Need Help with Carpentry and Air Conditioning

[BlueScarecrow]

Greetings!

Need help building out the interior of my bus. I'm no carpenter and I don't pretend to be. Basically I need a booth built. I'll purchase all the materials, but I'd like to work out the labor on a trade. I'm an electrician (both high and low voltage), telephone man, audio engineer. I have built several studios here in town. A Korean Studio, broadcasting on the sub-carrier of KJZZ, KPHX, KXXT and a VO Studio for KFNX. I'm also a videographer/editor and I have the entire Adobe Master Collection CS6 Suite. I produce all of the Dr. Sky content on YouTube and I also produce the Dr. Sky Show heard on KTAR. I have almost 2 decades of experience in the Motion Picture Industry; you can find me on IMDB; visit: https://www.imdb.com/name/nm0640449/?ref_=fn_al_nm_1.

I would also like help with an Air Conditioning Design. The design I have in mind has 3 zones and the compressor runs off the engine while driving or a 220vac motor through a Sprague Clutch, when parked. I've always thought that having to run a generator to power rooftop AC units while driving down the road was senseless; and my design is a lot quieter with no possibility of roof leaks. I redesigned my Dodge B3500 Ram Wagon AC. I took out the condenser in the front and installed a slightly bigger condenser, with two giant fans, between the real axle and the spare tire. Now I can sit at a stoplight in 120 degree temps and the van never overheats and the AC works very well. See attachment.

My Social Security Check isn't very big. I can offer a little money, my labor, video/audio work or even a 30 or 60 second spot on KTAR.

Any help would be greatly appreciated.

Thank you!


Mike

[Geoff]

I think you just stepped off a cliff.

[Brian Diehl]

Hi Mike,
I'd be happy to help with the carpentry items, but I am in Idaho.  Do you ever get up this way?
Brian

[TomC]

I started my conversion in 1994, finished in 2000. I use my bus all year round-usually about 5,000 miles a year, plus lots of use when sitting. I stripped the interior to the bones, welded two cracks over each door (transit bus). Then screwed 1x2 fir strips length wise at 16" centers. Where I was to mount overhead cabinets, used 1x3 ash strips. Then had spray insulation installed to the level of the strips-that gave 2.25" insulation.
Cabinets are all screwed with either 1" L brackets or T brackets to allow for twisting using 1x2 oak strips. Doors and walls are 3/4" Birch furniture grade plywood-which matches well to oak. Only glued is the wall joints for the bathroom. Kitchen is made the same.
As to the A/C, I have 3-13,500btu Coleman roof tops. I also have a 10kw Powertech/Kubota engine generator. I just run the generator going down the road. Usually two will cool nicely, with the third kicked on when the temp gets above 100. Granted I take about a 1/2 mpg fuel hit when the gen is running, but it is also simple, 100% reliable in the 24 years I've had it and cools very well. There's a really good reason why most all motorhomes, trailers, etc are using roof top airs-they are simple, easy to service. You'll notice band buses have 5.
But, if you want to attempt your complicated A/C system and be limited to only the RV parks that have 50amp service, go for it-that's why we make our own. Good Luck, TomC

[Jim Blackwood]

You know, that is an interesting concept. One I hadn't considered, and it does have some merit. The critical element of course is going to be the amount of horsepower you have available to drive the compressor. You said 220v but many camping sites do not have 220. So among other things to consider is the output of your genset.

Now I don't know the HP draw of the stock A/C compressor and it undoubtedly depends on the bus, but it could easily be around 20 HP. That's rather important. For instance, on my D series the A/C system has a combined capacity of 13-14 tons. There are undoubtedly charts you could use to convert that to HP required, depending on the Seer rating, which we don't know, but which we can guess might be around 10 or so. I don't have those charts, that'll take some internet searching. But with the HP requirement you'd be able to get the ampacity requirement and see just how feasible this plan might be.

Chances are extremely high that you will not have enough current available to run the system at full capacity so the fallback position is to base the drive motor size on the number of amps available. With this approach you would underdrive the compressor until the current draw is below what is available. That means a reduced compressor speed and a reduced output. How this affects cooling will depend on how much it is reduced. Again, basing on the D, each evaporator has a thermal expansion valve with a tonnage rating and it will allow freon through at a rate needed to achieve that tonnage, depending on evaporator temperature. So say you are discharging into the main evaporator only with a 10 ton rating and you only are producing enough with your compressor for 5 tons or two tons, you might have trouble keeping the freon liquid in the discharge line, meaning it might not work all that great.

Of course when parked you do not need 10 tons of cooling. Probably 3 or 4 tons would be plenty. (My entire house uses 4 tons and it is moderately large. It also has some goodly sized 220 breakers and a Seer 17 system.) Again going from the D that's a possibility because the dash air is 1 ton and each of the overhead bin units is fitted with a 1-1/2 ton TXV (expansion valve). Not only that but you can turn off any of the three units with solenoid valves which creates a very flexible foundation from which to build. It would be possible to add a solenoid valve in the line to the main evaporator to reduce the system size, and of course then the oversize condenser doesn't hurt. However the overall large size of the system including the condenser and the lines means it will take longer to draw down when first started.

What your bus is equipped with will have a lot to do with the best way to proceed, but let's say the 220 motor creates enough freon output (allowing power for condenser and evaporator fans and other loads) to give 2-3 tons of cooling and you only have a single main evaporator with say a 10 ton capacity. Is there a way around this? The main concern here is reducing the flow into the evaporator to 2-3 tons so that the liquid line will remain filled and the condenser can do it's job. That means using a smaller TXV. Provided you did this, most likely the TXV would always be running flat out (you might just as well use an orifice tube) and there might not be any effective way of throttling the output, but you'd get cold air. Just not as much of it and you'd want to slow down the evaporator fan accordingly. To do that you'd need the smaller TXV and a solenoid valve to switch the larger TXV in and out of the circuit. This could be done either in series or parallel with the solenoid either shutting off the large TXV or bypassing the small one. Probably the series/bypass scheme makes the most sense but space available might change that.

Maybe it sounds like this is getting complicated but it really isn't. It's just plumbing. You just have both gas and liquid to deal with.

Finally, is the sprague clutch and electric motor the best solution? What about a fully enclosed compressor such as used in residential systems? Totally leak free. Quiet. Just has to be plumbed in. And some of those are seer 22.

Jim

[TomC]

Round figures, you need 1hp per ton of cooling to power the compressor alone.

[Jim Blackwood]

Sounds about right. It depends on the efficiency of the compressor of course, a Seer 20 will be twice as efficient as a Seer 10 and therefore need half the Kw input. Both the pump and motor enter into the calculation.

Prof.