Increasing Window A/C Cooling = = Increased Fresh Air to Unit

MuttonChops

Early Modification Update = Seeking Comments on Next Steps

Background:

There are a few Forum threads and one lengthy Facebook post discussing increasing the fresh air to the Window A/C compressor and heat exchanger.  The goal being to increase the cooling provided by the 5K Btu unit during >90+ ambient temperatures days.

nüCamp's original window A/C builds had no additional fresh air intakes to the unit.  They quickly changed the builds to include a standard RV Waste Vent Pipe Cap and 4-inch fan to pull fresh air into the A/C cabinet.  This solution works well (enough) but the A/C still has cabin cooling issues on super hot days.

Issue:

The author of the Facebook post for increasing the fresh air volume decided to install a fairly large square vent replacing the original Waste Vent which included cutting a big hole and cutting out one aluminum structural cross-beam.  The Waster Vent only provides a 1.77 square inches open for fresh air.  While the 4-inch fan does increase the total amount of air entering the cabinet it is still limited.

My Approach:

I'm in the process of installing an ~4-inch vent with 14.2 square inches open for fresh air flow.  Without the fan changing from the 1.5-inch Waste vent to the 4-inch Vent will increase the available fresh air 8X. Plus I will keep the 4-inch fan in place.

This approach will increase the air flow while not reducing the roof structural support.

Status:

Here is a comparison of the standard vs. the larger fresh air source.

Questions for Forum Members:

1)  As currently planned there will be no water trap.
      Wind blown rain could enter the new vent.
      However, this is a Window A/C unit . . . designed to have most of its body exposed to rain and wind.
      So I'm thinking - - - no big deal - - - any rain water will drain out of the drip pan.
      Forum:  Am I being reasonable?

2)  Bug Screen.  The original Waste Vent has a bug screen.  While it will stop bigger bugs it also reduces
       the real air flow cross-section.  At this time I do not plan to include a bug screen.
       Forum:  Should I attempt to install some type of screen?
                    If so how - - - maybe a flat screen at top of 4-inch PVC coupler (that Vent Hood attaches to) . . .

3)  Orientation of Vent.  I'm using a RadonAway 76002 4-inch vent cap on this modification.
       The '76002' is not round.  Should I install it so normal driving wind passes through the vent.
           Which means much more rain water will be able to enter while driving.
       Or should it be installed left-2-right, wind rain won't enter driving but it provides more air resistance.

4)  I am wondering if the small pop-rivets holding the 'grill' to the base will with stand 65 MPH
    driving winds.  I've added cotter pins to the pop-rivets, mandrel is ~1/16 inch and one was already gone.

gulfarea

Good thinking, I am also looking into getting more air into that area. Because of mud dabbers I must include a screen.  I am looking for a better fan motor to put into the existing fan area, Art

Mickerly

I was thinking about trying something similar. As set up from the factory, I couldn't measure any difference in cabin temperature with the AC Fan ON or OFF. This looks good.

I purchased "Floor vent deflectors" from ACE Hardware. Their magnets stick to the screws on the outside vent. By preventing the hot exhaust air from re-entering with the cooling air, you can significantly increase the coldness of the air in the cabin. There are several other posts on separating the hot exhaust from the cold intake air.

Bayliss

@Mickerly, do you have any photos of the deflectors attached to the outside vent that you can post?

MuttonChops

@Bayliss,  my guess is that @Mickerly is using the exterior air deflectors that @Dalehelman seems to have had the original idea.  Or is at least credited with the idea.

This is a low quality (zoomed) picture of the Vents mounted on Dales's trailer.

Of course one must remove them before driving away

I do use the vents on my A/C.  I've also added extra foam to the backside of the A/C to reduce the hot exhaust air from bending around to the intake (in the gap between the A/C and exterior mounted floor vents.

My RadonAway Hood project (this thread) is to increase the Fresh Air being forced into the A/C intake side of the cabinet.

Mickerly

Muttonchops is correct. The idea came from here somewhere. I couldn't remember where. I saw the vents at ACE one afternoon and decided to give them a try. The magnets on the vents stick to the screws. They don't hold on well in the wind and do take some space for storage when not in use. I'm working on a cardboard box, more like a four sided tube, that would slip into the grill vanes and fold flat when removed.

I saw the opening in the roof vent was too small. I was thinking about opening it up to match the fan. I just hadn't figured out the cover yet. I have another project going now. This was for next year.

Getting the hot air out and cool air in is the key to good performance. The unit does a good job of exhausting the hot air, unfortunately, it mixes with the incoming cooling air. A better roof vent is an excellent solution. The stock vent doesn't allow enough air movement. The two solutions together are better than either alone.

MuttonChops

Mickerly said:

. . .  magnets on the vents stick to the screws. They don't hold on well in the wind . . .

I placed large diameter fender washers under the screw heads.
That helps keep the floor vents in place with light wind . . . but they still fall off time-2-time.

gulfarea

If anyone knows of a more powerful fan that will fit where that very week computer fan is in the roof we sure would like to know about it Art

pthomas745

Here is one of the threads that had a lot of testing of the AC, with pictures of the deflectors attached with magnets.

https://tab-rv.vanillacommunity.com/discussion/7176/t-b-320s-air-conditioner-hot-weather-testing/p1

This one may have precedence: a Pop Tab mod from 2016.

https://tab-rv.vanillacommunity.com/discussion/3564/air-conditioning-unit-change-out-part-2-ac-cabinet-modification/p1

I think what you might need is a 12V inline duct fan.  I can't get my head around the sizes of these, but I think the CFM and the focused stream may be better than a computer fan.

https://www.amazon.com/s?k=12v+duct+fan&crid=DVBVYG5WZZZI&sprefix=12v+duct+fan,aps,106&ref=nb_sb_noss_1

Another search for "inline duct blower".

https://www.amazon.com/s?k=12v+duct+blower&crid=3KEHW0WRNJ0QZ&sprefix=12v+duct+blower,aps,137&ref=nb_sb_noss_1

grassgd

I recently posted the modification I made to insure positive separation of the intake cold air and hot exhaust air from the vent on the side of the AC unit.  Here is the link to that post.  You can judge for yourself whats the best solution to take since there are many ways to attack the problem.

T@B Forum | nuCamp RV

https://tabforum.nucamprv.com/#/discussion/15627/danby-ac-hot-air-venting

MuttonChops

MuttonChops said:

Questions for Forum Members:

1)  As currently planned there will be no water trap. . . .
      Forum:  Am I being reasonable?

2)  Bug Screen. 
       Forum:  Should I attempt to install some type of screen?

3)  Orientation of Vent.
       Should I install it so normal driving wind passes through the vent.
       Or should it be installed left-2-right, wind rain won't enter driving but it provides more

       air resistance.

My final selections on the above 3-questions / options.

[ 1 ]   Will continue with no water trap for reasons stated in original post.

[ 2 ]   Will continue with no bug screen.  Will see had many (bad) bugs might be.

[ 3 ]   Decided on Hood Placement left-to-right.

         a)  I feel it looks better.

         b)  With angle to wind when fore-to-aft remain concerned it will increase wind pressure

              above the TV MPH adding stress to hood.

         c)   Not crazy about wind blown rain entering while driving.

After centering the 4-inch fan at the down-tube.  The speed of the fan seems faster and the volume of air blowing down is a huge difference from the original 1.5-inch vent opening.

Will see if larger vent stays in place and helps any over the next year or so.

Side Note on question # 3  {and just for fun}:
   The left-to-right placement provides a rounder wind profile than fore-2-aft.

2D Flow Simulation.  left-to-right at top.

MuttonChops

July 16th  Mini-Update

Not Real Data = = = Is Anecdotal

Today is a warmer day with 3PM ambient over 90F.
Trailer has been in the sun since 10'ism A.M. without its storage cover.
About 25-minutes ago I opened the trailer and turned on the A/C.
Cabin reference thermometer was 93F
After the 25-minutes (pre-cooling before I start cleaning up an earlier project)

Cabin reference thermometer was 85F, with A/C set on Low One Snowflake Cooling.

So I consider this a positive indication the A/C likes having a greater volume of fresh compressor & heat exchanger air.