Central AC use at night in hot / humid climates

[mesquito_creek]

Depends on model type.

Normal regular air conditioner with single speed compressor and thermostat with 1 or 2 degs C hysteresis will cycle less at night.
A 5 ton unit for 2500 sq ft house is on the overkill side unless your house is poorly insulated. 14 SEER is okay but still a little below typical more modern average of 15.

Typically thermostat works on temp with no regards for humidity.
Too high a btu unit for house area can cause temp to drop quickly and cycle off quickly with longer off period. This usually leaves house feeling like a damp cool cave. A/C only removes humidity when it is running when inside evaporator coils are cold and sweating water it condenses from inside air.

It takes much greater btu's to extract humidity from inside air then just cooling air around 50-60% relative humidity.
It is common for on to off duty cycle to get better at night as difference between outside and inside temp is less.

Some thermostats allow user to adjust the temp hysteresis to force a tighter temp control and decrease cycling period.

Power consumed when running is roughly 850-900 watts per ton (12,000 btu's), So 5 ton would be about 4400 watts (about 5 hp electric motor in compressor). Power factor is typically about 0.86 but changes based on compressor mechanical load. Around 15-16 amps at 240vac.

Max compessor load occurs for high outside temp, high inside temp, and high inside humidity. A typical condition if turning on A/C at 5 pm when you get home. Motor load can drop greater then 50% of maximum after inside temp and humidity is brought down. AC current does not drop so much because motor power factor decreases as mechanical low is reduced on compressor motor.

I have 4 ton central I run from two old series connected SW5548plus inverters. My central has Copeland scroll compressor which has a startup surge about as bad as you can get. I use a Micro-air EasyStart 348 cap boost/soft starter which gets the factory stock compressor startup surge from 200 amps @ 240vac down to 77 amps @ 240vac. Since poorer power factor results in greater inverter and cabling loss I use to 75 uF shunt cap for some PF correction improvement.


View attachment 58326

most importantly… how big is you pv array and how much battery?

 

[Charlie Woods]

I only pay .10kwh in my area and it makes very good financial sense for me. ROI in 6 years then free electric

The less you pay for grid power, the less viable solar becomes.

 

[Sanwizard]

The less you pay for grid power, the less viable solar becomes.

Until the grid goes down. That is the reason I dont like grid tie. Grid free is better.

 

[Zwy]

The less you pay for grid power, the less viable solar becomes.

True, however grid power is only going up in price from here.

That much I can guarantee.

 

[Charlie Woods]

True, however grid power is only going up in price from here.

That much I can guarantee.

There are no guarantees.

15 years ago I invested in downtown real estate near train stations and bio-Diesel because I could guarantee Peak Oil would make long-distance commuting from the suburbs impossible.

My suburban neighbors now commute to their office jobs in Ford F-350 duallys. I was very wrong.

 

[Cheap 4-life]

The less you pay for grid power, the less viable solar becomes.

Yes but even at only .10cents I still have a fast ROI.

 

[tglozano]

I have a 5 ton 14 SEER central AC system cooling my 1 story reasonably well insulated 2,600sqft house. I’m trying to determine in the Houston summer how much power my ac draws per hour to see if my potential battery backup will be sufficient to keep the AC going overnight.

How much does an AC typically run (utilization) at night in a humid climate at a 77-78 temp setting 50%? 33%? I know the wattage of my AC is 4,2xx but that is on for the full hour.

I cant see back far enough on my power company to see where I was in term of hourly power draw in 2020. In July I pulled 1951kw in total (63kw a day).

appreciate any insight as this is the gating issue to determining battery sizing.

what about combining a micro wind turbine? I know it might look hideous, but I've seen some 5ft wide and can do estimated 1600 watts for $1,100 as a complete kit.

 

[Zwy]

There are no guarantees.

15 years ago I invested in downtown real estate near train stations and bio-Diesel because I could guarantee Peak Oil would make long-distance commuting from the suburbs impossible.

My suburban neighbors now commute to their office jobs in Ford F-350 duallys. I was very wrong.

It's guaranteed here in the US as they shut down coal and are now shutting down nuclear.

Meanwhile they are spending hundreds of millions for wind farms ( I live right in the middle of this) and attempting to replace the nuclear power with solar (again, right in my area). And the 2 coal plants in my area shut down after DOE told them they had to have new scrubbers installed that would take 100 years to get paid off.

If you think that will come at no increased cost to the retail customer, I have a bridge to sell you.

 

[Cheap 4-life]

I agree. They are putting up solar farms in my area. They already have a few. What I pay per kWh isn’t going to go down

 

[Sanwizard]

Idealist stupidity in the face of reality. Like texas wind farms. Nuke baby!

 

[RCinFLA]

most importantly… how big is you pv array and how much battery?

For all night central A/C, I consume 250-350 AH's of battery capacity on 48v system. About double that for daytime. Roughly 35-40 kWH per day for hottest part of summer (in S. Florida, 92-94 degs F, 85% R.H) which is hurricane season. With rest of house, requires about 10 kW PV array to keep up, 40 panels. Then there is 15kW gen to make up any shortfall. 1500 AH 48v battery array.

 

[mesquito_creek]

For all night central A/C, I consume 250-350 AH's of battery capacity on 48v system. About double that for daytime. Roughly 35-40 kWH per day for hottest part of summer (in S. Florida, 92-94 degs F, 85% R.H) which is hurricane season. With rest of house, requires about 10 kW PV array to keep up, 40 panels. Then there is 15kW gen to make up any shortfall. 1500 AH 48v battery array.

Very cool… your real world example is pretty close to what I had guessed it would take in my earlier conversations! Thanks for the info.

 

[Charlie Woods]

It's guaranteed here in the US as they shut down coal and are now shutting down nuclear.

Again, there are no guarantees. That's my point. Just because things are trending in a certain way, it's not guaranteed that trend will continue.

In 1983 my high school teachers told me the Soviet Union would eventually take over Central America.

In 1993 I stocked up on exotic (at the time) AR-15's and 5.56 because it seemed like AR-15's would be outlawed eventually. Now they are common.

In 1995 I taught AIDS awareness classes to Healthcare Workers where I was required to show a slide from CDC stating that by the year 2000 70% of the population would be HIV positive.

 

[RickP]

Another Texan here, right off the Gulf Coast where humidity is omnipresent. I use solar for some smaller applications (running a fridge and an upright freezer) just to get some use out of my emergency solar setup built in 2020. I spent the last 3+ decades before a recent retirement in municipal government, in regular contact with contractors in my area. No one is running central AC units off non-grid-tie solar here.

Were it financially feasible, it would be out there. It can be done, no doubt. But it’s not being done, and there are some intelligent folks out there building homes, subdivisions, and commercials facilities. They have the money for up front costs, and the patience to recoup investment, yet… nothing. That tells me solar isn’t a fit for it yet, probably because having three or more days of autonomous power for a system that needs to run even when it rains for a week requires more PV and storage than is worth it. Most people don’t want a roof full of panels and a garage full of batteries just to avoid the AC part of their electric bill.

A room? Sure. A couple of rooms on mini-splits? Probably still squeezes into a cost vs return analysis on the positive side. Whole house requiring 5T and up? The mind says it can be done, the calculator and all the proof you can find on the ground says no. Or at least not yet.

Prove me wrong and you’ll be the next Elon Musk in Texas.

 

[curiouscarbon]

1) Pay for big battery and keep existing inefficient AC

2) Pay for more efficient AC and buy smaller battery

option #2 seems obviously more economically sound to me. i’m not in texas and don’t deal with oppressive humidity much. just seems a little silly to try and power through with such an inefficient unit. no offense intended. i’m trying to make off grid AC work too. step number one for me is reduce consumption up front by installing 30 SEER or close.

i’ve been using a midea U 8000 btu/hr unit for cooling and dehumidification for about a year and it’s never gonna cool an entire home, but it sure does pull the water out of the air.

if i wanted to scale up to 5T home, i would seriously look into install zoned mini split or multiple mini split.

Solar is Off Site Nuclear!

 

[Sanwizard]

For all night central A/C, I consume 250-350 AH's of battery capacity on 48v system. About double that for daytime. Roughly 35-40 kWH per day for hottest part of summer (in S. Florida, 92-94 degs F, 85% R.H) which is hurricane season. With rest of house, requires about 10 kW PV array to keep up, 40 panels. Then there is 15kW gen to make up any shortfall. 1500 AH 48v battery array.

Would love to see your setup! Are you using Lifepo4 or traditional batteries? Which inverters?

 

[Sanwizard]

Again, there are no guarantees. That's my point. Just because things are trending in a certain way, it's not guaranteed that trend will continue.

In 1983 my high school teachers told me the Soviet Union would eventually take over Central America.

In 1993 I stocked up on exotic (at the time) AR-15's and 5.56 because it seemed like AR-15's would be outlawed eventually. Now they are common.

In 1995 I taught AIDS awareness classes to Healthcare Workers where I was required to show a slide from CDC stating that by the year 2000 70% of the population would be HIV positive.

Yeah.. the "Experts" predictions. And according to Al Gore, NYC was supposed to be underwater by now.

An expert opinion is the same as a wild guess by you or me.

 

[Hedges]

what about combining a micro wind turbine? I know it might look hideous, but I've seen some 5ft wide and can do estimated 1600 watts for $1,100 as a complete kit.

"Estimated", that is the problem.
Actual output will be far less.
And for $1100 won't last long in wind that has it putting out much power.

Daytime, PV is quite effective, and economical if used continuously for years.
If house could be made comfortable and then coast through the night on good insulation, that would be best. But I don't live in that sort of place and maybe 24/7 AC is the only way to go.

 

[Zwy]

I had run across this video some time ago and this discussion made me think of it again. Yes, it will dehumidify the air, one would need to install a drain pan under the heat exchanger (radiator). As long as the ground temp is at that area around the 55F mark, this would actually work. Interesting idea.

 

[Supervstech]

I have a better idea for you...
Lower your ac load in the house to only need 3 tons of ac...
Seriously.
Describe the house.
Attic is a HUGE heat gain to the home, pull the roof off, and install insulation on the deck, set light color metal roofing on top, install full depth rockwool in the rafters, get the attic sealed, and bring it into the conditioned space environment.
Walls... 4" ? Pull the sheetrock, fir out the studs get 6" and vapor seal, then rockwool packed.
Crawlspace? Or basement? Get it air sealed.
All exhaust fans fed through an hrv... install dehumidification with ear exchange ventilation built in...
Then toss the 5 ton unit, install two units, one for the south side of the house one for the north.
Get 2 tons inverter driven unit on the south, 2 tons inverter driven north side... redundancy, and load balancing, and easy start loading.