Side air conditioning insufficient

Larryjb · 06-25-2017, 03:50 PM

I feel that the 10000BTU side air conditioner isn't cooling the TM very much. It is 32°C (90°F) outside today, and with the AC on full, it seems to keep the dinette at about 30°C. I will admit that I don't have any curtains up yet, and it's parked in the direct sunlight. I opened up the roof vents to try to vent hot air.

Given all of the above conditions, should the side AC be doing better, or is this normal?

Padgett · 06-27-2017, 08:24 AM

If you figure bright summer sun loading at 250-300 btuh/ft-2 and a 2720 has about 165 ft-2. Then you can see the roof can receive over 40,000 btuh & is too hot to touch.

Now the foam sandwich provides some insulation and reflectivity is higher on a white shiny surface which is how a 13,500 roof AC can pull my 2720 down to the high 70's on a hot summer day (90F+) but typically 10-15F down is all you can expect & why Floridians seek shade.

A second factor here is than an AC is more efficient when the air is dense (high humidity) which it is also good at removing.

Now with a 10,000 btuh side mount you have two things going against you:
- cold air sinks so blowing cold air at the floor level may do little at the ceiling.
- there are a lot of low obstructions to block flow.

The best answer for you is probably ducting to move the cold air to the ceiling and direct to each end. Just getting the air moving where people are will help.

Years ago I had a VW Westphalia (popp-up) and with ducting a 5,000 btuh window AC could make the interior quite comfortable if not in the sun.

All that said I would expect a 10kbtuh AC to do better than just a 2C/4F drop, is the filter clean and the output air cold ?

ps roof vents are good but where is the replacement air coming from ? Does the AC have a "fresh air" setting ? In general recirculating the air will be cooler than pulling in 90F ambient. The TM has enough "leakage" to keep the air fresh.

Final thought, blocking the hot air exit on the back side of the AC will dramatically reduce efficiency. It might help to prop open or remove the outside cover.

**Bill** · 06-27-2017, 08:38 AM

Quote:

Originally Posted by Padgett

Final thought, blocking the hot air exit on the back side of the AC will dramatically reduce efficiency. It might help to prop open or remove the outside cover.

Welcome back, Padgett - we missed you!

Larry -

Many years ago, one of our members (harveyrv) described his rebuild of the structure around the cabinet air conditioner. In particular, he described the air flow in the area you mention in great detail, saying exactly what Padgett is saying. The condenser in an air conditioner gets very hot, and must be cooled by blowing air over it. You must use outside air to cool the condensor, and you must prevent the interior air (cooled) from mixing with this exterior air stream if you hope to get ahead of the game. HarveyRV placed some sheet-metal baffles in the area behind the air conditioner to keep the airstreams separate. An Advanced Search should turn up his posts.

Incidentally, this is the problem with most (though not quite all) so-called portable air conditioners, the ones you can wheel around from room to room while putting a hose out through the window. They cool the interior air, then use a lot of it to cool the condenser.

Bill

Larryjb · 06-27-2017, 08:56 AM

Thanks Padgett and Bill,

It sounds as if my AC unit is performing as well as any 10000 BTU, so that is good, and what I essentially needed to know.

After setting up a fan to circulate the air better, I did get a better temperature drop, but probably only a 5°C/10°F drop. Now, that's without curtains at the moment as well, and there is a ton of heat radiating in from the sun through them. When I get curtains up, that should help a lot.

One reason I cracked the vents open a little was that the sun heated up the vent covers a lot. A little bit of reflective bubble insulation wrap would probably fix that and allow me to keep the vents closed.

I'll look to see if I can find any of harveyrv's threads on this. One quick fix I'll add is a little foam tape on the wooden trip pieces that surround the AC front panel, and I may even add some rigid foam insulation on the inside of the AC cabinet.

**wbmiller3** · 07-06-2017, 08:39 PM

We also have a 10K BTU side AC, and camp year round in Texas.

Yes, using a floor fan is critical. Otherwise only the area in front of the AC gets cooled.

Yes, if you can get the trailer in shade, that helps tremendously too. Fortunately most Texas state parks (on the eastern half of the state, anyway) have good shaded sites.

There is one procedural thing we do that helps. When you get to the campsite, make getting the electricity plugged in and the AC on a priority! If you let the trailer sit unairconditioned and it gets hot inside, it is a lot harder to get it comfortable. Get that AC on ASAP!

Larryjb · 07-07-2017, 12:44 AM

Thanks for the tips Bill. I think a huge factor on my part at the moment is a lack of curtains, but I can tell that a shady site would help a lot.

Padgett · 07-07-2017, 07:51 AM

My solar panels provide shade over the bed.

Larryjb · 07-07-2017, 09:09 PM

Quote:

Originally Posted by Padgett

My solar panels provide shade over the bed.

Show-off! :P

Actually, I have wondered just how much cooling can be achieve by absorbing the sun's rays to make electricity. Is there a difference in the cooling effect if the electricity is actually being produced and consumed? Is there reduced cooling if the electricity is not being used?

I'm not about to get solar this year. It's been an incredibly expensive year, and I may have to do brakes on the trailer, I haven't checked yet.

Padgett · 07-08-2017, 09:25 AM

I think of energy production, use, and disposal as a cycle. Any energy device from a gas or diesel engine, to a furnace, to an AC, to a nuclear device is just a matter of changing states and energy levels.

When thinking in absolute terms, the purpose of an AC is to cool (and incidentally dry) the air typically from about 95 to 75 degrees. To do this we first heat (compress) a fluid medium which increases the pressure. Then cool it while holding the pressure steady, expand (reduce the pressure) which cools the mixture, finally pass the cooled mixture through a radiator.

A swamp cooler is even simpler but requires dry air to start. It is just a device that passes air over a medium (usually a fabric in small ones) that is saturated with water. The process of evaporation removes heat from the air. These may remove 10F from the air while a compression cycle device can remove up to 70F (often have to prevent freezing the condensate). A cooler must have a quite large surface area compared to the area being cooled while a compression device can be quite small.

Which brings us back to the bottom line: there is not enough available roof area on a TM for an effective solar AC. You might get more cooling from the shade the panels would provide.

Larryjb · 07-08-2017, 03:03 PM

I realize that it's just the shade created by the panels that's providing the most cooling. I'm trying to suggest that solar panels by used to run an AC unit.

However, when the panels are absorbing solar energy and converting it into electrical energy, that amount of energy is not transferred and transformed into heat energy inside the trailer. This will be a small effect, but probably insignificant. I am curious if, when the battery is fully charged and no electricity is being consumed, that energy absorbed by the solar panel has to go somewhere. If it's not into electrical, it would likely be converted into heat energy, contributing to warming of the trailer. I would assume, however, this effect would be negligible compared to the shade effect of the panel itself.