Converting AC Powered Split Air Conditioners to DC Powered

[rgdaniels]

I have been wondering for some time now about the possibility of converting AC powered Air Conditioning units to DC powered units by using DC compressor units with their own 24v or 48v dc power supply, and leaving the rest of the wiring as is. The reason for this is to try to convert to using DC power, to cut operational costs, without having to replace the the existing air conditioning units that are working well. The DC power can come from solar in the day and batteries at night.

Any thoughts on this would be appreciated.

[Mr Bill]

Is it possible? Have you heard of inverter Technology in air conditioners?


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[rgdaniels]

There are currently hybrid ac/dc air conditioners available but the way I see it there would be no need for inverters as we are not converting ac to dc or vice versa. Simple taking dc power from a separate source to power the DC compressor and taking ac power from the normal house socket to power the rest of the unit with the AC compressor removed or disconnected.

[Mr Bill]

There are currently hybrid ac/dc air conditioners available but the way I see it there would be no need for inverters as we are not converting ac to dc or vice versa. Simple taking dc power from a separate source to power the DC compressor and taking ac power from the normal house socket to power the rest of the unit with the AC compressor removed or disconnected.

The rest of the unit would need 240 volts to operate the fan motor. If you install a DC Compressor in these units, what are you looking at for payback time? You must be planning on living a long time.

[Makeitcold]

The dc compressors in inverter units are using in the neighborhood of 300-400 vcd to operate. Your not going to get by using control voltages. Could you do it, yea. But building something reliable that won’t fry your compressor if a cloud goes overhead is going to be more expensive than an inverter setup. Just saying, theres a lot of R&D money spent developing inverters, so what’s your budget?

[rgdaniels]

The rest of the unit would need 240 volts to operate the fan motor. If you install a DC Compressor in these units, what are you looking at for payback time? You must be planning on living a long time.

Ok so the idea would be to lower the number of solar panels and batteries required to power a minimum of five 1.5 - 2hp units to a quarter of what would be required for using ac compressors. So reduce the installation cost of the solar plant for a small office or home and reduce the running cost of the plant by using solar and battery power. Payback time would be over 4 years by my calculation. Secondary saving is in reduce the cost of replacing the perfectly working air conditioning units again by 80% by only replacing the compressors and some minor modification in an area that required almost 24 hour air conditioning.

So engineering wise is it possible and simple enough to do if the business model is viable?

[pecmsg]

Your still going to need the same wattage!

[rgdaniels]

Your still going to need the same wattage!

Ok so my information is that it takes 50% less power when using a DC compressor versus the same size AC compressor. There are also some newer DC inverter compressors that have variable speed that use maybe 20% less than the normal AC compressors. So instead of say 2000Watts for a 2 HP Air conditioner the DC compressor will use like 800Watts. This is significant when using solar panels and batteries to power them as instead of say 10 250watt solar panels you would require only 5.

[pecmsg]

Ok so my information is that it takes 50% less power when using a DC compressor versus the same size AC compressor. There are also some newer DC inverter compressors that have variable speed that use maybe 20% less than the normal AC compressors. So instead of say 2000Watts for a 2 HP Air conditioner the DC compressor will use like 800Watts. This is significant when using solar panels and batteries to power them as instead of say 10 250watt solar panels you would require only 5.

Rather then convert an existing unit just buy a Mini Split...……...A Small one

Be advised unless there's bright sun you wont have enough to start it!

[martyinlincoln]

Interesting idea. Way above my pay grade but get some engineers working on it and you might come up with the next big HVAC change in areas with lots of solar.

[pecmsg]

Interesting idea. Way above my pay grade but get some engineers working on it and you might come up with the next big HVAC change in areas with lots of solar.

Small minis 1-Ton can start and run off of solar IF there’s enough panels.

[Makeitcold]

Why not just have enough solar panels to cover your daytime usage like everybody else that has solar? Your panels are only going to produce max wattage for a few hours of the day with the right weather conditions for only part of the year. Compressors don’t like over/under power supply, so you’d have to engineer near instantaneous power modulation from solar to battery and back. Take into account the battery packs probably have a service life of 10 years before costly replacement and the fact very few people would have any inkling of how it works. I think your expectations are way off, and that simpler, more cost effective ways already exist to lower your power needs that don’t involve having an in house engineering department. If money isn’t a factor though, than anything can be done, and let me be the first to turn in my resume!

[rgdaniels]

Why not just have enough solar panels to cover your daytime usage like everybody else that has solar? Your panels are only going to produce max wattage for a few hours of the day with the right weather conditions for only part of the year. Compressors don’t like over/under power supply, so you’d have to engineer near instantaneous power modulation from solar to battery and back. Take into account the battery packs probably have a service life of 10 years before costly replacement and the fact very few people would have any inkling of how it works. I think your expectations are way off, and that simpler, more cost effective ways already exist to lower your power needs that don’t involve having an in house engineering department. If money isn’t a factor though, than anything can be done, and let me be the first to turn in my resume!

Ok so there are two ways I am looking at this. First is to save on current power consumption. So without installing any solar panels or batteries, just using a dc inverter scroll compressor to lower power usage by 50-60% compared to the existing compressors. If you can half the power consumption then you can save $ 100 bucks per ac unit per month. So an office with 10 units can save $ 1,000 per month. That is significant and worthwhile for the company to invest to make the change for the 10 compressors.

The provision of backup solar power and batteries is a more costly option which will take more convincing and yes if you are spending all the money you might just as well buy enough panels and batteries and new dc based split units if cost is not a factor.

[Makeitcold]

Yes but you don’t get those energy savings just because you convert your compressor. High efficiency equipment is a group effort including usually much larger indoor/outdoor coils matched to smaller compressors and variable speed blower motors to ensure your getting the correct airflow. Problem one is you’ll have to replace the compressor(I think) to be compatible with high voltage 3 phase DC power, new control systems to run that, so there’s a couple grand right there.

Then you might see some percent in energy reduction but it’s not going to be close to 50% without having larger coils so a smaller compressor can handle the load. At that point you’ve completely rebuilt it with no warranty. If it were as simple as just slapping an inverter on it, everyone would do it

[Poodle Head Mikey]

Where did the "a DC compressor costs 50% less to operate than AC compressor" idea come from?

It takes about 750 watts per HP of work being done. I don't see how the voltage and current type alter that. How can that basic fact be gotten around?

PHM
---------------

Ok so there are two ways I am looking at this. First is to save on current power consumption. So without installing any solar panels or batteries, just using a dc inverter scroll compressor to lower power usage by 50-60% compared to the existing compressors. If you can half the power consumption then you can save $ 100 bucks per ac unit per month. So an office with 10 units can save $ 1,000 per month. That is significant and worthwhile for the company to invest to make the change for the 10 compressors.

The provision of backup solar power and batteries is a more costly option which will take more convincing and yes if you are spending all the money you might just as well buy enough panels and batteries and new dc based split units if cost is not a factor.

[pecmsg]

Spend several thousands and all your going to have is non UL Approved Equipment that your insurance company will not insure!

[pecmsg]

Let me guess your an Engineer?

[beenthere]

Ok so there are two ways I am looking at this. First is to save on current power consumption. So without installing any solar panels or batteries, just using a dc inverter scroll compressor to lower power usage by 50-60% compared to the existing compressors. If you can half the power consumption then you can save $ 100 bucks per ac unit per month. So an office with 10 units can save $ 1,000 per month. That is significant and worthwhile for the company to invest to make the change for the 10 compressors.

The provision of backup solar power and batteries is a more costly option which will take more convincing and yes if you are spending all the money you might just as well buy enough panels and batteries and new dc based split units if cost is not a factor.

Inverter systems save money by decreasing compressor capacity to match the load of the house/area/building. Not just by converting A/C to DC.

A DC motor is only about 30% more efficient than an A/C motor.

A 1 ton variable speed 48 volt DC mini split to use for 9 hours a day requires 5 hours of sun light, 3-300 watt solar panels, and 4-12 volt deep cycle 130 AH batteries.