I'm about to acquire a new project this weekend, a 1973 MC7 combo. Both roof airs need replacing and I'll most likely be installing basement A/C and I was wondering if it would make any difference if it was ducted through the floor or overhead. Seems like most examples I've looked at were overhead but it seems so much simpler to duct underneath. Opinions?
cold air falls. Floor ducting generally requires larger fans to force the air to the ceiling, otherwise you have nice cool socks but your head is kinda hot. Extra fan pressure means more noise, vibration and electrons. Now ducting it to the ceiling first requires far less fan speed because it is in a confined air space (4x10 or 4x12), not trying to push the heat and humidity out of the way in the bus cabin.
Ryan.
I figured that was part of it. But I should have mentioned that I was actually planning on not only basement A/C but also heat, in the form of a heat pump. I'm sure the preference there would be to have the heat ducted through the floor. But can't have it both ways. Still better to duct up top?
You may also consider a high mounted air return, with floor feed?
happy coaching!
buswarrior
You'll be happiest just replacing your roof airs. You'll notice even high end motorhomes and 5th wheels are using 2 or 3 roof airs. I have three Coleman 13,500btu A/C only and typically only need two to cool the bus. Good Luck, TomC
If you are doing a heatpump as well then you usually will already have a higher volume fan, so floor is ok. You generally want heat starting low inside the cabin, and cold starting up high. Dilemma dilemma.
Ryan.
Why does it have to be one or the other? Duct the cold to the top and the hot to the bottom with a servo operated door between. A HVAC man could show you how to set it up and you'd be able to eat your cake and have it too. Jack
That is very true. If you have the space, go for it.
Ryan.
One thing to keep in mind with ducted heat through your basement is, at least in our case, the bays get pretty chilly in winter. So you'll be spending a good deal of energy bleeding heat through the ducts before it actually makes it inside. While you may do this intentionally to keep your bays warm in winter, you'll probably need to insulate the bays well to keep that heat in. You could of course insulate the ducting, which will increase the overall diameter needed for your duct runs.
Also, not sure if it's part of your design, but keep in mind that heat pumps become really inefficient to useless below about 34 degrees and some aux heat source will be needed.
On the flip side with bay AC, the bays once again might be an issue, because they'll get pretty toasty warm in the summer and you'll have to make sure the coils are quite well vented to dump the exchanged heat outside. But that's likely already a part of your plan.
With cold air tending to sink, you'll have to really strategize on where to place floor vents, in order to ensure good convective airflow. A piece of furniture or similar in the way (not necessarily on top) of a vent (or return) will reduce smooth air flow and make for a very chilly piece of furniture and little else cold air getting around. With a bus, space is pretty tight as is, and it might be difficult to find the sweet spot to ensure obstruction free airflow.
Good luck,
George
My Newell has factory installed basement air and 2 more recently added roof airs. Inside the coach, the basement air is less noisy inside than the roof airs, but not by much. Outside, the basement air condenser fans are loud - as much or more noise than the generator.
The roof airs can be connected to a single plenum along the center of the roof. A heat pump in the center works well to chase the chill away. Toe kick heaters work well, so do the propane heaters.
Basement air requires ducting and room under the floor. That ducting takes up a huge amount of space. Space I would rather have for other uses.
In summary, I plan on eliminating the basement air and putting 3 low profile roof airs connected with a single ceiling plenum.
Your coach, your choice ;D
I have a 2 ton basement ac and have never been very happy with the performance. I'm considering replacing it with 2 or 3 roof ac's.
Tcolley
We also have a 73 7 combo. Basement airs. If you want to trade some pics and info, email me at emcemv at charter.net
Bruce
Right now, I'm researching a Thermo King Transit AC. I should be able to mount the guts in the back above the radiator fans in their own compartment with the other component on the roof. Not sure how to make it all work but anything is possible. Haven't received a price yet but I'm sure it's not cheap however it's VERY heavy duty which equals reliability.
Bruce
Very Heavy-duty also equals VERY expensive when it does break. There's a real good reason most all motorhomes and trailers have gone back to rood top airs-they are cheap, easy to replace and do a good job of cooling. Don't try to reinvent the wheel-just stick with the roof tops. Good Luck, TomC
I used to hate roof tops - then I experienced how easy it was on the pocket book & time wise to replace it. Very low impact on the interior too.
After that, roof tops look lots better to me.
The storage space taken by the basement air system reinforces the positives of roof air for me.
The vanity of the clean roof top was replaced with the practicality of use & service. ;D
My doctor's new Marathon has 4-15,000 BTU AC/Heat pumps this the first time he ever owned a Prevost with roof tops and he loves them
Hey George, the new heat pumps today are rated as low as -10 degrees F give or take.
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Quote from: Scott Bennett on January 31, 2016, 06:39:49 AM
Hey George, the new heat pumps today are rated as low as -10 degrees F give or take.
Interesting, I didn't know they had them working that efficiently now. I remember the one we had at the house sucked butt and would freeze solid at about ~20-25 degrees and had to run a regular defrost cycle (by reversing flow, i.e. taking heat out of the house).
Once it finally flamed out, I replaced it with a higher efficiency normal AC and no heat pump, and never looked back.
The house felt warmer and my (overall) bills went down :D
If you think about how they really work (basically an AC in reverse) I really don't see
how they can get them to work down that low. Seeing as how it's "pumping heat" there's not a lot of residual heat in -10 degrees
to pump, lol.
So they must be compressing the crikey out of that refrigerant. ;D
Lol. I can't say for sure, but check this out:
http://www.mitsubishicomfort.com/press/press-releases/industry-leading-hyper-heating-inverterr-mxz-outdoor-unit-is-first-cold-climate-heat-pump-for-multiple-zones-0
100% heating capacity down to 5F and guaranteed operation down to -13F. Crazy but the research I've found shows that they work. I seriously want to put a unit in our bus if I can find one with enough BTU output that is still 120v.
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It is the Freon of today the 410 is a high pressure Freon unlike the older Freon's it is around 400 psi operating.At -13 I would want a backup system ;D
Mini splits sound good on paper. But most units are not made for mobile use. Meaning the freon lines and coils are not reinforced as they are on either a basement or roof top. The A/C companies even make rough neck versions for use on big rig sleepers. I prefer the simplest equipment possible. Roof top airs, propane furnace, electric water heater, additional heat with resistant heaters. Good Luck, TomC
You could have it both ways, a/c on top & heat below. Van Hool uses baseboard hot water heat; you could use electric if you didn't like Webasto; and their a/c is one big rooftop unit. Probably expensive to fix.