rotating fans forcing out a large volume of air, so much so that at night lately, I turn one fan off and the other is at minimum speed. truth be told I kind of miss their white noise at higher speeds as my tinnitus has been annoyingly loud as of late.

Mostly i need a blanket slightly warmer than my thinnest with sheet, and less thick than my next one up, to maintain a good sleeping temp with adequate white noise levels/fan speeds to drown out my tinnitus.

I have designed a few larger mushroom style vents in my head around specific larger fans. Actually building one has yet to occur due to insufficient motivation. I think i would expend efforts at reducing more post fan flow restriction on my existing roof exhaust vent instead.

I am also keep on a push/pull fan setup as opposed to a more powerful exhaust fan and passivel inlet vents. Exhaust and intake fans working in conjunction, rather than a stronger exhaust fan and passive openings to allow the exhausted air to be passively replenished.

I can shut down my exhaust fans, yet keep them spinning when my intake fans are on high and all dors and other windows closed. i can't keep the intake fans spinning with my exhaust fans on high though. When its hot as FVck both sets of fans on high turn my van into a wind tunnel.

I've also made a front door window fan shroud with two 120mm fans exhausting loudly, conspiciously, so the unobservant would have difficultly not noticing that I have taken many steps to insure my dog cannot overheat in a parked locked van sitting in full sun, but I also insure she is not easily seen with some static cling vinyl one way mirror window tint, so she can still look out but not be easily seen.

https://www.amazon.com/dp/B07CXRVVGQ/ref...rd_w=ytYxb

This stuff also blocks an amazing amont of heat entering the windows.

Too bad all the pics are no longer operable in my 'ventilation enthusiast' thread, but the prototype front door window fan will soon be rebuilt into something more streamlined. Still obvious, but less noticeable to casual glancers, and need not be removed every time i drive. I love these two extra 120 mm fans flow though each one is rated at 105cfm at 12v. My roof exhaust fans are likely just over 100CFm through the mushroom vent and 150 with shrrom vent removed. My intake fans if they were unrestricted and at max speed would push ~465cfm into the van. not sure how much flow is reduced due to the screen and 1/4 inch galvanized security mesh behind them.

When i stay in a stick and brick I am horrified that i have to rebreathe my own, and my dog's exhalations. I am so used to all the air inside my van being completely exchanged once every 60 seconds or less with fans at full speed. I can dial this down to quit slow depending on outside temperature, but rarely do I have all the vents closed and fans turned off. Got to be sub 40f for that to occur.

In cooler temps my intake fans have activated carbon air filters on their intake side which further reduces their flow. One of my interior air circulation fans always has such a filter on it. Sleeping in a stick and brick seems to be such a downgrade in air quality. When i last stayed at my parents, I was sticking my square 12v computer fans in one window at night with cardboard shrouds, on the cooler nights, and was missing the bed in my van. These tiny fans one intake and one exhaust, worked better than larger round fans simply placed on the open window's sill.

The fan shroud is very important. a fan creates high pressure in front of the blades and low pressure behind it. Without a shroud preventing high pressure air to fill the voild of low pressure, much of the fans flow does a u turn and recycles back through the fan. With a shroud the high pressure air cannot fill in the low pressure gap behind the fan and a very high percentage of the fans flow exchanges inside air for outside.

A lot of people are oblivious of this and think a fan taking up a small portion of a window is effective. Perhaps it is good enough, but with a shroud, the fan's flow is many many times more effective at exchanging air, and thus cooling the area.
[-] The following 2 users say Thank You to sternwake for this post:
  • heron (08-11-2019), Snikwahjm (08-12-2019)
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#14
Good info^ everybody get your shrouds on. It's gonna BLOW !!
Stay Tuned
rvpopeye



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#15
Sounds great as I begin to swelter after a siesta in the heat collector my old Motorhome becomes in the afternoon. Time to go back outside. It’s a case of a unfinished project that got sidelined. It does not get hot until early afternoon due to the extra insulation on the roof and the covering of solar panels. But then the sun hits the back and heats up the bedroom. As I’m changing motorhomes I’m not very motivated. The solar energy equipment on the back of the Motorhome also gets hot in the afternoon. I partially shaded the equipment box with a sheet of aluminum and that helped some. But I can hear the charge controller fan working occasionally and should do active cooling on the box. You’re right on Tex, passive by itself doesn’t do the job when one really needs it. 
 I was wondering about the effect of a shroud. And turbulence. I’ve read a wind turbine spinning fast creates turbulence which reduces the efficiency. A inline duct Fan (blower) seems to blow a lot of air but long ducts would increase resistance. A short duct might work fairly well. And convenient in that they fit onto flanges that can be attached to a surface easily. But framing in a computer fan isn’t that difficult.   Been wanting to try the boat engine room blower I found at a junk shop. In solar they use these on battery boxes to prevent hydrogen gas build up. It’s important it’s equivalent to a coast guard approved engine room blower to prevent kaboom or fire. These fans are very expensive however compared to computer fans that SW has mentioned in the Ventilation wiki. And likely use a more power per CFM. 
 Sternwake, I don’t remember reading how you measure the cfm on these fan experiments? Do you have one of those little wind speed meters or something?
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#16
I cant measure cfm. I take the fans specs and estimate flow.reduction considering restrictions i n front ofnornbehind fans.

I guess one could see how long a.specific fan takes to balloon a 50 gallon trash bag and do some.math.

There are still over 950 of those e papst.24v fans avail for.10$, 15$ shipping you linked late last year.

Probably the best fan i own. Im buying more. The newer version is 12x as expensive!
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