Move whole-house AC or get a window AC unit?

[inowhavesolar]

My wife and I are having this debate on which would be better for keeping the house cool, and keeping electricity bill low. There are 2 options:

1. Purchase a high-efficiency window AC unit (12000+ BTU), and place it in the living room. Solar+battery will keep this running 24/7, blowing cold air into the room, which will slowly make its way throughout the house, lowering the house temp, thereby making the whole-house AC not needing to run. Pros: Powered 100% by solar. Keeps main AC from running. Cons: Visually unappealing window unit in main living space (ie: looks "cheap"). Cold air might not permeate to far edge rooms the house.
2. Move 50A AC breaker to critical loads panel. Perfectly sunny days should make 5-6K watts from panels, which will offset running the AC. (Sticker on the compressor unit says 35A running load x 240v = 8400W). The battery will supplement the remaining watts, which charges from grid once it drops below 30% SOC. Pros: Whole house AC. No unsightly window unit. Cons: Solar+Battery might only give 1-3 cycles of "solar powered AC" per day. The AC will probably cycle 15-20 times a day during 99F+ summer months.

I've got an EG4 18K + EG4 WallMount Pro (280Ah). Has anyone done this cost comparison? I'm in favor of option 1, while she likes option 2.

 

[Dinobot248]

Need more details like Kids? Size of house? Location? Daily keg usage?



For me, using portable ACs is by far , more efficient than central air. 3500w run the central air for the whole house along with many areas that I don’t need to cool. The portable AC cools the immediate area and takes 200 - 1000w based on weather (Ohio).

In terms of cost and effort, so much easier to spend $400 to get a portable AC and install in 1 hour. If you don’t like it, easy to change your mind and go with your plan B, c, etc.

 

[Ampster]

(Sticker on the compressor unit says 35A running load x 240v = 8400W).

That is a lot of power and I understand why you want to find a solution. I don't have specifics, but just a general sense that most window A/C units are not very efficient. There are some very efficient small minisplit systems from Mr Cool and others that might be able to be located more conveniently and get closer to your goal of energy efficiency. Look at Seer ratings to be sure. Many of those units are inverter driven which is one of the reasons they are so much more efficient compared to a window unit. They can modulate power versus the on off cycling that a window unit has to do.

 

[inowhavesolar]

Need more details like Kids? Size of house? Location? Daily keg usage?

Yes, kids (why does that detail matter?). 2400sqft. Hot/humid south.

 

[shopman]

The window unit will not work the way you're envisioning it. You have to take into account many things like heat load from windows, doors, insulation etc. as well as how many heat producing bodies are in the house. All of that will consume what you think is going to freely float around your home. Perform a manual J calculation to identify just how many BTU you need to cool your space and come back to reality.

 

[Bluedog225]

I put a window shaker in my master bedroom. I run it all day. It spreads around and keeps the house tolerably cool and the bedroom frosty. Turn it off at night and enjoy the chill.

 

[Brucey]

I have a two ton central air unit, 1300 sqft ranch. Very well insulated. Adding an 8000btu lg inverter window unit into sons room to offset some of the central AC use. if it works well I'll get a second for the living room and won't need the central at all. Will use the furnace fan on circulate to help move the air around.

 

[wpns]

Another vote for mini-split(s) where required. Much more efficient, quieter, and aesthetically appealing.

 

[sunshine_eggo]

Yes, kids (why does that detail matter?). 2400sqft. Hot/humid south.

It's rare that kids are conservative in their power use or are even aware that things like open doors and fridges left ajar are actually a bad thing.

Getting adults to behave responsibly is challenging enough. Kids are nearly impossible.

In those conditions, I wouldn't expect 1 ton of supplemental A/C to make a huge difference.

Even so, I'm seriously considering getting the 2 ton PV/AC hybrid minisplit to offset my 5 ton unit.

A good approximation of average power use is the BTU/h rating / SEER, e.g., 48000/14 = 3429W. If you can find an EER rating, the same relationship applies, but the power usage will be higher and a little more conservative.

 

[Ampster]

Will use the furnace fan on circulate to help move the air around

I have a similar situation with an abandoned FAU unit. I have used the fan to circulate and filter air when we have had local air quality issues with fires. My return air duct runs in the attic and I would have to insulate it if i were to use it to circulate cool air. Not a big issue and probably more efficient to replace the duct work with insulated flexible duct of a smaller diameter anyway. For that purpose I don't need the volume and could run a much more efficient smaller in duct variable speed fan.

 

[Brucey]

I have a similar situation with an abandoned FAU unit. I have used the fan to circulate and filter air when we have had local air quality issues with fires. My return air duct runs in the attic and I would have to insulate it if i were to use it to circulate cool air. Not a big issue and probably more efficient to replace the duct work with insulated flexible duct of a smaller diameter anyway. For that purpose I don't need the volume and could run a much more efficient smaller in duct variable speed fan.

Yeah my ducts are in the basement so no worries about insulation.

 

[robbob2112]

A window unit in one room won't do squat except in that room unless there is a fan blowing the cool air into another room.

I would suggest an audit with a FLIR camera to find all the air leaks and hot spots and seal them off. Gives you a reason to buy a cheap one, or you may be able to check one out of the library. Amazing how much heat/cold you loose from leaks.

Then add an extra layer or three of insulation in the attic and even under the floor between joists if you aren't on a slab. If your walls have insufficient insulation in them you have someone come and add more.

Then I would power the AC from your panels and if there isn't enough power from the panels to run the AC you add more panels. Or consider an upgrade to your AC if the outside unit is under 15 SEER.

 

[timselectric]

I'm adding mini splits around the house. And doing away with the 4 ton central.

 

[OffGridInTheCity]

I'm adding mini splits around the house. And doing away with the 4 ton central.

I was going to say... I'd add a mini-split instead of a window AC. Heat pump technology is generally more effecient (less power needed) for AC than a traditional compressor type AC. Plus you get heat as well.

 

[timselectric]

The other benefit to multiple units is zone control.
They only work as hard as they need to for the current needs of the area they serve.
In other words, if there's nobody in the room, that unit is just idling.

 

[sunshine_eggo]

We did an add on where we increased the size of our house by nearly 800 sq-ft. Essentially added three bedrooms and a bathroom. Unfortunately, the HVAC distribution is a bit off, and I've not been able to get it so that the whole house is uniform...

Had to fight hard to not buy 3X of the Midea "U" shaped 1 ton inverter window units when Costco had them for $275 each...

 

[Brucey]

We did an add on where we increased the size of our house by nearly 800 sq-ft. Essentially added three bedrooms and a bathroom. Unfortunately, the HVAC distribution is a bit off, and I've not been able to get it so that the whole house is uniform...

Had to fight hard to not buy 3X of the Midea "U" shaped 1 ton inverter window units when Costco had them for $275 each...

Just start with one and go from there. 3 tons for 800 sqft seems like a lot.

 

[Brucey]

I did notice the Midea non u inverter units also have a heat pump mode that's good to 41F? Could come in handy for shoulder seasons in the fall and spring before it drops below that

 

[sunshine_eggo]

Just start with one and go from there. 3 tons for 800 sqft seems like a lot.

Completely. We have three hot spots in the added-on parts, so one would just help one area.

I should have had the HVAC distribution plenum re-done right rather than being a cheap bastard...

 

[time2roll]

I had the central air and gas furnace combo removed from the closet. Installed a heat pump. Four ton compressor moved to the other side of the house so the compressor would not be near the bedrooms. Two air handlers in the attic. One has two zones including the office and the main living area. Second has three zones so each bedroom is controlled separate. Five thermostats. Each room or area can be cooled (or heated) separately as needed or OFF. DW gained a closet

System is magical. Good luck on your journey.