Running portable AC going down the road

[Mudfrog]

We have the smaller around 28 foot Sunova, bet it's the same as the OP's. Ordered ours with the 15,000 btu rooftop option and it keeps up at camp or going down the road. I have a feeling the OP's may be the standard 13,5 unit which may be where the problem lies. If so, an option may be to replace the smaller rooftop unit with the larger 15 or 14,8. There's a decent chance this would cost less than having the dash air repaired.

With the ducted ceiling air, there's only so much that can be done. Closing a couple of vents off in the back may help but closing too many would only end up restricting air flow which would make things worse.

Like others have said, I would not try to add a portable unit to the mix. If you have them, using the windshield defrost fans may help. Also as stated, running dash air in recirculating mode can help as well.

[Ray,IN]

Originally Posted by harryn

The two hose a/c units are sometimes used in van conversions - I have customers that use them locally.

The main things to keep in mind are:
- They are designed for sitting still - not vibrating down the road. As a result, they will likely fail faster than something designed for mobile use.

- The air intake / exhaust aspect just need to be thought through. Some people poke holes through the floor or roof for more permanent mounting.

The hoses are relatively thin plastic, so noise will come through.

One thing that you could try is to just run the hoses into the back area of the coach while driving. That would basically be using the main a/c to keep take the down the extreme outdoor temperature to the 80 - 90 F range, and then use your portable like a spot cooler.

I would think that it would work better if the hot air outlet is directed "up" to flow the hot air across the ceiling and the air inlet is pulling cooler air from lower in the room, but that is speculation.

Some two hose units will evaporate the condensate water into the exhaust hose to help improve efficiency, but that assumes that the hot humid air is not a problem.

Some units have drain hoses that could be directed down through the floor.

I am not saying that this is ideal, but neither is the current situation and let's face it, many RV a/c are not meeting their owner's desired goals either.

The hose positioning you describe is not feasible. Hot exhaust air must be directed outside the vehicle, any other positioning(directing hot air to the ceiling) will result in re-cooling the hot air trapped inside the vehicle. (zero effectiveness)

[SarahW]

Originally Posted by Ray,IN

The hose positioning you describe is not feasible. Hot exhaust air must be directed outside the vehicle, any other positioning(directing hot air to the ceiling) will result in re-cooling the hot air trapped inside the vehicle. (zero effectiveness)

Not to mention the "drain hoses can be directed down through the floor." Um... drill a hole in the RV floor? Not a great solution, IMO.

[harryn]

Perhaps some of my suggestions should be put in the context of the existing situation vs perfection.

- It is an older RV, not a brand new $300K one
- While "technically" the main air conditioner is working, it isn't meeting the end user needs / desires.
- A/C specs tend to be based on I think ASHRAE, which is all fine and dandy to have "standard ways to compare things" but if you really want to have 70 F while sitting in the cab of your RV during a 110 F bright sunny day - it is insufficient.
- Some people are comfortable at 80 or 90 F and that is great. Some people aren't or cannot strip down for driving.

Life is all about having options and not letting other people force you into their way of thinking.

Depending on the person, RVs are either "the finish line" or "the starting point to making it the way you want it to be".

Obviously the OP is not satisfied with the current situation, so it is more of a starting point.

[harryn]

People install solar panels on RVs all of the time, which requires drilling.

They change the battery pack, upgrade inverters, etc - all require drills and screws.

There are perfectly good ways to run a drain line through the floor - if required.

It seems like a small price to pay to be comfortable, IMHO, but I can understand why people would be reluctant.

As I mentioned, it isn't a requirement if they purchase the correct model, but people buy what they are going to buy - it is their money.

[harryn]

Originally Posted by Ray,IN

The hose positioning you describe is not feasible. Hot exhaust air must be directed outside the vehicle, any other positioning(directing hot air to the ceiling) will result in re-cooling the hot air trapped inside the vehicle. (zero effectiveness)

In general you are correct about the normal way to duct these units, but it isn't the only way.

They are only going to use the "spot cooling" portable while driving, not for general use while stationary. If they were going to use both a/c units while stationary, you are right, the ducting would need to be to the outside.

Consider that the typical RV (and portable) a/c unit becomes increasingly less efficient and less able to delivery cool are as the outside temperature increases.

In situations where you are forced to use US approved refrigerants (which are frankly not very good ) and the target temperature is lower than can be achieved with a single stage unit, it is common to use 2 - stages of cooling.

The idea is that each "stage" lowers the temperature part way until the desired temperature is achieved. This is done in professional uses routinely, not just 2 stages, but many stages.

The DIY version of a 2 stage system can be achieved by using the main a/c as stage 1, and the portable / spot cooler as stage 2.

Suppose it is 80 - 85 F in the back, the portable will be able to use this substantially cooler than the outside air to produce 70 F ish temperatures locally - at the driver / passenger area.

The heat from stage 2 (the portable unit) will be removed by the roof a/c unit. That is why the hot air exhaust duct should be directed toward the roof a/c return air and the intake should be directed to pull in cooler air.

Not ideal, but workable. It also eliminates the need to cut large duct holes in the RV for the intake and exhaust.

Obviously when they are using the RV in a stationary location and no longer driving, they spot cooler should be turned off, or the ducts need to be re-positioned to use the windows for air intake / exhaust.

Again - I am not saying that this is ideal, but it is an option.

[Ray,IN]

Originally Posted by harryn

In general you are correct about the normal way to duct these units, but it isn't the only way.

They are only going to use the "spot cooling" portable while driving, not for general use while stationary. If they were going to use both a/c units while stationary, you are right, the ducting would need to be to the outside.

Consider that the typical RV (and portable) a/c unit becomes increasingly less efficient and less able to delivery cool are as the outside temperature increases.

In situations where you are forced to use US approved refrigerants (which are frankly not very good ) and the target temperature is lower than can be achieved with a single stage unit, it is common to use 2 - stages of cooling.

The idea is that each "stage" lowers the temperature part way until the desired temperature is achieved. This is done in professional uses routinely, not just 2 stages, but many stages.

The DIY version of a 2 stage system can be achieved by using the main a/c as stage 1, and the portable / spot cooler as stage 2.

Suppose it is 80 - 85 F in the back, the portable will be able to use this substantially cooler than the outside air to produce 70 F ish temperatures locally - at the driver / passenger area.

The heat from stage 2 (the portable unit) will be removed by the roof a/c unit. That is why the hot air exhaust duct should be directed toward the roof a/c return air and the intake should be directed to pull in cooler air.

Not ideal, but workable. It also eliminates the need to cut large duct holes in the RV for the intake and exhaust.

Obviously when they are using the RV in a stationary location and no longer driving, they spot cooler should be turned off, or the ducts need to be re-positioned to use the windows for air intake / exhaust.

Again - I am not saying that this is ideal, but it is an option.

The Delta differential for air conditioners is approx. 20° lower than intake air. OK, direct the hot exhaust air to the ceiling from the portable unit and the roof unit will never put out chilled air cooler than 20° from that hot air from the portable unit.

I really don't care whether the OP does this or not, I merely voiced my opinion based on my experiences. Hot exhaust air cancels out the chilled air from the same unit when both are inside a closed room/RV.

[Whirrlly]

agree with others, put money into dash ac fixed.....or if you truly are scared of this old can of worms, seriously look into trade/newer unit maybe? sometimes it is best to cut and run if needed than to bandaid a zillion low cost fixes at things that end up never working.

[hohenwald48]

Originally Posted by Ray,IN

Hot exhaust air cancels out the chilled air from the same unit when both are inside a closed room/RV.

This is 100% correct. Actually, the hot air will eventually win due to cooling inefficiencies and heat produced by friction in compressors and motors and wiring losses.

All multi-stage cooling systems I've ever seen exhaust all condenser air outside the envelope to be cooled. I think what harryn is describing is the equivalent of an expensive and inefficient box fan moving air from one area to another.

[Mudfrog]

Originally Posted by Ray,IN

The Delta differential for air conditioners is approx. 20° lower than intake air. OK, direct the hot exhaust air to the ceiling from the portable unit and the roof unit will never put out chilled air cooler than 20° from that hot air from the portable unit.

I really don't care whether the OP does this or not, I merely voiced my opinion based on my experiences. Hot exhaust air cancels out the chilled air from the same unit when both are inside a closed room/RV.

I agree, ducting condenser air into the same space you're trying to cool isn't going be very productive. I've actually never heard of anyone suggesting doing this until this thread.

But really, a person can make the portable work ok if they want to go through the trouble. Ideally, the unit would need to be rigged to supply outside air to the condenser and then exhaust that same heat exchanged air back to the outside. Wouldn't be the prettiest set up but supply and exhaust ductwork could be fastened to a template made to fit into the nearest window opening. And of course, you have to worry about emptying a water tank or plumbing it to a drain.