Air conditioning electrical power question

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JMyers1

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The 650 is a great plane, but it's a really tight fit for two people. The 750 has waaaaay more interior room. The bubble canopy on the 650 makes it a greenhouse, so you should keep that in mind if heat is a concern. You can crack the canopy during taxi, but you can keep the doors on the 750 completely open, which is way better. I have problems with heat, and that's the primary reason I chose the 750 over the 650, even though the lower speed didn't really appeal to me either. Mine is a STOL because the Cruzer didn't exist yet when I bought my kit. The other primary reason was the space. But sitting in them is the right thing to do. That's how I finally made up my mind. I'm hoping to be there next month too, so maybe we'll see each other.
My understanding is the Cruzer has the same wing they just remove the slats and add wheel pants, but that airfoil seems to have a huge amount of drag much over 100 knots and throwing and extra 20 hp at it doesn't do much.

I wonder if they considered putting the CH650 airfoil on it, "cruzer 750B". Probably a lot of work, but then again we have solidworks now so maybe something they are considering. They 750 is very popular, I imagine if they sold a 120knot version of it it would sell in large numbers.
 

JMyers1

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Have you considered one of the cooler (ice chest) based models that use way less power? They don't cool as well as an air conditioning system, but I've seen reviews saying they do a good job of taking things down comfortably for short periods, like waiting in line for takeoff.


That's just one of the reviews I've seen. Aviation Consumer reviewed several not long ago, but I can't find that issue right now.

This is the one AvWeb chose:
Yes I have, that is a good option and if you do the math on the BTUs for melting ice it's actually in the ballpark of the other unit.

Drawbacks are:
- It's big and it’s 25lbs of ice plus the unit itself
- You have to remove it and dump the water and then refill with ice each time you use it
- Cooling output drops after 30 minutes
- It looks like a cooler with a pump in it and a dryer vent on it, which is what it is. Sorta cheap looking (subjective).

Advantages:
- It’s simpler
- It’s cheaper
- No drain needed
- No exhaust vent needed
 
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Rhino

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Just thought I'd offer a cheaper and much simpler option. On the bright side, you could have a real conversation piece at Zenith gatherings and airshows. Quite probably the only air conditioned 750 on the planet.
 
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JMyers1

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Just thought I'd offer a cheaper and much simpler option. On the bright side, you could have a real conversation piece at Zenith gatherings and airshow. Quite probably the only air conditioned 750 on the planet.
Yes thanks for the input, I actually edited my above post because there are a few other advantages. And coming from the certified world and being frustrated at the lack of options this is a pretty cool world!
 

8davebarker

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I always like the Rovac airconditioner of 50 years ago.
Used double port rotary vane compressor/expander with only single radiator. Working fluid is ambient air. Air was compressed to 35 psi, cooled buy the radiator and then expanded on the other side of the the rotary vane compressor. Yielded an 80 degree temperature Drop. Mixed with cabin air filtered to extract water. Low power required. But was believed too noisy for automotive application. That would be less of an issue in the typical GA plane.
The Rovac Automotive Air Conditioning System750403
The ROVAC air conditioning system, a new system that employs air as the refrigerant, is a combination rotary compressor/expander unit. A prototype has been modeled, designed, fabricated, laboratory tested, and field tested in a full size four door 1973 Dodge Coronet. The description of the new system, the analysis, design and actual test results are reported here.
The objective of the engineering program was to demonstrate and prove the capability of the ROVAC system to effectively and efficiently air condition automobiles. The prototype system installed in the Dodge Coronet produces delivered cooling capacity on the order of one to one and a half tons per thousand rpm and has produced delivered coefficients of performance at relatively high humidity levels (150-180 grains water per pound of dry air) rivaling the best developed conventional vapor compression air conditioning systems.
While the present system reported herein has not reached the levels of performance predicted by detailed computer models, continued hardware improvement is facilitating actual performance very near the levels predicted to be practically achievable.
During actual in-car jury tests, the prototype ROVAC air conditioning system brings the average passenger compartment temperature from a thermally soaked condition of 107°F down to 72°F in less than two min with five passengers at an average road speed of 30 mph.
 

JMyers1

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I have been looking at low voltage air conditioners as part of a solar office build. One interesting unit is this one:

They have a 24V version, too. When I get my retirement office built, I am planning to use solar power to run this during summer months. 10A is not too hard to achieve with a solar panel system. And, at 12 lbs, can be put most anywhere. Plumbing it in for me is not hard, and I would think that a solid package panel inside the baggage compartment would support it rather well. It is only about 1,500 BTU, but an aircraft cabin is not that large, so this may be usable.

Derswede
I think two of these would fit in front of the access port in the tail, assuming CG was ok:


I’m suspicious of the btu rating as it says it pulls 150 watts but then says 10 amps at 12 volts.
 

Vigilant1

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When it is sunny out, a typical small plane gains a LOT of heat. I don't think the contributions of a 1500 BTU air conditioner would even be noticeable.
We would need to decide if we want ventilation with copious amounts of ambient air OR the AC refrigeration. Unless the AC unit is big enough to provide more cooling than the ambient airflow (to include effects of airflow over exposed skin surfaces) it won't be very useful on the days where heat is a big problem.
 
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TiPi

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As a simple calculation, the sun at midday will provide roughly 1kW/m2. This is the cooling power that is needed to maintain the same temperature (minus the re-rediated heat). So with a full clear canopy, measure the horizontal area and the heat removal required is roughly proportional to the 1kW/m2. Working in BTUs is your problem:)
 

JMyers1

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When it is sunny out, a typical small plane gains a LOT of heat. I don't think the contributions of a 1500 BTU air conditioner would even be noticeable.
We would need to decide if we want ventilation with copious amounts of ambient air OR the AC refrigeration. Unless the AC unit is big enough to provide more cooling than the ambient airflow (to include effects of airflow over exposed skin surfaces) it won't be very useful on the days where heat is a big problem.
This has been talked about on beechtalk and other forums a lot recently. Two of these, which a 50 amp alternator aircraft could reasonably power (and lift), is about 3,000 btu. For context:

A car may have a 2 ton air conditioner, which is 24,000 btu. This makes 3,000 seem very small. However, 2 tons is also enough to cool a two bedroom home in much of the country, which makes 3,000 seem sufficient. Cars have huge cooling capacity primarily to cool a 130 degree interior to a comfortable temp in a minute or two. If your house was that hot it would probably take all day to cool down.

in other words, if the cabin of a small airplane has been baking in the sun this isn’t going to cool it down in any reasonable period of time. But if it was in the shade (or under a fabric cover), it will make the cabin noticeably more comfortable, or at the very least less uncomfortable. Aim the vents directly at your face, and I have to believe this is useful.
 

JMyers1

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As a simple calculation, the sun at midday will provide roughly 1kW/m2. This is the cooling power that is needed to maintain the same temperature (minus the re-rediated heat). So with a full clear canopy, measure the horizontal area and the heat removal required is roughly proportional to the 1kW/m2. Working in BTUs is your problem:)
That is good to know. I would tint the canopy as it appears most 650s do, and also put a retractable shade like the RV-14s usually have. And presumably some energy is reflected? The cabin is in fact about a meter wide, and a bit more than that long (not sure exactly), so say 1.5kw. If half makes it through and is absorbed and we don’t consider the heat from avionics and human bodies, that is about 5,100 btu/2 = 2,550 btu, or 450 btu left to lower the temp from ambient, so basically it’s enough to keep the cabin from warming up In direct sun. If you aim the vents at your face, this math in practice changes a bit, but not exactly an ice box. Some have put some heavy tint on that looks like it blocks more like 90%, but I’d like to fly at night.

Anecdotally there seem to be some very satisfied B-Kool customers, which depending on how fast you melt the ice has about the same or less cooling capacity (and for a shorter period and higher weight).

Worst case I have some small improvement and a fun project.
 
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rv7charlie

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I've flown bubble canopy a/c for most of the last 30 years. They are 'greenhouses'; re-radiation does little to help. Consider that a typical 2seat bubble canopy will likely need as much cooling as a cabin twin, and has 1/4 to 1/2 the HP available to power the cooler. Even cabin twins typically say to shut down the ac during take off.
I'll bet the fan on front with an open canopy does more in 30 seconds than a 3000 btu ac will do in 30 minutes.
 
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Dothetime

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I always like the Rovac airconditioner of 50 years ago.
Used double port rotary vane compressor/expander with only single radiator. Working fluid is ambient air. Air was compressed to 35 psi, cooled buy the radiator and then expanded on the other side of the the rotary vane compressor. Yielded an 80 degree temperature Drop. Mixed with cabin air filtered to extract water. Low power required. But was believed too noisy for automotive application. That would be less of an issue in the typical GA plane.
The Rovac Automotive Air Conditioning System750403
The ROVAC air conditioning system, a new system that employs air as the refrigerant, is a combination rotary compressor/expander unit. A prototype has been modeled, designed, fabricated, laboratory tested, and field tested in a full size four door 1973 Dodge Coronet. The description of the new system, the analysis, design and actual test results are reported here.
The objective of the engineering program was to demonstrate and prove the capability of the ROVAC system to effectively and efficiently air condition automobiles. The prototype system installed in the Dodge Coronet produces delivered cooling capacity on the order of one to one and a half tons per thousand rpm and has produced delivered coefficients of performance at relatively high humidity levels (150-180 grains water per pound of dry air) rivaling the best developed conventional vapor compression air conditioning systems.
While the present system reported herein has not reached the levels of performance predicted by detailed computer models, continued hardware improvement is facilitating actual performance very near the levels predicted to be practically achievable.
During actual in-car jury tests, the prototype ROVAC air conditioning system brings the average passenger compartment temperature from a thermally soaked condition of 107°F down to 72°F in less than two min with five passengers at an average road speed of 30 mph.
 

Dothetime

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I remember reading about the Rovac system 30 years ago. If it works why hasn’t it been embraced by the auto industry?
If it sounds too good to be true, it usually is.
 

Vigilant1

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I remember reading about the Rovac system 30 years ago. If it works why hasn’t it been embraced by the auto industry?
Noise and efficiency were the primary shortcomings compared to the existing systems.
 

JMyers1

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Rhino

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My understanding is the Cruzer has the same wing they just remove the slats and add wheel pants, but that airfoil seems to have a huge amount of drag much over 100 knots and throwing and extra 20 hp at it doesn't do much...
Don't know why I didn't see this before. No, it's not the same wing. It's optimized more for speed, though as you note, it isn't a whole lot more.

I'll be at the open hangar next month. Maybe we'll see each other.
 

wsimpso1

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I always like the Rovac airconditioner of 50 years ago.
Used double port rotary vane compressor/expander with only single radiator. Working fluid is ambient air. Air was compressed to 35 psi, cooled buy the radiator and then expanded on the other side of the the rotary vane compressor. Yielded an 80 degree temperature Drop. Mixed with cabin air filtered to extract water.
How do you "filter" water vapor from air?

You are describing an air cycle AC unit. This stuff is taught in Thermodynamics classes. AC works on an air cycle in many pressurized airplanes - the compressed bleed air comes from either the compression stage of a turbine engine or the compressor of the piston engine turbocharger. The compressed air goes through the first HX (cooled with outside air) while at high density (the atmosphere has more energy per pound as you go up, and all compressor inefficiency shows up as raised temps too), expanded to near cabin pressure, then through the second HX (also outside air) to trim temps the last few degrees for the cabin. Want heat? Throttle the air on one or both of the HX's more than when you want AC. Sound familiar? On a turbocharged piston scheme, the AC typically costs almost zero performance and fuel burn because you usually have enough excess compressor capacity to do this, the wastegate just runs a little more closed when pressurized to spin the assembly a little faster. On turbine engines, it costs fuel to run the compressor faster without getting more air to the burners, so cabin pressure/heat/AC costs performance and/or range.

A drawback to air systems is that unless you get the air below its dew point, you do not remove any water vapor. The solution is to cool air down below 60F to get the dew point down, and then pump that into the cabin. That works fine if you are cooling the cabin, not so good when you want heat. If you need a 72F cabin, you either add another HX (with more bleed air) to take the temp back up after dehumidifying or just do not cool the air below dew point.

The thing they do not tell you is that the "conventional" AC processes became the convention because Freon based cycles have far lower pumping losses, and thus use less power for any increment of cooling than air cycles do.

In the Boeing 787, the conventional air bleed based pressurization has been replaced by electrically driven compressors, although they are still air cycle systems. You have to get deeper into thermodynamics to settle that argument than I will go through today.

In any event, the OP was interested in wiring his system designed for hot rods. If it is big enough to do the job, the OP will have to figure that out too. But run a defunct company's defunct AC system in a Zenith?

Billski
 

JMyers1

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Don't know why I didn't see this before. No, it's not the same wing. It's optimized more for speed, though as you note, it isn't a whole lot more.

I'll be at the open hangar next month. Maybe we'll see each other.
I am planning to attend, it is right after the September workshop. Do many people attend? I'm curious to ask how Zenith ended up in Mexico. I hope to learn much and pick and engine, airframe, and order the kit. I did see that the wing is different. I think I had assumed it was the same since the 650 is so much faster on the same engine, but it has a smaller cabin, so maybe that explains it.
 

pfarber

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How do you "filter" water vapor from air?

You are describing an air cycle AC unit. This stuff is taught in Thermodynamics classes. AC works on an air cycle in many pressurized airplanes - the compressed bleed air comes from either the compression stage of a turbine engine or the compressor of the piston engine turbocharger. The compressed air goes through the first HX (cooled with outside air) while at high density (the atmosphere has more energy per pound as you go up, and all compressor inefficiency shows up as raised temps too), expanded to near cabin pressure, then through the second HX (also outside air) to trim temps the last few degrees for the cabin. Want heat? Throttle the air on one or both of the HX's more than when you want AC. Sound familiar? On a turbocharged piston scheme, the AC typically costs almost zero performance and fuel burn because you usually have enough excess compressor capacity to do this, the wastegate just runs a little more closed when pressurized to spin the assembly a little faster. On turbine engines, it costs fuel to run the compressor faster without getting more air to the burners, so cabin pressure/heat/AC costs performance and/or range.

A drawback to air systems is that unless you get the air below its dew point, you do not remove any water vapor. The solution is to cool air down below 60F to get the dew point down, and then pump that into the cabin. That works fine if you are cooling the cabin, not so good when you want heat. If you need a 72F cabin, you either add another HX (with more bleed air) to take the temp back up after dehumidifying or just do not cool the air below dew point.

The thing they do not tell you is that the "conventional" AC processes became the convention because Freon based cycles have far lower pumping losses, and thus use less power for any increment of cooling than air cycles do.

In the Boeing 787, the conventional air bleed based pressurization has been replaced by electrically driven compressors, although they are still air cycle systems. You have to get deeper into thermodynamics to settle that argument than I will go through today.

In any event, the OP was interested in wiring his system designed for hot rods. If it is big enough to do the job, the OP will have to figure that out too. But run a defunct company's defunct AC system in a Zenith?

Billski
Long winded and not really informative.

In laymans terms: When you let compressed air expand, it cools the surrounding area. Imagine pointing an air nozzle at a piece of metal. Pull the trigger and the moving air cools the metal. Now if you use the cold piece of metal to cool cabin air, you get cold air. I would think this is more about gas law than thermodynamics. Pressure inversely affecting temperature.

A modern car AC system uses about 4hp (about 2800 watts) so these small units operating at 24v 20A are < 500watts. That should give you an idea of how well they operate.
 
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