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Old 03-29-2010, 11:02 AM   #23 (permalink)
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Originally Posted by slowmover View Post

"If someone were so inclined, a good project helpful to all would be to design an alternative air-conditioner shroud, as those roof units are used on all types. That the manufacturers have low-profile units now only illustrates the problem."

An inexpensive alternative that is sometimes used, is to mount a conventional 5000 BTU window air conditioner to the front or back of of the travel trailer. Either location fills part of an aerodynamic low pressure area that otherwise creates drag. Also this arrangement does not add to the frontal area as a roof top unit does. If need be, you could install ducting to carry cool air to the opposite end of the trailer. Often you could also arrange to park the trailer so that the air conditioner is in the shade most of the day which would make it a little more efficient. Of course you would need to hook up to an AC source when parked or use a large capacity DC to AC converter.
Yes, but . . window frames are not built for this load; the A/C must be secured somewhere for travel (damage potential all around), etc. I have seen A/C mounted internally (done very well), but it takes up storage space that is usually at a premium (where weight, shape and road performance take precedence). It is favorable, however, that the roughly 100-lbs of weight is lower on the chassis, but a roof mount directly over the axles helps offset this problem of COG and FF/RR balance.

Todays RV A/C units are, unfortunately, disposable unlike those of yesteryear. Cheaper in all ways with no field serviceable parts. So any shell mods must accommodate ease-of-removal. Even for mobile command units, etc, the tendency is to use roof-mount, for sliding a new one in place takes not much longer than describing the work. Obtaining the services of a factory-trained technician and parts/supplies for something more exotic is not tenable for time-critical operations.

Granted that, somewhere, there is a combined HVAC unit for heat & cooling. Initial expense, size, NVH would all be problems, even on high dollar units (one must, essentially, go to units spec'd for million-dollar buses [NEWELL]). Obtaining the services of a factory-trained technician and parts/supplies for something "exotic" is not tenable for time-critical operations OR ordinary travelers.

There is a "solution" for combining water heating and space heating in the PRECISION TEMP line of models, but, again, ducting, water & gas plumbing, plus electrical must be re-engineered. This would free space for an A/C unit, but overall costs at this point have become quite high once an internal-mount A/C is specified. Ducting a small trailer is fairly straightforward, but for larger (say above 25') expenses mount.

For safety' sake, an engineer should be employed to review such major changes as above. RV's are both houses and cars, with a bit of sailboat thrown in. Plumbing for water (from pressurized external source OR from internally-pressurized tank[s]), propane, two electrical systems (12V and 120V), two and three-way operable appliances, etc, etc. There are any number of governing bodies one may argue take precedence: Shall it be RVIA, USCG or NEC? UL or . . . ?

Remember that in many regions A/C is a necessity for a majority of months. Shade is desired but not always available. Combine the viable lack of A/C options and the the desireability of some aero work becomes clearer (where mpg is chasing small margins all over the place). Simplest solution is where economy and long-life are not affected by safety/space/damage concerns.

Thus the point about a more aero A/C enclosure. It is in line with the OP request, ought to be fairly low cost for DIY, and, hopefully, help to manage airflow a bit. It is applicable to virtually every RV. Other roof vents (plumbing, kitchen oven, refrigerator; ventilation passive or powered) tend to be "low profile", but once one adds a second A/C (on larger RV's), storage "pods", solar panels, multiple telecomm antennas, etc, well, . . a "dirty" roof needs all the help it can get.

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