A rare Liberty

[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?