Solar powered AC air conditioning, a bummer or a challenge?

[K7ABE]

I think the big difference between these A/C's and the inverter driven devices like the mini-split is:

1) Startup surge. With a typical induction motor you get a huge startup surge every time the compressor turns on, since induction motors try to come up to speed instantly. With an inverter drive you don't see a large surge since the motor is ramped up more slowly. This might mean that a 500 watt air conditioner needs a 1500 watt surge to start - and that all has to come from the house inverter. An inverter drive might only need 600 watts to come up to speed.

2) Cycling. A typical A/C, running under a moderate setting, might cycle on for 1 minute every 3 minutes to keep the room cool. So if your average power draw is 500 watts, it is taking 1500 watts while it is on and just a few watts when it is off to run its fan.

The above means that - even if the two A/C's are the same efficiency - the mini-split with the inverter drive will be a lot easier on the power system. In one you have to design for 1500 watt loads, in the other 600 watt loads.

An important note:
An inverter drive motor uses a _separate_ inverter to drive its own motor; this is not the house inverter. This is a detail of motor design, not a requirement. There is no reason that a window unit can't use an inverter drive, but none that I have seen do. Split systems, on the other hand, often do.

Spent a few hours researching inverter mini split AC units. One of the better ones I found is 650 Watts and 9000 BTU and about a thousand dollars with self install (Need a license HVAC for warranty to be valid). It still has a 15 amp fuse that allows for more than double for startup. However the operational efficacy numbers are impressive. Did my limited research miss some key points here?
Abe

[Mike90250]

A high Farad capacitor from the automotive stereo industry Would handle the inrush for a 12 volt DC system.

Are you sure you are a ham ? calculate what useable power is in the cap from 13V to 12.5V

I am not aware of any AC capacitors for a 120 volt system that will handle that load.

oh boy - Capacitors can not store AC. They can phase shift AC signals. You are not a ham for sure, or else you had someone else take the test.


So at some point, this poppycock is going to stop, or we are going to either clean the thread, put a disclaimer on it of "this contains factual errors", or lock it down. Choice is yours.

[K7ABE]

I think the big difference between these A/C's and the inverter driven devices like the mini-split is:

1) Startup surge. With a typical induction motor you get a huge startup surge every time the compressor turns on, since induction motors try to come up to speed instantly. With an inverter drive you don't see a large surge since the motor is ramped up more slowly. This might mean that a 500 watt air conditioner needs a 1500 watt surge to start - and that all has to come from the house inverter. An inverter drive might only need 600 watts to come up to speed.

2) Cycling. A typical A/C, running under a moderate setting, might cycle on for 1 minute every 3 minutes to keep the room cool. So if your average power draw is 500 watts, it is taking 1500 watts while it is on and just a few watts when it is off to run its fan.

The above means that - even if the two A/C's are the same efficiency - the mini-split with the inverter drive will be a lot easier on the power system. In one you have to design for 1500 watt loads, in the other 600 watt loads.

An important note:
An inverter drive motor uses a _separate_ inverter to drive its own motor; this is not the house inverter. This is a detail of motor design, not a requirement. There is no reason that a window unit can't use an inverter drive, but none that I have seen do. Split systems, on the other hand, often do.

A high Farad capacitor from the automotive stereo industry Would handle the inrush for a 12 volt DC system. I am not aware of any capacitors for a 120 volt AC system that will handle that load.

[russ]

Google off grid air conditioner. About the third or fourth thing down was a Mother Earth News article that describes using an air conditioner that uses the water over the condenser for improved efficiency. Says pumps the water over the condenser but what I saw in mine was the fan splash the water up onto the condenser. And I believe the article said these little window units are about $100 each, 400W, & 5000BTU. Similar to the units I have.
Abe

Mother Earth News? I was unaware it contains anything worth reading.

[billvon]

Yes I replaced three of the old ACs with twists knobs with these units in the rentals. They use a couple hundred watts less, give you the same cooling, and run much quieter. Spending $100 for the new technology AC would save several hundred dollars in the solar panel and inverter needed to run the old technology,less efficient AC.
Abe

I think the big difference between these A/C's and the inverter driven devices like the mini-split is:

1) Startup surge. With a typical induction motor you get a huge startup surge every time the compressor turns on, since induction motors try to come up to speed instantly. With an inverter drive you don't see a large surge since the motor is ramped up more slowly. This might mean that a 500 watt air conditioner needs a 1500 watt surge to start - and that all has to come from the house inverter. An inverter drive might only need 600 watts to come up to speed.

2) Cycling. A typical A/C, running under a moderate setting, might cycle on for 1 minute every 3 minutes to keep the room cool. So if your average power draw is 500 watts, it is taking 1500 watts while it is on and just a few watts when it is off to run its fan.

The above means that - even if the two A/C's are the same efficiency - the mini-split with the inverter drive will be a lot easier on the power system. In one you have to design for 1500 watt loads, in the other 600 watt loads.

An important note:
An inverter drive motor uses a _separate_ inverter to drive its own motor; this is not the house inverter. This is a detail of motor design, not a requirement. There is no reason that a window unit can't use an inverter drive, but none that I have seen do. Split systems, on the other hand, often do.

[K7ABE]

Hmm. Every A/C I've seen in stores recently does this. It's pretty simple; just design the drip pan to drain towards the fan, then put the fan close to the surface of the drip pan.

Yes I replaced three of the old ACs with twists knobs with these units in the rentals. They use a couple hundred watts less, give you the same cooling, and run much quieter. Spending $100 for the new technology AC would save several hundred dollars in the solar panel and inverter needed to run the old technology,less efficient AC.
Abe

[billvon]

Google off grid air conditioner. About the third or fourth thing down was a Mother Earth News article that describes using an air conditioner that uses the water over the condenser for improved efficiency. Says pumps the water over the condenser but what I saw in mine was the fan splash the water up onto the condenser.

Hmm. Every A/C I've seen in stores recently does this. It's pretty simple; just design the drip pan to drain towards the fan, then put the fan close to the surface of the drip pan.

[paulcheung]

To the OP, when is these 5 to 7 hours operation time? during the day when sun is shining or in the dark night when you go sleep?

[K7ABE]

Hey Sunking, I really mean types of batteries not brands. I really have no knowledge at all about the subject, only that AGM is supposedly very good and low on maintenance.




Abe I've said this before, but I don't mind saying one more time. It's the individual components that I'd like to keep down in cost. For instance, a 24VDC 12,000 BTU air conditioner would be at least $1700.00 (<-- the only one I found with a price tag on it). Or a solar array professionally installed for $10k. A few batteries for a couple hundred each is not an extreme cost. The first question on this thread was is it viable to have a sustainable working system that won't break the bank when one of the individual components fail.

Google off grid air conditioner. About the third or fourth thing down was a Mother Earth News article that describes using an air conditioner that uses the water over the condenser for improved efficiency. Says pumps the water over the condenser but what I saw in mine was the fan splash the water up onto the condenser. And I believe the article said these little window units are about $100 each, 400W, & 5000BTU. Similar to the units I have.
Abe

[Mike90250]

A mini split (the variable speed models) have a poly-phase adjustable motor, so they can start slowly and do not have a "death spike" like a window shaker would. They can be set to low speed only and only consume a couple hundred watts instead of 1500 watts.

[billvon]

It's really kind of like this: First and foremost I don't want to install one because success of this experiment is contingent on low-priced components. Second, Wall construction to a home addition is not permenent, and if I find that I don't like the configuration or if I don't want to have to deal with solar panels anymore and decide to tie it all in to the grid electricity, or the city discovers that I have changed this once carport-converted storage room into a heated and cooled space without permits, then I can easily change it to make code.
With a permenent mini split system installed working exclusively on the solar system,,,well that is an extra layer of garbage I'd have to deal with when I do change it. A 600watt window unit is easily changed into a mini split later, but getting a mini split now leaves me with fewer options later, more headache later, higher start up cost, and thus a failed experiment.

Going with an inefficient window unit now will probably also result in a failed experiment one of two ways:
1) A cheap inverter + battery bank will have trouble starting the A/C, and won't last long, leading to expensive and frequent battery and A/C replacements
2) A good inverter + battery bank + solar panel capable of starting and running the less efficient unit will be quite expensive - likely more than the mini-split

By the way, you're like the third guy to praise the mini split. Unless I'm wrong, and I often am, I was under the impression that whole house mini split saves a bunch of energy compared to a ducted system, but it's not like it's over 50% better...right? Good but not great isn't enough to spend the extra $ on the components when I'm purposefully attempting to keep them low.

For solar, a good inverter driven mini split can be over 50% better. Lower starting surge means your inverter can be smaller (and hence more efficient overall.) Lower power requirements means cheaper battery bank and solar array.

And did I forget to mention that a mini split isn't attractive in your room? They stand out like sore thumbs in a room that is less than 11' wide. More so than window and through the wall units anyway.. The cool and new technology factor will wear off very quickly after looking at a bulky wall component for a few weeks.

Well, I guess you can choose a bulky sore thumb high up on a wall or a bulky sore thumb blocking a window. You'll pay a lot more for the bulky sore thumb blocking your window in the long run.

Of course you can do whatever you want. But in your first post it sounded like you were looking for advice on "a low cost solution (low cost build and maintenance) for a completely off-grid addition that I'm planning for my house." You're free to ignore the advice and proceed with what you want to do, we're just pointing out that there are better ways to do what you want to do that will increase your odds of (at least partial) success.

[K7ABE]

Hey Sunking, I really mean types of batteries not brands. I really have no knowledge at all about the subject, only that AGM is supposedly very good and low on maintenance.




Abe I've said this before, but I don't mind saying one more time. It's the individual components that I'd like to keep down in cost. For instance, a 24VDC 12,000 BTU air conditioner would be at least $1700.00 (<-- the only one I found with a price tag on it). Or a solar array professionally installed for $10k. A few batteries for a couple hundred each is not an extreme cost. The first question on this thread was is it viable to have a sustainable working system that won't break the bank when one of the individual components fail.

The weakest link I saw in your model was the inverter. Eliminate the charge controller the inverter and the batteries and put that money into an AC that would work directly off of the solar panels. There is at least one refrigerator company on the market that does not need an inverter a charge controller or batteries. it is designed to work during the day time directly from the solar panel and you are advise not to use a refrigerator in the evening or at night. It was four or five years ago when I priced that compressor at $1250. I did not check on the duty cycle to see if it would work for an air conditioner, I was investigating refrigeration.
Abe

[russ]

And did I forget to mention that a mini split isn't attractive in your room?
They stand out like sore thumbs in a room that is less than 11' wide. More so than window and through the wall units anyway.. The cool and new technology factor will wear off very quickly after looking at a bulky wall component for a few weeks.

Look at the various models available - some are quite OK. Your analysis is 100% off.

[PhillyTitan]

And did I forget to mention that a mini split isn't attractive in your room?
They stand out like sore thumbs in a room that is less than 11' wide. More so than window and through the wall units anyway.. The cool and new technology factor will wear off very quickly after looking at a bulky wall component for a few weeks.

[PhillyTitan]

You can hit all those goals except "inexpensive." Again, going to a very efficient A/C (a mini-split) will be the best first step in getting close to your goal.

The "DIY knowledge" is troubling, though. You can certainly DIY. But if you are worried about installing a mini-split - which after all comes with detailed instructions, mounting templates, on line support etc - then building the kind of solar system you describe is going to be ten times harder. There won't be any instructions or manuals or videos showing you exactly what to do, and you'll still have to do all the drilling, venting, pulling wire etc that either project entails.

Not worried about installing a mini-split. It wouldn't be easy but I have seen how to vids on YouTube and the difficulty is not that high.
It's really kind of like this: First and foremost I don't want to install one because success of this experiment is contingent on low-priced components. Second, Wall construction to a home addition is not permenent, and if I find that I don't like the configuration or if I don't want to have to deal with solar panels anymore and decide to tie it all in to the grid electricity, or the city discovers that I have changed this once carport-converted storage room into a heated and cooled space without permits, then I can easily change it to make code.
With a permenent mini split system installed working exclusively on the solar system,,,well that is an extra layer of garbage I'd have to deal with when I do change it. A 600watt window unit is easily changed into a mini split later, but getting a mini split now leaves me with fewer options later, more headache later, higher start up cost, and thus a failed experiment.

By the way, you're like the third guy to praise the mini split. Unless I'm wrong, and I often am, I was under the impression that whole house mini split saves a bunch of energy compared to a ducted system, but it's not like it's over 50% better...right? Good but not great isn't enough to spend the extra $ on the components when I'm purposefully attempting to keep them low.