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Old 05-17-2017, 11:24 PM
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Don't like propane? What kind of compressor would you use for ammonia? My old boss had one in the basement from the time before j.c. I rewired all the wiring and it cooled good and was ancient it only used 20% more ac current than the most efficient new frig.
Was it a vapor compression unit? I know ammonia used to be used as a refrigerant in old vapor compression units (yeah, around the time before j.c.). I don't know what kind of compressor, but ammonia is not compatible with copper.
Old 05-17-2017, 11:33 PM
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Originally Posted by Guntoteninfadel View Post
Actually they are 12v systems, or at least my carrier is. There is a great article on northern Arizona solar about converting them for a great efficiency increase while using solar.

The compressor and the fans all have "soft start" tech which also reduces loads by not requiring the initial bump to get going.

As far as the codes go, the units come with a manual that tells you what the numeric error codes mean. There is only so many things that can go wrong with the machine as they are hammer simple.
Thanks. I will check this out .
Old 05-18-2017, 02:45 AM
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KISS. (Keep it simple stupid.) Not directed at anyone.

Bury copper tubing in the ground on a bed of sand, and be sure to fill around the sides and tops with sand so that the tubing is completely protected from rocks or other objects that could puncture through.

Have it cycle through a box in your home, using a small DC pump, possibly a boat bilge pump or a pump for fish tanks or ponds.

In the box, install transmission coolers that the water can pass through before returning back to the ground.

Install a DC fan behind each transmission cooler. Have vents directing airflow in the desired direction. Run the pump and fans with solar power (very minimal power draw).

Add RV antifreeze to the water if you wish or if you live where winter temps are extreme and the frost Line is deep. By having fill caps installed at the high points in your system, you can add water/antifreeze as needed, or even siphon it empty for winter.

So the idea is the water/coolant circulates through the ground where temps are cooler. It then passes through the the transmission cooler(s) where it is further cooled by the fans blowing on them and forcing the air through the vents into the room. Once the coolant has made a complete cycle, it will return to the ground cooler due to the transmission coolers. Don't forget to vent behind the fan(s) so the cooling air in the room can return. Cooler air blowing on the transmission coolers will increase the efficiency as the system runs.

Transmission coolers and automotive fans can be found at any auto zone.

If you wanted, I suppose you could even insulate your tubing. If you have access to ice, on really hot days, you could have an insulated box for your tube to pass through, with ice packed around it.

Add a thermostat to switch the pump/fans off and on.

Keep some spare pumps and fans on hand as well as thermostats. These items will have minimum power draw compared to motors and other gizmos and all the parts are easy to obtain. Maintenance is also simple and minimal.
 
Old 05-18-2017, 09:25 AM
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Originally Posted by Goody View Post
Good, I want to see these systems drop in price. I do think it's just a matter of time. I look forward to a low cost DC window a/c unit. Now that would be awesome. You mentioned "your cost". What's the current cost for average folks including installation? Of course, in the off grid setting a power inverter is required. However, I understand these units have low starting amperage, is that right? So, a less expensive inverter should suffice. Do they require pure sine inverters?

You mentioned diagnostics on these units comparing it to modern automobiles. That's great, but average folks have to take their cars to a mechanic (muy pricey). One of the benefits of the kind of system I'm discussing is the ability for average folks to service the system. Really, that's the primary benefit.

NOTE: I'm pretty sure these units do not make use of 12v DC. Rather, I suspect the inverter is part of a variable frequency drive that allows for varying compressor motor speed. The DC voltage after the converter is likely much higher than 12v. I'm not sure, but I believe the system then uses pulse width modulation to control the speed of what is actually a brushless DC motor. Although, I speculate here. The ability to operate at lower cooling loads is perhaps the primary feature that increases efficiency. Basically, a lower mass flow rate of refrigerant lowers the head loss and condenser temperature, and both reduce compressor discharge pressure. However, the motors are more sophisticated (and more efficient as well).
I do installs for single-zone units depending on type of structure and access for $1800-2500, multi-zone units do run higher. Diagnostics on the Units are codes that read out on the inside unit when a fault occurs, all the codes are listed in the owners and/or installation manuals. I have installed several of these units in hunting cabins, that are totally off grid, most have generators but one runs completely on solar and wind.
For the diagnostics on your vehicle go to Harbor Freight, and get an OBD scanner they start at $50, or any of the major Parts stores will run the codes for free. The combination and a Chiltion's Manuals aligned with mechanical ability, most problems can be easily fixed on the cheap.
Old 05-18-2017, 12:05 PM
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Wouldn't it be easier to bury about 100 feet of pipe 3-4 feet down? Intake at one end, vent at the other into the home? Convection laws would draw the air cooled by the earth into the house as the heat rises out of the home. You could also use a solar fan with a switch to increase the air flow. There are various ways of controlling humidity.

BTW, I'm assuming this is a DIY project in the event something happens.
Do you really think 100' of pipe is going to provide significant cooling and air flow?

Rely on convection and you might get some coolish air out of the pipe, but not enough airflow to cool enough space to be worthwhile. Use a fan to get enough airflow and you lose most of the cooling.

Better to dig a cavern of several hundred thousand cubic feet to store air at ground temperature to use year round -- or to locate where one is already available.
Old 05-18-2017, 12:12 PM
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How much space are we attempting to cool with this system? Maybe a shed or 2 room space?
Old 05-18-2017, 12:31 PM
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Originally Posted by Cherokee Prepper View Post
So the idea is the water/coolant circulates through the ground where temps are cooler. It then passes through the the transmission cooler(s) where it is further cooled by the fans blowing on them and forcing the air through the vents into the room. Once the coolant has made a complete cycle, it will return to the ground cooler due to the transmission coolers. Don't forget to vent behind the fan(s) so the cooling air in the room can return. Cooler air blowing on the transmission coolers will increase the efficiency as the system runs.
You were doing fine until you demonstrated that you have no clue what a "transmission cooler" is or does.

In your application, the fluid flowing through the system would be WARMED by the transmission cooler, not cooled by it. (Unless, of course, the indoor temperature where you have located the transmission cooler is already lower than then ground temperature.

Bottom line: TANSTAAFL! It is possible to generate heat but it is NOT POSSIBLE to generate cold. The only way to cool some place is by transferring the heat to some other place nearby. THAT is what air conditioning does.

In your scheme, during summer the fluid would be in the pipe in the ground, at ground temperature (somewhat cooler than the air temperature), when you pump the fluid into the transmission cooler (which is just a radiator) the fluid would absorb heat from the radiator fins, thus bringing down the temperature of the radiator fins to nearly the temperature of the fluid; air being blown across the radiator fins would transfer some heat to the fins, thus cooling the air. Meanwhile the now-warmer fluid would be continuing its travel through the pipe where it would transfer some heat to the ground. During winter (when the ground temperature is warmer than the air temperature) the system would work exactly the same way to transfer heat from the ground to the inside air.

The difference between your scheme and a conventional "air conditioner" is that an air conditioner uses a compressor to add heat to the refrigerant before passing it through a radiator where it gives off some of that heat, THEN the heated refrigerant passes through an evaporator where it is decompressed, thus losing the heat that it got by being compressed, THEN the now-cooled refrigerant passes through another radiator where it absorbs heat thus cooling the fins which in turn absorb heat from the air. The compression/decompression parts of the cycle make the temperature swing much greater thus making the whole system more effective allowing it to achieve colder results, but the principle is the same and in any case the system only moves heat from one place to another. It does NOT create any cold.
Old 05-18-2017, 04:43 PM
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How much space are we attempting to cool with this system? Maybe a shed or 2 room space?
Assuming you're referring to the original post, I first considered it to cool a "tiny" solar powered house boat with living space of only about 150 square feet. So, the system I considered was limited to only 1/2 ton cooling at max output. Incidentally (just for interest), the energy to provide propulsion for the boat also is provided by photovoltaics via a DC drive motor on a large slow moving prop. I expect a 1/2 ton a/c unit to consume electricity at a rate of about 400 watts assuming a water cooled condenser. Placing an inexpensive PWM controller on the compressor motor would allow for operating at a reduced cooling rate (such as at night to reduce battery discharge), and a simple mechanical thermostat would actuate the rheostat for the controller. Although, it does not require a controller to function.

NOTE: This kind of system can show high cooling rates. Many are not aware that automotive compressors can push a lot of refrigerant. Most compressors are easily capable of supporting a 2 ton cooling rate. Also, the compressor can supply multiple evaporators which are sold separately.
Old 05-19-2017, 12:54 AM
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Originally Posted by xaunloc View Post
You were doing fine until you demonstrated that you have no clue what a "transmission cooler" is or does.

In your application, the fluid flowing through the system would be WARMED by the transmission cooler, not cooled by it. (Unless, of course, the indoor temperature where you have located the transmission cooler is already lower than then ground temperature.

Bottom line: TANSTAAFL! It is possible to generate heat but it is NOT POSSIBLE to generate cold. The only way to cool some place is by transferring the heat to some other place nearby. THAT is what air conditioning does.

In your scheme, during summer the fluid would be in the pipe in the ground, at ground temperature (somewhat cooler than the air temperature), when you pump the fluid into the transmission cooler (which is just a radiator) the fluid would absorb heat from the radiator fins, thus bringing down the temperature of the radiator fins to nearly the temperature of the fluid; air being blown across the radiator fins would transfer some heat to the fins, thus cooling the air. Meanwhile the now-warmer fluid would be continuing its travel through the pipe where it would transfer some heat to the ground. During winter (when the ground temperature is warmer than the air temperature) the system would work exactly the same way to transfer heat from the ground to the inside air.

The difference between your scheme and a conventional "air conditioner" is that an air conditioner uses a compressor to add heat to the refrigerant before passing it through a radiator where it gives off some of that heat, THEN the heated refrigerant passes through an evaporator where it is decompressed, thus losing the heat that it got by being compressed, THEN the now-cooled refrigerant passes through another radiator where it absorbs heat thus cooling the fins which in turn absorb heat from the air. The compression/decompression parts of the cycle make the temperature swing much greater thus making the whole system more effective allowing it to achieve colder results, but the principle is the same and in any case the system only moves heat from one place to another. It does NOT create any cold.
I didn't claim it would work the same or be as efficient as a power hungry air conditioner. Your 4th paragraph states that it would cool the air. That's the objective. Even if the fluid returns to the ground warmer, if your tubing is long enough, and your pump is slow enough, that heat will be dissipated by the time the fluid returns to the transmission cooler. As the room temperature gradually decreases, the system becomes more efficient. I suggested an ice box for hotter days, so that colder water will flow through the transmission coolers. The ice could alternatively be arranged so that the fans are drawing the cooler air from the ice and blowing across the transmission coolers.

If a blowing fan does not cool (remove heat), then why do people with no A/C often set up fans for relief?

I'm no authority on air conditioning, just throwing out ideas for off grid cooling. If you have to have a constant 69° all summer, buy a ton of solar panels and batteries, and an air conditioner.
Old 05-19-2017, 05:31 AM
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After going back and reading the past 3 pages.....

Here is my take.
The ideal of using an automotive AC system and running it off of D.C. Powered electric motors......won't work.
Why you might ask....well the automotive Ac compressor requires a lot of energy to operate. It is more than just a pump....it's a compressor. One of its main duties
You ever notice how it can pull down the RPMs of your engine when the compressor is operating?
Need I say more?....
The large electric motor....huge battery bank to run this electric motor.....and the large amount of solar panels to keep this huge battery bank charged...
So the thought of using an automotive type compressor.....powered by a 12v motor.... forget it

As for these other ideals I have been reading. Some need to study up on Refrigeration.
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Old 05-19-2017, 06:35 AM
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No, I have not built it. However, it is straightforward.
Are you kidding? Even a small AC unit needs around 3 horsepower. A DC motor to run it will run at maybe 2500 watts? 200 amps if hooked to 12 volts. AC is the last thing I'd be thinking about during a disaster - but. If I wanted to build an AC unit - I'd use a small gas engine to power an electric generator and use a 120 volt AC unit. The first AC in cars used its own gas engine to power it.
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Old 05-19-2017, 11:45 AM
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Are you kidding? Even a small AC unit needs around 3 horsepower. A DC motor to run it will run at maybe 2500 watts? 200 amps if hooked to 12 volts. AC is the last thing I'd be thinking about during a disaster - but. If I wanted to build an AC unit - I'd use a small gas engine to power an electric generator and use a 120 volt AC unit. The first AC in cars used its own gas engine to power it.
(Goodwrench, take note) No, I'm not kidding, ;-). Here's the problem with yours and Goodwrench's assessment: you did not do the math.

It's necessary to be more objective here. What is a "small" AC unit? The smallest readily available system is 5000 btu/hour. These consume electricity at a rate of about 500 watts. The motors are on the order of 70% efficient. So, the actual power requirement for this system is about 0.45 horsepower. Actually, the DC permanent magnet motors I have considered have similar efficiency. So, all else equal, the DC electricity consumption rate would be the same. However, as I mentioned before, designing the system oneself would allow for using larger heat exchangers and even water cooling the condenser, and this will increase efficiency dramatically by reducing the compressor discharge pressure.

Also, it's best to use at least 24v for anything beyond about 500 watts. Actually, for my application I considered a 24v motor rated at 15 amps (roughly 350 watts). This would provide a cooling rate on the order of about 5000 btu/hour with a water cooled condenser.

The thing to consider here is that the automotive compressor is, as Goodwrench noted, just a compressor. Hence, the power requirement is a function of both the differential pressure and the speed at which it's rotated. So, if you turn the compressor more slowly and you reduce the discharge pressure, then the power requirements fall in direct proportion.

The only possible problem I have considered with this approach is the ability for the TXV to properly meter the refrigerant at relatively low flow rates. If this proves to be problem, then a different TXV could be installed. However, I don't expect a problem.
Old 05-19-2017, 11:52 AM
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(Goodwrench, take note) you did not do the math.

The smallest readily available system is 5000 btu/hour. These consume electricity at a rate of about 500 watts.

I did not "fail" to do math here. I work as an electrician and do not find this complicated. I also have a 5000 BTU window unit. I have tested it and it runs at 1000 watts. not 500 watts. It starts with a surge of around 2600 watts.

A typical RV air-conditioner needs at least a 2500 watt generator to run it and that is only for a small 9-11K BTU unit.
Old 05-19-2017, 02:28 PM
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(Goodwrench, take note) No, I'm not kidding, ;-). Here's the problem with yours and Goodwrench's assessment: you did not do the math.

It's necessary to be more objective here. What is a "small" AC unit? The smallest readily available system is 5000 btu/hour. These consume electricity at a rate of about 500 watts. The motors are on the order of 70% efficient. So, the actual power requirement for this system is about 0.45 horsepower. Actually, the DC permanent magnet motors I have considered have similar efficiency. So, all else equal, the DC electricity consumption rate would be the same. However, as I mentioned before, designing the system oneself would allow for using larger heat exchangers and even water cooling the condenser, and this will increase efficiency dramatically by reducing the compressor discharge pressure.

Also, it's best to use at least 24v for anything beyond about 500 watts. Actually, for my application I considered a 24v motor rated at 15 amps (roughly 350 watts). This would provide a cooling rate on the order of 1/2 ton (6000 btu/hour) with a water cooled condenser.

The thing to consider here is that the automotive compressor is, as Goodwrench noted, just a compressor. Hence, the power requirement is a function of both the differential pressure and the speed at which it's rotated. So, if you turn the compressor more slowly and you reduce the discharge pressure, then the power requirements fall in direct proportion.

The only possible problem I have considered with this approach is the ability for the TXV to properly meter the refrigerant at relatively low flow rates. If this proves to be problem, then a different TXV could be installed. However, I don't expect a problem.
I don't need math to know your contraption will not work. I have decades of automotive AC experience to back that
Old 05-19-2017, 03:20 PM
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I did not "fail" to do math here. I work as an electrician and do not find this complicated. I also have a 5000 BTU window unit. I have tested it and it runs at 1000 watts. not 500 watts. It starts with a surge of around 2600 watts.

A typical RV air-conditioner needs at least a 2500 watt generator to run it and that is only for a small 9-11K BTU unit.
If your 5000 btu/hour rated window a/c unit is drawing 1000 watts electrical, then there is a serious problem. All such units draw between 450 and 600 watts. This is easily verifiable. Countless examples can be shown. It is not controversial and not up for debate. The starting surge is very high. However, I am considering only average running watts.

Next, yes, RV air conditioners generally need at least a 2500 watt generator to run it. This is required to supply the starting surge. Using a 2500 watt generator to power a 9-11K btu/hour air conditioning unit does not imply the unit consumes electricity at a rate of 2500 watts.
Old 05-19-2017, 04:02 PM
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IUsing a 2500 watt generator to power a 9-11K btu/hour air conditioning unit does not imply the unit consumes electricity at a rate of 2500 watts.
I was not trying to "imply" 2500 watts is need in normal running. Also - a 2500 watt generator can often surge to 3500 watts or more. 2500 is just the continuous rating.

The original post discusses doing this with solar. So - even a small 5000 BTU, if running all the time - is using a steady 600 watts (on average). To run AC for a 24 hour day - assuming the sun comes out - at least 3000 watts in solar-panels would be needed. And batteries? Assuming backup is wanted to at least get by for the low or no-sun part of the day? Need quite a bit.
Old 05-19-2017, 05:47 PM
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I was not trying to "imply" 2500 watts is need in normal running. Also - a 2500 watt generator can often surge to 3500 watts or more. 2500 is just the continuous rating.

The original post discusses doing this with solar. So - even a small 5000 BTU, if running all the time - is using a steady 600 watts (on average). To run AC for a 24 hour day - assuming the sun comes out - at least 3000 watts in solar-panels would be needed. And batteries? Assuming backup is wanted to at least get by for the low or no-sun part of the day? Need quite a bit.
Of course, the system would not be operated "all the time" at full output. Sure, running an a/c system on solar requires a substantial array. Panels can now be purchased at well under $1 per rated watt. So, a substantial array can be had for a reasonable price. Remember, we're talking about off grid here. If one desires a/c, then it's pretty much solar or petroleum. Solar is by far the less expensive alternative in the long run. Also, the setting I considered for this system is a small solar powered house boat. Hence, the condenser has access to cooling water that never drops below about 80F. This will increase efficiency dramatically. Hence, I actually expect on the order of 400 watts for a 1/2 ton unit. Now, the motor may be operated with a PWM controller to permit variable output. So, assuming the TXV operates properly at the lower outputs, then it could be operated for extended periods at night and at a lower output to lessen battery discharge rate. Running the system as an opportunity load while the array is producing will not present any difficulties at all. In fact, it's not uncommon for small window a/c units to be operated as opportunity loads on solar arrays in the off grid setting - and yes, they draw about 500-600 watts from the inverter when doing so. However, running it during other times will require intermittent operation and/or operation at a reduced output. Note I'm talking about a 150 s.f. living space here.

I'm not seriously considering the claim that "it will not work". That's asinine. Of course it will work. The only issue is the power requirements presented by you and Goodwrench.
Old 05-19-2017, 06:18 PM
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I don't need math to know your contraption will not work. I have decades of automotive AC experience to back that
Experience does not trump physics. Of course the system will work. In fact, that should not be a sincere concern. The only concern you have presented is the power requirements. Fundamentally the problem with your assessment is you tacitly assume that the compressor in this application must be operated at the same rate as in the automotive application. Of course, I consider operating at a much lower output. Second, you tacitly assume the efficiency of the system will be same as compared to the automotive setting. This is a false assumption. Don't take my word for it. What is the condenser differential pressure during normal operation in an automotive air conditioning system (normal operation, not while idling). You will see it is much higher as compared to residential a/c systems. Also, the TXV is set lower as compared to residential a/c systems. Of course, both of these adversely affect the efficiency of the system. This is done because these heat exchangers are relatively small for the high output called upon from the system. So, higher temperature differentials are necessary to achieve the required heat transfer rates. Now consider what would happen by aggressively cooling the condenser with river water and operating the compressor at a reduced output. You think the differential pressure across the compressor might drop precipitously? You think maybe the same mass flow rate of refrigerant could be supported with a lot less power?

The only problem might be the TXV. Will it operate normally at very low outputs? Is the setting perhaps too low for this application?
Old 05-20-2017, 04:47 AM
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Experience does not trump physics. Of course the system will work. In fact, that should not be a sincere concern. The only concern you have presented is the power requirements. Fundamentally the problem with your assessment is you tacitly assume that the compressor in this application must be operated at the same rate as in the automotive application. Of course, I consider operating at a much lower output. Second, you tacitly assume the efficiency of the system will be same as compared to the automotive setting. This is a false assumption. Don't take my word for it. What is the condenser differential pressure during normal operation in an automotive air conditioning system (normal operation, not while idling). You will see it is much higher as compared to residential a/c systems. Also, the TXV is set lower as compared to residential a/c systems. Of course, both of these adversely affect the efficiency of the system. This is done because these heat exchangers are relatively small for the high output called upon from the system. So, higher temperature differentials are necessary to achieve the required heat transfer rates. Now consider what would happen by aggressively cooling the condenser with river water and operating the compressor at a reduced output. You think the differential pressure across the compressor might drop precipitously? You think maybe the same mass flow rate of refrigerant could be supported with a lot less power?

The only problem might be the TXV. Will it operate normally at very low outputs? Is the setting perhaps too low for this application?
Yes experience and training out rank physics that you are stating. Theories and such are like ass holes...everyone has one.
Compressors in an automotive AC system have 2 jobs....
1. They draw the low side of the system down
2. They compress the low pressure low side gas into a high pressure high temperature gas and discharge it into the high side.

So regardless of all your yack yack.... they require a lot of energy from the engine or motor to start compressing and continue compressing. Have you ever noticed loss of fuel economy while using AC? It's because the compressor is taking a lot of power from the engine.
So before you start worrying about a thermostatic expansion valve.....and boring me to tears with all this other nonsense. You should think about how to operate that high energy robbing Automotive AC compressor
The design of an automotive Ac compressor is different from the design of a refrigerator or AC air conditioner

You state you want this on a boat.... unless it's an aircraft carrier...you won't have enough room for all the batteries and solar panels....and large D.C. motor that it will take to operate this compressor

Example....back when are cars had carbs. We had to use a dash pot solenoid to move the throttle plate off the idle position when the AC was turned on at idle...why? Because if not...the compressor would pull down the rpm of the engine. Sometimes on the smaller 4 cylinder engines...causing them to shut off

So before you go throwing your physics in front of my experience.... go test your so called physics. Build your contraption. Don't just talk about it on the internet. Build it.

Another thing.... all your talk about pressure differential at the condenser .. hmmm. You do know the job of the condenser is heat exchanger. We change a high pressure/ high temperature GAS to a high pressure Liquid by removing heat from the gas. Thus condensing it to a liquid. There is no concern about pressure differential...unless you have clogged cores in your condenser
Old 05-20-2017, 07:11 AM
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Of course, the system would not be operated "all the time" at full output. .
The incipient post here says nothing about actual size of area being cooled how well insulated, or what the ambient temps are. We get a few days a year here in N. MI when temps are high 90s. We use a 5000K window unit and it runs 100% full-time when on and does not cool our house all that much. One room feels pretty good where the window unit is mounted. So it is NOT strange at all for a small unit to run all the time.

iIf you are talking a boat? With 3000 watts in solar and maybe 600 lbs. in battery bank? What do you have - and air-craft carrier?

Note - I have two rural homes.. One on 5400 watts of grid-tie solar, and one on 2000 watts of off-grid. It is not as if I have no experience with solar power.
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