Adding road a/c to a rear engine bus? - Page 2

cadillackid · 11-12-2016, 03:14 PM

A/C capacity is another tging to think about too.. you need much more capacity going down the road than when parked.. a properly sized system running on the road can easily become a grossly over-sized system when parked...

I personally like the idea of completely separate systems... I realize many of you may not go to campgrounds often but if you do and have only small-diesel A/C then you cant shut down that engoine and use the already-paid-for electricity in the campground...

Road A/C for the road and electric A/C for when parked.. esp since a Genny is likely in the bus already anyway so it can be sized to run an A/C or two.. and you have the option if shore-docked to use that power...

-Christopher

PNW_Steve · 11-13-2016, 10:23 AM

Too many options.....

How about a 4 cylinder diesel (20-30hp?) with a compressor already attached?

https://boise.craigslist.org/hvo/5839421522.html

cadillackid · 11-13-2016, 11:03 AM

I dont see why not depending on the compressor and capacity... at the very least the motor could be repurposed i would think..

the compressor needs to be designed to work with R-134A, I dont know what refrigerantas those use but my guess is 134A... the only issue i can see is that I know some reefers are direct drive compressors with no decouple.. so the compressor spins anytime the engine is on.. in a reefer trailer the cycle time is a lot longer than in that of a vehicle interior, which would result in a lot of starts and stops for that engine..

if its one that has a decouple on the compressor then the engine will idle down when not calling for service.. since TK is still in business you may be able to still get specs / service info on it...

the engine itself seems like something worth having.. at the worst, fab up some brackets for a compressor and alternator and you have a mini-genny (for inverter stuff) and your A/C.. a lot of the TK stuff is actually not too noisy either..

-Christopher

PNW_Steve · 11-13-2016, 11:13 AM

Seltec MT16 spec sheet: Valeo Compressors » Technical specifications: TM13 / TM15 / TM16

looking at the performance graph it appears that it would take a minimum of about 10hp to get 30k Btu using this compressor.

Not my area of knowledge. Am I interpreting this properly?

PNW_Steve · 11-13-2016, 11:17 AM

Quote:

Originally Posted by cadillackid

I dont see why not depending on the compressor and capacity... at the very least the motor could be repurposed i would think..

the compressor needs to be designed to work with R-134A, I dont know what refrigerantas those use but my guess is 134A... the only issue i can see is that I know some reefers are direct drive compressors with no decouple.. so the compressor spins anytime the engine is on.. in a reefer trailer the cycle time is a lot longer than in that of a vehicle interior, which would result in a lot of starts and stops for that engine..

if its one that has a decouple on the compressor then the engine will idle down when not calling for service.. since TK is still in business you may be able to still get specs / service info on it...

the engine itself seems like something worth having.. at the worst, fab up some brackets for a compressor and alternator and you have a mini-genny (for inverter stuff) and your A/C.. a lot of the TK stuff is actually not too noisy either..

-Christopher

I have never worked on a refer unit but I have plenty of time with one parked outside of my bedroom window......

The engine runs 24 hours. It does not shut down when the target temp is reached like an electrically driven compressor. I would have expected it to have an electric clutch like an automotive a/c or engine driven marine refrigeration.

How do they make it play without a clutch?

cadillackid · 11-13-2016, 12:06 PM

some reefers shut down some dont... ive heard them both ways... I just dont know which type that one in the ad is..if they dont shut down then it will likely have a clutch as you mentioned unless it simply uses unloaders in the compressor or a variable ratio compressor.. similar to the newer cars which dont cycle... (a concept that was once used in cars for many many years a variable valve on the older cars.. nowadays computer controlled compressor)..

I run my TM-16 compressor (bought from ProAir LLC) with about 50-60k of evaporators and it still maintains pressures and cools good.. im not dure of the horsepower pull.. but I definitely notice it on my DT-360 esp when its really hot out.. I had to go to a wider Belt because the included one didnt have enough exposure on the pulley and always wanted to slip.. since the new Gates belt it hasnt slipped..

the unit in my new bus is rated at 42k BTU and is using a TM-16 compressor.. it seems to cool good though I only have the experience of driving it form texas to florida in september and the unit was a little low on freon but still kept me cool... it is at the rear of the bus so I need to fashion a dash evaporator up front or i'll freeze out anyone riding back there in the hot summer..

the TM-21 is a bigger beefier compressor but will be tough to spin with a single V-belt unless you have an idler to get good surface area on both the drive and driven pulleys.. its pad mount similar to the old tecumseh compressors...

I rarely see a bus using it.. most times people install 2 separate smaller systems using TM-16's..
-Christopher

AlleyCat67 · 11-13-2016, 02:01 PM

Quote:

Originally Posted by PNW_Steve

Too many options.....

How about a 4 cylinder diesel (20-30hp?) with a compressor already attached?

https://boise.craigslist.org/hvo/5839421522.html

That's an older TK unit than the ones I'm familar with.... but if it works the same way the engine would start and stop to maintain temperature in the trailer box. As far as cooling power I'd sat at least 100000 BTUs since they are designed to get a semitrailer cooled down in a hurry. The temperature on the ones I know could be set anywhere from +80 to -20 so it definitely has the power to cool a bus.

cadillackid · 11-13-2016, 02:33 PM

sounds like repurposing a reefer might be a good option if you dont mind the engine stop and start.. it is important to properly size the evaporators and condenser to each other..

the form factor of a reefer isnt ideal for a bus, however like any refrigeration piece it can be disassembled and modified... ive certainly done enough of HVAC modding.. again following the science behind it (including oil return to the compressor).. success can be had!
-Christopher

AlleyCat67 · 11-13-2016, 02:40 PM

Indeed. The thought of doing something similar crossed my mind as well, with the reefer unit everything you need is in one package, just would require a diagram showing how everything is interconnected, and some metal fabrication skills to be able to rearrange it all to work in a bus. The added advantage would be that if you're in a cold location you set the reefer unit to low to mid 70s and it functions as a heater as well.

cadillackid · 11-13-2016, 02:58 PM

do some Reefers have a heatpump or does it use some of the engine heat to a re-heat coil to help maintain temperature?.. the One I saw had a very small electric coil on it.. few hundred watts.. reefer trailers are insulated VERY WELL so it doesnt take much to keep it above freezing.. im really interested to know the actual capacity of them though... the coils dont look near big enough to be 100k BTU... of course im sure they are like any other device, different sizes made..
-Christopher

AlleyCat67 · 11-13-2016, 02:58 PM

These are the reefer units I know.

https://grandrapids.craigslist.org/hvo/5845816682.html

cadillackid · 11-13-2016, 03:13 PM

those are the nice ones!!!

also gives an idea of Horsepower needed for A/C...

the units at a higher temperature are around 62,000 btu and has a 34 horsepower engine... my guess is you arent far off estimating capacity at 75-80k if running it at say 75 degrees inside temp or so...

of course super hgh CFM blowers which is normal since it has to get air to the back of the trailer..
-Christopher

AlleyCat67 · 11-13-2016, 03:50 PM

Yep. From what you said I may have overestimated the BTU output of the units, but the super high CFM of the blowers kind of makes up for the lower BTUs, plus in the trailers the output air is also ducted across the ceiling to an output at the rear of the trailer, and the channels in the trailer floor allow for the return of air to the reefer... so those would be considerations for repurposing the unit.

The control unit could be mounted on the wall in the drivers area or another convenient location for control from inside the bus.

The engine could be mounted in a fabricated compartment secured in a convenient location underneath the floor with the fuel tank hung near the main diesel tank (a reefer tank is typically 25 gallons which on cycle sentry can give you several days of runtime, if you have it on continuous it will last about a day to a day and a half depending on engine load if memory serves.

PNW_Steve · 11-13-2016, 05:53 PM

Getting old sucks....

I remember trying to sleep with the all night racket of a refer parked 30' from my bedroom window. I can assure you that they never shut down.

I suspect that, maybe, they may have made some design changes since 1976.....

From a user standpoint I would not mind the engine starting and stopping but looking at it from a longevity standpoint I think it would be a bad thing. In refer duty I would expect fairly long run time followed by long pauses. As a "bushold" air conditioner it would likely short cycle.

If using the factory compressor is not viable you could fab a serpentine pulley and mounting brackets to run a conventional compressor and alternator from the refer engine. Pretty much just robbing the refer of its engine.

I am a tinkerer and love the idea of a DIY APU that would have the 42k Btu compressor and a 140amp alternator together with a start/stop & throttle controller that would vary engine speed based on load.

Run all 120v items from an inverter & battery bank and supply the DC for battery charging and inverter load from the APU.

Not sure I have time to go all McGiver on this though....

I have a Honda inverter generator that works in a similar manner. At low load you can hardly hear it run from inside my 5er.

Kubla · 11-13-2016, 06:10 PM

I drove refer trailers for 6 months, most use unload-er valves and have no clutch, valve opens and bypasses the refrigerant instead of compressing it, also refers have a defrost cycle, either heat pump or heating coils since the coils are below freezing they ice up and have to be defrosted

my short bus has 2 AC compressors, one for each unit, front and back

cadillackid · 11-13-2016, 07:26 PM

I think it may be the newest reefers that have shut down cycles.. and I was thinking unloaders more than clutch.. in commercial HVAC its common to unload one or more cylinders in a compressor and leave the motor run until the call is such that the minimum run was too much and the motor would shut down. its hard on electric motors to turn them on and off as well..

I had forgotten that reefers would have a hot gas bypass cycle to handle frozen condensation on the coils... so the makings of a heat pump are already in them if they use a true reverse cycle valve and not just a liquid dump into the evaporator..

ice machines just use a liquid dump and dont actually go into reverse to free the ice up from the freezing trays.. reefers are much more advanced these days..

its kind of unusual to see dual compressors in a short bus... .. depends on the climate it came from as to how much A/C capacity was installed..

-Christopher

Kubla · 11-13-2016, 07:52 PM

it is actually 2 separate systems on my bus, front and back

AlleyCat67 · 11-13-2016, 08:44 PM

The reefers I pulled had two settings, cycle sentry and continuous. The cycle sentry setting shuts the engine down once the desired temperature is reached.... when the temperature rises I think it was 5 degrees above that level it kicks back on to cool it down again. On continuous the engine runs constantly with the compressor kicking on and off to maintain temp.

cadillackid · 11-14-2016, 07:13 AM

Quote:

Originally Posted by AlleyCat67

The reefers I pulled had two settings, cycle sentry and continuous. The cycle sentry setting shuts the engine down once the desired temperature is reached.... when the temperature rises I think it was 5 degrees above that level it kicks back on to cool it down again. On continuous the engine runs constantly with the compressor kicking on and off to maintain temp.

that makes sense as to why ive seen them both ways... depends on which setting the trucking company was using. would the engine from one of those physically fit under a bus on a tray or is it too tall since the reefers themselves are designed to be tall vs wide?

-Christopher

AlleyCat67 · 11-14-2016, 02:12 PM

The engine itself is not that large.... it would be a tight fit but do-able. if you look at the unit the engine and compressor are behind the lower doors on the unit. The engine radiator is behind the upper door which opens up as opposed to side by side like the lower doors. The condenser and evaporator are accessed from inside the trailer.

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