Another tedious A/C addition thread

[wiredgeorge]

Well when we went out camping last year and it was triple digits in direct sunlight, I couldn't get the cabin much under 83F even after doing EVERY trick plus putting very dark tint on the windows. Ducts seals, noodles in place, new vents that can be closed and rotated... etc.

Even doing this stuff, we were HOT and it was too hot to do anything outside so off to Best Buy We went and I bought an 8K btu LG portable A/C. I exhausted the thing out the window using one piece of their window vent kit and used duct tape to seal the rest of the opening best I could. This took it down into the upper 78-79F. OK, life was now bearable again.

When I got hole I fashion inserts out of plywood so the exhaust part would seal nicely in the window.

The 8K btu LG just isn't very powerful and a 5K window unit pushes a lot more cold air. Don't want a window unit because although I am a redneck, they look kind of, well redneck. Was thinking of a 13K or 14K btu portable. Since these guys get near 15A on start up, would likely have to make some more electrical mods (another extension cord type deal).

Anyone ever have any luck with a larger portable in hot climates to augment a new 15K btu on the roof?

[Roscommon48]

A/C units can usually only drop about 20 degrees from the outside temp. that is the reality of the whole thing.
additional of any a/c always could help however.
'How much can an air conditioner drop the temperature in your home? Air conditioners are designed to lower the temperature of your home's air by about 20 degrees. So if the air in your home is 85 degrees, for example, your air conditioner can lower your air's temperature to about 65 degrees.'

[xrated]

Originally Posted by Roscommon48

A/C units can usually only drop about 20 degrees from the outside temp. that is the reality of the whole thing.
additional of any a/c always could help however.
'How much can an air conditioner drop the temperature in your home? Air conditioners are designed to lower the temperature of your home's air by about 20 degrees. So if the air in your home is 85 degrees, for example, your air conditioner can lower your air's temperature to about 65 degrees.'

Your explanation is mostly wrong. An A/C unit, when functioning at peak performance can and does drop temperatures by roughly 20 degrees. But, that number is based on the difference between the inside air temperature and the output of the unit. If you start an A/C unit and the inside air temp is let's say 90 degrees, the outlet air temperature (best case scenario) is going to right at 70 degrees coming off of the evaporator coil. So then what happens, as that cold air recirculates in the house, the inlet air to the evap coil is at a lower temperature, and the A/C unit is still running so it gets a 20 degree differential across the evap coil. This cycle continues over and over until the thermostat is satisfied and the A/C shuts off. So if the inside air temperature is now 72 degrees, and the thermostat turns the A/C back on, the inlet air going into the A/C unit is 72 degrees and the outlet air is roughly 52 degrees. At maximum efficiency, an A/C unit will maintain a 20 degree differential between inlet air and outlet air.........within it's operating parameters. Of course there is always some degree of air infiltration from the outside, and if the outside temperature is higher than the setpoint air temperature inside, the A/C will just have to run longer and more often to keep the setpoint of the thermostat satisfied. Outside air temperature does play a part in the efficiency of the A/C unit, as that is where the condenser does it's job of transferring the heat that was removed from the house, to the outside air....by removing latent heat from the refrigerant as it passes through the condenser coils. See, isn't that simple?

[wiredgeorge]

Has anyone tried a higher BTU portable to augment a well functioning roof mount Dometic Brisk II (15K BTU) A/C? I kind of understand the theories; our home A/C can keep the inside temps very low on very hot days far exceeding this hypothetical 20 degree thing. The Cougar isn't insulated well; especially the roof so I don't think this is an apples to apples comparison (home A/C vs RV). Just like to know if anyone has used a portable. Before I shell out some serious money, would love to know.

[JRTJH]

The "key to coolness" is BTU capacity.

Your home system is probably a 3-4 ton unit (36000-48000 BTU) system and the house is "sufficiently insulated" to prevent the "heat gain" from being more btu's than the capacity of the air conditioning system.

In a travel trailer with one air conditioner, I'd suspect that on a hot day, if sitting in the sun, the "sun may add 17000-20000 btu's" to the trailer. With minimal insulation, that solar gain goes straight to the interior cabin. "Pushing the heat out" (actually absorbing heat and blowing it out of the air conditioner rooftop unit) at a rate of 15000 btu's, well you can see how the interior temperature creeps up throughout the day.....

The easiest means to effectively cool the trailer more is to increase the btu capacity of the air conditioning system. Most people add a second rooftop unit, some "redneck it" and install a window unit or a stand-alone unit. I had one of the earlier Solara stand alone units. It worked great, but in Louisiana, the humidity was so high that the A/C couldn't evaporate it as fast as it collected and the unit would shut down when the evaporator pan was full. I wound up building a larger pan with a drain line, but I don't know if the newer systems have solved the "what to do with the collected water" problem.

I'd guess that using a stand alone unit, if you can vent the absorbed heat out of the trailer, would be an effective means to cool the trailer interior. As with any "cooled space" if you can get the btu capacity of the heat removal equipment greater than the btu capacity of the heat adding components (sun), then you'll cool the interior. It's going to take "lots of btu capacity" to keep any "barely insulated box that's sitting in the sun" from getting hot during the heat of mid day.

[wiredgeorge]

I already have used an 8K btu LG portable in conjuction with my new 15K Dometic roof unit and it keeps the interior passable at 80F or just below when it is 105F outside in the direct sun. We have never had to dump the tank while camping due to full over a 4 day weekend. I attach a hose and run it out the front door.

Quite a few of the newer designs claim to use the condensation to help cool the fins or something of the sort and this is supposed to keep the condensation tank from filling but many of the reviews in humid climate have folks complaining there isn't a great way to empty the tank. Lifting and bath tubs are mentioned. If constant draining were needed, I think I would drill a hole through the floor and put a dump valve in similar to the fresh water tank. I was really hoping to hear some real-world experience from anyone using a 13K or 14K portable. You have to guess a larger unit would keep the cabin cooler than 78-80F on triple digit days.