Undermount AC option

bob323

New member
Just learning about this option and am seriously considering including it in my 2017 Adventurous RS specs; however, after a brief chat session with a Roadtrek Sales Support guy, he recommends that in hot/humid climates I might should order the EcoTrek 800 option. Problem is, the Roadtrek 'Build Your Own' tool offers ONLY the EcoTrek 400 option which I was already planning to include.

As it currently stands, the options I'm considering are as follows: VoltStart, EcoTrek 400, Solar Panel 270w, Induction Stovetop, Under Hood Generator and Undermount A/C. As such, the vehicle will be propane-free. The only question I now have is whether or not the Undermount A/C will have problems running more than a couple hours before the batteries run dead, OR will the VoltStart crank the engine, recharge the batteries and the A/C keep humming without interruption? Anybody out there know or have experience with such a combo of options - esp re the Undermount A/C performance under high temp/humidity situations?

Thx for your help.
 

Old Crows

Calypso 2014 View Profile
RE: UNDERMOUNT AC.

Since you asked. I've not data or experience. Only, observations.....

First, this thing better be armor plated and bullet proof. I think you can sort out all the possibilities of a rock, debris, chunk of rubber tread, a stray 2x4 lost on roadway hitting the condenser and taking out the system. Probably, sometime before you start to use it after you get to your destination on a Friday evening somewhere between Lost and Found.

These RVs aren't noted for ground clearance. It is unlikely that you would jam it into something but any kind of off road event or a backing up situation could cause some problems if you happened to ding it on a curb or rock.

Under the RV is going to be just plain dirty. Debris, leaves, paper and plastic bags, etc, may get sucked up in the intake. Then there's dust, sand, road salt, and fine debris that will get packed into the unit. That looks like a problem to me..... a perpetual maintenance issue.

Last.... That might work in Canada. Not sure how efficient that puppy will be where it gets H-O-T. Here in Texas, and much of the US south and west of the Mason Dixon line (maybe even south of Detroit) temperatures are going to be stinky hot much of the summer time. If you are on the road.. or even in a campground, the surface temperature of the asphalt can be hot enough to melt tar.... which is pretty hot! The air just above the surface is also very hot. If the van is moving down the road there's going to be heat from the drive train blowing back under the RV. That is going to be STINKIN HOT under the RV. And if you have the Sprinter AC running.... well you could cook a side of beef under your camper. Really.... you can't touch anything under the hood or under the camper without gloves on a 100+ day. Heck you can't even lay on the asphalt with out something under you......

Tucked under your RV and behind the rear axle... it's going to be really, really hot and that unit is going to work quadruple time trying to cool the interior just because it doesn't have access to 'cooler' air like a top mounted unit.

Humidity doesn't have much to do with the efficiency of the condenser.... it doesn't care about the dew point and humidity. BUT, the inside of the RV will care and YOU will care. To be comfortable, you have to cool and dehumidify..... a hard enough job in a Class B/C with a 15 something BTU top mount A/C on a 100F+ day. If under mounted, I'm afraid it just would be up to the performance of a top mount due to the loss in efficiency due to the super heated air under the RV. UNLESS, they have give you a unit big enough to cool a hopsital....

The added problems of an under mount appear to drastically off set the advantage of having a few more square inches of solar collector on the roof.

But I'm a Crow.... so I could be wrong.
 
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avanti

2014 GWV Legend 3500 I4
Well, THAT'S a pretty bleak assessment.:idunno:

I have been seriously considering an undermounted split system to replace my rooftop unit for awhile now. My primary motive is noise. Such a system is bound to be much quieter than the roaring unit directly above our heads. We find our present unit almost worthless due to the noise.

Here are some thoughts:

--I agree that it must get pretty hot down there while driving down a Texas highway in summer. But, we have almost never felt a desire to run the coach A/C while driving. Our Sprinter unit does the job just fine. Our goals are limited to campground use.

--I agree that dehumidification is of paramount importance--more, in fact, than cooling. But, smaller-capacity units are often BETTER than larger ones at keeping humidity under control. The reason is that they have longer duty cycles, so they spend more of their time dehumidifying. Split systems are available in a variety of capacities. The one I am considering has dual danfoss compressors and so can run at several levels of cooling.

--I am not overly worried about damage. I don't see how these condensers are much more fragile than tanks, plumbing, gensets, macerators etc that most RVs have down there. After all, most vehicles have the OEM condenser stuck right up front, where they are exposed to pretty harsh road conditions. In any case, protecting them with some kind of shield or box does not sound that difficult.

--Clearance doesn't appear to be an issue, either. Lots of split condensers are available in all shapes and sizes.

All things considered, I am pretty excited about adding a quiet, unobtrusive, DC-powered, efficient split system. Looks like a huge win to me.
 

irvingj

2015 RT SS Agile (3.0L)
Let us know how it works, when & if you get one. I, too, was extremely disappointed in the noise level of the rooftop unit on our Agile: wicked! I did learn that the t-stat also controls fan speed, and was able to set that on "low" but have yet to really see if it made a difference.

My wife always wants to listen to Mike Wendlandt…. he seems OK with his undermount AC, FWIW.
 
I can't help with the issues of performance but the unit is somewhere around 36,000 btu or more as I recall, with two compressors and it only uses the second compressor when needed to reduce battery load.

In terms of length of time it will run off of batteries, I think 2 hours on a 400 AH Ecotrek is a reasonable estimate (320 usable AH), maybe longer, it depends on the temperature and how much cycling of the compressors is needed. Using Voltstart when parked will probably add 2 more hours of runtime before it needs to be reset manually.
 

Old Crows

Calypso 2014 View Profile
Finally...... Found a Youtube video ....

https://youtu.be/wBF0xf6IxGk

Not sure it eases my concerns a whole lot....at least not enough to get one.

With twin compressors and 18K BTU, it will more than adequately cool a Class B anywhere. But at what cost? Dropping the temperature 20 some degrees in 15 minutes (in the shop...whatever that means) or on a cloudy cool day is fine. I'd like to see what it can do sitting in the sun, heat soaked for a day, on a 105F day. How many compressors running? What's the steady state AMP draw??? Getting the temp down quickly is one thing. (Showmanship.) Keeping it there without two compressoes may be a bit more challenging. So, one or both or those compressors are going to be pulling duty ... a lot. That means amps used. So you have to keep it in the hot sun to constantly refill the batteries, I'm thinking.

We 'mericans worship speed. Any speed. Cooling speed - like speed anywhere - comes at great price.

So, its the noise? Yes. Ceiling mounts, even ducted ones are/can be noisy. It is caused by the circulation fan, vents & duct work, not so much by the compressor. Speaking from experience with a Class B XLXT, you need at least 13.5 BTU (15 would be more better) to cool & dehumidify on HOT - HUMID day in the worst conditions. It does not take long.

Other than cooling power, you need great circulation. That means a fan with high CFM to avoid "stagnation" and heat/cold layering. It is going to be noisy unless the duct and return is carefully designed. In the video, the Lad has to step to the front of the van to finish his presentation. That is a big Crow clue. It IS going to be noisy in the lounge/bedroom. I'd test drive it on full blower by making up the bunk and laying down in it for a pretend nap.

There might be some hacks that would make it slightly quieter. But likely not.

I'll note...(from just seeing the video) that it appears that the 'split' expansion/circulation fan is mounted in the rear overhead. That's one solution. But it takes up useable storage space. Class Bs are really shy on storage. You need every hidey hole, comparment, under bench and overhead storage you can get - and more because there is "nada" outside.

Which brings the Crow back to the "old school" roof mount. There are good reasons why they are popular: doesn't take up interior or storage space, easy install/replacement/upgrade/repair, no interior piping and drains, minimal ceiling intrusion,. Inexpensive! Just about any RV shop can work on them. Newer models are less tall and more aero depending on mfgr and present a "cleaner look" than old ones. And, unless you are standing 25 feet away or looking down on the RV they are mostly unseen. So who cares?

Last...lower profile. Our Ventura was 9'6". With great care, we got it into a 10' garage ONCE to install heat resistant window film. Calypso, the View Profile is 11'3" (due to the height of the Jack antenna! Not the AC shroud). You just have to live with what you got. They are what they are....
 

Old Crows

Calypso 2014 View Profile
I can't help with the issues of performance but the unit is somewhere around 36,000 btu or more as I recall, with two compressors and it only uses the second compressor when needed to reduce battery load.

In terms of length of time it will run off of batteries, I think 2 hours on a 400 AH Ecotrek is a reasonable estimate (320 usable AH), maybe longer, it depends on the temperature and how much cycling of the compressors is needed. Using Voltstart when parked will probably add 2 more hours of runtime before it needs to be reset manually.
Thanks...18K BTU according to video. I take that as with both compressors.
Thanks for the runtime numbers.

Look everyone...this is not a bad idea or system. It's probably great for a "leisure or touring van" where the AC use is limited to parking and a couple hours of use at a time and long regen cycles.

But....I'm not sure its up to dry camping over night in HOT HUMID locations.
 
Thanks...18K BTU according to video. I take that as with both compressors.
Thanks for the runtime numbers.

Look everyone...this is not a bad idea or system. It's probably great for a "leisure or touring van" where the AC use is limited to parking and a couple hours of use at a time and long regen cycles.

But....I'm not sure its up to dry camping over night in HOT HUMID locations.
Other than the fact that it probably no quieter than the roof air, I don't see why it would be any less capable in hot humid conditions. These units have been in use in those conditions in other vehicles such as ambulances and shuttle buses for a long time...

http://www.proairllc.com
 

avanti

2014 GWV Legend 3500 I4
I would be very surprised if a well-designed split system weren't MUCH quieter on the inside. The overhead ones (in addition to being poorly designed and cheaply built) just have too much going on way too close to the occupant. Note that the dash A/C is quite quiet most of the time, so it can be done. The only thing that needs to be inside the van is the evaporator unit. I have the perfect place for it tucked in back of a rear cabinet--hard to use space, no great loss.

I don't live in Texas, and I don't go out of my way to camp there in July. That may help account for the difference in perspective.
 
I would be very surprised if a well-designed split system weren't MUCH quieter on the inside. The overhead ones (in addition to being poorly designed and cheaply built) just have too much going on way too close to the occupant. Note that the dash A/C is quite quiet most of the time, so it can be done. The only thing that needs to be inside the van is the evaporator unit. I have the perfect place for it tucked in back of a rear cabinet--hard to use space, no great loss.

I don't live in Texas, and I don't go out of my way to camp there in July. That may help account for the difference in perspective.
True, but at least for the Roadtrek installation, reports are that it is not much different than the roof AC in terms of noise level. They clearly did not do much redesign inside, they stuck it where it was easy to locate...
 

avanti

2014 GWV Legend 3500 I4
True, but at least for the Roadtrek installation, reports are that it is not much different than the roof AC in terms of noise level. They clearly did not do much redesign inside, they stuck it where it was easy to locate...
Yeah, I am not defending the RT design--I know little about it. In any event, if I do this I will put in a significantly smaller unit. For my purposes, the 11K roof unit I have now is overkill (cycles too much under most conditions). I am basically looking for a little relief when it is very humid without slowly going deaf.
 

Trekker

Trekker
:2cents:

I agree with the Crow on this one. Having had our 2008 RS for 8 years now and logging 125K miles on more than a dozen cross country trips, we find that although we rarely use the roof AC while driving, when we stop at a rest stop for lunch, it's nice to have it. And the temp on the blacktop parking lots can get really high, especially in the South in the summer (or these days, anywhere in the country). Yes, the rooftop unit is loud, and that cancels the ability to use it overnight while you sleep. But, if the new battery powered undermount can only run a few hours, that doesn't get you through the night.

Yes things break. Our experience proves that. Some from factory defects or just plain wearing out, some from owner accidents. We've had a few, and I would say we are more cautious than the general public. But accidents still happen. Guards? Yes, for example, the guard on our macerator pump just fell off one day while driving. Why? In theory a simple replacement, but I don't carry those type of tools on trips.

IMHO, anything mounted under the van is subject to damage, given enough miles, and will eventually sustain some type of damage. These RVs are complicated enough without adding more complexity. They aren't the easiest thing to get fixed while you are on the road either (and that's where all the breakage occurs, not at home in your driveway). I hate having my vacation interrupted by breakage and repairs, so keeping things as simple as possible is my vote, and this undermount system sounds way complicated. The OP asked for advice. Would I buy one if I were buying a new RT? No. :thumbdown:

:2cents::thinking::2cents:
 
Yeah, I am not defending the RT design--I know little about it. In any event, if I do this I will put in a significantly smaller unit. For my purposes, the 11K roof unit I have now is overkill (cycles too much under most conditions). I am basically looking for a little relief when it is very humid without slowly going deaf.
Manufacturers seem very reluctant to provide air conditioning that will not cool a very hot van off quickly, that seems to be the standard expectation of the majority of the customers, so, I don't expect them to ever offer anything less...
 

avanti

2014 GWV Legend 3500 I4
Manufacturers seem very reluctant to provide air conditioning that will not cool a very hot van off quickly, that seems to be the standard expectation of the majority of the customers, so, I don't expect them to ever offer anything less...
Yes. These rigs are designed for sales, not for use. The priority is to look good on paper and in the showroom, so big numbers and fast action are the ticket.
 

Old Crows

Calypso 2014 View Profile
Manufacturers seem very reluctant to provide air conditioning that will not cool a very hot van off quickly, that seems to be the standard expectation of the majority of the customers, so, I don't expect them to ever offer anything less...
Thanks all a good discussion.

As before, in my experience.... 9.2 & 11K BTU units (roof or not) are not enough to chill out a Class B. You need a high efficiency 13.5 or 15/15.5 job. Most of it is in the better CFM (and airflow noise, 00ps!) coming out of the unit.

On both of ours, cranking them up from a hot start, they will start cooling the coach down in minutes. Within 15-20 minutes you have gotten a lot of the humidity out and then it will keep on chilling till setting. Nothing lightning fast about it. But it works.

I can't really see why one would want to be colder than say 68-72F. Probably closer to 75-76 with the air circulating. Lower than comfort is wasteful.

I keep thinking about this.... .not a bad idea... but lots of hold backs for me.

An Agile is like our Ventura. It's about 40% glass. Black glass. Hotter than clear glass. Glass transfers heat and solar energy to the coach. It would be better to have a smaller unit 15/15.5 BTU lets say, and apply heat/solar resistant film to the inside of all the windows. That's the heat load. Windows. True, they would have to so some of the windows before putting in the furniture... but it is doable and not expensive.

So.... I'd vote "NOT AT THIS TIME" & go for a 15.5K roofer. And, heat film the windows.
 

TooMuchHair

Active member
Does anybody know why the variable speed compressors that you see on residential mini-split systems with smarter control systems don't seem to make it to the RV market? More efficient, more consistent comfort (reduced or eliminate compressor cycling) plus quieter operation, reduced start amps etc.. If they do exist, please tell me more. Any known hackers?
 

HarryN

Well-known member
Yes. These rigs are designed for sales, not for use. The priority is to look good on paper and in the showroom, so big numbers and fast action are the ticket.
The need for rear a/c and how powerful it is depends a lot on where you live and how much indoor parking space you have.

As an example, we have a 2000 dodge minivan, it is parked outdoors, and it is routinely 90 - 105 F here in the summer, with fairly high solar intensity. The good news, is that solar PV panels work well in this area, the bad news is that it heats things up fast with a lot of UV and IR. This van serves as my beater utility vehicle and it is sort of like the energizer bunny - not impressive but keeps going.

Even in this relatively modest size van, it is nearly impossible for someone to sit in the middle or rear seats without the rear a/c running. Similarly, the single most important feature on any vehicle we buy are rear air conditioning vents, and that includes our 4 door sedan and a small suv.

A fast cool down is not an option here, it is a necessity. A car parked outside on a hot day in a parking lot for even 15 minutes will be too hot to get into, in 60 minutes, you literally have to turn on the a/c and stand outside in 108 F weather on the blacktop, and let the car cool down before your kids get in so that they don't burn themselves.

You can bet that I spend some time thinking about a/c off of batteries and am getting closer.
 
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