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1st time planning to power window ac unit (midea 8k btu U shaped ac)

S

Scrugs

New Member
Joined
Nov 27, 2023
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Location
Texas
Hi all, I am finally ready to start purchasing solar and want to start small. Then get the 18k inverter later. First project is to power a window ac unit, it is a midea U snapped ac unit (8k btu) specs are below. Your help in design and specifying the solar equipment would be much much appreciated. The initial though is to purchase mounting (Integra rack ir3o mounts), aptos 370 watt biracial panels, some type of inverter… , battery , and wire it all up to power the little unit.

I like to plan very well, before spending $ and making mistakes. all I ordered so far is the kuman kw47 power usage monitor ( $12 ) to see actual power consumption and to be able compare to attached data sheet specifications of the window unit.

Next steps, determine how many aptos 370 watt solar panels to purchase and how many integra rack or 30 mounts, wiring, battery and inverter to purchase.

Ideally these items would be able to be used with the eg4 18k ( once I am more comfortable with understanding solar, then I would go for a big system).
( so this is a requirement of the little project, design such that can use the same equipment for the big system or as much of it as can be used )

as I go along I will share what ever I learn here and track the progress of the project.

Your comments and review and experience and knowledge will be a large part of my training :)

Appreciate you and thank you in advance for help and ideas to move forward.

Chad S
 

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Here are some photos the midea 8k Btu window unit. I purchased it about 2 years ago. I assume the data sheet that I found today is still same or very close as I purchased the unit 2 years ago.
 

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I think the next step is to determine the power consumption and peak power consumption. Of course I am doing learn as you go.

Chad S
 
Update: I just purchased the power monitor and plugged in the AC unit, then set the AC unit for highest fan speed and coldest temperature setting. The power monitor (kill a watt ) reads: 410 watts, 115 volts, 4.9 amps,
The specifications state 710 watts, but I get 410 watts.

Before changing the settings, it was in auto mode and was reading in the 370s ; it did not break 400 watts in auto mode.
 
Options are endless man. That unit is so small and has a variable speed compressor so little to no surge. You mentioned an 18. That's crazy huge. Oversized inverters are usually a waste due to the standby power and lower efficiency when you don't utilize all of it.

Look into the eg4 6000xp's
you can expand them indefinitely and as long as you dont desire grid export, they're an awesome, more cost effective option than a 12k or 18k.

Three 6000xps rather than an 18 k gives you more $$ for batteries. Like I said, they're expandable so you can start with just one for now, and scale up as you need, both with solar and additional solar.

If you go this route:
Grab 7 or 8kw of solar so you can run two strings and max out the 6000xp and then double it for the next, and again and again, and so on.

This way you don't waste 6-800$ on a small AIO that you'll immediately grow out of the second you get more solar.

As for how many batteries, take your desired run time and your usage and do the simple calculation.

Get as many as you can afford while they're cheap and before more tarrifs get added.. 48v will keep you with current available tech and is the most efficient.

Stick to 16s batteries(51.2v) avoid 15s. They can't be mixed.

The server rack batteries are an amazing option because you can just keep growing, starting with as little as 1.

The power pro eg4 batteries are super cool too, and they mate right up to the 6000xp if that's more your jam. They're a bitch to move though. 300lb

Good luck, and great job wanting to do it right. You'll save lots of money by researching your head off for a few days. This forum is an invaluable resource
 
I would use the manufacturer specs to make sure you're covering when the compressor is running. Depends on temp, house efficiency, insulation, etc. Can make some assumptions, say the unit runs 12 hours a day @710 watts = 8.5 kWh. Assume the standard of 5 solar hours per day for the panels to absorb you need enough panels to cover 1.7kwh for 5 hours to make up the 8.5kwh (need 5 Aptos 370w panels). This also assume optimal sun conditions, no shading, no clouds.....ever. You will also need at least a 10kwh battery to store this power to run the AC outside of the 5 peak solar hours.

Knowing the weather is never optimal, I would double everything I said above if not more to run this AC.
 
Scrugs said:
The power monitor (kill a watt ) reads: 410 watts, 115 volts, 4.9 amps,
The specifications state 710 watts, but I get 410 watts.
Click to expand...

This is a fine starting point and enough for just this AC. Looking more broadly, here are some places to improve methodology.

Kill-a-watt does not analyze surge (though this appliance does not have it) like a clamp meter with surge measurement can, and it doesn’t show timeseries data like an Emporia Vue would. It also can’t handle 240V. Which Vue and Clamp meter can handle.

Scrugs said:
or no battery ?
Click to expand...
No battery requires more engineering prowess, you need to decide whether the cost savings of going from zero to one battery are worth the complexity.

Kind of a meme, but IMO in the U.S. successfully going batteryless with an inverter is more of a flex on how clever you are than a good cost savings measure.

Batteryless with a hybrid heat pump will raise the hackles of the forum faction that thinks it is silly to pay a premium for a hybrid and have solar panels that can only power the hybrid. Which is a ding against how much you can flex on people as a 🧠 DIYer or engineer
 
BTW I also like how you're proceeding in this project carefully and methodically.

The 6000XP and 18kpv question, I think is also determined by what level of code compliance you want to hit. For some reason it seems that a lot of Texas members are not that bothered with UL9540. Yet, I just looked on Upcodes for Texas residential code, and it has largely the same text for R328 as California does.

For grid tie system, you can also consider MidNite One (is promised to be 9540 compliant to same tier as 18kpv). This is an All-in-one.

For fancier off grid alternatives, you can look at Rosie, or Victron, these are modular inverter/chargers to which you would need to add a separate SCC. 6000XP will easily beat these in price/performance and while being in the same equivalence class wrt code compliance.
 
I'll add that going battery less and going without an interconnection agreement is a recipe for even more problems. With batteryless you need some kind of fallback power source, or a very large system.

The hybrid heat pumps can legally achieve this drawing from grid power without an interconnection agreement.
 
Agree with @zanydroid but check your local requirements. For my area in the U.S., a 6000xp works perfectly fine and is compliant with it's UL listing as we are not allowed to have an interconnect or sell back to the grid.
 
For the 6000xp, does it need to be mounted indoors ? I have an outdoor tool shed that could be insulated and place a window unit in it then use it to store the inverter and battery in it.
 
Scrugs said:
For the 6000xp, does it need to be mounted indoors ? I have an outdoor tool shed that could be insulated and place a window unit in it then use it to store the inverter and battery in it.
Click to expand...
It can't be installed outside in weather. Take a look at the spec sheet for run conditions (temp and humidity).
 
Actually, I was thinking to start small. I am not looking to purchase the 18k inverter now. I want to learn the basics on a small system to power the little 710 watt ac (actually around 410 watts) and maybe one or two other small consumers ( I have the ego lawn equipment with batteries so possibly charge those….but needs evaluation and not a requirement, just if it made since).

To start for me would look like:

An inverter something like 1200 watts + or - ( small one )
Minimum panels ( to match the small inverter capacity )
a lifepo4 battery ( I need to learn about these, at times second hand batteries are available )
 
Scrugs said:
Actually, I was thinking to start small. I am not looking to purchase the 18k inverter now. I want to learn the basics on a small system to power the little 710 watt ac (actually around 410 watts) and maybe one or two other small consumers ( I have the ego lawn equipment with batteries so possibly charge those….but needs evaluation and not a requirement, just if it made since).

To start for me would look like:

An inverter something like 1200 watts + or - ( small one )
Minimum panels ( to match the small inverter capacity )
a lifepo4 battery ( I need to learn about these, at times second hand batteries are available )
Click to expand...
Again, if you want to run that AC, I would look at what I typed in comment #7 above as the bare minimum, you can choose the inverter based on what your power needs are but you need a good amount of panels and battery to run that AirCon all day. I would rely on manufacture specs rather than those kill-a-watt devices.

I would start with:
  • 10 panels: ~$2,000
  • Battery: ~$3,000
  • Inverter: ~$1500
 
Look at MPP3048LV.
48v, 3k watts.
www.watts247.com

I use a pair of them in split phase configuration to power most lights, residential fridge, freezer, mini fridge, two computers, two televisions, Network gear, 9k BTU window unit, coffee maker, microwave, toaster oven. Pellet stove in winter.
I feed them grid AC so if my battery gets too low they automatically switch over to grid. Also, if I overload one of them they switch over to grid.
The only issue I have is trying to make heat with two devices simultaneously in the kitchen.
Let the microwave finish before turning on the toaster oven. And all it does is flip to grid bypass for the time when both appliances are on.
No power co. agreement.
5.9k of used panels connected.
Flawless for over 2 years.
 
110 panels
ChrisG said:
Again, if you want to run that AC, I would look at what I typed in comment #7 above as the bare minimum, you can choose the inverter based on what your power needs are but you need a good amount of panels and battery to run that AirCon all day. I would rely on manufacture specs rather than those kill-a-watt devices.

I would start with:
  • 10 panels: ~$2,000
Click to expand...


10 400 w / 375 w panels should be about a grand maybe 1200 if you have to pay for shipping
 
Keep in mind with the window AC that there's a pretty high start up current. So even though it may say ~700W it's likely to be more like 2K+ startup watts. Trust me I know. I just tried to run a 1200w inverter with a small 5K BTU window unit and by its self it wouldn't power in due to the inrush current. I had to install a custom switch with an Inrush current Limiter resistor which works perfectly, but the entire unit is all manual...So I have to start it up and shut it down myself... So make sure you get a big enough inverter to power the inrush. I'd guess at least a 2K, probably more like 3K would be good. If you want, get a fluke amp clamp and measure inrush current. That will be a good guide to what inverter size you need. And I wouldn't trust any surge wattage from any inverter, just go based on the max continuous rating.

Another thing to keep in mind is that AC head pressure changes based on temperatures.... so if its a SUPER hot day out, the head pressure will be higher since the hot side won't be as efficient dumping excess heat.... For instance, my AC unit draws about 510W when its 100F outside...but when its 80F out it only uses 400W... pretty big difference. If its 74F out, it's only pulling 350W so it varies.
 
matttelz said:
Keep in mind with the window AC that there's a pretty high start up current. So even though it may say ~700W it's likely to be more like 2K+ startup watts. Trust me I know. I just tried to run a 1200w inverter with a small 5K BTU window unit and by its self it wouldn't power in due to the inrush current. I had to install a custom switch with an Inrush current Limiter resistor which works perfectly, but the entire unit is all manual...So I have to start it up and shut it down myself... So make sure you get a big enough inverter to power the inrush. I'd guess at least a 2K, probably more like 3K would be good. If you want, get a fluke amp clamp and measure inrush current. That will be a good guide to what inverter size you need. And I wouldn't trust any surge wattage from any inverter, just go based on the max continuous rating.

Another thing to keep in mind is that AC head pressure changes based on temperatures.... so if its a SUPER hot day out, the head pressure will be higher since the hot side won't be as efficient dumping excess heat.... For instance, my AC unit draws about 510W when its 100F outside...but when its 80F out it only uses 400W... pretty big difference. If its 74F out, it's only pulling 350W so it varies.
Click to expand...
The Midea has a variable speed compressor and fans. It has no startup surge. I have the 12K, and it is running off of my solar system.
 
That is interesting about the midea; I did not know that it does not have the start up surge.
 
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