diy solar

diy solar

Central AC use at night in hot / humid climates

longhorn77

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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.
 
Good luck.
I suggest that you might want to consider a 6,000 BTU window unit in the bedroom, you are talking about some substantial investment in battery and inverters just to get that unit to start. At least 3x surge on startup.
 
Fellow Texan here.

I am on the same boat as OP, and keep getting the same answer: "buy a window AC". You guys don't realize the change in quality of life it represents for us to have central AC.

I actually did buy the 8kBTU Midea U Inverter unit. It is fantastically efficient on solar panels with my AC200P, but does not pass the wife test for permanent install. And it only works for one room. It got put it away for emergencies.

Panels, inverters and batteries are getting cheaper and better by the day. Why the resistance from the community? (you currently can buy 12kw inverter for $1-2k, $320/kwh LiFePO4-new, half that used. Free storage if you have an EV. $100 for .35kW used panels).

Yes the AC needs a ton of electrons to start, but it only starts a few times per hour. We have sun, roof real estate, space in the garage and dollars. Why the resistance to start the AC? we just need to channel the electrons that fall on the roof. Hard and soft starters seem like 1970s toys and don't really work to soften the blow. a capacitor? a Triac ? come on it is 2021, something better than that has to exist.

Is it really the case that nobody has solution at this point in time?
 
Fellow Texan here.

I am on the same boat as OP, and keep getting the same answer: "buy a window AC". You guys don't realize the change in quality of life it represents for us to have central AC.

I actually did buy the 8kBTU Midea U Inverter unit. It is fantastically efficient on solar panels with my AC200P, but does not pass the wife test for permanent install. And it only works for one room. It got put it away for emergencies.

Panels, inverters and batteries are getting cheaper and better by the day. Why the resistance from the community? (you currently can buy 12kw inverter for $1-2k, $320/kwh LiFePO4-new, half that used. Free storage if you have an EV. $100 for .35kW used panels).

Yes the AC needs a ton of electrons to start, but it only starts a few times per hour. We have sun, roof real estate, space in the garage and dollars. Why the resistance to start the AC? we just need to channel the electrons that fall on the roof. Hard and soft starters seem like 1970s toys and don't really work to soften the blow. a capacitor? a Triac ? come on it is 2021, something better than that has to exist.

Is it really the case that nobody has solution at this point in time?
i am using a window AC 6000btu from costco and its working fine on my 3000 growatt inverter with 600AH SLA battery 300AH useable with no issues and uses maybe 500 watt kwh max 700
 
You can do it, you just have to size accordingly. First, put an amp clamp on your AC and figure out how many actually amps it draws. You can guess or estimate, but it won't be accurate.

So I am in southern utah which is very dry unlike Texas. I can run my coleman 15000 btu AC overnight or to be more accurate, I can run my AC from the time the PV array stops producing electricity around 5 pm in the afternoon until the next morning when the sun comes up. My AC is about a 1.3 ton unit. In order to do what I do I have a 4000 watt PV array and four - 48V 103 amp hour batteries. I bought my batteries "off the shelf" from a known battery company. My batteries cost about $2,000 each for a total cost of approx $8000 dollars.

You are asking to do about 4X the amount of Air conditioning that I am doing. This is still just a rough estimate, becuase TX AC demand is different that UT AC demand. If you wanted me to just "throw something out there" for a battery estimate. I would say you need about 12 to 16 48V 100 amp hours of battery. So you are going to need to spend about 25K in batteries minimum. You will need about 4X the amount of PV that I have or 15000 to 20000 watts of PV.

The solution is going need to be much more thought through than my internet quarterbacking. But I would guess that a DIY system is going about 40-50K. Your cost may come down by building your own batteries etc..
 
i am using a window AC 6000btu from costco and its working fine on my 3000 growatt inverter with 600AH SLA battery 300AH useable with no issues and uses maybe 500 watt kwh max 700
thanks for your reply. I am seeing about the same numbers from the fancy midea inverter AC. what I like is that it doesn't do on/off control, rather it ramps up and down the rpm. Regargless, your numbers are on par with mine. 200w if the room is already cold, 800w when initially cooling it down.

For "fun" I did open the door to the room where it was installed, and the poor little thing tried to cool down the whole house (you can tell team entropy won). However it was fun to see the AC200P working through its paces, capturing sun wherever it could to keep the battery up. It was at 50% by sundown, which I think is remarkable keeping the AC going full blast for ~7 hours.
 
You can do it, you just have to size accordingly. First, put an amp clamp on your AC and figure out how many actually amps it draws. You can guess or estimate, but it won't be accurate.

So I am in southern utah which is very dry unlike Texas. I can run my coleman 15000 btu AC overnight or to be more accurate, I can run my AC from the time the PV array stops producing electricity around 5 pm in the afternoon until the next morning when the sun comes up. My AC is about a 1.3 ton unit. In order to do what I do I have a 4000 watt PV array and four - 48V 103 amp hour batteries. I bought my batteries "off the shelf" from a known battery company. My batteries cost about $2,000 each for a total cost of approx $8000 dollars.

You are asking to do about 4X the amount of Air conditioning that I am doing. This is still just a rough estimate, becuase TX AC demand is different that UT AC demand. If you wanted me to just "throw something out there" for a battery estimate. I would say you need about 12 to 16 48V 100 amp hours of battery. So you are going to need to spend about 25K in batteries minimum. You will need about 4X the amount of PV that I have or 15000 to 20000 watts of PV.

The solution is going need to be much more thought through than my internet quarterbacking. But I would guess that a DIY system is going about 40-50K. Your cost may come down by building your own batteries etc..
thanks for sharing your numbers. I do believe I need 4 times the starting capacity, but maybe not 4 times the storage. Newer houses are well-insulated to be able to keep energy consumption reasonable. (as OP calculated)

Here's food for thought. An entire Nissan Leaf can be had for $5K, 24kwh pack included. Say 10kwh of those are still usable, that'd probably do the trick even if you have to sip it out slowly. However, there's nothing out there that can start a powerful AC from an inverter, reasonably. (i.e. without 12 inverters)
 
Fellow Texan here.

I am on the same boat as OP, and keep getting the same answer: "buy a window AC". You guys don't realize the change in quality of life it represents for us to have central AC.

I actually did buy the 8kBTU Midea U Inverter unit. It is fantastically efficient on solar panels with my AC200P, but does not pass the wife test for permanent install. And it only works for one room. It got put it away for emergencies.

Panels, inverters and batteries are getting cheaper and better by the day. Why the resistance from the community? (you currently can buy 12kw inverter for $1-2k, $320/kwh LiFePO4-new, half that used. Free storage if you have an EV. $100 for .35kW used panels).

Yes the AC needs a ton of electrons to start, but it only starts a few times per hour. We have sun, roof real estate, space in the garage and dollars. Why the resistance to start the AC? we just need to channel the electrons that fall on the roof. Hard and soft starters seem like 1970s toys and don't really work to soften the blow. a capacitor? a Triac ? come on it is 2021, something better than that has to exist.

Is it really the case that nobody has solution at this point in time?
Technology has changed and we now have inverter condensing units that don't require hard start or soft start and have the surge in power requirements. These are found in high efficient mini splits.
 
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.
I'd install a mini split in the main rooms used and zone the cooling. Bedroom has it's own, living room/kitchen/dining area depending on layout get their own mini split evaporator and/or condenser. This allows different zones to run at different temps, plus you get the added benefit if higher SEER and inverter units.

I stayed with a friend at a house she owned in the Caymens and those 7 ton units ran all day, everyday. Just wild thinking about the watt meter spinning on just those and electricity isn't cheap there.
 
Technology has changed and we now have inverter condensing units that don't require hard start or soft start and have the surge in power requirements. These are found in high efficient mini splits.
I hear you. Minisplit systems are beautifully efficient. However, that's major renovation to install that around the house. wiring and electronics come easier than walls and paint to some of us.
 
hmmmmm 10kwh panel from santan solar with 1000AH of battery useable might work
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.
 
I hear you. Minisplit systems are beautifully efficient. However, that's major renovation to install that around the house. wiring and electronics come easier than walls and paint to some of us.
You have walls and lines require a small hole, then just a drain line.

Doesn't sound major to me. Condenser mounts easily outside.

I've done major, mini split install is not major.
 
thanks for sharing your numbers. I do believe I need 4 times the starting capacity, but maybe not 4 times the storage. Newer houses are well-insulated to be able to keep energy consumption reasonable. (as OP calculated)

Here's food for thought. An entire Nissan Leaf can be had for $5K, 24kwh pack included. Say 10kwh of those are still usable, that'd probably do the trick even if you have to sip it out slowly. However, there's nothing out there that can start a powerful AC from an inverter, reasonably. (i.e. without 12 inverters)
It’s a game of chess with 1000s of ways to win..
You can’t win until you play the game. 99% of new players underestimate their power consumption and cost. I got close on my third system but still would like more “buffer” with more panels and more batteries. Since you appear to be grid tied your under powered system can lean on the grid until you get it right. I am off grid so I can’t make those mistakes or I pay by being real hot in my bed at night:
 
It’s a game of chess with 1000s of ways to win..
You can’t win until you play the game.
amen. Well said.

what do you guys think are the chances of this vs a 5ton ACwith 134 LRA?

Sigineer Power Inverter Charger,18000W 48V DC to 120V 240V AC Pure Sine Wave,Split Phase,Low Frequency,54000W Surge,for Home,Off Grid Solar System https://www.amazon.com/dp/B093L3C9J...t_i_93M73TNRJ01C4NZCES3A?_encoding=UTF8&psc=1

I have searched the forum, but it appears to be a new product.
 
If you are keeping the grid connected to your home, you can utilize the grid for surges to start your 5ton A/c. That’s what I do. You would need a battery powered grid tie or hybrid inverter with grid tie mode.
My rough calculations for battery capacity for my 3.5ton A/c (1500sqft home) to be completely powered by batteries/solar 24/7 is 40kwh. But that’s if sun is shining. Clouds could mean I larger battery is needed. But A/c isn’t needed much in my area when it’s cloudy. That’s also if you safely only use roughly 28kwh of the battery so it last a decade or so. I live in west Tennessee which has kinda similar temps to Texas. I have 18.6kwh of 60v Chevy volt batteries. I use 11kwh of that. My battery in the summer gets to LVD every night between 2am to 4am. Maybe some of my rambling will help ya
 
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.

You can monitor your grid electricity usage in 15-minute intervals by making a free account at https://www.smartmetertexas.com

This website provides data from your meter. You can download the data for offline analysis.

You will conclude that in Houston it does not make financial sense to use solar instead of grid power.

Here is a snapshot of my data...

data.jpg
 
I only pay .10kwh in my area and it makes very good financial sense for me. ROI in 6 years then free electric
 
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.
Get yourself an Emoria Vue to monitor your power coming in to the house. I had the same questions, and the Emporia was VERY helpful in determining the draw of my two 3 ton trane units. Each unit draws around 2KW, with surge to 3KW when starting. I found both units never exceed 5KW. I am going to purchase a Micro-air easy start for each unit to see how much that helps. I have two LV6548's in split mode, so 13KW, which should be just fine. Batteries are another story. I have been waiting since Feb 14th for my other Lishen 280ah bank to show up from Michael's group buy. They have not left china yet. I do not feel comfortable running 5KW of AC on only 280ah. So I have 48 more cells coming.
 
thanks for sharing your numbers. I do believe I need 4 times the starting capacity, but maybe not 4 times the storage. Newer houses are well-insulated to be able to keep energy consumption reasonable. (as OP calculated)

Here's food for thought. An entire Nissan Leaf can be had for $5K, 24kwh pack included. Say 10kwh of those are still usable, that'd probably do the trick even if you have to sip it out slowly. However, there's nothing out there that can start a powerful AC from an inverter, reasonably. (i.e. without 12 inverters)

So lets look at the OPs consumption " In July I pulled 1951kw in total (63kw a day)."

63000 watts in one day, divide that by 24 hours and on avg he uses 2625 watts an hour. You are only going to make good solar power for about 5-6 hours best case. Lets say from 10 am to 4 pm. That is being very generous. But lets focus on the time that you don't make solar, from 5 pm to 9 am, that is 16 hours.

16 hours at 2625 = 42000 watt hours of battery. So now during the 6 hours you make PV power you need to cover your load 15,750 + recharge 42000 watts or a total 57,750. Your array would need to make about 10000 watts an hour over that 6 hours. Probably need a 15K watt array to cover it. You gave yourself Zero room for error or other loads and you have designed it for 1 day with no reserve. You get anything less than your 6 full hour of PV and you are short.

Best way would be to find someone in Texas who is doing it with real world experience on a house with 5 tons of AC. There is a youtuber called "Texas Off Grid Guy" who is a little rough with his methods and wiring, but he is doing something similar. He is up to about 60000w of batteries and only is running a couple of ductless split ACs, but he's doing it!

Will has a great video with a system that powers his shop with AC fully off the grid, Its a smaller building but its a good starting point to extrapolate your needs. At the end of the day I have found that overkill is your friend in the solar game.

My main residence is in Phoenix metro and is a single story 2000 sq ft ranch style home with a 5 ton Trane 14 seer AC. But i have a pool... and I used 94 kwh for July. I won't even try to run my AC on solar, but I may do some critical loads off grid style.
 
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.


4 HP motor power-factor.png
 
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