Air conditioners ... open windows to cool things down?

[rvexodus]

Ok here is a new one. New one to me at least. We just got a new kz venom toy hauler earlier this year. We’ve been doing a number of upgrades from solar to turning the garage into an office while trying to get our house ready for sale. The 5th wheel is parked on my dads property in the northwest valley. I only get 15a from his outlet and use my inverters and lithium bank as well as solar to run 2 of my 3 air conditioners. In 110+ weather two air conditioners can’t keep this enormous rv cool and temps inside can go into the 90s.

So, I’m sitting on the throan today and cranked on the fantastic fan for a little white noise and ventilation. You have all been there right? Anyhow, I noticed that the AC duct in the bathroom actually started blowing harder and it started to cool down. Ok let’s take this out of the lab and trial it in the real world.

I then opened the fantastic fan in the kitchen, cracked a window and immediately felt the ambient air get cooler. Ducts that barely blew were flowing like never before. Within about 15-20m the inside temp dropped from 92 to 87. We were packing up to head back to the house so I didn’t play much more with the idea. However, at one point I closed the window and cranked the fan from 20% up to around 80% and it looked like it was starting to warm up. There is likely a sweet spot here.

I think there’s one of two things happening here or maybe a combination. Static pressure ... eg, heavy warm air can make it harder for the AC to blow and circulate air. Also, as many know when they have cranked on their roof vents with no windows open the fans are powerful enough to pull air from anywhere including grey and black tanks. I’m guessing the fan is actually improving airflow from the AC ducts much like a booster or inline fan would in a residential situation.

I’ll play around with this to see just how far I can pull temps down running just two AC units but thought I would share this with anyone that is having problems cooling their rv in hot as heck weather. Even a few degrees can make ia big difference.

Curious, has anyone else experienced this effect?

Thanks, Kirk

[SoundGuy]

DiskDoctr wrote:
Get the hottest air out first, provide cooler air to the A/C to further cool, and reduce any inside pressure by allowing a good exhaust while you replace that air with ever cooler air.

Not sure of the mystery here :h - this is exactly the same approach with any vehicles I've ever owned. Hot summer day, vehicle has been sitting cooking in the sun, first thing I do after starting is roll down all the windows, fire up the A/C, and allow it to force hot air out before replacing it with cold air. Much more efficient than leaving all that hot air trapped in the vehicle and trying to slowly replace it with cold air. We don't use A/C in the camper often but when we do it's exactly the same procedure. 🙂

[rvexodus]

yillb wrote:

MrWizard wrote:
he said the 15amp shore power and his solar are supplying charge to his 'Lithium battery bank

he is running the a/c from inverter power

I assume,, he has a deficit during the day using more power from batteries than is generated, and gets the batteries fully charged overnight ?

He's running TWO ac's from the inverter. I don't think it matters how many batteries you have, that's a lot of power. I'm pretty sure he's not even running the compressor, and it's just the fan as someone else pointed out. It happens on our venom toyhauler all the time.

Btw ... I do find it kinda annoying that the power management system will shut down the compressor if loads are too high but still allow the fan to run. If I turn on all 3 AC units one of those the power management system will shut down and only the fan runs. When I installed my two 3000w inverters I had to trick the power management system into thinking the generator was running by applying 12v to one of the pins on the power management panel. Otherwise, it thought I was running on 30a and restricted me to just one AC unit.

At one point I had the two inverters running splitphase (120v@30a x 2 each shifted 180 degrees from one another). This is how 50a service is configured, two 50a 120v legs 180deg out of phase which prevents the common from carrying the potential 100a combined load. The problem I was running into was that one inverter alone was not enough to run two AC units. That configuration let me run the living room AC on L1 and one of the other ACs on L2. I could not run the two ACs on L2 at the same time. I reconfigured the inverts to be stacked (120v @ 60a shared across L1 and L2) and can now run any two ACs. The power management system and the 50a breaker I have on the inverters prevents me from running all 3. But I do have the horse power to pull it off between my two Honda’s , solar and the two inverters.

[rvexodus]

time2roll wrote:
The real solution is to pull 50 amp power to the RV.

Otherwise the air just recirculates so the vent fan may concentrate cool air in one area but in the end is pulling heat in somewhere else. RVs are generally not well sealed. If you have a hot box from driving all day it may help to push some of the hottest air out. Soon you need to just close up and let it work.

This is a temporary location while we work on our handful of projects. Once the house sells we will head north. However, temps will likely be manageable by then. I have considered running 50a service. However, I’m around 200 ft from the main box. I wasn’t willing to drop the $$$. But yes I dream of 50a service on a regular basis.

[rvexodus]

MrWizard wrote:
week ago sunday, it 109F here
and we are expecting triple digits latter part of this week
today was 95F
with a 3400w generator and 109f, i can only run (1) of my (2) a/c units
but with a little shade i can keep it about 85f in the front halve of the RV
leaving the rear on blower, and various fans going
for a nap, i will switch the front a/c to blower and turn the bedroom on cold

shade cloth over the RV might help as will pulling in the slides
yeah some RV's leave no room too move around when you pull in slides

still it something to 'think' about, might help you be a little cooler
during those triple digit days

Ours isn’t too bad with the slides in and would considering doing it. We do have the aluminum bubble wrap stuff in our windows which helps. Interestingly we can turn on the garage AC and shut the door and it alone will bring temps down to 83 when it’s 108 out but it’s a small space with no slides.

We are unfortunately in full sun which doesn’t help a bit of course. My dads acrerage is flat and baron. Not too worried about the heat as we go there on weekends to work on it and can retreat any time to our home AC. What was interesting was how opening the roof vent actually helped cool down the rv. Outside temps were 111. Inside temps 92ish before running the vent and 87ish after opening and running the vent. Kinda cool no pun.

[MrWizard]

week ago sunday, it 109F here
and we are expecting triple digits latter part of this week
today was 95F
with a 3400w generator and 109f, i can only run (1) of my (2) a/c units
but with a little shade i can keep it about 85f in the front halve of the RV
leaving the rear on blower, and various fans going
for a nap, i will switch the front a/c to blower and turn the bedroom on cold

shade cloth over the RV might help as will pulling in the slides
yeah some RV's leave no room too move around when you pull in slides

still it something to 'think' about, might help you be a little cooler
during those triple digit days

[rvexodus]

yillb wrote:

MrWizard wrote:
he said the 15amp shore power and his solar are supplying charge to his 'Lithium battery bank

he is running the a/c from inverter power

I assume,, he has a deficit during the day using more power from batteries than is generated, and gets the batteries fully charged overnight ?

He's running TWO ac's from the inverter. I don't think it matters how many batteries you have, that's a lot of power. I'm pretty sure he's not even running the compressor, and it's just the fan as someone else pointed out. It happens on our venom toyhauler all the time.

No sir. Both compressors are running. When two ACs and the fridge are all running I’m showing an AC output of over 4500w on the victron and the power management system shows 35-45a power draw. I’ve also tested temps coming from the ducts in each room to ensure I’m getting 10-15deg diff between return register and vents. I really wish it were that simple. However, my inverts are capable of running two ACs with out a hitch of the lithium bank. If I have no solar and no shore power, I can only do that for a few hours before I’m out of juice but it’s absolutely possible.

[rvexodus]

MrWizard wrote:
he said the 15amp shore power and his solar are supplying charge to his 'Lithium battery bank

he is running the a/c from inverter power

I assume,, he has a deficit during the day using more power from batteries than is generated, and gets the batteries fully charged overnight ?

That was the concept. I’m actually finding that I charge the batteries slowly during 5-6 hours of the day due to all the solar I have. However, from about 5pm until 8pm I’m loosing my solar and starting to drain batteries at around 40+ah. Then as we retire to the bedroom, I shut down one AC but the bedroom ac runs until about 11pm until temp drop into the low 90s ... seriously it can still be in the 90s at 1am.

Around 3am the power consumption starts to equalize with power I’m receiving from shore power and I start to charge the batteries. I really dream about 50amp RV service or better yet cooler temps but need to finish up a few projects before I can move the beast.

If you guys want to see my setup, search YouTube for rvexodus. I have a series on lithium and solar. Catch episodes 8 or 9. I have since added a second victron. Just haven’t published the video.

Anyhow, the crack a window / turn on a fan makes sense as long as it’s not to the point you are pumping out more cold air and pulling in hotter air. There seems to be a balance. I’ll have to see how much I can improve things. I was excited about 5 deg. It is counter intuitive to open a window when running an AC though 🙂

Someone asked about humidity. We are around 25% with outside being around 10%. Seems about right.

[rvexodus]

yillb wrote:

For two, if that is happening, you're likely causing damage, they had to replace the unit because it burnt out the compressor, trying to run 2 ac units on so little power seems to be an expensive problem, at least with the venom they own. I'm not sure how you're turning 15A into enough starting amps, let alone running amps to power nearly 30 amps worth of AC units. If' im not mistaken, two of the three you have are 15k units, they take quite a bit to start, and just a little less to run, that's not including all the others you're using. Though, they don't have solar, so I can't speak to that.
.

I have two victron 3000w inverter chargers stacked to provide 6000w continuous and well over that in peak. The victron will take a set amperage from shore power and supplement whatever the load needs using battery power. I have 400ah @24v lithium banks. When the shore power isn’t enough I can kick over 2x Honda eu2000 in parallel for 26a. In addition I have over 2000w of solar. I have enough starting power to kick over 3 ac units but that will run down my batteries after a few hours and really isn’t sustainable. Because the victron matches the input voltage, I see 114v+ on my dads and the Honda’s kick out a beautiful 119.4-119.8v consistently. The victron logs all this detail so it’s real easy to see what’s happening when AC units kick on.

You made me laugh saying that many don’t experience 110+ deg. Yah I guess not. It was 111+ today. That’s just crazy. When I was younger it didn’t seem to bother me. But indeed extreme.

I think you are incorrect in saying more AC units won’t cool it any more. I believe each AC can lower the temps 10-15 deg. Collectively I should be able to drop the temps 30 deg minimum. I could be wrong. I’ve only owned single AC homes and RVs.

Thanks for the response boss. Good to know others experiences.

[yillb]

MrWizard wrote:
he said the 15amp shore power and his solar are supplying charge to his 'Lithium battery bank

he is running the a/c from inverter power

I assume,, he has a deficit during the day using more power from batteries than is generated, and gets the batteries fully charged overnight ?

He's running TWO ac's from the inverter. I don't think it matters how many batteries you have, that's a lot of power. I'm pretty sure he's not even running the compressor, and it's just the fan as someone else pointed out. It happens on our venom toyhauler all the time.

[time2roll]

The real solution is to pull 50 amp power to the RV.

Otherwise the air just recirculates so the vent fan may concentrate cool air in one area but in the end is pulling heat in somewhere else. RVs are generally not well sealed. If you have a hot box from driving all day it may help to push some of the hottest air out. Soon you need to just close up and let it work.

[MrWizard]

he said the 15amp shore power and his solar are supplying charge to his 'Lithium battery bank

he is running the a/c from inverter power

I assume,, he has a deficit during the day using more power from batteries than is generated, and gets the batteries fully charged overnight ?

[DiskDoctr]

rvexodus wrote:
Curious, has anyone else experienced this effect?

I offered similar advice just within the past 24hrs to a fellow who posted he was having trouble getting his camper to cool down.

Not only do you allow more air into the camper, you are REMOVING the hottest air from the ceiling with the fan.

Ever notice in your car how the fan in the dash blows more air when you open a rear vent? Or how much faster it cools down on a hot day when you lower the rear windows a bit and have the dash blowing A/C on high?

Get the hottest air out first, provide cooler air to the A/C to further cool, and reduce any inside pressure by allowing a good exhaust while you replace that air with ever cooler air.

[yillb]

Sounds to me like you need a little more info, hopefully I can help.

My father has a venom with three ac's, and this is actually pretty easy to explain why it's happening. Though, it would help if you had a couple more bits of information.

for one, if you're trailer is at 90 degrees with two ac's running, something's wrong, it's 98 today in south texas, and we got theres down to 78. That said, one is on a thermostat, two are knobs on the cooler. The particular one with knobs in the bedroom says it's on, but if you read the manual, it's actually not. Your FAN will run on just 12volts, the compressor will not. Have you actually verified that you're getting cold air out of the actual AC, and the fan isn't just running.

For two, if that is happening, you're likely causing damage, they had to replace the unit because it burnt out the compressor, trying to run 2 ac units on so little power seems to be an expensive problem, at least with the venom they own. I'm not sure how you're turning 15A into enough starting amps, let alone running amps to power nearly 30 amps worth of AC units. If' im not mistaken, two of the three you have are 15k units, they take quite a bit to start, and just a little less to run, that's not including all the others you're using. Though, they don't have solar, so I can't speak to that.

Back to my initial statement though, 90 degrees would be semi expected, if it's actually 110 degrees outside, very few places in the states are actually seeing those temps right now, if you're unlucky enough to get in one, then that's 20 degrees lower than the outside temps. That's about what you can expect, adding another AC won't really change that, these units can only lower the temp by about 20 degrees, it wouldn't matter if you had 100 ac units, if the temperature coming out of them is only 20 degrees lower than the ambient temp, then that's as low as it's going to get, period.

As for why the fans cause it to feel colder, you already nailed that one. At 110 degrees, the static pressure in your cabin is likely extremely high, nauseating almost. It's hard to say for sure, because so few people actually get to expereince such extreme temperatures while in an RV, so what you're seeing is extremely uncommon. Nonetheless though, i think you're right with that one, super hot air is extremely dense, though, depending on the unit, and where the intake is, could stop that. I'm assuming they are all internally inducted, thus using that super hot, likely humid air. I know it's dry outside, but with a 20 degree difference between inside and outside, i'm going to assume your humidity levels are off the charts.

With all of that said, what you're describing isn't all that bad, 20 degrees is decent. I said initially something might be wrong, because it's hard to fathom actual 110 degrees beating down on a big metal box.

Don't forget to take into account the super hot dense air will rise up, so if you're in a small-ish room with a single duct ( like a bathroom ), then you start to push hot air out, you'll feel a noticeable increase in ambient temperature, increase as in, a change, not a literal increase of temperature literally. When you do this on a large scale, the intake can breath more heavily, thus resulting in a higher blower. Unfortunately, with the windows open, you might blow faster, but you likely won't achieve an actual lower temperature, the temperature is static in the sense it's always going to be the same, relative to the ambient temperature outside. so while you can achieve the affects of a cooler trailer, based on logic alone, you can't actually get those, at least nothing that would be worthwhile.