Danby not Cooling as it should

Sneakle

 Florida panhandle on a very hot day.
Right now I’m sitting inside my TAB with the Danby AC on. It’s 98 outside and I’m holding at 93 inside after over an hour of runtime.  I wonder if, like some home ac units, the coils can freeze and require thawing before operating normally? Same problem yesterday until later in the day when outside temp dropped to 80s and was able to get to 75 with the Danby. 

Sneakle

I researched the subject here on the forum (as I should have done to begin with) and followed the suggestion to crack a window and the top fan hatch. The inside temp has dropped 10 degrees since I did it. Also  saw a suggestion to put diverters on outside AC vent so the AC won’t be drawing in it’s own hot exhaust air instead of cooler air. 

jgram2

Good on you @Sneakle! The more times I read those tips, the likelier it is I’ll remember them when needed!

Marceline

@Dalehelman came up with a way to direct hot air from the exhaust away from the intake. Apparently it helps.
 

Sharon_is_SAM

@Sneakle, did you have the accessory fan turned on?  That helps.

Sneakle

Sharon_is_SAM said:

@Sneakle, did you have the accessory fan turned on?  That helps.

yep

DougH

@Sneakle, you probable saw the threads on what folks do to keep the hot air conditioning exhaust from mixing with fresh air.  Like others did, I took the side vent off, stuck a thermometer half way into that A/C box at various places, then tried every combination of sealing and diverters I could try, to see what worked best on lowering the temperature of the intake air.

Even with thermometer at locations across the top of the A/C, the aux fan on or off didn't make as big a difference (not even close) as sealing the A/C to the side of the trailer and using diverter(s).  My best results came from using duct tape to seal the back of the A/C to an area around 2/3s the total side hole size on one side of that vent cover hole... an airtight seal forcing all A/C exhaust to leave the box.  The other third of the port becomes the intake and it pulls to all the intake vents on the sides of the A/C.  Then add a diverter, magnetic or mechanically attachable, on the outside after the vent cover is back on to force the hot air to come further out and away from the intake air.

The hot air has to go right up to the vent cover then it's pushed an extra 3-5 inches away from the T@B and maybe even in the direction opposite the intake air.  Sort of like a chimney wall.

I tried having the exhaust come straight out with sealing and diverter or a rectangular chimney box, with intake air coming in from both sides...  but that didn't work as well as just creating one intake air side, and one larger exhaust side. 

It's a bit of a bother to have to take the cover off, use a strong duct tape to create an internal chimney, then rig up a removable external chimney side..   but if you do all that you can get 12-17F difference in internal cabin versus external temperatures, even in muggy upper 90s weather. 

Sneakle

Thanks DougH. Very informative.

DougH

Haven't needed it for a while though.  Currently in Idaho and I need the Alde most nights when it hits the 40s  (just trying to get some groans from anyone suffering through August in the South).   

Sneakle

groan!!

DougH

Ouch!

DougH

@Sneakle ;  Driving SE from the Tetons early this morning.  28F.

gulfarea

DougH Could you take a photo of what you did to seal off the AC ? I am a little confused as to where you put the seal tape. Thanks in advance Art

DougH

Will do when I get home.

gulfarea

Thanks DougH Art

DougH

@gulfarea ; My last night of trip this week was in the TX panhandle at 100F in direct sun.

As you've no doubt read on this forum, the 1" insulation in the roof cannot really compete with the Southern sun.  Biggest cooling is to be found with shade...  a tree, a shade cloth canopy over the T@B, clouds, etc. 

But I got 15F cooler than ambient in the late afternoon in under a half hour that last day with no shade once I found an RV park, and then the interior temperature got quickly down to 70F once the sun set... though still 89F outside.  I also use a 9" fan on the floor near the bath pointed at the top passenger corner to swirl the A/C cold output air about the cabin as it cools off for the first 20-30 minutes once I turn on the air.  I always have the top vent open going down the road so I'm not starting significantly hotter than the outside temperature if it's in the 90s or above outside, and once I turn on the A/C, I completely close all windows and vents.

My LG replacement A/C is slightly wider, and slightly shorter than the Danby, but hopefully these pics show the tape pattern. I taped in 2-3 layers from the edge of the air conditioner rear, to the side of the camper on the left, bottom, and top.  On the right side I created a slanted air dam a few inches in front of the fins and a few inches left of the right edge.  Again, attempting to get around 2/3rds exhaust area, and 1/3rd intake air area on the right.  I've had no problem with the Gorilla 2.88" extra wide duct tape melting or coming undone even when initially 120F inside and over some pretty bad roads.



A closeup of the right air dam made of duct tape, to separate exhaust and intake paths.  Air tight on all sides of the exhaust area. Watch out, the fins can be razor sharp.



Top left close up...



And all closed up with a deflector attached to further separate the intake air from the exhaust. 



This is overkill in any area that doesn't have 100+ temperatures with 80% humidity.  But in low altitudes along the Southern coast, the stock setup just wasn't even coming close to cooling the cabin.

But why go with crude duct tape when you could do that whole steam-punk look with thin copper plate used to completely separate the exhaust and intake air flows?  Can't really screw it on to the rear sides of the Danby without risk of puncturing a coolant tube, but maybe an industrial adhesive?  Or maybe you can find a rectangular plastic sleeve that stretches over the back of the Danby that you can just seal to the side wall of camper instead of using a half roll of duct tape?

gulfarea

Thanks DougH great photos Art

BrianZ

Interesting approach, and thanks for sharing the photos, @DougH.

I can't help but wonder though, doesn't closing off the left side air intake area reduce the total amount of outside air getting into the unit?  I understand that you have directed the hot exhausted air away from the intake with an angled baffle, but that doesn't really increase the inside opening size on the right, does it?  However, I do see how that arrangement could reduce the net amount of hot air getting sucked back into the intake stream, so maybe a better tradeoff.

The other thing I wasn't sure about is what's going on in the last photo - is there a clear hood of some sort over the intake area?  Hard to really tell what I'm looking at.

So, to clarify,  this arrangement with a single intake performed better than having an intake with baffles at both sides?

PS:  One more thought..  Would it be any better to reverse it & put intake at left, so the air dam maybe won't catch as much wind while traveling (assuming the deflector mounted on outside can be removed).

Sharon_is_SAM

Is the intake and exhaust different on the back of the LG than the Danby?

DougH

@BrianZ , @Sharon_is_SAM : In my elderly state, my memory is not always what it once was. So while I know there are intake vents on the top, left, and right sides of the LG...  I'm not sure if the Danby is the same.  I assume it is, because the air flow through the secondary side is considerable, and any designer wouldn't create a choke-point with only limited intake venting on one surface. Please correct me if I'm wrong, since it would make sense to make the distance from the intake vents to an external cool air source as small as possible. I did verify that with the air intake on only one side the incoming air was wrapping around to all sides of the unit and flowing to all available intake vents. And as you state, having one large intake on one side DID work better than baffles on both sides, for me, and I'm not sure why.  I built a wooden box chimney with the outer vent cover off to move hot air six inches from the unit.  That helped on the dual baffle (both sides) approach, but not as much as shifting the exhaust all to one side, first with the homemade large chimney, then with a simple diverter. I can only hazard a guess that two 1.5-3" slots on both sides of the hot exhaust have either more of a flow resistance to getting sucked in...  or more chances of exchanging hot air with the exhaust.

I also verified that the volume of air being sucked into the secondary side of the A/C is much more than the vent fan can deliver.  If you don't seal the front of the box, it will happily suck air from the cabin as there's still negative pressure in the box even with the aux fan on.  Which is one reason hot exhaust is pulled back into the box without diverter(s). So finding a much higher CFM fan to bring air down from the roof might make all the sealing and diverting unnecessary.  Maybe a box at the top of the vent with two pushing fans in series?  The days of testing were all with the LG, not the Danby.  Yes, the LG is allegedly slightly more BTU, but I bought it to have a remote and more modes... it doesn't pull that many more watts.  I did try a different Frigidaire unit instead of the Danby (at the same wattage), but it cooled even less than the Danby.

I have worked with CFD simulations before in my previous engineering career, and have OpenFOAM on my laptop, but by gawd, I'm retired now, and I refuse to try and model all the flows and heat transfer in a partially enclosed A/C box.       But like puttering about in a garden, it's semi-fun to try and instrument a problem and find improved configurations.  The real answer would probably be to mount a lightweight 10k BTU unit on top...  or move far enough north or up in altitude where the stock Danby in a box is sufficient. 

Another idea comes from the installation manuals for most of these smaller window units.  They say never enclose the air conditioner, and have free flow of air across the entirety of the unit outside of the window. The opposite of what we have. So it might be interesting to cut the bulk of the internal box away, and just have a two position locking system with the A/C on a sliding rack.  Want to use the A/C?  Push / slide it out from the camper until it locks in place with a click against the air seals.  No drain pan, no vent, no pan drain, no aux fan, and a well ventilated secondary side, with more room in the camper.  A T@B slide-out of sorts. 

Yes that's a large plastic air vent diverter on the right side of the last pic.  Comes out at a 45 degree angle.

And yup the dam would have been better the other way.  With a screen on the vent cover I'm not worried about picking up the passing bug or two.  And the A/C is off when I'm traveling.  But it might scoop in some extra dust / pollen and trap it near the bottom of all that duct tape against the side of the camper.  If I'm going to redo it though, the slide-out idea might be attractive to prototype. I can weld. Want to form a company and sell the prototyped kit to the thousands of T@Bs and vans with window units?   We'd be rich in no time.  I don't believe that intellectual property (IP) is intellectual, nor property.  But we should at least come up with a name for this. The SAM-amatic?  We can't call it the BDS-slide or we'll run afoul of the anti-boycott laws in some states.  A spring loaded flap on the outside improves coefficient of drag when driving...  is pushed up when deploying the slide-out.  With all the extra cabin space when deployed, we'll have a more expensive version with a nice set of ash wooden racks where the A/C sits when traveling.

P.S.  The DW just granted permission to build the thing.  Hmmm...

Sharon_is_SAM

The Danby air intake is on both sides and the exhaust is in the middle.  

The TaG forum members are discussing modifying a plenum that exists from the construction of the AC in a box.  I think it may involve a more powerful fan to assist the exhaust.  They could use your expertise @DougH!

The slide out idea would eliminate the need for the roof vent and eliminate the drain issue.  Still think the humidity problem will persist, but should be better for us up north, but still not good for Florida!

DougH

LG has dry mode.  Have often cooled off the camper, then flipped over to that mode for rest of the night.  Doesn't pull out 3 pints/hour like their bigger units, but it helps.

And it's 87% humidity in N TX right now, and supposed to be 102F  / heat index 115F tomorrow. Florida may be more comfortable?

I did waste some money on one of those small Peltier dehumidifiers.  More like 6oz/day rather than pints per hour.  Quiet...  but ineffective.

BrianZ

Thanks, @DougH, for confirming, and for your in-depth explanation.  The slide out A/C idea sounds like it has potential, and I wish you great luck if you decide to pursue it.  I may at least try sealing the exhaust section & adding interior baffles plus exterior diverter(s).  

BogieMeister

Which brand of LG did you purchase? Does it have the eco-mode where it shuts itself off when it reaches a given temperature? Did you have to modify the case to fit the LG?

DougH

@BogieMeister ; LW6017R. Yes. Yes. 

I am drooling for the newer tech
    https://www.amazon.com/dp/B07V48X7HG
...but they've not released a small unit yet.  Would love 14 SEER and 40 dB quiet A/C in the T@B. 

Had to remove one vertical support, and shift a horizontal support for the right side 1.5" to the right. And then change up front wood piece with a wider / shorter surround. A/C has yet to fall onto bed in over a year of use.  Ecomode does still periodically cycle to test if it needs to come on...  but can go all night on battery bank if not too hot out, unlike cool mode.

What fits in existing box:
  https://tab-rv.vanillacommunity.com/discussion/comment/120271#Comment_120271

Dalehelman intake air diverters:
  https://tab-rv.vanillacommunity.com/discussion/comment/103162#Comment_103162

Before/After: