A rare Liberty

[Jon Wehrenberg]

Here is the Liberty answer for those who don't want OTR.

http://www.prevost-stuff.com/2006Liberty7056ALiberty.htm This coach has no OTR.

[Sawbonz]

This was our second choice this weekend. It's really nice, but the floor plan on the 2004 suits us better. I guess we will have to live with OTR! ;)

[jack14r]

Liberty just sold a new H double slide #725 which did not have OTR

[Jon Wehrenberg]

OTR...........RIP

[merle&louise]

Why do these Libertys not have OTR?

[Gary Carmichael]

The new ones probably because of the number of slides

[jack14r]

As I understand it,it comes down to price OTR is $16,670 in the XLII and $17,904 in the H3,in reality this is not much in the total price of a converted coach,or even in the price of the shell,it really does not make much financial sense to exclude it to me.OTR must be deleted in the 3 slide and 4 slide coaches because there is no way to duct the air.The positive is that the deletion of OTR saves 700 LBS,that is before more inverters and alternators are installed.

[Sawbonz]

The new ones probably because of the number of slides

The two mentioned above are both double slides. So, possible...

[Jon Wehrenberg]

OTR has a substantial cooling capability, and from a driver's perspective nothing is easier than pushing a button and having the coach comfortably cool no matter what the conditions outside. And when the end of the day arrives and the coach is parked the entire coach is cool and comfortable, and if the use of CAs is required to keep the coach cool they are not trying to cool down parts of the bus that were not cooled when driving. It is especially nice to not have a bedroom that has the temperature of a sauna.

But OTR is not without its drawbacks. The initial cost may be less than $20,000 for the option, but I will bet all the converters that have made coaches with OTR spent some serious money engineering the flow paths for supply and return air, and even more money building the interior to provide for that air flow. It may sound simple but I am sure balancing the air flow the length of the coach is not as easy as it sounds. So it does carry a higher cost possibly a significant one.

For those who need every cubic foot of space available OTR does take some away. You cannot hang clothes in the return or supply ductwork so upstairs there is a modest loss of space. Air flows require double wall construction. In the 3rd bay about 20 to 24" on each side is lost to the condenser and evaporator. That lost space however is a focal point for every salesman trying to sell a coach without OTR, but it actually amounts to less than 1/2 bay.

OTR does have weight and it does take energy to run it. As far as the energy used to run it, another argument salesmen use against OTR, the reality is if you intend to cool the entire coach to the same temperature using OTR, CAs or roof airs, running via an engine driven compressor, inverters, or the generator you are using exactly the same amounts of energy only varying by small degrees due to loss of efficiency.

When OTR is not installed weight is saved, but often the converters of coaches without OTR use more batteries or heavier inverters so if an owner chooses some ACs can be run off inverters while driving. The reality is even if the lack of OTR saves weight, it is probable the owner is unaffected and does not care because his coach will have more items stuffed into the extra bay space or the coach will have more slides which easily add more weight than what is required for OTR.

If I owned a coach that did not have OTR, as much as I like CAs, I would want roof airs, at least 4 and possibly 5 of them. I would operate the coach like the entertainers do. I would start the generator as soon as I started the coach and I would crank up as many roof airs as I needed to maintain my desired temps throughout the entire coach. I have a big generator and I want to use it. It is likely to last longer than 30,000 hours so even if I run it every minute my bus engine is running I would have to travel about a million miles or more before I wore it out. I did not buy a Prevost to be uncomfortable or to "rough it". Otherwise I would take Don up on his generous offer to learn how to pitch a pup tent.

We are seeing the end of OTR if Liberty is getting away from it. They cannot offer a three or four slide coach with it as Jack points out. And even with two slide coaches I suspect it costs Liberty a bunch of money building the interior allowing for all the needed air flow paths. And if there ever was a product that was created to follow the advice "put your money where it shows" our conversions are the epitome.

Where the debate rages is in different interpretations of comfortable. For example, my aunt and uncle who live in FL will not use AC until the house temps hit 85 degrees. By that time I am laying on the floor gasping for breath. I keep my house and bus at 72 degrees. I am not happy unless it is that cool so while some may be happy with a non OTR coach whose temps are maintained with one roof air and driver's air, I would be suffering heat stroke. People who ride in our coach may be looking for blankets or sweaters, but I'm enjoying the cool air.

[Sawbonz]

We are seeing the end of OTR if Liberty is getting away from it. They cannot offer a three or four slide coach with it as Jack points out. And even with two slide coaches I suspect it costs Liberty a bunch of money building the interior allowing for all the needed air flow paths. And if there ever was a product that was created to follow the advice "put your money where it shows" our conversions are the epitome.

On the '06 you originally mentioned on this post, the salesman told me (whether or not it's true is another issue) that it was ordered without. And I believe your points about 3-4 slides making it impossible.

Personally, we will be going from 4 slides to 2 and I don't think we will miss it at all. I drove a triple slide H and thought the slide was a waste.

[rfoster]

Jon. Sounds like i will have to reorder more funeral home fans.

[jack14r]

Roger,Make sure that they come with plastic roof covers.

[Jon Wehrenberg]

Jon. Sounds like i will have to reorder more funeral home fans.

Hey King......I tried to make that post OTR neutral. It's all kind of a moot point anyway because once Liberty stops building them with OTR it's all over.

[phorner]

Sounds to me that OTR buses have become value-added buses!!

If you want a bus with real, Prevost-factory-installed Over The Road bus air, it looks like your choices will be diminishing as the years go by.

Hopefully that will mean that the surviving coaches with OTR will see a premium attached to their value.

[Jon Wehrenberg]

I suspect there will always be a premium attached to an OTR coach. I have never seen an OTR coach for sale on sites that offer a description of the coach in which an OTR coach was not described as having OTR. Nobody ever says "this coach does not have OTR so it has extra storage space."

Seated coaches are always going to have whole bus heat and air which means Prevost is always going to build coaches with it. The question is if it will be available on conversions. If so a buyer could special order it.

[johnklopp]

I’m putting my 2 cents into the ring without any knowledge of OR air beyond what I have read on this forum and knowing that I may have just thrown myself under the bus so to speak.

I’m not sure if over the road air is really needed or not. It appears based on the comments from many POG members that it is desirable and may even increase the value of a coach. The application sounds like there is only one evaporator requiring a large blower to circulate the air through ducts taking a substantial amount of space.

If that’s indeed the case, from my perspective OR air is a major waste of space.

Has anyone considered why your coach is heated with circulated hot water modulated through fan coils to provide multiple zones of heat with individual zone control? Why doesn’t the OR just have a single hot water coil to heat all the areas with the same air flow that is used to cool the coach? The reason is simply better zone temperature control.

A single evaporator with a large enough blower to circulate the air would be substantially larger than a refrigerant to water heat exchanger. A 10 ton refrigerant to water heat exchanger would be approximately 6 x 12 x 18 inches and be connected on the refrigerant and water sides of the heat exchanger by tubing less than 1 inch in diameter.

A simple system would use cooling heat exchangers with drip pans similar to the ones used to heat the coach with the Aqua Hot boiler. Cold water would be circulated with one or more pumps and the zone temperature controlled by modulation valves on each zone fan coil.

A more complex system would use the same or similar heat exchangers and existing tubing distribution system currently used to heat the coach. The pumps used on the Aqua Hot system would be used to circulate the coolant with automatic isolation valves to eliminate mixing of hot and cold coolant.

It’s not a radical idea. It just hasn’t been done on a bus, yet.

[johnklopp]

Note that if the above liquid cooling system were employed, the same cooling circulation pumps, tubing and cold water to air heat exchangers could easily be connected to a CA units producing chilled water instead of cold air. All of the remote CA evaporators and air distribution ducting would also be eliminated.

[Jon Wehrenberg]

Simplicity......I think OTR is designed as it is because for a commercial coach to be practical it needs fast turn around in service work. The OTR as built is centrally located and the condensing side, evaporator side and the compressor are all accessible by opening a door.

For heating in my Liberty I can use the OTR system which is a whole coach system with one set of temperature control, or the Webasto which has multiple thermostatic controls. When the coolant is heated the Webasto burner never fires, but the heated coolant from the engine is circulated through the various heat exchangers throughout the coach.

As to using water for condenser coolant don't we still have the problem of getting rid of the heat the water has absorbed? Using water cooled CA condensers would be easy because they are located in two general areas so plumbing would not be excessively complex, but the heat still has to be removed from the water.

[truk4u]

I wanted OTR this time around since the Cruiseairs will shut down in the heat and the dash air just can't keep up. Now that I have this Royale without OTR, it's really not needed. Last week was the heat test, 95 degree's and Ms Truk used a blanket for part of the trip. Royale adds a 2nd evaporator and fan in the overhead above the driver and with both dash and overhead airs running, we were very comfortable and no need for the gen and roof airs.

Just one more example of how the various Converters did things different.

[GDeen]

To John's very knowledgeable and technical based post....

OTR is a bludgeon with which to cool or heat your bus. No real zonal precision to it (aside from the driver/coach split). In the summer, just turn the goodie knob to cold or colder, and the fan knob from low to high. I imagine that is rooted in simple motorhome adaptation from seated coaches for which it was employed.

I love having that hammer particularly in the summer. Nothing like pulling into a rest stop in July to walk his royal highness, and having the sunglasses fog over immediately upon stepping out in the searing heat.

[LNDYCHT]

Note that if the above liquid cooling system were employed, the same cooling circulation pumps, tubing and cold water to air heat exchangers could easily be connected to a CA units producing chilled water instead of cold air. All of the remote CA evaporators and air distribution ducting would also be eliminated.

The system which John describes is basically a "chiller" system which is already used in large yachts. One of these systems could be adapted by a converter and powered by a engine driven compressor while under way and electrically driven when stopped. It would free up a great deal of space but would be a much more complicated and expensive system than what is presently used.

[johnklopp]

Jon,

Your conclusion is absolutely correct, but the problem as I understood it was the inability to have OTR air due to the duct work when slides are added to the coach. If indeed the desire is to have the OTR air on future coaches the requirement will be to have a liquid cooling system.

Heat transfer is simply the movement of heat from one area to another. Due to a significant difference in the specific heat of water versus air a major difference in the volume of the heat transfer medium (air/water) exists.

Looking at the numbers, you would have to move or transfer approximately 400 cubic feet of air per minute to transfer 1 ton of cooling. The duct required would likely be 6 x 6 inches or more depending on the available blower power to push the air through the duct work at various velocities.

Using a liquid (water) the same 1 ton of heat could be transferred with approximately 2 cubic feet of water. The hose required would be less than 1 inch in diameter.

The heating mode still uses hot water to produce heat. You have 2 sources of heat, 1 from the engine coolant or the second produced by a diesel boiler. The OTR air probably uses a single hot water coil to heat the air supplied by a single blower then distributed with duct work. Zone heat is distributed to multiple fan coil units with modulated liquid flow to control the heat in each zone. A single heating coil is simple and may never break down. Zone heat is accurate and heats each zone as required without problems. In spite of what may be considered complex, hydronic heat with zone controls is used in many applications and is typically considered one of the most uniform dependable systems in use today. Most commercial buildings over a few stories high and many homes in extreme climates are heated with fan coil units.

The advantages of using a liquid to transfer heat and cooling are the simplicity of the package unit. The package unit can be built in a factory and fully tested without the dependence on a refrigeration technician to properly layout, and connect high pressure refrigerant connections. The installation into a coach or any other location would be simply locating the chiller unit and connecting hoses to remote fan coil units for each zone to be cooled. The condenser heat would be rejected to similar but larger fan coil unit or units to reject the heat from the liquid cooled condenser. Due to the small size of hoses required to transfer the heat, the liquid cooled condenser heat could be easily rejected on the roof or any other location or locations deemed desirable to accommodate the design of the coach. If the water cooled CA chiller failed, you would simply remove four water hoses and the electrical connections to remove and replace the failed unit. No AC tech required. The tech would repair your CA unit on the bench in his shop. You would find that the mystery and high price of repair would be eliminated by putting the chiller in a package instantly understood by the average technician.

The cost to upgrade would be higher but I believe a system designed from scratch for a new installation would be cost about the same with a significant increase in performance.

[Jon Wehrenberg]

A variation of what you describe may in fact be a good substitute for the existing system. If you recall the good old days early coaches had OTR "packages" hung on the rear of the bus approximately where a rear window would be. To deal with the lack of sidewall ducting on slide coaches a series of evaporators or a relatively long single evaporator can be placed on the roof along with, but separated from a roof mounted condenser coil placed for maximum heat rejection (such as in the front air flow).

With a single spine type ducting system across the center ceiling the evaporator can cool the entire coach and zone control can be by air or electrically operated vents.

Relocating the system as described eliminates the current ducting issue, and with a good efficient design it could easily perform as well or better than the current system using less fuel and costing less due to simplicity of air flow. When the coach is not being driven an elecrically driven AC compressor could be used to operate the system, adding only the weight of the new compressor and a few valves. The downside is if there is a system wide problem the coach has no back up available.

[johnklopp]

Jon.

Good ideas, great thread and a fun interchange. With the wide scope of knowledge and Fields of expertise exhibited by the POG members we should be able to correct, upgrade or modify just about any systems on POG members coaches.

Do we have a coach available to experiment on?

[Jon Wehrenberg]

It will have to be yours John. Mine already has OTR. You may already have the ductwork in place so all the mods can take place on the roof. You may have to move some stuff out of the way to get one of the Carrier compressors where it belongs but I agree. I think we have the ability right here in POG to restore OTR to coaches AND make it desirable for owners and converters.

[gmcbuffalo]

John could you not convert your CA units over to Chilled water and used the current small freon lines to transport the water and still out preform the freon system. I was thinking that you could ty the Webasto and CA systems together but you would only have hot or cold and know one like cold hot water showers. The discharge of heat would be at the same location as currently being done on the CA system, out the floor of the coach. Where do you get the chilled water? Would on CA unit be the chiller for the a second CA water unit? I this case you would only need two CA units not three or four.

[Jon Wehrenberg]

A water cooled condenser such as one to replace the existing air cooled ones on our coaches is a completely different animal, can have a different shape entirely, but remember, even if the condenser is water cooled there still must be some "radiator" or multiple radiators to pull the heat from the water. Even if our water tank was full of 50 degree water it would not take long before the CAs had the water in the tank to temperatures that would make it unusable. The heat taken from the coach interior at some point has to be transferred to the atmosphere in the absence of a reliable continuous cool water source.

[johnklopp]

John could you not convert your CA units over to Chilled water and used the current small freon lines to transport the water and still out preform the freon system.

It could be done but is not advisable. The small refrigerant lines would require a high velocity water flow and a resulting increase in pump horse power.

If I was going to convert my coach to OTR air and CA units I would run a supply and return chilled water line (manifold) from the front to the back of the coach. Each line manifold would have branches for supply and return chilled water to heat exchangers in different areas. The CAs units in the front located in the spare tire area would supply the chilled water manifold in parallel. A similar connection at the back of the bus would connect the chilled water from the OTR air units. This would allow a continuous circulation around the chilled water loop with a single chilled water pump. A few automatic flow control valves would ensure the required distribution was achieved when either the rear chiller (OTR) or the front chiller (CAs) were operating. A similar manifold would allow condenser water to reject the condenser heat in several locations.

Am I going to do this so I have OTR air? No, I like my roof air units and my drivers air already has multiple evaporators. I may consider adding a single custom CA units with 2 to 2.5 tons of capacity in the tire bay if I find another place to put the deionized water filters and pressure washer.

[gmcbuffalo]

John
My problem with the dash air maybe a leak in the system from a coolant gas change. I only have one evaporator blowing cold air under the dash, powered by a York compressor belt driven off the engine. . You have a dual evaporator where are they located?

It sounds like the best optional (expense wise) is to booster the existing CA units with increased motors, fans and larger radiators.

[rfoster]

So what kind of A/c does Liberty use on a coach that has no OTR a/c?

[johnklopp]

You have a dual evaporator where are they located?

I have one evaporator in the dash and a second one in the bedroom. Keeps the bedroom area and the driver cool any time im driving.

[jack14r]

Liberty uses Cruise Airs,I understand that Frank figured out the problem with the CA condenser air flow and they now work at speed like they should.I heard that there was a vacuum created under the coach at speed and the condensing unit had very little airflow at speed,Liberty re-directed air and they got the CA to perform as it should.

[Denny]

Prevost has an upgrade for the dash air available that gives about a 50 percent increase in cooling capacity. It is a big improvement over the stock setup.

[gmcbuffalo]

Denny More info please

I wonder if a scoop was placed on the air intake to the CA unit to increase airflow into the CA while driving. One like you see on the the old MCI and GMC buses for the engine radiators. I know the exhaust hole is scooped, only to direct flow away from the intake.

The other thing and John mentioned it, is the air exhaust hole in the floor is only about a 6x6 inch area.
John what would should the optimal size of this hole be? I think I have a large intake hole but a small exhaust hole.

[jack14r]

The exhaust hole is the size of the blower exhaust,so it is as large as it needs to be.

[Denny]

Greg, the upgrade is a new system that replaces all the components. The compressor, evaporator, expansion valves, etc are all replaced. As I understand it, the original system is designed for commercial trucks which have a smaller area to cool than a bus. Therefore, on a bus the system is working overtime and wears out faster. The new compressor is replaced with a larger, heavy duty one along with all downline components. The increase goes from a 2 ton system to a 3 ton system.

[johnklopp]

Generally you want the intake and exhaust duct work to have a large cross section with a short length. Longer duct work or a smaller cross section will increases the air velocity and the pressure drop in the duct work reducing air flow.

The discharge air will be on the bottom of the coach and the blower discharge will probably be just the blower scroll passing through the bottom of the enclosure. A deflector may be used to turn the discharge air away from the patio area as well as the intake air location.

If the coach is not moving, no scoops etc. should be needed to pick up the intake air. If the coach is moving, care must be used to select the location of the intake. The coach will likely have a boundary layer present when moving that may be in a negative pressure condition creating a reduction in air flow across the condenser. The only way to optimize the intake location would be instrumentation with a magnehelic gauge to measure the air pressure at the intake location.

[Jon Wehrenberg]

I cannot speak for all Libertys or other conversion but on my coach I have a crosswise baffle beneath the coach separating the air intake from the condenser air discharge. That baffle extends almost to the ground. It's first function is I presume to separate intake air from discharge air (which is directed away from the baffle) so when at rest the CAs are not recirculating air through the condenser.

The benefit of the baffle when moving appears to be that in front of it I suspect is an area of high pressure which is a huge benefit for intake air, and directly behind it in the area of the discharge baffles is a low pressure area so it appears to supplement the work of the squirrel cage fan.

I wonder why the same concept is not employed with a transverse full height flap behind the tag axle wheels to create a low pressure area to assist flow through the engines radiator. All converters put a full width flap across behind the engine under the rear bumper which just seems counter intuitive. I removed that flap on both my buses as soon as I got them.

[JIM CHALOUPKA]

Who will be the first to buy a magnehelic gauge?

Spell check didn't like that word.:D

JIM :cool:

[Jon Wehrenberg]

We ain't that sophisticated. I propose we attach short lengths of yarn and then watch the air flow based on how the yarnreacts to air flow.

We probably will need ear muffs however because the person we strap beneath the bus to watch the yarn and report on the air flow is likely to be screaming. Especially when we get the bus up to highway speeds.

[gmcbuffalo]

My exhaust baffles point the the sides.