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

[rvexodus]

BarneyS wrote:
As Durb has mentioned, it sounds to me like you may have an inside the air conditioner leak. There is a divider (usually stiff foam) that separates the "warm" or intake side of the air conditioner with the "cold" or output side. If that divider has slipped out of place or was not installed correctly you could have some of that cold air being forced out the exhaust of the intake instead of into the trailers air conditioning ducts.

Also, the ducts themselves, where they attach to the air conditioner, may not be sealed up correctly and you are loosing cold air to the space between the roof and the inside ceiling covering.

Maybe not but would sure be worth checking. Need to drop the inside cover and bottom plate to see.
Barney

Thanks Barney. Only my garage has the ceiling cover. The main AC and the bedroom AC have no inside portion. Sounds like I will need to pull the covers off the unit on the outside and possibly pull up the unit. Will have to wait until we have sub 100 deg days. For now, I’m limping along 🙂

[BarneyS]

As Durb has mentioned, it sounds to me like you may have an inside the air conditioner leak. There is a divider (usually stiff foam) that separates the "warm" or intake side of the air conditioner with the "cold" or output side. If that divider has slipped out of place or was not installed correctly you could have some of that cold air being forced out the exhaust of the intake instead of into the trailers air conditioning ducts.

Also, the ducts themselves, where they attach to the air conditioner, may not be sealed up correctly and you are loosing cold air to the space between the roof and the inside ceiling covering.

Maybe not but would sure be worth checking. Need to drop the inside cover and bottom plate to see.
Barney

[rvexodus]

Durb wrote:

rvexodus wrote:

Durb wrote:

pnichols wrote:
The OP's air conditioining may not be operating as a "closed system" ... in that the A/C's air intake is not 100% circulating only air from the house interior. In other words some of the A/C's intake air is continuously made up of some new (hot) outside air that is leaking in. This means that there is an "outside air leak" somewhere in the A/C's intake system.

If the OP's A/C system is otherwise operating properly with no intake air leaks and with all windows/vents closed and is 100% using "recirculated intake air" like it's supposed to be, then it's outlet air into the interior is always around 20 degrees lower than it's intake air. Since the intake air is supposed to be 100% coming from the interior of the house, it's outlet air temperature is always getting colder and colder until limited by the thermistat setting ... THAT IS IF the BTU capacity of the A/C system is great enough to, at any expected outside temperature, swamp out the continual heat gain from the outside through the ceiling, the walls, and the floors.



One should always buy a new RV with the maximum BTU size air conditioning system(s) offered - just in case they find themselves having to camp in unexpectedly high temperatures. IMHO, that's part of the "self-containment" goal of an RV.

BTW, a leak in the intake system would also explain why opening some windows would help with cooling from an air-leaking system. The slight pressure increase in the interior - as maintained by the air conditioning system's fan(s) trying to pull in some air from the outside, when they shouldn't be - would be relieved by the open window(s)r - thus permitting flow of some extra cooled air from the leak on out the open window(s).

I Have the same problem with my Carrier air conditioner. The best it could do was lower the trailer to 88 when 92 outside. This post inspired me to get on the roof and pull off the cover and shroud. I had a spot where the coper tubing enters the plenum where hot air could come in but it was minor and I fixed it with some foam tape.

I did notice there was a large opening between the intake and output sides within the air conditioner house portion. The installer stuck a piece of foam in front of the gap and not sealing it. The fan was just circulating air within the unit not pulling it over the cooling coils and not pushing it out the vents. I sealed the gap thoroughly. Turned it on and I now have about 3 times the air volume coming out of the vents and it is cold.

I'm excited to test the air conditioner in a couple of weeks on our trip to some hot locations. Thank you pnichols.

That’s awesome news. I’m going to do the same when it’s not 117 out.

As a follow up I just returned from our trip. Outside air was 101 degrees, inside 81 degrees. 20 degree drop, I'll take it. This air conditioner tune up could have been completed from inside the trailer.

Awesome and congrats. There is hope for me yet!

[Durb]

rvexodus wrote:

Durb wrote:

pnichols wrote:
The OP's air conditioining may not be operating as a "closed system" ... in that the A/C's air intake is not 100% circulating only air from the house interior. In other words some of the A/C's intake air is continuously made up of some new (hot) outside air that is leaking in. This means that there is an "outside air leak" somewhere in the A/C's intake system.

If the OP's A/C system is otherwise operating properly with no intake air leaks and with all windows/vents closed and is 100% using "recirculated intake air" like it's supposed to be, then it's outlet air into the interior is always around 20 degrees lower than it's intake air. Since the intake air is supposed to be 100% coming from the interior of the house, it's outlet air temperature is always getting colder and colder until limited by the thermistat setting ... THAT IS IF the BTU capacity of the A/C system is great enough to, at any expected outside temperature, swamp out the continual heat gain from the outside through the ceiling, the walls, and the floors.



One should always buy a new RV with the maximum BTU size air conditioning system(s) offered - just in case they find themselves having to camp in unexpectedly high temperatures. IMHO, that's part of the "self-containment" goal of an RV.

BTW, a leak in the intake system would also explain why opening some windows would help with cooling from an air-leaking system. The slight pressure increase in the interior - as maintained by the air conditioning system's fan(s) trying to pull in some air from the outside, when they shouldn't be - would be relieved by the open window(s)r - thus permitting flow of some extra cooled air from the leak on out the open window(s).

I Have the same problem with my Carrier air conditioner. The best it could do was lower the trailer to 88 when 92 outside. This post inspired me to get on the roof and pull off the cover and shroud. I had a spot where the coper tubing enters the plenum where hot air could come in but it was minor and I fixed it with some foam tape.

I did notice there was a large opening between the intake and output sides within the air conditioner house portion. The installer stuck a piece of foam in front of the gap and not sealing it. The fan was just circulating air within the unit not pulling it over the cooling coils and not pushing it out the vents. I sealed the gap thoroughly. Turned it on and I now have about 3 times the air volume coming out of the vents and it is cold.

I'm excited to test the air conditioner in a couple of weeks on our trip to some hot locations. Thank you pnichols.

That’s awesome news. I’m going to do the same when it’s not 117 out.

As a follow up I just returned from our trip. Outside air was 101 degrees, inside 81 degrees. 20 degree drop, I'll take it. This air conditioner tune up could have been completed from inside the trailer.

[rvexodus]

Durb wrote:

pnichols wrote:
The OP's air conditioining may not be operating as a "closed system" ... in that the A/C's air intake is not 100% circulating only air from the house interior. In other words some of the A/C's intake air is continuously made up of some new (hot) outside air that is leaking in. This means that there is an "outside air leak" somewhere in the A/C's intake system.

If the OP's A/C system is otherwise operating properly with no intake air leaks and with all windows/vents closed and is 100% using "recirculated intake air" like it's supposed to be, then it's outlet air into the interior is always around 20 degrees lower than it's intake air. Since the intake air is supposed to be 100% coming from the interior of the house, it's outlet air temperature is always getting colder and colder until limited by the thermistat setting ... THAT IS IF the BTU capacity of the A/C system is great enough to, at any expected outside temperature, swamp out the continual heat gain from the outside through the ceiling, the walls, and the floors.

One should always buy a new RV with the maximum BTU size air conditioning system(s) offered - just in case they find themselves having to camp in unexpectedly high temperatures. IMHO, that's part of the "self-containment" goal of an RV.

BTW, a leak in the intake system would also explain why opening some windows would help with cooling from an air-leaking system. The slight pressure increase in the interior - as maintained by the air conditioning system's fan(s) trying to pull in some air from the outside, when they shouldn't be - would be relieved by the open window(s)r - thus permitting flow of some extra cooled air from the leak on out the open window(s).

I Have the same problem with my Carrier air conditioner. The best it could do was lower the trailer to 88 when 92 outside. This post inspired me to get on the roof and pull off the cover and shroud. I had a spot where the coper tubing enters the plenum where hot air could come in but it was minor and I fixed it with some foam tape.

I did notice there was a large opening between the intake and output sides within the air conditioner house portion. The installer stuck a piece of foam in front of the gap and not sealing it. The fan was just circulating air within the unit not pulling it over the cooling coils and not pushing it out the vents. I sealed the gap thoroughly. Turned it on and I now have about 3 times the air volume coming out of the vents and it is cold.

I'm excited to test the air conditioner in a couple of weeks on our trip to some hot locations. Thank you pnichols.

That’s awesome news. I’m going to do the same when it’s not 117 out.

[Grit_dog]

Maybe explained already. Didn't read 3 pages, but yes the OPs experience is valid.
Cold air sinks, heat rises, opens roof vents and/or a fan and you're exhausting hot air and lowering the air pressure the fan on the AC is fighting to blow air into the camper.
Assume an air tight space. Pretty soon the space is going to pressurize to the same pressure the the blower is capable of producing and then no more air flow. If the camper is closed up then you get less air flow.
That's why re circ on the car cents blow harder. Not trying to pressurize the cabin with "new" air. Same effect by rolling down a window in normal mode.

[Durb]

pnichols wrote:
The OP's air conditioining may not be operating as a "closed system" ... in that the A/C's air intake is not 100% circulating only air from the house interior. In other words some of the A/C's intake air is continuously made up of some new (hot) outside air that is leaking in. This means that there is an "outside air leak" somewhere in the A/C's intake system.

If the OP's A/C system is otherwise operating properly with no intake air leaks and with all windows/vents closed and is 100% using "recirculated intake air" like it's supposed to be, then it's outlet air into the interior is always around 20 degrees lower than it's intake air. Since the intake air is supposed to be 100% coming from the interior of the house, it's outlet air temperature is always getting colder and colder until limited by the thermistat setting ... THAT IS IF the BTU capacity of the A/C system is great enough to, at any expected outside temperature, swamp out the continual heat gain from the outside through the ceiling, the walls, and the floors.

One should always buy a new RV with the maximum BTU size air conditioning system(s) offered - just in case they find themselves having to camp in unexpectedly high temperatures. IMHO, that's part of the "self-containment" goal of an RV.

BTW, a leak in the intake system would also explain why opening some windows would help with cooling from an air-leaking system. The slight pressure increase in the interior - as maintained by the air conditioning system's fan(s) trying to pull in some air from the outside, when they shouldn't be - would be relieved by the open window(s)r - thus permitting flow of some extra cooled air from the leak on out the open window(s).

I Have the same problem with my Carrier air conditioner. The best it could do was lower the trailer to 88 when 92 outside. This post inspired me to get on the roof and pull off the cover and shroud. I had a spot where the coper tubing enters the plenum where hot air could come in but it was minor and I fixed it with some foam tape.

I did notice there was a large opening between the intake and output sides within the air conditioner house portion. The installer stuck a piece of foam in front of the gap and not sealing it. The fan was just circulating air within the unit not pulling it over the cooling coils and not pushing it out the vents. I sealed the gap thoroughly. Turned it on and I now have about 3 times the air volume coming out of the vents and it is cold.

I'm excited to test the air conditioner in a couple of weeks on our trip to some hot locations. Thank you pnichols.

[pnichols]

Kirk,

The "leaks" I'm referring to are not leaks in the house windows, doors, etc.. It's leaks directly within the intake path leading to the air conditioner sucking in air from the outside in addition to the recirculated air it's sucking from inside the house.

What this type of leak does is constantly introduce hot outside air into the air conditioning unit's intake - which of course raises the temperatue of the air entering into the house from the air conditioner over what the temperature that air would be if it was only coming from recirculating air originating in the interior of the house.

This type of leak may result from the air conditioning unit not being sealed down tight enough onto the RV's roof. I almost annually tighten the bolts that pull our A/C unit into the rubber seal between it's intake and the coach's roof.

[rvexodus]

pnichols wrote:
Kirk ... are you sure no leaks?

Opening windows should not increase perceived cool air flow in a leak-less recirculating system unless you are feeling some other effect such as two or more open windows creating air cross-flow from outside breezes..

Nope its not perceived. When I turn on the roof vent around 20%, I can feel more are flowing from AC vents. At 100% that airflow increases a little but not significantly.

I’m thinking through this a bit so thanks for calling me out.

If there is no outside are being introduced I should hear the fan struggle while it’s trying to create a vacuum.

If i have say a leaky door I should maybe feel a cross breeze.

If my duct or ac unit has a leak I will feel that outside air being pulled through the ducts causing an increased airflow.

Am I catching on to what you are saying.

What about the theory that it’s static pressure keeping the AC from moving cold air? It does seem to blow better at night when the temps are cooler. Also what is the best way to test for a leak other than physicsl inspection?

[pnichols]

Kirk ... are you sure no leaks?

Opening windows should not increase perceived cool air flow in a leak-less recirculating system unless you are feeling some other effect such as two or more open windows creating air cross-flow from outside breezes..

[rvexodus]

pnichols wrote:
The OP's air conditioining may not be operating as a "closed system" ... in that the A/C's air intake is not 100% circulating only air from the house interior. In other words some of the A/C's intake air is continuously made up of some new (hot) outside air that is leaking in. This means that there is an "outside air leak" somewhere in the A/C's intake system.

If the OP's A/C system is otherwise operating properly with no intake air leaks and with all windows/vents closed and is 100% using "recirculated intake air" like it's supposed to be, then it's outlet air into the interior is always around 20 degrees lower than it's intake air. Since the intake air is supposed to be 100% coming from the interior of the house, it's outlet air temperature is always getting colder and colder until limited by the thermistat setting ... THAT IS IF the BTU capacity of the A/C system is great enough to, at any expected outside temperature, swamp out the continual heat gain from the outside through the ceiling, the walls, and the floors.

One should always buy a new RV with the maximum BTU size air conditioning system(s) offered - just in case they find themselves having to camp in unexpectedly high temperatures. IMHO, that's part of the "self-containment" goal of an RV.

BTW, a leak in the intake system would also explain why opening some windows would help with cooling from an air-leaking system. The slight pressure increase in the interior - as maintained by the air conditioning system's fan(s) trying to pull in some air from the outside, when they shouldn't be - would be relieved by the open window(s)r - thus permitting flow of some extra cooled air from the leak on out the open window(s).

It is an RV so I can’t say there are any leaks in the system. However, the delta between intake temps and output are with expected 15deg or better. The point you make around btu and one I breezed over is that I’m running only two of my three AC units due to limited power. Total BTU versus total area to cool is definitely out of balance.

The core of my post was not so much help me, why is my rv so hot. AZ summers and limited power is a good enough answer to that question for me 🙂 My post was really related to my finding that after hours of AC use, venting some of the hot air improves the airflow and therefore improves the cooling.

Moving out of Phoenix helps as well 🙂

[pnichols]

The OP's air conditioining may not be operating as a "closed system" ... in that the A/C's air intake is not 100% circulating only air from the house interior. In other words some of the A/C's intake air is continuously made up of some new (hot) outside air that is leaking in. This means that there is an "outside air leak" somewhere in the A/C's intake system.

If the OP's A/C system is otherwise operating properly with no intake air leaks and with all windows/vents closed and is 100% using "recirculated intake air" like it's supposed to be, then it's outlet air into the interior is always around 20 degrees lower than it's intake air. Since the intake air is supposed to be 100% coming from the interior of the house, it's outlet air temperature is always getting colder and colder until limited by the thermistat setting ... THAT IS IF the BTU capacity of the A/C system is great enough to, at any expected outside temperature, swamp out the continual heat gain from the outside through the ceiling, the walls, and the floors.

One should always buy a new RV with the maximum BTU size air conditioning system(s) offered - just in case they find themselves having to camp in unexpectedly high temperatures. IMHO, that's part of the "self-containment" goal of an RV.

BTW, a leak in the intake system would also explain why opening some windows would help with cooling from an air-leaking system. The slight pressure increase in the interior - as maintained by the air conditioning system's fan(s) trying to pull in some air from the outside, when they shouldn't be - would be relieved by the open window(s)r - thus permitting flow of some extra cooled air from the leak on out the open window(s).

[TyroneandGladys]

Bottom line on any refrigerated air conditioning system is a 10 degree drop in temperature. If the temp of the air going into the AC is 110 if the air is coming out is 100 then the AC unit is working. You might get more than 10 degrees but 10 is the minimum.
That does not mean that it will only cool a 110 degree space to 100. When it gets to 100 the temp coming out will be 90 when it gets to 90 then it will be coming out 80.
This is provided that the area is not to large for that drop to occur or if there is not to much heat gain.

[rvexodus]

SoundGuy wrote:

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. 🙂

I agree. It’s not a mystery that you would crack a window in a hot car. However, typically after it cools down you close it and all is good. The mystery here is that two AC units in my 43ft toyhauler could only bring temps down to 92f give or take. This was after running all day. Opening a vent and cracking a window dropped that by around 5f in a very short period of time. So this isn’t about initial cooldown as much as it is about improving AC efficiency through out warmer periods. Leaving a window open all day is counter intuitive. But if your AC units are struggling to keep temps down, leaving a window cracked or a vent open and running may help bring those temps down further than keeping everything closed. I did not expect that and know many others in the SW are in similar situations. Let’s not even bring up refrigerators 🙂