A/C temp outside vs inside

[97flhtcui]

It was 115 degrees for the high in San tan valley today. With both a/c's on constantly the inside temp was 92 deg. No carport or shade to cover the Rv. That is a 23 deg difference between inside and outside. Before I put slide toppers on we had a 17 degree difference when our high was 111. We should be able to do even better when we get our thermopane Windows installed. FYI for those that feel you a/c is not cold enough.

[johnm1]

Question (well, more of a statement) ... I thought A/C didn't work very well in AZ due to the dry air. Isn't that why most houses use a swamp cooler kind of thing?

I'm just asking because I don't know and I'd like to.

[dieselguy]

As far as RV's and hot weather go ... if you can get a 20 degree differential between outside and inside temps ... you're doing well. Sitting in the shade ... maybe a bit more. I have a friend with a dark color full body paint SOB ... it makes it even harder to cool yet.

[SeaDog]

The difference between outside air and inside air temp does not give an indication of how well the AC is working. You need to measure the air temp at the return air grill of the AC and at the closet outlet for cold air. If you get a difference of 20* or so your unit is doing what is was designed to do. This is the reason for starting your AC prior to the inside of the trailer getting to 80*

[dieselguy]

I understand the preferred temp differential of 16 - 20 degrees as measured from the intake to supply air on an A/C system. (humidity and cleanliness effect that number) With the limited amount of possible insulation in any RV ... I was just "off the hip" saying that getting a 20 degree differential between inside and outside air temps is doing good. 92 inside sounds hot till you read what the outside temp was.

[97flhtcui]

Johnm1,
I don't consider 92 degrees comfortable. I noticed the difference between outside and inside became greater as it got hotter. When you are in this type of heat, it gives you a opportunity to measure your temps at differ times of the day, then find hot spots so you have an idea what can be done to make the Rv more comfortable later. We are getting thermopane Windows when we are in Goshen for the rally in August. We are getting new painted caps under warranty so I am going to have more insulation put behind them because the cabinets in the living room and closet seem to be very hot during the day. The a/c units are working at capacity so I am going to fix everything else.

[johnm1]

97flhtcui - Please don't mistake my post as me thinking that 92 is comfy and your whining. Heck no ... and wholly cwap I think that'd be HOT. I've been in 100 in South Carolina with darn near 100% humidity and it was absolutely brutal. We'd go from the too warm ocean to the A/C in the RV ... hardly spent any time outside!

I'm just trying understand what RV A/C's are capable of in a hot and dry climate like AZ. I'd guess our single 13.5 wouldn't ever shut off.

[TURBS]

Originally Posted by johnm1

97flhtcui - Please don't mistake my post as me thinking that 92 is comfy and your whining. Heck no ... and wholly cwap I think that'd be HOT. I've been in 100 in South Carolina with darn near 100% humidity and it was absolutely brutal. We'd go from the too warm ocean to the A/C in the RV ... hardly spent any time outside!

I'm just trying understand what RV A/C's are capable of in a hot and dry climate like AZ. I'd guess our single 13.5 wouldn't ever shut off.

A 15k would never shut off.

Sent from my SCH-R530U using Tapatalk

[97flhtcui]

Johnm1,
I understand you. You want to know what to expect. If you don't have ducted unit, the air is cooler coming out. Our cardinal had ducting in the living and kitchen and non ducted in the bedroom so we could get chilled while in the bedroom and would be sweating in the living. So you know our cedar creek that I took the temp readings on, those a/c's ran continuously since 11 am till 6 pm yesterday. We full time so I have a lot of time to research and analyze.

[waiter21]

John M;

Actually, AC units will perform better in dry environments because the AC unit isn't expending thermal energy in converting gaseous water to liquid water

Swamp coolers work on the exact opposite principle, They convert liquid water to water vapor. When they do this, thermal energy is extracted from the air and stored in the water vapor thus cooling down the air. i.e. water evaporating will cool the surrounding air.

The reasons swamp coolers work so well in high altitude deserts;

1) Thinner air allows the water to evaporate easier.

2) Dry air (low relative humidity) can more easily evaporate liquid water.

The big advantage of a swamp cooler is you only need to run a blower motor and a small water[pump.

There is no need to run the big compressor thats used in a AC unit.

Another advantage of a swamp cooler is that it adds a little moisture to the air, making it a little more comfortable to breath.

[bob dirt]

Originally Posted by johnm1

Question (well, more of a statement) ... I thought A/C didn't work very well in AZ due to the dry air. Isn't that why most houses use a swamp cooler kind of thing?

I'm just asking because I don't know and I'd like to.

That's the funniest thing I have ever heard


Most houses have A/C. I have made my living off of fixing them or replacing them for the last 40 years starting at 18. I happen to have 2 a/c units on my house AND an evaporative cooler. The evap works great until the dew point hits around 50 degrees or the ambient temp hits 110*. Yesterday it was 118-120 where I live in north Phoenix. It wasn't that bad. I did yard work until 1:00 then decided that it WAS too hot.

I just turned my RV a/c on. I'm curious how cool it will be at 3:00. It's 107 right now with 10% humidity.

I have been in Bullhead City when it was 113* out with the a/c plugged in and it kept my toy hauler at 80* all and cooled down more at night. We were riding jet skis.

[lbrjet]

My A/C works better in dry air than wet air.


2010 F250 5.4L 3.73
2011 Flagstaff 831FKBSS
Equal-i-zer 4pt 12K

[DesertDrew]

Yesterday in Parker, Arizona...



RV in Full sun.
All windows covered with tight-fitting Reflectix.
Outdoor temperature sensor underneath trailer in shade.
34' open-plan toyhauler, 15,000 btu in living room, 13,500 in bedroom, fan in bedroom blowing air down hallway into living room.

Supposed to be 124F today! Will post results.

[johnm1]

waiter21 - I learned something new today. I also figured our 13.5 (ducted) wouldn't shut off much, if ever.

[florabama]

Yeah, as much as I hate the eventual window fogging I'm seriously leaning toward ordering dual pain windows in my Cedar Creek.

[johntaylor]

Originally Posted by johnm1

I thought A/C didn't work very well in AZ due to the dry air. Isn't that why most houses use a swamp cooler kind of thing?

An AC unit is more efficient in dry air, because it doesn't have to remove the heat from the condensing water vapor. 1 pound of water vapor gives off 970 BTUs as it condenses, and the AC unit has to take that heat away.

Swamp coolers are used in the desert because they are cheaper to buy and operate. They also increase comfort by adding humidity. Because they work by evaporating water, they are not suited to high humidity regions.

[DouglasReid]

Originally Posted by johnm1

Question (well, more of a statement) ... I thought A/C didn't work very well in AZ due to the dry air. Isn't that why most houses use a swamp cooler kind of thing?

I'm just asking because I don't know and I'd like to.

An AC unit will work just fine in a dry climate. Since they have an RV with poor insulation compared to a house a 20 degree drop is good. Better insulation would equal a better drop. It does however entail a HUGE amount of electrical energy to popwer teh compressor and fans compared to a swamp cooler.

a swamp cooler cools by evaporation of water and requires only a water source to drop down the jute pads and a fan to power a large Squirrel cage fan to pass the air into the house, etc. Not very practical for an RV though.

[DesertDrew]

Today the forecast was for 124*, it actually hit 125*!

Here is my indoor/outdoor thermometer reading...

Thermometer is at elbow level next to couch.

These are real numbers folks...
I didn't hold it next to the A/C outlet or put it in the fridge.

I have been achieving similar numbers here in the Arizona desert for the last 15 years, last 2 summers in the SP34T toyhauler (pictured in sig) that we have now, the previous 9 years in a 1976 Holiday Rambler Presidential 3300 TT (30' w/ single 15,000 btu), and the first 4 years in a 1972 24' Dodge class A w/ single 15,000 btu A/C.

Turn your RV into a cave, put tight-fitting Reflectix reflective insulation in all windows, vents and skylights. Keep A/C(s) set at 80% or less to avoid freezing up. Use a fan to circulate cool air better. Don't cook or take hot showers during the day. Avoid going in and out during day.

The heat can be tolerable in almost any rig. I have helped many others get their RV more comfortable for summer camping using these methods.

Stay cool,
Desert Drew

[Tom48]

Originally Posted by johnm1

Question (well, more of a statement) ... I thought A/C didn't work very well in AZ due to the dry air. Isn't that why most houses use a swamp cooler kind of thing?

I'm just asking because I don't know and I'd like to.

In a dry climate the water cooler works well and is much less expensive than refrigeration in extreme heat.

[johnm1]

Thanks all for teaching me the ways of the swamp cooler vs traditional A/C. I really thought A/C needed moisture in the air to work and that's where the swamp coolers come in. I'm feeling so smart now!

Thanks again!