Air conditioners that can work in any orientation

[radar_macgyver]

I have an application housed in an enclosure that's mounted to a moving platform such that the enclosure can be at any angle with respect to vertical. Most air conditioner compressors that I've come across cannot be operated in any orientation other than vertical, so that rules out their use here. My understanding is that the lubrication systems in the compressors depend on being mounted vertically to drain down into a sump. On previous iterations of the design, I've used commercial thermoelectric cooler modules to regulate the enclosure temp, though these are very inefficient and expensive. I'm curious if there are any non-TEC cooler modules available for this purpose that can tolerate being rotated away from vertical.

[coppice]

I have an application housed in an enclosure that's mounted to a moving platform such that the enclosure can be at any angle with respect to vertical. Most air conditioner compressors that I've come across cannot be operated in any orientation other than vertical, so that rules out their use here. My understanding is that the lubrication systems in the compressors depend on being mounted vertically to drain down into a sump. On previous iterations of the design, I've used commercial thermoelectric cooler modules to regulate the enclosure temp, though these are very inefficient and expensive. I'm curious if there are any non-TEC cooler modules available for this purpose that can tolerate being rotated away from vertical.

You don't just have to put most heat pumps the right way up. You have to leave them that way for some time before switching them on, or you can stall them. I think even the chillers made for refrigerated trucks still have to be used the right way up. I believe they have special designs to tolerate the sloshing around of oil as the truck moves, but it wouldn't be OK to completely reorient the thing while in operation. I wonder what is available for airborne use?

[ejeffrey]

I don't know of any air conditioner that can do that, you might be able to modify one?  Like a dry sump oil system on a racing engine that pumps oil into a secondary reservoir that then feeds the main oil pump?  Can you guarantee a certain amount of time in normal orientation?  Or is it required to be able to turn upside down and run indefinitely? 

I'm guessing you have to keep your product all together inside the enclosure, otherwise I would look at mounting the compressor somewhere else and using flexible refrigerant lines or a chilled water loop with flexible lines, or even rotary couplings to allow infinite rotation.

[NiHaoMike]

I would say putting a regular heat pump in a large gimbal would be the easiest solution, but still not that easy.

[radar_macgyver]

You don't just have to put most heat pumps the right way up. You have to leave them that way for some time before switching them on, or you can stall them.

Most industrial enclosure coolers come with a warning that they must be left upright for a minimum of a few hours after installation, prior to switching them on.

I wonder what is available for airborne use?

That's what I was wondering too, this is the only other instance I can think of where one would need an off-vertical AC. Civilian aircraft don't spend much time in steep banks and dives, I suppose.

The end application is for a radar receiver that's mounted on a scanning antenna. As the antenna scans around, it can be moved off-vertical. It is returned back to zero degree elevation periodically, but I don't want to risk a compressor failure and loss of cooling. I'm aware of at least one design that uses a water chiller and a glycol loop passed through a rotary union. The folks who operate those systems complain about the leaks, so that's something I would like to avoid.

The total heat load in this enclosure isn't much - just about 150-200W. TEC coolers are available in this capacity, though they are bulky and super inefficient through most of the useful delta-T range.

[Berni]

This does sound like a pretty tricky cooling implementation.

Is it not viable to hang the air conditioner by a gimbal and then run a flexible water hose up out of it? It is not like you have to hold it perfectly level. Pretty sure most compressors are perfectly happy running at a 20 degree tilt just fine, as long as the oil collects in the right general area. So the gibmal only has to have enough range to reduce the tilt down to something reasonable.

[coppice]

The end application is for a radar receiver that's mounted on a scanning antenna. As the antenna scans around, it can be moved off-vertical. It is returned back to zero degree elevation periodically, but I don't want to risk a compressor failure and loss of cooling. I'm aware of at least one design that uses a water chiller and a glycol loop passed through a rotary union. The folks who operate those systems complain about the leaks, so that's something I would like to avoid.

The total heat load in this enclosure isn't much - just about 150-200W. TEC coolers are available in this capacity, though they are bulky and super inefficient through most of the useful delta-T range.

If you only need to cool a small volume like that, look at the stirling cooler devices made for the high end thermal camera market.

[RoGeorge]

I have an application housed in an enclosure that's mounted to a moving platform such that the enclosure can be at any angle with respect to vertical.

Can you post a picture of it?

All compressor-based heat pumps I've seen rely on the orientation, unless the air cooler is a peltier element, or just a lump of cold ice with a ventilation fan. 

[TopQuark]

Two fairly esoteric cooling (heat pump) tech I've read about:

Elastocaloric shape memory alloy heat pump:
https://www.sciencedirect.com/science/article/abs/pii/S235249282100698X

Electrocaloric capacitor heat pump:
https://arstechnica.com/science/2023/11/capacitor-based-heat-pumps-see-big-boost-in-efficiency/
https://www.science.org/doi/10.1126/science.adi5477

Both should be orientation-agnostic. I don't think either of them have moved beyond the lab research phase, but it is interesting tech. 

[alpher]

Absorption type cooling should work:
https://en.wikipedia.org/wiki/Absorption_refrigerator
May not be more efficient than pelletier though.

[radar_macgyver]

Can you post a picture of it?

Here's a screengrab from 3D model of the overall radar. The enclosure in question is the one labeled 'Receiver'. You can kinda see the existing TEC (Peltier) cooler module on the back. I've already built out the receiver enclosure, and discovered during testing that the cooler isn't powerful enough (once ambient temps are > 35C, it's unable to maintain the 35C setpoint). At the moment, I'm looking at adding a second TEC, though I felt "surely someone must have a compressor AC that works in any orientation" and discovered that I could not find a suitably unique set of search phrases for Google to find this out I believe the main issue is the TEC runs on 48VDC, and the 48V power supply is inside the enclosure. When the TEC pulls ~7A to start cooling, the PSU heats up. I'm also looking at swapping out the PSU for one that's conduction cooled, and dump the waste heat directly outside the enclosure. This has a chance of working since the PSU gets above 35C in operation, so a heatsink to ambient will cool it.

If you only need to cool a small volume like that, look at the stirling cooler devices made for the high end thermal camera market.

The enclosure is about 0.75m x  0.75m x 0.5m. From a quick search on Stirling coolers, the commercial ones seem to be made to cool a surface, and are also quite expensive. The one exception is a Coleman cooler I found on Amazon of all places. Looks interesting, though it's not an 'industrial spec' product so I probably need to experiment with one before using it on a project like this. Also it's discontinued...

Is it not viable to hang the air conditioner by a gimbal and then run a flexible water hose up out of it? It is not like you have to hold it perfectly level. Pretty sure most compressors are perfectly happy running at a 20 degree tilt just fine, as long as the oil collects in the right general area. So the gibmal only has to have enough range to reduce the tilt down to something reasonable.

It is possible, though this is a system that must run 24/7, in a remote location with maybe once a year maintenance visits. The fewer mechanical parts the better, and in my experience, anything with liquid cooling will eventually leak. A colleague has a similar radar (of commercial origin) that uses a liquid cooler in the radar shelter, and runs coolant through the antenna positioner. This avoids the gimbal, but to run the coolant through the rotary axes requires a rotary union, which can leak especially when subjected to large temperature fluctuations.

A bit more background: the two transmitters right behind the antenna dissipate a fair bit of heat (about 2 kW each) so I have flexible ducts that bring conditioned air from the shelter. I sized the HVAC units in the shelter for the solar load of the radome surface plus the TX electrical load. This should maintain the radome at < 40C on most days of the year, in the environment that the radar will be ultimately deployed. The receiver contains the RF chain, LNAs and also data acquisition and signal processing computer. These need to be maintained at < 35C for the longest life (the SP FPGA can get toasty even at room temps). The antenna can scan continuously in azimuth, elevation is from -5 to +100 degrees and while greater than +20 is rare, it can happen.

Thanks all for the suggestions, I'm the only engineer on this project so there aren't others to bounce ideas off.

[Swake]

Is watercooling an option?
The chiller can stay outside the dome. Hoses are as flexible as electric cable. If that is not good enough all kind of joints exist, also for 360°.
For heat exchanger ideas you can have a look at computer water cooling, that might not be reliable or sturdy enough in your situation but it gives good ideas of what is possible.
By controlling the pumping speed you control the temperature.

[jmelson]

I worked at NASA Wallops Station MANY years ago.  We went over to the Advanced Data Acquisition System location to put in a boresight camera.  We couldn't do it physically, so they had to point the dish at the horizon so we could lift the camera into position.  They had an air conditioner to cool the receiver electronics that was mounted on a gimbal, with some sort of bearing on the ductwork.  It is definitely doable.
Jon

[Conrad Hoffman]

Can you put the AC someplace stable and cool with piped cold air? Nobody would notice a few leaks!

[CaptDon]

You probably can't find one in small enough scale but the rotary vane compressors and the screw compressors have no sump and rely on the refrigerant carrying the oil within the freon loop. They generally include an accumulator / dryer which serves as an expansion tank / reservoir.

[ejeffrey]

There are air-conditioning units intended to retrofit classic cars. Some advertise versatility in mounting orientation.  It's still not "any orientation" but it's at least designed to have some range, maybe up to 120 degrees?  Probably the people who run them are used to answering weird packaging questions as well and might be able to help you find a unit that will work.

I don't have familiarity with any specific examples but that might help narrow down your googling.

[CaptDon]

Are you re-deploying the old Gap Filler radar stations like the one that used to be on High Rock in the Pidgeon Hills area near Hanover Pa.? That closed probably late 60's and for years sat un-attended and grown up in weeds. Vandals and partyers used to hang around the sight after dark and the dirt access road was mostly paved with beer cans and latex. The lower access road is chained off and now controlled by the radio broadcasters using the mountain top site. In the days of Gap Filler there was also a U.S. Forestry fire watchtower on the site which became an antenna pedestal for the original 98.5 WYCR / WHVR radio outlet as well as ham radio 'field day' activities.

[johansen]

Im reasonably certain that if you add 6 or so ounces of oil to any off the shelf 1 ton rotary piston compressor (they type that has an accumulator on the side of the compressor and the discharge line comes out the top) then they would work up to 45 degrees from vertical.

[amyk]

Absorption type cooling should work:
https://en.wikipedia.org/wiki/Absorption_refrigerator
May not be more efficient than pelletier though.

Definitely not, they rely on gravity.

[radar_macgyver]

Is watercooling an option?

It would be, if the ambient was always lower than the enclosure's internal temp. This is not always the case here, so I need some form of heat pump. There do exist air-to-air heat exchangers for industrial enclosures, but the requirement to go below ambient means I can't use them either.

I worked at NASA Wallops Station MANY years ago.  We went over to the Advanced Data Acquisition System location to put in a boresight camera.

Cool! I was at Wallops late last year to install one of our radars there. We were on a tight time budget so I didn't get to see the dish farm except from a distance.

They had an air conditioner to cool the receiver electronics that was mounted on a gimbal, with some sort of bearing on the ductwork.  It is definitely doable.

Understood - this is certainly something we could look at for a new system. I was hoping there was a handy commercial solution I could use on my current design to overcome the capacity limits of the existing TEC.

You probably can't find one in small enough scale but the rotary vane compressors and the screw compressors have no sump and rely on the refrigerant carrying the oil within the freon loop. They generally include an accumulator / dryer which serves as an expansion tank / reservoir.

I didn't know that screw compressor units don't have a sump, but I did come across those in much larger sizes (suitable for a building, for example - Daikin makes some).

Can you put the AC someplace stable and cool with piped cold air? Nobody would notice a few leaks!

I'm doing that right now for the entire radome (cool air from the HVAC units in the shelter is ducted through the dome). Due to imperfect seals and effectively zero thermal insulation (the radome is a single layer of fiberglass), the thermal load due to solar insolation is quite high so this is just used to vent the waste heat from the transmitters. The receiver + signal processor enclosure needs a bit more cooling - hence the TEC. Oversizing the shelter HVACs would result in condensation when temps fall below ambient dewpoint.

There are air-conditioning units intended to retrofit classic cars.

Thanks for the tip! Again, something I might look into for a new design, since I'll have to provide a motor and packaging, unless someone has a pre-packaged unit for industrial enclosure cooling.

Are you re-deploying the old Gap Filler radar stations like the one that used to be on High Rock in the Pidgeon Hills area near Hanover Pa.?

Not in this case - this is a new design, with dual GaN solid-state C-band transmitters. Our group does manage a radar built around an old FPS-18 gap filler radar, though it's kinda long in the tooth. Interestingly, NASA Wallops still operates a couple of FPS-18 transmitters to support SPANDAR.

Im reasonably certain that if you add 6 or so ounces of oil to any off the shelf 1 ton rotary piston compressor (they type that has an accumulator on the side of the compressor and the discharge line comes out the top) then they would work up to 45 degrees from vertical.

Is the thinking that there's enough oil circulating to be recaptured when the compressor's tilted?

[uer166]

Is watercooling an option?

It would be, if the ambient was always lower than the enclosure's internal temp. This is not always the case here, so I need some form of heat pump.

I think they meant a water cooling system (with slip rings or whatever), that connects to a normal heat pump chiller that is stationary. That way at the heat source there's only water/glycol connections required, which is surely much easier than refrigerant.

[donlisms]

Did I understand you to say the power supply running the TEC coolers is inside the very cabinet being cooled?

And something else I wondered... how do the existing TEC's dump the heat to the outside?  Is it a passive heatsink, or with a fan, or something else?

And something else I wondered - is there any thermal insulation at the walls of the box?

Just curious.  I'm learning heat transfer.

[radar_macgyver]

Did I understand you to say the power supply running the TEC coolers is inside the very cabinet being cooled?

And something else I wondered... how do the existing TEC's dump the heat to the outside?  Is it a passive heatsink, or with a fan, or something else?

And something else I wondered - is there any thermal insulation at the walls of the box?

The TEC I'm using now is the Ice Qube IQ300TE, you can refer the datasheet for the fan details. The box is insulated with 25mm foam panels, with an additional layer of aluminum foil. And yes, the 48V power supply is inside the same box. I'm working on a mod to use a conduction cooled supply, mounted to the box wall, with an external heatsink.

[johansen]

Is the thinking that there's enough oil circulating to be recaptured when the compressor's tilted?

nah, its that there is enough oil in the compressor to reach the bottom of the shaft when it is tilted. i can post photos of what they look like internally.

The shaft is hollow and picks up oil about 1cm above the bottom.