diy solar

diy solar

I am always fantasizing about having a energy efficient air conditioner for van life, anyone seen any concepts in tech news or anything?

Zwy said:
9K BTU is the smallest, too big for my application.
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it's variable speed, it doesn't matter. It can run at 2000 BTU all day long.

When you go to inverter / variable speed HVAC, you still should size your units somewhat correctly, but it's not as big of an issue then with single speed A/C compressors.

Those variable speed go usually down to about 20% of their max capacity. So if you are still in that range for your load - you are still fine.

My Van needs about 5.000 BTU - so my 8000 BTU Midea inverter is "oversized" so it almost never runs at full capacity.
 
GSXR1000 said:
that's a fact of preasure tempature relationship... not a sensor or anything else.. just what happens
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That is true for a compressor that functions in a normal way. My LG non inverter, single speed compressor, window AC uses anywhere from 570 -660 watts depending on how hard it has to work based on the ambient temperature. Inverter ACs alter the frequency of the compressor from 10-120 Hz. It might be possible to trick the outdoor thermistor in order to keep the AC running at a lower, more efficient, frequency. Still, working at 10 Hz with a high ambient temperature would use more watts than working with a low ambient temperature at 10Hz. Before I bought the Midea, I expected inverter ACs/mini-splits to work somewhat like MPPT. They would only as hard as they needed to, to maintain a set temperature. This would be based on the volume cooled, insulation value, etc. They only partially work like that. Hypothetical Ex. If someone was trying to cool a small closet, even if was 110F ambient, why would they want the AC to work at 120Hz(poor efficiency), when working at 10HZ(best efficiency) would get the job done, but in a longer time period. If tricking the outside thermistor works, it would be necessary to modify the ambient temperature it sees, so the HZ are high enough to keep up with the inside set temperature. (Not an engineer. Just guessing it would work. Might be easy to test with a mini-split. On a hot day, put outdoor thermistor into cool 75F or so whatever. See what happens with the wattage draw.)
 
rcrracer said:
(Not an engineer. Just guessing it would work. Might be easy to test with a mini-split. On a hot day, put outdoor thermistor into cool 75F or so whatever. See what happens with the wattage draw.)
Click to expand...
Electrical Engineer here.

Somebody put together those Inverter units with the frequencies how they defined is the most efficient. Electricity and efficiency is not straight forward in motors. Watch a few of the Tesla Motor teardowns.

Something which is efficient in a high rpm environment is not efficient in a low rpm motor.
Motors which needs a lot of torque is different from a motor which is made for peak power.

So you can not say - because this high frequency it's not efficient.
www.researchgate.net

(PDF) Effects of Low Frequencies on Three Phase Induction Motor Performance Operating in Close Proximity to Rated Speed

PDF | Variable speed drives (VSD) are adhered to induction motors in most of the present industrial applications. And since the world has become more... | Find, read and cite all the research you need on ResearchGate
www.researchgate.net www.researchgate.net

you may have some other effects happening in low frequencies. Magnetic field has various sizes - so the motor size in the compressor may limit what frequencies you can use. For some applications you need a fairly large diameter for low frequency.
 
rcrracer said:
That is true for a compressor that functions in a normal way. My LG non inverter, single speed compressor, window AC uses anywhere from 570 -660 watts depending on how hard it has to work based on the ambient temperature. Inverter ACs alter the frequency of the compressor from 10-120 Hz. It might be possible to trick the outdoor thermistor in order to keep the AC running at a lower, more efficient, frequency. Still, working at 10 Hz with a high ambient temperature would use more watts than working with a low ambient temperature at 10Hz. Before I bought the Midea, I expected inverter ACs/mini-splits to work somewhat like MPPT. They would only as hard as they needed to, to maintain a set temperature. This would be based on the volume cooled, insulation value, etc. They only partially work like that. Hypothetical Ex. If someone was trying to cool a small closet, even if was 110F ambient, why would they want the AC to work at 120Hz(poor efficiency), when working at 10HZ(best efficiency) would get the job done, but in a longer time period. If tricking the outside thermistor works, it would be necessary to modify the ambient temperature it sees, so the HZ are high enough to keep up with the inside set temperature. (Not an engineer. Just guessing it would work. Might be easy to test with a mini-split. On a hot day, put outdoor thermistor into cool 75F or so whatever. See what happens with the wattage draw.)
Click to expand...
boss I do AC for work... as outdoor temperature goes up so does head preasure you can't truck it back down... the outdoor thermistor is there to slow the outdoor fan on cool days to increase head preasure to minimum preasure and to deforst system in heat pump mode

100 PSI difference between fall 65f and summer 95f outdoor temp.. no compressor changes can change thatScreenshot_20210501-112019_Adobe Acrobat.jpg
 
eXodus said:
it's variable speed, it doesn't matter. It can run at 2000 BTU all day long.

When you go to inverter / variable speed HVAC, you still should size your units somewhat correctly, but it's not as big of an issue then with single speed A/C compressors.
Click to expand...

Not entirely true, oversized can and will lead to inefficiencies. But you did note, "you still should size your units somewhat correctly"
eXodus said:
Those variable speed go usually down to about 20% of their max capacity. So if you are still in that range for your load - you are still fine.

My Van needs about 5.000 BTU - so my 8000 BTU Midea inverter is "oversized" so it almost never runs at full capacity.
Click to expand...
There is a minimum it can run, as the unit gets larger, the minimum will be higher.
 
Zwy said:
Not entirely true, oversized can and will lead to inefficiencies. But you did note, "you still should size your units somewhat correctly"

There is a minimum it can run, as the unit gets larger, the minimum will be higher.
Click to expand...
Yes, there is sometimes in the manual a minimum BTU and the maximum.
My 12000 BTU mini split runs between 3500 and 13000 BTU.

Sure it's likely more efficient at the rated capacity. But on 80% of the days of a year a somewhat correct sized inverter A/C is better then a correct sized single speed.
 
Zwy said:
Not entirely true, oversized can and will lead to inefficiencies. But you did note, "you still should size your units somewhat correctly"

There is a minimum it can run, as the unit gets larger, the minimum will be higher.
Click to expand...
It seems if the engineers would program the computer so the unit works most efficiently with the recommended room size, such as 350 sq. ft. for a 8K BTU unit. My LG single speed compressor is rated for 8K BTU using 650 watts. The Midea is rated for 8K BTU using 750 watts. It would appear the LG is more efficient even though it's SEER is 12.5 and the Midea is 15 SEER. It has to do with how units are tested which I have posted elsewhere. Mini-splits have reach a SEER of 42. It's as if the physics of gas laws no longer exist. I think the higher SEER units are gaming the testing methods, (VW dieselgate anyone) by always keeping the frequency below 30Hz(?) or so. Take a normal 20K BTU system, then suppress the max frequency and rate it 8K BTU. If that is true, trick the outside thermistor. In effect, turn a 8K BTU unit into a 4K(?) BTU unit. Semi-related, low temp., geared site: https://ashp.neep.org/#!/product_list/. Years ago I searched for 0-12K BTU, single zone, non ducted. Each unit's details are where the interesting info is located.
 
eXodus said:
Electrical Engineer here.

Somebody put together those Inverter units with the frequencies how they defined is the most efficient. Electricity and efficiency is not straight forward in motors. Watch a few of the Tesla Motor teardowns.

Something which is efficient in a high rpm environment is not efficient in a low rpm motor.
Motors which needs a lot of torque is different from a motor which is made for peak power.

So you can not say - because this high frequency it's not efficient.
www.researchgate.net

(PDF) Effects of Low Frequencies on Three Phase Induction Motor Performance Operating in Close Proximity to Rated Speed

PDF | Variable speed drives (VSD) are adhered to induction motors in most of the present industrial applications. And since the world has become more... | Find, read and cite all the research you need on ResearchGate
www.researchgate.net www.researchgate.net

you may have some other effects happening in low frequencies. Magnetic field has various sizes - so the motor size in the compressor may limit what frequencies you can use. For some applications you need a fairly large diameter for low frequency.
Click to expand...
I've posted elsewhere the frequency range of inverter LG and Midea window ACs. They range from 10HZ to 120HZ. At 100 watts my Midea can produce a delta T of 12F. The max delta T I've seen is 24F at 750(?) watts. This is with auto fan speed. 100 watts would be cool out door temp. min fan speeds, 750 watts high outdoor temp, max fan speeds.
 
rcrracer said:
I've posted elsewhere the frequency range of inverter LG and Midea window ACs. They range from 10HZ to 120HZ. At 100 watts my Midea can produce a delta T of 12F. The max delta T I've seen is 24F at 750(?) watts. This is with auto fan speed. 100 watts would be cool out door temp. min fan speeds, 750 watts high outdoor temp, max fan speeds.
Click to expand...
you are comparing system watts and focusing on one component - the compressor.

Both systems contain at least 3 different electric motors.
Interior Fan
Compressor
Exterior Fan

On both the Fans the Mini Split has a build factor advantage - the Window Unit uses far less efficient fans since they need much higher rpm to move the same amount of air.

Like I posted earlier - the Mideas interior Fan alone consumes 140w on high - while my mini split fan (which is a long tube style fan) only needs like 40-50w
That would already explain the difference. Midea cheaped out on the Fan. My minisplit has true variable speed for both fans. While the Midea has 4 speeds taps for both fans.
 
like everything there is ab sweet spot...
rcrracer said:
It seems if the engineers would program the computer so the unit works most efficiently with the recommended room size, such as 350 sq. ft. for a 8K BTU unit. My LG single speed compressor is rated for 8K BTU using 650 watts. The Midea is rated for 8K BTU using 750 watts. It would appear the LG is more efficient even though it's SEER is 12.5 and the Midea is 15 SEER. It has to do with how units are tested which I have posted elsewhere. Mini-splits have reach a SEER of 42. It's as if the physics of gas laws no longer exist. I think the higher SEER units are gaming the testing methods, (VW dieselgate anyone) by always keeping the frequency below 30Hz(?) or so. Take a normal 20K BTU system, then suppress the max frequency and rate it 8K BTU. If that is true, trick the outside thermistor. In effect, turn a 8K BTU unit into a 4K(?) BTU unit. Semi-related, low temp., geared site: https://ashp.neep.org/#!/product_list/. Years ago I searched for 0-12K BTU, single zone, non ducted. Each unit's details are where the interesting info is located.
Click to expand...
the indoor sensor decides the capacity... geez why are you hung up on a outdoor ambient temperature sensors
 
eXodus said:
you are comparing system watts and focusing on one component - the compressor.

Both systems contain at least 3 different electric motors.
Interior Fan
Compressor
Exterior Fan

On both the Fans the Mini Split has a build factor advantage - the Window Unit uses far less efficient fans since they need much higher rpm to move the same amount of air.

Like I posted earlier - the Mideas interior Fan alone consumes 140w on high - while my mini split fan (which is a long tube style fan) only needs like 40-50w
That would already explain the difference. Midea cheaped out on the Fan. My minisplit has true variable speed for both fans. While the Midea has 4 speeds taps for both fans.
Click to expand...
My 8000 BTU Midea inverter AC has a tube type inside fan, like a mini-split. Interior fan only on, 6.8 watts low, 8.0 watts med, 11.0 watts high measured a few min. ago. My non- inverter 8K BTU LG, each of the two fan motors draw 62 watts on high for a total of 124 watts when both on high, just as their nameplates state. Everything says you don't have a Midea inverter AC but instead a non-inverter AC. Every Midea inverter has the same SEER and they all look identical, U-shaped. https://www.energystar.gov/productfinder/product/certified-room-air-conditioners/results I believe they all mount on the same bracket. Picture of u-shaped Midea inverter AC. https://www.amazon.com/Midea-Invert...ty-Installation/dp/B08677DCKN?ref_=ast_sto_dp
One reason Mini splits are more efficient is fin surface area and airflow into and out of the outside unit.. 8K Midea outdoor fin area aprox. 18" x 11.5". No idea what the depth is.
 
Altide8 said:
I should have some numbers for you this weekend.
Click to expand...
I am still trying to figure out how to work the unit properly and how to get it set up. (no real documentation) Although it is pulling about 380w on medium setting and fan on 3/5. The temp of the air coming out of the unit is about 40f.
 
Altide8 said:
I am still trying to figure out how to work the unit properly and how to get it set up. (no real documentation) Although it is pulling about 380w on medium setting and fan on 3/5. The temp of the air coming out of the unit is about 40f.
Click to expand...
Any further updates? I'm itching to pull the trigger on one of these for my solar tiny house.

I've been using both a Midea U inverter unit (8k btu) and a very normie non inverter Frigidaire 8k to manage my 400sq ft space during harsh summers. I need to free up my inverter for other tasks and I hate the Frigidaire for its ability to wake the dead cycling the compressor.

hows the noise? Does the inside fan have auto on off cycling or speed changing?
 
My Coleman Mach something 13000 btu can run off 24v lifepo4 bank and lv2424 for a while and cool van down but will kill batteries pretty quick. 1100 watts once running. When plugged in to 15amp shore power works like a champ....though fan is high or low....no cycling so bit noisy. Old ears don’t care and can still sleep.
 
Swamplizard said:
My Coleman Mach something 13000 btu can run off 24v lifepo4 bank and lv2424 for a while and cool van down but will kill batteries pretty quick. 1100 watts once running. When plugged in to 15amp shore power works like a champ....though fan is high or low....no cycling so bit noisy. Old ears don’t care and can still sleep.
Click to expand...
Those things are incredibly inefficient. You could cut your power consumption by a huge amount by replacing that with a mini-split inverter AC system.


Of course your insulation plays the largest part in it. 300-400 watts can cool down a van sized space with ease if there's enough insulation.
 
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