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Lancslad

SE VA

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Posted: 08/11/19 02:21pm Link  |  Quote  |  Print  |  Notify Moderator

We put Reflexit on all exterior walls inside the cabinets and closets. It makes a big difference in the inside temps.


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bsheet2

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Posted: 08/11/19 04:23pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

Just for your info. The REAR is a 13,500 BTU They do not make a 12,500 BTU. 37 foot units need 2- 15K AC units for Texas heat. That extra 1500 BTU will do wonders in Texas Heat. Doug



Ok, you are correct. 13,500 BTU AC in the back. Actually it does very well in the bedroom even in this heat. The front has a new 15,000 BTU unit that was put in as part of the purchase.

Thanks for info. My take away is that the AC units are doing their job. It is just too dang hot.

Actually the AC did better today. I started everything early in the morning and we minimized going in and out. It stayed decent in the heat of the afternoon.

I will take some of the good advise in the above posts and try to improve the insulation to keep some the heat out.

Thanks everyone!

DFord

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Posted: 08/11/19 10:39pm Link  |  Quote  |  Print  |  Notify Moderator

When the sun's baking the outside of your RV in the middle of the day, it's always going to be hard to keep cool but running continuously should make it feel pretty good inside. When the sun lets up, the air conditioners will catch up. Many permanent sites put a "roof over" (like a big car port) their spot to prevent that summer sun from beating on the roof and sides during midday.


Don Ford
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Kamphiker

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Posted: 08/12/19 04:44am Link  |  Quote  |  Print  |  Notify Moderator

As far as testing the AC units:

Measuring Intake Air Temp And output air temp (at closest air registrar if you cant measure in the main Plenum) you should see 15 - 20° differential.

dougrainer

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Posted: 08/12/19 06:16am Link  |  Quote  |  Print  |  Notify Moderator

bsheet2 wrote:

dougrainer wrote:

Just for your info. The REAR is a 13,500 BTU They do not make a 12,500 BTU. 37 foot units need 2- 15K AC units for Texas heat. That extra 1500 BTU will do wonders in Texas Heat. Doug



Ok, you are correct. 13,500 BTU AC in the back. Actually it does very well in the bedroom even in this heat. The front has a new 15,000 BTU unit that was put in as part of the purchase.

Thanks for info. My take away is that the AC units are doing their job. It is just too dang hot.

Actually the AC did better today. I started everything early in the morning and we minimized going in and out. It stayed decent in the heat of the afternoon.

I will take some of the good advise in the above posts and try to improve the insulation to keep some the heat out.

Thanks everyone!


In a Motorhome, the REAR AC will perform colder than the front AC, regardless of AC size. The Rear AC turns over less volume of air and will yield colder output, even with a ducted system. Doug

bsheet2

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Posted: 08/12/19 08:01am Link  |  Quote  |  Print  |  Notify Moderator

Kamphiker wrote:

As far as testing the AC units:

Measuring Intake Air Temp And output air temp (at closest air registrar if you cant measure in the main Plenum) you should see 15 - 20° differential.


Thanks for the replies everyone.

I do want to comment on the 15-20 degree temperature differential though. I am an engineer, sorry I can't help it. I have heard this temperature differential quoted a few times. However, I do not think this is accurate. I think we should be seeing 18 to 20 degrees temp differential -- minimum. This is an educated guess right now based on a knowledge of how home AC is designed. I have been trying to find design info about our RV AC units but have not laid my hands on any yet. But I think most AC units are designed to achieve a 20 degree temp differential. Then they allow for a 10% (or 2 degree) loss of cooling due to ducting or other losses. I am certain this is the basis for a home AC.

Background - if you want it.
Several years ago when we purchased a new home the AC was not working well at all. After a saga with the contractor he finally sent a consultant over to take a look. The consultant was a retired lead designer that had worked for Carrier. Everything changed as soon as he walked onto the site. I learned the basis of how the AC system is designed. It should achieve a delta T of 20 degrees measured immediately after the blower fan before going into the ducts. They then allow for the air to gain 2 degrees of heat in the ducts running through the attic. So, you should see at least 18 degrees delta T at each and every duct outlet. If not, something is wrong.

The issues we found in my house:
- The attic was too hot. Not enough ventilation.
- Not enough flow in some ducts. Slow flow allows more heat input from the attic and not enough volume of cool air in that room. Larger diameter ducts needed.
- Some main ducts were very long. Long length allows extra heat into the duct. Larger diameter and double insulation was the cure.

By the end of this saga I learned a lot about AC system design and what we should be seeing to meet what it is designed for.

The question is, is the design basis the same for RV AC's??

wa8yxm

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Posted: 08/12/19 08:33am Link  |  Quote  |  Print  |  Notify Moderator

I would say two things
1`: Your report sounds "Normal"
2: When the rear fails and it will, may take a decade or two but it will. Upgrade to 15000 or whatever is biggest when it happens.

Still won't keep you all that cool in full sun.


Home is where I park it.
Kenwood TS-2000 housed in a 2005 Damon Intruder 377


dougrainer

Carrolton, Texas

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Posted: 08/12/19 08:50am Link  |  Quote  |  Print  |  Notify Moderator

bsheet2 wrote:

Kamphiker wrote:

As far as testing the AC units:

Measuring Intake Air Temp And output air temp (at closest air registrar if you cant measure in the main Plenum) you should see 15 - 20° differential.


Thanks for the replies everyone.

I do want to comment on the 15-20 degree temperature differential though. I am an engineer, sorry I can't help it. I have heard this temperature differential quoted a few times. However, I do not think this is accurate. I think we should be seeing 18 to 20 degrees temp differential -- minimum. This is an educated guess right now based on a knowledge of how home AC is designed. I have been trying to find design info about our RV AC units but have not laid my hands on any yet. But I think most AC units are designed to achieve a 20 degree temp differential. Then they allow for a 10% (or 2 degree) loss of cooling due to ducting or other losses. I am certain this is the basis for a home AC.

Background - if you want it.
Several years ago when we purchased a new home the AC was not working well at all. After a saga with the contractor he finally sent a consultant over to take a look. The consultant was a retired lead designer that had worked for Carrier. Everything changed as soon as he walked onto the site. I learned the basis of how the AC system is designed. It should achieve a delta T of 20 degrees measured immediately after the blower fan before going into the ducts. They then allow for the air to gain 2 degrees of heat in the ducts running through the attic. So, you should see at least 18 degrees delta T at each and every duct outlet. If not, something is wrong.

The issues we found in my house:
- The attic was too hot. Not enough ventilation.
- Not enough flow in some ducts. Slow flow allows more heat input from the attic and not enough volume of cool air in that room. Larger diameter ducts needed.
- Some main ducts were very long. Long length allows extra heat into the duct. Larger diameter and double insulation was the cure.

By the end of this saga I learned a lot about AC system design and what we should be seeing to meet what it is designed for.

The question is, is the design basis the same for RV AC's??


RV roof top systems are all sealed systems and ALL models of the same model number have the exact same performance. NO variables except for correct install. This is from the Service manual of RVP(Coleman). Doug
•An ideal cooling system should give you an output temperature range of 16-22 degrees lower than the temperature taken in at the filter. Humidity is a significant determining factor in this temperature difference.

PS, you cannot take a residential or commercial design and install and relate it to a RV roof top AC. Totally different design and charging aspects. Residential systems vary in size of the Evap and outside tonnage of condenser. Then you must charge with the Supercool method as there is NO exact point of lbs of coolant like on a RV AC unit. As you found out, having a knowledgable installation of any residential is critical to optimum performance.

Groover

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Posted: 08/16/19 07:02am Link  |  Quote  |  Print  |  Notify Moderator

I had the same struggle recently with my Thor Palazzo about the same size. My AC's are ducted and I used an infrared thermometer to measure the temps inside the ductwork. I was actually getting 25 to 30 degree temperature drop so I came to the same conclusion as you, the unit just isn't very well sealed/insulated. At least with ducted AC's I could have both units working on the kitchen/living areas and managed to keep them comfortable. I don't know what type of stove that your camper has but mine is a little bit older unit and came with a gas stove. In expectation of heat being an issue I bought a 2 burner induction cooktop for the trip and believe that cooking on it instead of the gas cooktop helped a lot. The cooktop was $180 and I found a surprisingly good set of induction cookware for another $80 so altogether $260. It really did reduce the amount of heat put into the coach and is much easier to clean up.

About the only other easy things would be to make sure that you have double layer covers on your Fantastic roof fans and to pull in a slide during the day if that doesn't cause too much discomfort.

One final thing but it would be a bit expensive. I have heard claims that the Atwood AC's have more real capacity than the other brands and are quieter. I can't vouch for that so take it with a grain of salt. I have been trying to figure out how to compare brands myself but haven't come up with a good way yet.

dougrainer

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Posted: 08/16/19 07:17am Link  |  Quote  |  Print  |  Notify Moderator

Groover wrote:

I had the same struggle recently with my Thor Palazzo about the same size. My AC's are ducted and I used an infrared thermometer to measure the temps inside the ductwork. I was actually getting 25 to 30 degree temperature drop so I came to the same conclusion as you, the unit just isn't very well sealed/insulated. At least with ducted AC's I could have both units working on the kitchen/living areas and managed to keep them comfortable. I don't know what type of stove that your camper has but mine is a little bit older unit and came with a gas stove. In expectation of heat being an issue I bought a 2 burner induction cooktop for the trip and believe that cooking on it instead of the gas cooktop helped a lot. The cooktop was $180 and I found a surprisingly good set of induction cookware for another $80 so altogether $260. It really did reduce the amount of heat put into the coach and is much easier to clean up.

About the only other easy things would be to make sure that you have double layer covers on your Fantastic roof fans and to pull in a slide during the day if that doesn't cause too much discomfort.

One final thing but it would be a bit expensive. I have heard claims that the Atwood AC's have more real capacity than the other brands and are quieter. I can't vouch for that so take it with a grain of salt. I have been trying to figure out how to compare brands myself but haven't come up with a good way yet.


1. You CANNOT use a IR Thermometer to performance test a AC unit--Home or RV
2. BTU's are BTU's. Regardless of Brand, they will put out the BTU's they are designed and built for. Atwood is trying to get into the RV market. I find noise complaints funny. You are putting a large AC on top your roof of your RV and then you complain about any noise???????
Ever Had a Residential house with a AC unit outside your Master Bedroom area? I HAVE. When we purchased our last 2 houses, the criteria was NO AC unit outside the Master Bedroom area. Noise is Noise. While some state Atwoods have a quieter signature, I will go with the 2 brands that have been around for almost 50 years--Dometic and Coleman. There have been a few companies that have tried to enter the RV market in the past 10 years and they quietly walked away leaving customers with no parts or support. That is why I would not advise going to any AC unit other than Dometic or Coleman. They are here and will still be here in the future. Doug

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