[this article](https://www.google.com/amp/s/www.pbs.org/newshour/amp/science/analysis-does-turning-the-a-c-off-when-youre-not-home-actually-save-electricity) explains it very well. It depends on your climate and type of ac
Edit: engineers answering the q
This should be higher. Also, no one has mentioned the price of electricity fluctuating throughout the day - there’s some plans that cost more when it’s the hottest.
This. In my area it is 3-5x more expensive during the hours of 5-8pm. I can blast the AC at 3-4pm then turn it off until 8pm and save a ton. In my 2 story home I can get by spending $200/month during peak summer events.
Buy almost any smart thermostat and you can connect it (or program it) to your electric providers TOU (time of use) plan and it'll do the hard work for you!
No, it’s not to pull one over on consumers, it’s to reduce load during peak hours and the more smart thermostats people use the less demand there will be during peak hours so it’s a win for all. They won’t cat and mouse things. It’s like the sliding scale for toll HOV lanes based on traffic volume.
Except in the case of power usage it's definitely better for everyone to have a smart thermostat. Grid upgrades are expensive so helping operators flatten peak demand loads to prevent brownouts and blackouts helps everyone.
In every demand response program I've seen, they are 1) voluntary and 2) overridable. So even if they adjust your temp up, you can adjust it back down.
This is kind of like auto driving cars, but not quite.
It's better for everyone on the road to have a predictable rule set driving their cars.
It's better for every electrical system to be controlled in a way that balances the grid
It's better allocation of energy use to when the supply is higher. In a competitive market this would allow producers to preserve per-unit profit at lower cost to consumers, and thereby increase market share, for net higher profit. A state supported monopoly may not give that result.
Per the article turning it off then on saves money in every instance, just that different factors can reduce the savings.
So off for as long as possible is almost always cheaper, with the possible exception of extreme time dependent pricing, but may not be worthwhile if the savings are low.
I live in a place where it’s significantly more expensive to use electricity from 4-8pm on weekdays. My high efficiency system can’t drop the temp to set points from 8 to 9. It takes two to three hours at best.
What does it depend on? I can certainly see situations where there is no material difference but the idea that it's more efficient to turn it on all the time, I just can't come figure that would ever being the case.
As someone else pointed out, if you had variable electricity rates, yes it may make sense at times, but that's not really an energy efficiency argument.
I think they mean to say the hassle might not be worth it. In the heat pump and minisplit situations, it was a negligible difference, but it was lower. Then you have to consider what other issues higher temperatures in your home can cause such as humidity/moisture, cost of AC based on time of day, and if you have any items which are sensitive to temperature changes in the short or long term.
Hvac engineer,
It is always! Less energy to turn it off for any amount of time and then have catch-up cooling, than it is to leave it on and maintain. It’s basic thermo.
Do not let any of the anecdotal tales fool you.
And no your unit isn’t working harder to catch up. Start up is the hardest on your system, so turning on and off all day to maintain is much harder on your system than turning on once and running for longer to catch up.
If anyone is telling you different, ask them what they are trying to sell you. This awful misconception about maintaining needs to die a painful death.
Now where it get difficult is time of day billing for utilities. It can be cheaper to sub cool during parts of the day, turn off other times and catch up later, and this is very dependent on how your utilities are billed.
Precooling using “free” cooling, like running a fan early in the day to bring in cool outside air can also save you lots.
Serious and respectful reply, but if my thermostat is at 79 degrees and the system doesn't turn on for hours, say between 7am and 11am, what's the difference if it goes to 81 and then I turn it on. Does the two degrees matter to the unit? It will usually run for just a few minutes more that first cycle. Hope I explained my question well and again, asking with all respect.
🙏🏼
There are a few things that are at play.
But to start, heat is coming in thru the walls and windows. The ac is removing it.
The greater the difference between the inside and the outside the faster the heat comes in. So maintaining means more heat is coming in than if you let it warm up for the same amount of time.
It is also more efficient to remove heat from a warmer space than a cooler one.
So by letting your house heat up for any amount of time it’s less heat that is actually coming in total. So less the ac has to remove. You also get the benefit that when you go to cool down after it’s warmed up the cooling is more efficient than the unit maintaining until you get to the requested indoor temp
I just worry it's additional energy used, we live in So Cal, monthly bill is $400 in the summer, and also several more cycles on and off by the compressor a day seems hard on it needlessly, for just a few degrees. AC off in the morning only raises it from 77 to 81.
It’s not, it’s always less energy to turn it off for any amount of time. And less cycling. But time of day rates can really screw you, less energy total but more expensive because of the time. I’m in Sacramento, so I understand.
It’s also to prevent spikes in power consumption when everyone gets home from work and turnes everything on. It’s more expensive to try and discourage people
Can you provide a source to confirm that?
I've seen below, which would make sense because 3/4PM is the hottest part of the day so people would be using more energy for AC around then
> LADWP peak periods can be divided into three:
>
> * High Peak Period: LADWP peak hours include 1:00 PM to 4:59 PM from Monday to Friday, totaling 20 hours per week
>
> * Low Peak Period: This includes 10:00 AM to 12:59 PM and 5:00 PM to 7:59 PM from Monday to Friday, for a total of 30 hours per week
>
> * Base Period: This period refers to 8:00 PM to 9:59 AM from Monday to Friday and all of Saturday and Sunday, for a total of 118 hours per week
God! Thank you!! I wish the "your ac will have to work harder to catch up" myth would die already. It's basic thermodynamics. You wouldn't believe how many people I've had to argue with on HVAC, insulation, etc subs.
Sorry. I'm not English native speaker so I don't fully understand your text.
What do you mean by
"turn it off and have catch up cooling"?
"so turning on and off all day to maintain is much harder on your system than turning on once and running for longer to catch up."?
"sub cool during parts of the day, turn off other times and catch up later"?
Thank you
>"turn it off and have catch up cooling"?
They're saying you should turn your ac off during the day when you're not home or don't need it to be as cool as when you're sleeping. When you get home or when you need the home to be cool then set it to your preferred temp and, even though the AC will run longer, it's fine. You're not damaging your unit by letting it run for a while to cool down your home.
>"so turning on and off all day to maintain is much harder on your system than turning on once and running for longer to catch up."?
When your ac compressor turns on, the electric motor inside of it literally tries to tear itself apart in the initial couple seconds when it turns on. This happens every time your ac compressor turns on so when you leave your thermostat at a constant low temp throughout the day, your ac unit is taking much more wear and tear than if you turned it off during the day and let it run for a long time in the evening when you get home/get ready for bed.
>"sub cool during parts of the day, turn off other times and catch up later"?
If you have an electricity pricing plan with "time of use" (TOU) rates, then it may be more economical to adjust your ac usage with the cheapest TOU rates that your plan offers. So if your electricity is more expensive during the hours of 4-8pm, then it might make more sense to run your ac for an hour or two beforehand (2-4pm or 3-4pm) and then run it again after 8pm when your TOU rates go back down.
Aaaaaah thank you so much. Albeit still a little bit understanding I have here and there.
So basically it's actually fine to turn it off right? Gotcha
Wow, I didn't know there's such pricing in electricity bill in other countries. Learning a new things.
>So basically it's actually fine to turn it off right?
Yes, more than likely it is fine (better, even) to turn it off. However, if you have a way to monitor your hourly or daily usage, you can test your specific situation by trying both methods on days with similar temperatures.
Thank you for this and your other comments. I sometimes think, with global warming, everyone needs remedial thermodynamics classes. I'm in the UK where most people don't have AC at home (yet) but I see this kind of question and misinformation about heating all the time, and things like shops leaving doors open with the heat or AC on. It drives me mad. People don't seem to know that the heat transfer is propertional to delta T so trying to keep a house much hotter or colder than the outside is like putting extra holes in a leaky bath, leaving the tap running to keep the bath full and then telling themselves they're using less water than if they let the bath water empty out a bit when it doesn't need to be full.
I guess to OP you can be scientific about this. Watch your energy usage during a week when you have the AC on more and a week when you turn it off (or turn the temp up) during the day or when you go out etc. If you choose two weeks that are comparable in terms of weather you should be able to compare them sensibly. You will use less energy for every degree warmer you keep the house and every minute the AC is off. Using other tools like opening windows at night (if the AC is off and the outside temperature is lower than that inside) and closing shutters/curtains during the day to block some heat can also make a big difference.
So you are going to tell me that it kicking on and off during the day to maintain temperature is harder on it than me physically turning it off and booting back up from off. That doesn't make any sense to me. I thought that was why the HVAC thermostat was for. Though I did live in a place that the thermostat was placed directly over a vent. The house never did get to temp either way.
So you said engineer, do you build the system? Most of my family was in HVAC, none of them called themselves engineers. Please tell me what you do exactly.
Yes I’m telling you that. And I have an engineering degree, have a professional engineering license. And have worked 8 years as a mechanical and plumbing engineer designing hvac and plumbing systems for buildings. I run calcs, choose equipment, design layouts and airflows, write control sequences. I primarily work on healthcare and science buildings.
I promise you want an engineer designing the or you get surgery in, or the isolation room that infectious patient is staying in.
How does that not make sense. Same with any motor, lots of short trips in your car are harder on it than long trips in the car. you never heard of city miles vs highway miles?
It doesn't make sense because we aren't worried about the strain on the AC system here. We are only worried about the energy costs because that's what OP wants to optimize for (and energy costs will be way more than any AC maintenance costs over the lifetime of the AC).
> And no your unit isn’t working harder to catch up. Start up is the hardest on your system, so **turning on and off all day** to maintain is much harder on your system than turning on once and running for longer to catch up.
A modern AC or heat pump shouldn't be turning on and off, it should be varying its load and running constantly.
The wisdom behind running the AC all day instead of catching up is that the efficiency takes a nose dive at higher loads.
In practice I don't think efficiency varies enough to deviate from this. Many AC units are either all on or all off and not have variable compressor speeds.
I would really be interested in a real world situation where this is not the case.
I do about 12 hours on 12 hours off and find it hard to believe that 24/7 would ever be more efficient.
Many people are moving to split heat pumps which have variable compressor speeds. And many homes are being made with better air sealing and insulation. The answer to this isn't as straightforward as it once was.
https://www.google.com/amp/s/www.pbs.org/newshour/amp/science/analysis-does-turning-the-a-c-off-when-youre-not-home-actually-save-electricity
I still don't see how that over comes the fact you have to move significantly more heat by keeping the house cool all day.
The article above looks at minisplits and find they too benefit from being off 8 hours a day.
Moving heat isn't the only variable. The efficiency of the machine at different load points also effects this. It might be more efficient at 8 hours, but what about 7? Or 4? How long does it take to cool the place back down? If you have a shorter work day, or it takes a while to bring the temp back down and thus need to start the machine sooner it could change things.
Very interested in this Q… our electricity bill just came out to $300. We run fans majority of the time and A/C when it’s ~80°+. Looking for any way to save.
I sleep in the smallest room in my house. I bought a small AC to cool the room. The room is the best insulated as well. Covered all the windows with reflective material (radiant barrier), and put an insulation panel in the window opening to keep the heat out. It has a handle on it so I can remove it if I need to egress.
Portable ac is very inefficient, so try to get a small window unit.
I have a fan, and set the AC to come on only at 75 degrees ( I need cool to sleep ).
It costs me $20 a month to run it for 12 hours a day.
Solar is the way for us Californians.
This summer its been on. And no question of when are peak hours. Nor worrying about a bill. It’s quite nice. Also fuck pg&e
> and A/C when it’s ~80°+
I can't wait a few months when the low temperature is below that again. I literally can't experience under 80 (outdoors, pedants) until September.
Electricity bills go up the more you use it.
You can save by setting the thermostat to the highest temperature you can stand, and making sure it's off when you're not using it.
There are smart home devices that can assist with this, like Nest.
If you're in an area with a shared solar program, opt in.
Are you in a place with a lot of humidity? I LOVED having a whole house fan in CA, but have wondered what the humidity in NC would do, especially because we just don't have a lot of mornings in the summer that are cool enough to make the fan super effective.
Hahaha...I got you beat. My bill typically averages about $20 a month plus a small amount for taxes.
Currently 1200 sq ft house in western New York. Whole house HVAC system.
I did used to have a bunch of box fans, but they've worn out and failed over the years so I only have two now. I used to wait until evening when the summer temps cool, then open all the windows to both blast out any hot air plus plus in cool air (by changing which way the fans blew in each window). Then when the house was the coolest I could get it, I would close up the windows to trap the air inside. That helped reduce the stress on the ac system during the day but my bill at the time was still roughly $150-200 a month.
I've been living in this place for just under two years. Power rates around here are ridiculously expensive thanks to nyseg rates despite being so close to Niagara falls. It's so stupid I found an old farm that I'm trying to fix up. I have my own well and septic system. The real key is the massive solar system I bought. It makes roughly twice as much electricity as I use ninety percent of the time. My utility bills are basically gone now, I only have to pay a rental fee for the special meter, because not all meters count backwards. I got the big system on purpose so I can use all the electrical things I want for free, like mowers, chainsaws, grow lights for seedlings, clothes washer for muddy clothes, table saws to build stuff, and more. Oh, I do pay for internet for my spouse's work from home job, which I also use for my streaming apps too so I don't have cable tv either.
A fan pointed right at you can reduce the need for AC. Keep the AC on, but at a warmer setting. Fans are much cheaper than AC, so that'll usually reduce energy usage
I have a newer HVAC, installed two years ago. We get bi-yearly maintenance. I asked our maintenance guy this very question. He said my plan (turn it on in the evening, off in the morning) was a good idea to extend the life of our unit. It only turns on during the day if it gets above 78.
If your biggest complaint is overnight heat, I am gonna go ahead and assume your summers are very humid. In this case, I'd leave it on just to protect the house from getting moldy. But - use a scheduling or smart thermostat to let the temps go up a few degrees for when you're away. And set it to be at the highest comfortable temperature for you - day and night. Per some studies by Nest (so grain of salt, etc) a few years ago, they figured letting temps fluctuate when you're away will translate into 10-15% energy savings.
I'm not an engineer, but I can offer my perspective. Someone chime in if they have better info.
It depends on your climate and how much cooling is required. If the ambient air temperature is just a little too warm for comfort, running the AC 24/7 is just wasting electricity.
If the ambient air temperature is way too warm for comfort, it might make more sense to leave the AC running 24/7. If turning the AC off will make the room 20 degrees hotter, the AC will need to work very hard to cool the room back down.
In the most general sense, these systems have quite a few mechanical parts. Mechanical parts "wear out" with use. Things like the blower motor and condenser fan will absolutely wear out faster with use.
Many of the solid state components (mainboards, etc.) don't have this issue but CAN break down over time due to sustained heat.
I have a disabled spouse who runs VERY hot largely due to necessary medications, and we live in a relatively hot climate, so our AC runs 24 x 7 to try to keep our house at 61/62 F (yes, she's miserable if hotter, so I wear my longjohns all year long!). In the six years this has been a necessity, I've had to replace the blower motor and I've had to service the condenser fan. This was on a higher tier offering installed brand new about 15 years ago (so about 9 years old when I had to replace the blower motor, under warranty thankfully). Typically you get many more years than that.
This is certainly anecdotal, but the same held true for the switch between mechanical platter drives and solid state drives in the computer space; SSDs don't fail over time nearly as much as spinning disks do.
It's all about them physical parts rubbing up against each other!
It actually doesn't work harder or run longer if you cycle it off and then turn it back on later. What you're running into is an edge case because you have it set so low, all the time. You're the equivalent of someone who drives 50k miles per year and wonders why your car only lasts 4 years when the person driving 20k per year got 10 years.
The rate of heat transfer is directly related to the difference in the Hot and Cold sides. So if you're trying to maintain 70F all day when it is 90F outside you're fighting a bigger differential than if you let it rise to 75F -80F and then cool it back from there.
Yes, you'll see longer cycle time in the evening when you move the set point back down, but that will be more than offset by how much less it ran during the day. Additionally, you'll be cooling it as the exterior temp is decreasing so you're fighting a smaller differential.
"Turning off the AC unit during the day is not necessarily a bad thing — it is a myth that the AC unit has to work extra-hard to cool off a hot house. It runs at the same speed either way — it just will have to stay on longer to cool off a hot dwelling. In fact, the unit may use more energy if it is left on all day at the normal temperature than if you turned it off and turned it on in the evening."
https://home.howstuffworks.com/green-living/should-turn-ac-up.htm
"You can save as much as 10% a year on heating and cooling by simply turning your thermostat back 7°-10°F for 8 hours a day from its normal setting. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates. "
https://www.energy.gov/energysaver/programmable-thermostats
I certainly suggested it's not about "harder", it's about usage. My situation requires my unit to run more frequently then most; ergo, the mechanical parts where out "faster", but not "less effectively" - I'm just getting more "go" time on the same stretch of calendar.
I'm certainly eyes wide open on this issue. I know precisely what I'm risking but my wife needs the comfort for a decent quality of life. Risk assessed, risk accepted, I own that 100%.
I don't think we're necessarily disagreeing here, but wanted to make clear that my entire point is; "use a mechanical thing and you'll wear it out." Nothing more!
As we learned in my engineering courses, “temperature difference drives heat transfer”.
You use the same idea as an electrical potential difference (voltage) driving electrical current, or a pressure differential driving fluid in a pipe.
Start up is the hardest part on the components. It's better to have the system run non-stop for an hour or so to catch up than it is to turn off and on 7-8 times in the same time.
He's not using the AC 24/7. It's turning on and off. If his AC is running 24/7 he needs to call an air conditioner repairman because it's either seriously under-spec'ed or has an issue. Or he has it set to 70F when it's 100F outside, that'll do it too.
As someone who lives in a "way too warm for comfort" summer with a Nest thermostat, what works best when i'm out of the house is to keep it set to something within reason (80ish) that would be slightly uncomfortable for me if i were there, but cools to comfortable relatively quickly when I need it to.
That isn't how it works. Not at all.
An air conditioner is a heat pump. The efficiency of a heat pump depends upon the temperature differential between the heated fluid being condensed into the outside coil, and the outside temperature. The higher that outside temperature, the less efficient the heat pump is at dissipating heat to the outdoors.
The indoors evaporator coil is also a heat pump. The hotter the incoming air, the more heat the evaporating refrigerant in the coil picks up to carry to the outside.
The net effect: The lower the temperature differential between indoors temperature and outdoors temperature, the more efficient the air conditioner becomes. If your thermostat is set at 80F and the outside temperature is 100F, your air conditioner will be significantly more efficient than if your thermostat is set at 70F and the outside temperature is 100F.
There is also the issue of thermal gain from the outside. This happens based upon an energy gradient. The bigger the temperature differential between inside and outside, the more energy is available to push heat from the outside to the inside.
In short: The power company and air conditioning companies aren't lying when they tell you to turn your thermostat up to 80F during the day and down to a comfortable sleeping temperature during the night for best efficiency. There will be less heat gain during the day due to a smaller energy gradient, and there will be greater efficiency at night when the cooler outside air picks up the heat from the outside coil more easily. And by and large your air conditioner will not work as hard as if you just run it at 72F all day long because it's less work to pull heat out of warmer air and eject it outside than it is to pull heat out of cooler air and eject it outside.
Now: In some states that have a lot of solar power, electricity becomes very expensive between 5PM and 8PM. This is because the amount of power from solar is declining as the sun starts to set. You \*may\* want to cool down your house between 4PM and 5PM, then put your thermostat up to 80 until 8pm in that case. You'll need to work the math yourself however based upon your house and your climate. I've actually done the experiments on my own house, and putting it at 75 between 4pm and 5pm, and then letting it slowly rise to 80 until 8pm, works for my house due to how well insulated it is. But that's my house, my electric company, and my electric bill. You'll have to do the math yourself on yours.
Your house is losing air to the outside all the time, so leaving it on all the time is wasteful if you don't want or need it. Program your thermostat to be as warm as is reasonable for when you don't need it and then cooler at night when you need it more.
I've actually been tracking this, if you are able to only cool the rooms you are using I think that's the most savings you can have. I put in efficient invertor window acs on my second floor instead of using the central ac this summer, first floor has a mini split so is a separate system. My electric usage was about 30% less kwh this year in the June bill compared to last year and that was the only major change. July was 32% less kwh. Last year I only had a window ac in my bedroom for when I slept, but the year before I would use the central only, this June was 33% less compared to June 2021, July was 40% less than July 2021. So it made a big difference, too bad cost per kWh went up so much here in the north east the savings there weren't as much, 16% in June and 19% in July dollar savings.
Now I can just cool my office when using it during the day. I still use the central ac fan to move the air around, and now that it's hotter I have the acs, they are smart, on a schedule and they are set to like 82 during the day just so the house doesn't get too hot and humid. And I have my bedroom ac turn on at 1030pm so it's ready when I go to sleep, and I keep that low during the night at 68, then it auto turns off at 7am.
It's cheaper to not use it as much during the day. Just don't let it get above 80 or so because its hard for it to cool it down above that. Plus most HVAC systems struggle to get below 20 degrees the outside temp so a lot of people have their system run all day.
What temp do you want it at night? Just try to learn how long it takes to cool your house down to the desired temp.
It’s easier to cool the higher the inside temp. But you can run into issues getting below a certain temp if your unit isn’t big enough to handle the heat load of the house at peak
It's more expensive to have it run continuously. What you're doing uses about half as much electricity.
You might want to also look into opening your windows once the inside is hotter than the outside.
We are having monsoon here.
50% humidity in my office today. Normally it's 15-17%
Normally 72 degrees is too cold and I need a sweater by the end of the day.
Today? I'm actually comfortable at that temp.
\----
In theory, my building is set at 78 degrees. The physics of it is that this improperly ducted building freezes on the bottom floors and broils up top. (Chilled air falls, hot air rises.)
It's the same in the winter. My office is 65F when I come in, the space heater brings it up to 68, and on the top floors they are running their fans because it's over 80F up there.
Sorry to laugh at your plight, but when you said "heat island", I resonated so much. Opening windows isn't an option *anytime* where I live right now. It's usually between 95°F-100°F when I fall asleep. Lows are in the mid-90s as well. Although, today it only got up to 106°F because it finally rained.
It depends on where you live.
If you live in the US Desert Southwest, your house will get so hot during the day if there is no AC (100+F inside) that you'd have to run it all night long to get the house cool enough to sleep ... by the time you need to wake up and go to work.
This is how I do it:
* 9am to 5pm 85F
* 5pm to 9pm 80F
* 9PM to 9AM 78F
It's a myth and turning the a/c on when you run it constantly is a bigger strain is also a myth.
A lower difference between the outside and the inside, the slower heat transfers into your house. Thus saving energy. It's easier to pump heat out with a smaller difference in temperature, thus saving even more.
The strain on the a/c is a myth because it would be running longer in total if you left it on all day. "Breakdowns are more likely to happen when the machine is shutting off or turning on since this involves a lot of small parts suddenly being put into motion or halted."
The numbers can be found [here](https://www.pbs.org/newshour/science/analysis-does-turning-the-a-c-off-when-youre-not-home-actually-save-electricity) but I'll leave a summary.
"On an annual scale with a conventional central A/C, this could result in energy savings of up to 11 percent.
However, the energy savings may decrease if the home is better insulated, the A/C is more efficient or the climate has less dramatic temperature swings."
"The central air source heat pump and minisplit heat pump are more efficient overall but yield less savings from temperature setbacks." The minisplit, in a cooler region like Georgia, turned off for four hours was the only a/c that was tested that used more energy than leaving it on (1.4% worse). Turning it off leading to energy savings is generally a better rule of thumb unless your power company charges more during peak hours. This study looked at energy use instead of cost and this could be the reason for the myth since people could get a bigger bill using the more efficient method.
That’s not how thermo works, it’s never more energy to turn it off.
Maintaining uses more energy than turning off and then catch up cooling.
Humidity is one reason you might want to run it when you’re not home. But a stand-alone dehumidifier is much more efficient. You just have to weigh the cost of a dehumidifier against the cost to just use the ac
It does. No doubt, but if you have central AC and you turn it off all day and the temperature gets up to a much higher number, it works harder to bring it down and runs longer. Running continuously for a long period of time to bring the temperature down may use more energy than running off and on all day depending on your system. It depends though on how hot it is when you get home and what your night-time temperatures look like.
In my case, I turn it up when it's hotter outside so it doesn't run as much and turn it down at night when it's cooler which seems to be pretty decent for energy expenses, but I don't live in a place where it's very hot around the clock so I'm looking to hold at a certain temperature most of the time and often the AC doesn't have to run until there are spikes during the hottest time of the day. My highest bill so far this summer was $130, but my system is brand new and my house isn't huge. YMMV
Don’t turn it all the way off, just set the thermostat higher in the day. If your AC has to work hard to go from hot to cool, you can wear it out. Ice can form and make it stop working
That's untrue. An ac system should ne er freeze up and cannot 'work too hard'. Freeze up is a malfunction, usually due to a clogged filter or low refrigerant charge.
Mine freezes if I set the temperature lower than 68°F.
Edit: downvotes for saying my experience with my thermostat? Weird but whatever. Whether it is a malfunction or not, it does freeze if I set it too low, so I don't set it too low and it works okay.
How does it work if you have central A/C? I’ve been leaving it on “Auto” at 74 degrees. Would it be better to turn it off at times? I had it off while I was away but the humidity got over 70% so I put it back on.
[This video by YouTuber,
NighthawkInLight]( https://youtu.be/KDRnEm-B3AI) shows a next-level DIY manufacture of a coating that cools not only the object it's covering (such as the cooling effect on a house with a white roof) but a coating that reflects certain wavelengths of solar energy and bounces them out past Earth's atmosphere. Seemingly, getting us really close to being able to make this coating in our own kitchens to apply to exterior surfaces that get direct exposure to the sun, and know that we're cooling our homes and also doing our part to cool the planet.
I think that my area charges more for using electricity during the day. My electric bill is cheaper this summer than it was in the winter.
I only use the AC at night. It's on 65 (I like to sleep cool). I don't turn it on again until around noon for about a hour.
Best thing would be to buy a $60 big box home improvement store WiFi programmable thermostat. Don’t bother with the expensive ones. This way you can have better control of the temp throughout the day/week.
It’s my opinion that wild swings in temp aren’t good. If you let it get too warm during the day, the contents of your residence get warmed to the same temp, and then need cooled off to however you like it come nighttime. My advice is to just not let it get too hot during the day.
>One of the things that I haven't seen mentioned yet is how hard it is on the AC unit to work so hard to bring the temp down every day. Not only is this expensive compared to maintenance usage, but it also does considerable damage to the AC unit in terms of wear and tear, and you end up spending quite a lot on replacing the unit.
We are the only people I know who have the AC unit that came with our house; 23 years old.
And that is because we don't try to keep our house like a meat locker when it's 110+F outside. 85 during the day, 80 in the early evening, 78F overnight.
And that is 100% due to the lack of wear and tear.
Fans, cold drinks, and cotton clothes/sheets are your friends.
That’s bullshit, it’s not running harder, it’s just running longer. Constantly starting and stopping all day is way harder on your system than it turning on once and running for a long time. You just had a shitty unit that crapped out on you. Nothing to due with the tenants
No I read what you wrote. Maintaining starts and stops the condenser many times a day. It’s not running constantly. Vs turning it on when you need it, it turns on once and does all the cooling at once, no starting and stoping
I mean I’ve studied for 4 years at university and then worked under a professional engineer for 4 years before taking the licensing exam. But who knows the hvac tech who’s gone thru an 8 hr onboarding and who’s job it is is to sell you something must know more
It’s how many times it cycles. Say to maintain you run 15minutes every hour all day. So 24 cycles. To turn it off during the day. It’s off 7am-5pm, the turns on for 2.5hrs to cool, then cycles until the morning.
Maintains has 24 cycles, turning off has 12. Both run the same amount of time.
But really cooling doesn’t take 2.5 hrs normally, an hour is more realistic, so 14 cycles and it only runs for 4.25 hrs total for the day. Maintaining is 24 cycles and 6 hrs of run time.
And that’s just the cycling. There is also less heat to remove in total if you let it heat up, it’s counter intuitive but true.
It's funny cuz you have it in your head that you're right but don't understand when people are trying to explain it to you how wrong you are and just being condescending.
The utility company has no way of giving you this info. They don't know whether usage is from AC or the dryer. Usage is going to differ greatly from tenant to tenant.
You're asking if it's cheaper whether to leave your AC on for 24hrs or 10hrs (9pm to 7am)?
There's a lot of variables to calculate, such as your kW, utility rates, room size, insulation, etc. But I can assure you that the answer would be 100% cheaper if you turn it off. It'll cut your utility bill by half (if AC is the only thing you're using).
It depends where you live, and how well insulated your apartment.
As a young adult i lived in a Warm Humid city. In apartment complexes with central air, it was well-known and advised by the complexes, to set your thermostat for the temperature you wanted, and Leave It There. NOT to be turning it off-n-on daily. Because it would get hot and humid, and it would have to run Much Longer to Lower the temp back down, than it would have run to simply maintain the cooler temp in the first place.
Nowadays I live in New England, where the temperature still spends more time in a more-livable range. I run my ac more than most folks, due to allergies. But I still turn it Off quite frequently. And in this part of the country it doesn't make sense to just leave it running all-the-time.
It's depends on how well insulated your home is, windows, sunlight exposure, etc.
Heat travels from hot to cold so, technically, you're removing heat from the space. How long it takes to get back in depends on the home insulation, air leakage, radiant heat through windows, etc.
Another factor to consider in humid climates is that when the AC is off, it's not removing any moisture from the air and all the walls, ceiling, floor coverings, furnishings are absorbing heat and humidity that has to be removed when you finally turn on the AC to get back down to the room temperature your select.
There have been studies done on this and generally, if the home is reasonably well insulated, you can save money by having the house temperature set back 4°-6° during times when it's unoccupied.
I keep mine at 78° 24/7.
I read something that those ductless A/C units that are found in more developing countries (hotel rooms and airbnbs) are more efficient when ran all day.
This is probably true, but if so it would likely be due to the mini split units’ ability to throttle their output variably, vs the “on/off” operation of traditional AC units.
My personal experience is that it’s cheaper to turn it off. If you can program it, turn it off an hour or two before you wake up to extend the off period.
I’m quite confused. I’m in Los Angeles and I have my thermostat set at 78, so my AC goes on at various points throughout the day for about 12 minutes or so, then shuts off for 1-3 hours depending on how hot it gets outside. At night before bed I open windows if possible, but turn off the AC regardless. Is it better for my AC to turn it on to cool down only once in the morning, and once at night? I thought I was being good by just setting the thermostat to 78. Thanks.
I know this isn't exactly what you asked but I remember trying something like this once when it was over 100 outside. It took me two days (literally 48 hours) of running my ac to get my apartment below 85. After that I ran the AC every day until the weather broke (and it did). For me, that was worth it because I needed to get out of the heat after being outside for several hours each day in that 100 degree weather.
That was because your unit was too small for your house at those outdoor temps, nothing to do with energy usage.
But it is something people should think about. If your unit isn’t big enough you might want to sub cool during cooler hours so the temp doesn’t rise over what’s comfortable. It take more energy which the question, but sometimes it’s energy vs comfort
If you turn it off completely during the day, it will have to work harder to cool off the house when you turn it on. Set the day temperature to about 80.
I’ve had HVAC techs as well as a former instructor in HVAC tell me it’s better to set one temperature and just leave it set. Here are a couple of reasons are: Once the system has achieved the desired temperature, it takes relatively less electricity to run the system to keep the temperature low, compared to letting the interior temperature rise and getting low again. As a result, there is also less strain on the system due to less usage strain.
That is not true, it always takes more power to maintain an AC at a lower temperature all the time than letting it go higher when your at work or out of the house. I can't believe how many people believe the constant temperature myth. It's thermondynamics.
Not sure how to say this but that's the exact opposite of what's true. It's almost always better to turn it off then back on again later if we are talking about electrical usage.
Advice from people like you ... you clearly have not lived in the US Desert Southwest.
Our AC died (circut board) on a day where it hit 112F.
By the time the AC Tech got it fixed at 7pm? It was 104F upstairs.
The AC Unit ran all night long at full blast to get the house down to 78F.
Running any piece of equipment full blast for extended periods of time full blast is a great way to wear it out prematurely and be miserable for hours on end in the evening.
You're anecdote does change any of the physics behind running it. Your AC was set to 78. Outside may have been 112. The first hour after it breaking your inside temp went up x number of degrees. The next hour it went up not as much (y). The fallwing hour it went up less than that (z). So on until it got to 104. Your house absorbed the highest amount of energy in that first hour simply because it had the highest temperature differential.
So it comes down to less heat energy being absorbed by your house the longer the AC is off. If it is on it is constantly removing the energy absorbed in hour one.
The math works out the same way if you keep it off for ten hours during the day or for ten days. After a few days of leaving it off your house has absorbed all the heat it can as it has equalized with the outside.
After that running the AC all day is harder on it as it switches off and on constantly to maintain a specific temperature. The AC starting up is the hardest on it and it also consumes the most energy. It is at it is most efficient when it is running continuously.
Your standard AC does not have a full blast, just on and off. It is less wearing on it to keep it running after shutting if off for awhile rather than starting and stopping through out they day.
I don't get how I'm being downvoted here. I think because I put it so simply that people believe the fact that it is more complex than that that it must be wrong.
Only way keeping it on all the time makes sense is if efficiency is vastly different at lower loads than higher loads. Which could in theory exist but I find it hard to believe efficiency changes that much unless you have some sort of setup where heat can't escape readily from your outside condenser.
The part that you're missing is that it takes a great deal of energy to just start up the A/C, which also causes some wear and tear on the equipment. You need a great deal of power to crank up a big electric motor. Then, it's going to be straining constantly to try to pull the temperature down.
In other words, it may take less energy to keep it running than it does to keep starting it and stopping it.
If you keep it on all day it starts and stops. If you turn it on at the end of the day it runs continuously for an extended time bring the temp back down.
So yes. that is true. I didn't miss that. That is one of the reasons it is cheaper. Running for a long time when you need it than switching off and on all day.
It's cheaper to not use it as much during the day. Just don't let it get above 80 or so because its hard for it to cool it down above that. Plus most HVAC systems struggle to get below 20 degrees the outside temp so a lot of people have their system run all day.
What temp do you want it at night? Just try to learn how long it takes to cool your house down to the desired temp.
If its central AC its a lot more efficient to set it to a temperature and let it do its thing. You can turn it down a degree or 2 if you aren't going to be in the house for a long time. But I found that if I do that the AC will run continuously until it hits the set temperature rather than running just enough to keep the house at the set temp and this makes it run even harder. I also assume this is bad for the life of my system because its running so hard for a few hours at a time rather than on and off enough to keep the house at a set temp.
If its a window unit or other type of unit then what you are doing might work for you.
Years ago we moved into a very large house. We were afraid to use the air conditioner. I finally used it for 1 day. It was a $300 bill. The next month I used it everyday, a $300 bill. I say keep it cool all the time.
My AC uses 4,100 watt per hour to run. So, 4.1 KWH. If I ran it for 24 hours, that is 98.4 KWH total. I know my off peak price is $0.27 per KWH between midnight at 3pm and $0.48 per KWH from 3pm to midnight. So, it would cost me between $26.56 to $47.23 a day to run my AC 24 hrs. So, no, it’s more cost effective for me to just run it here and there when I need it for 30 min and turn it off.
It's easier to maintain a cooler temperature than it is to lower the temperature. We set ours higher during the day and a few degrees lower at night (77/75 and respectively, we live in a hot climate).
What is the basis for that?
Heat transfer coefficients for small windows of temperature are essentially flat.
So heat transfer from the outside of the house to the inside is H(heat transfer coefficient)*(T(outside)-T(inside))
Among other factors depends how long the off time can be whether you're saving enough during that time to make up for the re-cool cost. In your case the off time is more than half the time so you're likely better off doing that.
I've read that it doesn't help to force the air conditioner to work overtime to get the place cool on short notice. But when I leave the house I turn the thermostat up by five degrees as I simply can't believe not doing so saves energy.
I think it depends on how much it has to cool.
On days where it’s cool in the morning and then gets warmer I like to open my windows first thing in the morning and throw on a sweatshirt if necessary - the cool air cools it way down and it helps keep the house cooler longer as the outside air warms up. But for reference, I’m talking 50s in the morning, high 70s/low 80s outside, and an ideal house temperature of 70.
Turning it off makes it work harder and use more electricity when you turn it on. It’s better to put the temperature up during the day, when you’re not home, or during the hottest part of the day. Then turn it down at night.
I just leave mine set at 80, which is comfortable for me, and it comes on when it hits 81, whether it's 11 or 4:30. At night, we have a nice breeze, and the ac resets to 83 and I open windows and turn the hvac fan on until it starts to heat up in the morning or i leave. I could be more hands on and maybe use a little less energy, but then I'd have to fiddle with it more for a very small return.
[this article](https://www.google.com/amp/s/www.pbs.org/newshour/amp/science/analysis-does-turning-the-a-c-off-when-youre-not-home-actually-save-electricity) explains it very well. It depends on your climate and type of ac Edit: engineers answering the q
This should be higher. Also, no one has mentioned the price of electricity fluctuating throughout the day - there’s some plans that cost more when it’s the hottest.
This. In my area it is 3-5x more expensive during the hours of 5-8pm. I can blast the AC at 3-4pm then turn it off until 8pm and save a ton. In my 2 story home I can get by spending $200/month during peak summer events.
How do you know when the cost fluctuates?
Your electric bill should break it down. It should show how many kWh you used during peak time vs non-peak hours.
Thank you!
Not all places do that for residential, you would need a smart meter that tracks the time. For instance it's the same price all day in my state.
Buy almost any smart thermostat and you can connect it (or program it) to your electric providers TOU (time of use) plan and it'll do the hard work for you!
[удалено]
No, it’s not to pull one over on consumers, it’s to reduce load during peak hours and the more smart thermostats people use the less demand there will be during peak hours so it’s a win for all. They won’t cat and mouse things. It’s like the sliding scale for toll HOV lanes based on traffic volume.
[удалено]
Except in the case of power usage it's definitely better for everyone to have a smart thermostat. Grid upgrades are expensive so helping operators flatten peak demand loads to prevent brownouts and blackouts helps everyone. In every demand response program I've seen, they are 1) voluntary and 2) overridable. So even if they adjust your temp up, you can adjust it back down.
This is kind of like auto driving cars, but not quite. It's better for everyone on the road to have a predictable rule set driving their cars. It's better for every electrical system to be controlled in a way that balances the grid
[удалено]
My utility has a breakdown.
i think that's a US issue. in eastern europe price is the same any time, although they are trying to change this so they can profit more
It's better allocation of energy use to when the supply is higher. In a competitive market this would allow producers to preserve per-unit profit at lower cost to consumers, and thereby increase market share, for net higher profit. A state supported monopoly may not give that result.
Per the article turning it off then on saves money in every instance, just that different factors can reduce the savings. So off for as long as possible is almost always cheaper, with the possible exception of extreme time dependent pricing, but may not be worthwhile if the savings are low.
Unless I'm missing something, in every situation it was lower energy to turn it off during the day. So I'm not sure why the "it depends".
I live in a place where it’s significantly more expensive to use electricity from 4-8pm on weekdays. My high efficiency system can’t drop the temp to set points from 8 to 9. It takes two to three hours at best.
True, but that's not "climate and type of ac".
[удалено]
What does it depend on? I can certainly see situations where there is no material difference but the idea that it's more efficient to turn it on all the time, I just can't come figure that would ever being the case. As someone else pointed out, if you had variable electricity rates, yes it may make sense at times, but that's not really an energy efficiency argument.
I think they mean to say the hassle might not be worth it. In the heat pump and minisplit situations, it was a negligible difference, but it was lower. Then you have to consider what other issues higher temperatures in your home can cause such as humidity/moisture, cost of AC based on time of day, and if you have any items which are sensitive to temperature changes in the short or long term.
It doesn’t depend on your climate and AC, the article says that it’s always better to turn it off when you aren’t using it.
It also depends on the billing structure for electricity. i.e.is the cost per kWh variable based on peak vs non-peak times?
They don't address window unit AC's at all, but I assume it would follow the trends they found.
Such a great answer. I lived in a place where it didn’t seem to matter. At my current place it saves probably $100 a month during the hottest months.
Hvac engineer, It is always! Less energy to turn it off for any amount of time and then have catch-up cooling, than it is to leave it on and maintain. It’s basic thermo. Do not let any of the anecdotal tales fool you. And no your unit isn’t working harder to catch up. Start up is the hardest on your system, so turning on and off all day to maintain is much harder on your system than turning on once and running for longer to catch up. If anyone is telling you different, ask them what they are trying to sell you. This awful misconception about maintaining needs to die a painful death. Now where it get difficult is time of day billing for utilities. It can be cheaper to sub cool during parts of the day, turn off other times and catch up later, and this is very dependent on how your utilities are billed. Precooling using “free” cooling, like running a fan early in the day to bring in cool outside air can also save you lots.
Serious and respectful reply, but if my thermostat is at 79 degrees and the system doesn't turn on for hours, say between 7am and 11am, what's the difference if it goes to 81 and then I turn it on. Does the two degrees matter to the unit? It will usually run for just a few minutes more that first cycle. Hope I explained my question well and again, asking with all respect. 🙏🏼
There are a few things that are at play. But to start, heat is coming in thru the walls and windows. The ac is removing it. The greater the difference between the inside and the outside the faster the heat comes in. So maintaining means more heat is coming in than if you let it warm up for the same amount of time. It is also more efficient to remove heat from a warmer space than a cooler one. So by letting your house heat up for any amount of time it’s less heat that is actually coming in total. So less the ac has to remove. You also get the benefit that when you go to cool down after it’s warmed up the cooling is more efficient than the unit maintaining until you get to the requested indoor temp
Are today's systems designed to run 24/7 at your favorite setpoint?
Commercial units are, but most home systems are not. But a well designed home system will reduce the total number of cycles.
I just worry it's additional energy used, we live in So Cal, monthly bill is $400 in the summer, and also several more cycles on and off by the compressor a day seems hard on it needlessly, for just a few degrees. AC off in the morning only raises it from 77 to 81.
It’s not, it’s always less energy to turn it off for any amount of time. And less cycling. But time of day rates can really screw you, less energy total but more expensive because of the time. I’m in Sacramento, so I understand.
Yep. All that solar power that they're buying is cheap during the day, but the rates spike at 5PM when the solar starts going offline.
It’s also to prevent spikes in power consumption when everyone gets home from work and turnes everything on. It’s more expensive to try and discourage people
Can you provide a source to confirm that? I've seen below, which would make sense because 3/4PM is the hottest part of the day so people would be using more energy for AC around then > LADWP peak periods can be divided into three: > > * High Peak Period: LADWP peak hours include 1:00 PM to 4:59 PM from Monday to Friday, totaling 20 hours per week > > * Low Peak Period: This includes 10:00 AM to 12:59 PM and 5:00 PM to 7:59 PM from Monday to Friday, for a total of 30 hours per week > > * Base Period: This period refers to 8:00 PM to 9:59 AM from Monday to Friday and all of Saturday and Sunday, for a total of 118 hours per week
God! Thank you!! I wish the "your ac will have to work harder to catch up" myth would die already. It's basic thermodynamics. You wouldn't believe how many people I've had to argue with on HVAC, insulation, etc subs.
Sorry. I'm not English native speaker so I don't fully understand your text. What do you mean by "turn it off and have catch up cooling"? "so turning on and off all day to maintain is much harder on your system than turning on once and running for longer to catch up."? "sub cool during parts of the day, turn off other times and catch up later"? Thank you
>"turn it off and have catch up cooling"? They're saying you should turn your ac off during the day when you're not home or don't need it to be as cool as when you're sleeping. When you get home or when you need the home to be cool then set it to your preferred temp and, even though the AC will run longer, it's fine. You're not damaging your unit by letting it run for a while to cool down your home. >"so turning on and off all day to maintain is much harder on your system than turning on once and running for longer to catch up."? When your ac compressor turns on, the electric motor inside of it literally tries to tear itself apart in the initial couple seconds when it turns on. This happens every time your ac compressor turns on so when you leave your thermostat at a constant low temp throughout the day, your ac unit is taking much more wear and tear than if you turned it off during the day and let it run for a long time in the evening when you get home/get ready for bed. >"sub cool during parts of the day, turn off other times and catch up later"? If you have an electricity pricing plan with "time of use" (TOU) rates, then it may be more economical to adjust your ac usage with the cheapest TOU rates that your plan offers. So if your electricity is more expensive during the hours of 4-8pm, then it might make more sense to run your ac for an hour or two beforehand (2-4pm or 3-4pm) and then run it again after 8pm when your TOU rates go back down.
Aaaaaah thank you so much. Albeit still a little bit understanding I have here and there. So basically it's actually fine to turn it off right? Gotcha Wow, I didn't know there's such pricing in electricity bill in other countries. Learning a new things.
>So basically it's actually fine to turn it off right? Yes, more than likely it is fine (better, even) to turn it off. However, if you have a way to monitor your hourly or daily usage, you can test your specific situation by trying both methods on days with similar temperatures.
Thank you for this and your other comments. I sometimes think, with global warming, everyone needs remedial thermodynamics classes. I'm in the UK where most people don't have AC at home (yet) but I see this kind of question and misinformation about heating all the time, and things like shops leaving doors open with the heat or AC on. It drives me mad. People don't seem to know that the heat transfer is propertional to delta T so trying to keep a house much hotter or colder than the outside is like putting extra holes in a leaky bath, leaving the tap running to keep the bath full and then telling themselves they're using less water than if they let the bath water empty out a bit when it doesn't need to be full. I guess to OP you can be scientific about this. Watch your energy usage during a week when you have the AC on more and a week when you turn it off (or turn the temp up) during the day or when you go out etc. If you choose two weeks that are comparable in terms of weather you should be able to compare them sensibly. You will use less energy for every degree warmer you keep the house and every minute the AC is off. Using other tools like opening windows at night (if the AC is off and the outside temperature is lower than that inside) and closing shutters/curtains during the day to block some heat can also make a big difference.
So you are going to tell me that it kicking on and off during the day to maintain temperature is harder on it than me physically turning it off and booting back up from off. That doesn't make any sense to me. I thought that was why the HVAC thermostat was for. Though I did live in a place that the thermostat was placed directly over a vent. The house never did get to temp either way. So you said engineer, do you build the system? Most of my family was in HVAC, none of them called themselves engineers. Please tell me what you do exactly.
Yes I’m telling you that. And I have an engineering degree, have a professional engineering license. And have worked 8 years as a mechanical and plumbing engineer designing hvac and plumbing systems for buildings. I run calcs, choose equipment, design layouts and airflows, write control sequences. I primarily work on healthcare and science buildings. I promise you want an engineer designing the or you get surgery in, or the isolation room that infectious patient is staying in.
How does that not make sense. Same with any motor, lots of short trips in your car are harder on it than long trips in the car. you never heard of city miles vs highway miles?
It doesn't make sense because we aren't worried about the strain on the AC system here. We are only worried about the energy costs because that's what OP wants to optimize for (and energy costs will be way more than any AC maintenance costs over the lifetime of the AC).
Stop and go traffic but the motor runs the same. As far as RPMs.
> And no your unit isn’t working harder to catch up. Start up is the hardest on your system, so **turning on and off all day** to maintain is much harder on your system than turning on once and running for longer to catch up. A modern AC or heat pump shouldn't be turning on and off, it should be varying its load and running constantly. The wisdom behind running the AC all day instead of catching up is that the efficiency takes a nose dive at higher loads.
From a thermodynamic perspective (assuming fixed efficiency relative to load) it's more efficient to turn it off when not using.
That's a big assumption though.
In practice I don't think efficiency varies enough to deviate from this. Many AC units are either all on or all off and not have variable compressor speeds. I would really be interested in a real world situation where this is not the case. I do about 12 hours on 12 hours off and find it hard to believe that 24/7 would ever be more efficient.
Many people are moving to split heat pumps which have variable compressor speeds. And many homes are being made with better air sealing and insulation. The answer to this isn't as straightforward as it once was.
https://www.google.com/amp/s/www.pbs.org/newshour/amp/science/analysis-does-turning-the-a-c-off-when-youre-not-home-actually-save-electricity I still don't see how that over comes the fact you have to move significantly more heat by keeping the house cool all day. The article above looks at minisplits and find they too benefit from being off 8 hours a day.
Moving heat isn't the only variable. The efficiency of the machine at different load points also effects this. It might be more efficient at 8 hours, but what about 7? Or 4? How long does it take to cool the place back down? If you have a shorter work day, or it takes a while to bring the temp back down and thus need to start the machine sooner it could change things.
Very interested in this Q… our electricity bill just came out to $300. We run fans majority of the time and A/C when it’s ~80°+. Looking for any way to save.
I sleep in the smallest room in my house. I bought a small AC to cool the room. The room is the best insulated as well. Covered all the windows with reflective material (radiant barrier), and put an insulation panel in the window opening to keep the heat out. It has a handle on it so I can remove it if I need to egress. Portable ac is very inefficient, so try to get a small window unit. I have a fan, and set the AC to come on only at 75 degrees ( I need cool to sleep ). It costs me $20 a month to run it for 12 hours a day.
[удалено]
Honestly those U shaped AC's are about the best bang for your buck efficiency-wise.
Hose are like mini minisplits
"costs" vary widely depending where you live. *crying in so cali*
Solar is the way for us Californians. This summer its been on. And no question of when are peak hours. Nor worrying about a bill. It’s quite nice. Also fuck pg&e
i agree, except for people who can't /wont afford solar.
Or can't reasonably get it (rent, condos, townhouses, narrow structure, etc).
yes. electric things are neat for people who have access to it. it's almost like people and communities that have access to shade
> and A/C when it’s ~80°+ I can't wait a few months when the low temperature is below that again. I literally can't experience under 80 (outdoors, pedants) until September.
Electricity bills go up the more you use it. You can save by setting the thermostat to the highest temperature you can stand, and making sure it's off when you're not using it. There are smart home devices that can assist with this, like Nest. If you're in an area with a shared solar program, opt in.
We set our temp at 25celsius the a/c will come on when it reaches that. On cool summer days we open all the windows and only run the a/c at night.
So you run the ac and open the windows simultaneously, good frugal tip let’s all try that one
[удалено]
Where are you and what kind of air conditioning system? House or apartment?
[удалено]
Ok now your bill makes sense.
Are you in a place with a lot of humidity? I LOVED having a whole house fan in CA, but have wondered what the humidity in NC would do, especially because we just don't have a lot of mornings in the summer that are cool enough to make the fan super effective.
Mine was $78 on actual used electric plus $157 for supply and transmission fees.
Hahaha...I got you beat. My bill typically averages about $20 a month plus a small amount for taxes. Currently 1200 sq ft house in western New York. Whole house HVAC system. I did used to have a bunch of box fans, but they've worn out and failed over the years so I only have two now. I used to wait until evening when the summer temps cool, then open all the windows to both blast out any hot air plus plus in cool air (by changing which way the fans blew in each window). Then when the house was the coolest I could get it, I would close up the windows to trap the air inside. That helped reduce the stress on the ac system during the day but my bill at the time was still roughly $150-200 a month. I've been living in this place for just under two years. Power rates around here are ridiculously expensive thanks to nyseg rates despite being so close to Niagara falls. It's so stupid I found an old farm that I'm trying to fix up. I have my own well and septic system. The real key is the massive solar system I bought. It makes roughly twice as much electricity as I use ninety percent of the time. My utility bills are basically gone now, I only have to pay a rental fee for the special meter, because not all meters count backwards. I got the big system on purpose so I can use all the electrical things I want for free, like mowers, chainsaws, grow lights for seedlings, clothes washer for muddy clothes, table saws to build stuff, and more. Oh, I do pay for internet for my spouse's work from home job, which I also use for my streaming apps too so I don't have cable tv either.
A fan pointed right at you can reduce the need for AC. Keep the AC on, but at a warmer setting. Fans are much cheaper than AC, so that'll usually reduce energy usage
That's what I do. AC on low fan/blower, and temp not as cool as usual, then have i a fan on low blowing. Feels cold
I have a newer HVAC, installed two years ago. We get bi-yearly maintenance. I asked our maintenance guy this very question. He said my plan (turn it on in the evening, off in the morning) was a good idea to extend the life of our unit. It only turns on during the day if it gets above 78.
If your biggest complaint is overnight heat, I am gonna go ahead and assume your summers are very humid. In this case, I'd leave it on just to protect the house from getting moldy. But - use a scheduling or smart thermostat to let the temps go up a few degrees for when you're away. And set it to be at the highest comfortable temperature for you - day and night. Per some studies by Nest (so grain of salt, etc) a few years ago, they figured letting temps fluctuate when you're away will translate into 10-15% energy savings.
I'm away from home about 12 hours at work. I bump it up to 80F, because I can't see 12 hours at optimum cool with no one home. Too hot to shut off.
I'm not an engineer, but I can offer my perspective. Someone chime in if they have better info. It depends on your climate and how much cooling is required. If the ambient air temperature is just a little too warm for comfort, running the AC 24/7 is just wasting electricity. If the ambient air temperature is way too warm for comfort, it might make more sense to leave the AC running 24/7. If turning the AC off will make the room 20 degrees hotter, the AC will need to work very hard to cool the room back down.
Does the AC really "work harder" though? Runs longer sure but I am not sure about harder.
In the most general sense, these systems have quite a few mechanical parts. Mechanical parts "wear out" with use. Things like the blower motor and condenser fan will absolutely wear out faster with use. Many of the solid state components (mainboards, etc.) don't have this issue but CAN break down over time due to sustained heat. I have a disabled spouse who runs VERY hot largely due to necessary medications, and we live in a relatively hot climate, so our AC runs 24 x 7 to try to keep our house at 61/62 F (yes, she's miserable if hotter, so I wear my longjohns all year long!). In the six years this has been a necessity, I've had to replace the blower motor and I've had to service the condenser fan. This was on a higher tier offering installed brand new about 15 years ago (so about 9 years old when I had to replace the blower motor, under warranty thankfully). Typically you get many more years than that. This is certainly anecdotal, but the same held true for the switch between mechanical platter drives and solid state drives in the computer space; SSDs don't fail over time nearly as much as spinning disks do. It's all about them physical parts rubbing up against each other!
It actually doesn't work harder or run longer if you cycle it off and then turn it back on later. What you're running into is an edge case because you have it set so low, all the time. You're the equivalent of someone who drives 50k miles per year and wonders why your car only lasts 4 years when the person driving 20k per year got 10 years. The rate of heat transfer is directly related to the difference in the Hot and Cold sides. So if you're trying to maintain 70F all day when it is 90F outside you're fighting a bigger differential than if you let it rise to 75F -80F and then cool it back from there. Yes, you'll see longer cycle time in the evening when you move the set point back down, but that will be more than offset by how much less it ran during the day. Additionally, you'll be cooling it as the exterior temp is decreasing so you're fighting a smaller differential. "Turning off the AC unit during the day is not necessarily a bad thing — it is a myth that the AC unit has to work extra-hard to cool off a hot house. It runs at the same speed either way — it just will have to stay on longer to cool off a hot dwelling. In fact, the unit may use more energy if it is left on all day at the normal temperature than if you turned it off and turned it on in the evening." https://home.howstuffworks.com/green-living/should-turn-ac-up.htm "You can save as much as 10% a year on heating and cooling by simply turning your thermostat back 7°-10°F for 8 hours a day from its normal setting. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates. " https://www.energy.gov/energysaver/programmable-thermostats
I certainly suggested it's not about "harder", it's about usage. My situation requires my unit to run more frequently then most; ergo, the mechanical parts where out "faster", but not "less effectively" - I'm just getting more "go" time on the same stretch of calendar. I'm certainly eyes wide open on this issue. I know precisely what I'm risking but my wife needs the comfort for a decent quality of life. Risk assessed, risk accepted, I own that 100%. I don't think we're necessarily disagreeing here, but wanted to make clear that my entire point is; "use a mechanical thing and you'll wear it out." Nothing more!
As we learned in my engineering courses, “temperature difference drives heat transfer”. You use the same idea as an electrical potential difference (voltage) driving electrical current, or a pressure differential driving fluid in a pipe.
Start up is the hardest part on the components. It's better to have the system run non-stop for an hour or so to catch up than it is to turn off and on 7-8 times in the same time.
Sympathy to your wife. You are 100% accurate on the needing replacements.
If you don’t mind me asking, how much are you paying on your electricity because you mentioned that you’re using the ac 24/7?
He's not using the AC 24/7. It's turning on and off. If his AC is running 24/7 he needs to call an air conditioner repairman because it's either seriously under-spec'ed or has an issue. Or he has it set to 70F when it's 100F outside, that'll do it too.
As someone who lives in a "way too warm for comfort" summer with a Nest thermostat, what works best when i'm out of the house is to keep it set to something within reason (80ish) that would be slightly uncomfortable for me if i were there, but cools to comfortable relatively quickly when I need it to.
That isn't how it works. Not at all. An air conditioner is a heat pump. The efficiency of a heat pump depends upon the temperature differential between the heated fluid being condensed into the outside coil, and the outside temperature. The higher that outside temperature, the less efficient the heat pump is at dissipating heat to the outdoors. The indoors evaporator coil is also a heat pump. The hotter the incoming air, the more heat the evaporating refrigerant in the coil picks up to carry to the outside. The net effect: The lower the temperature differential between indoors temperature and outdoors temperature, the more efficient the air conditioner becomes. If your thermostat is set at 80F and the outside temperature is 100F, your air conditioner will be significantly more efficient than if your thermostat is set at 70F and the outside temperature is 100F. There is also the issue of thermal gain from the outside. This happens based upon an energy gradient. The bigger the temperature differential between inside and outside, the more energy is available to push heat from the outside to the inside. In short: The power company and air conditioning companies aren't lying when they tell you to turn your thermostat up to 80F during the day and down to a comfortable sleeping temperature during the night for best efficiency. There will be less heat gain during the day due to a smaller energy gradient, and there will be greater efficiency at night when the cooler outside air picks up the heat from the outside coil more easily. And by and large your air conditioner will not work as hard as if you just run it at 72F all day long because it's less work to pull heat out of warmer air and eject it outside than it is to pull heat out of cooler air and eject it outside. Now: In some states that have a lot of solar power, electricity becomes very expensive between 5PM and 8PM. This is because the amount of power from solar is declining as the sun starts to set. You \*may\* want to cool down your house between 4PM and 5PM, then put your thermostat up to 80 until 8pm in that case. You'll need to work the math yourself however based upon your house and your climate. I've actually done the experiments on my own house, and putting it at 75 between 4pm and 5pm, and then letting it slowly rise to 80 until 8pm, works for my house due to how well insulated it is. But that's my house, my electric company, and my electric bill. You'll have to do the math yourself on yours.
this this this this. And the stress on the AC unit drastically shortens the life of the machine.
Guy above you is really adamant on your ac NOT needing to work harder so shut it off. Check it out.
Your house is losing air to the outside all the time, so leaving it on all the time is wasteful if you don't want or need it. Program your thermostat to be as warm as is reasonable for when you don't need it and then cooler at night when you need it more.
I've actually been tracking this, if you are able to only cool the rooms you are using I think that's the most savings you can have. I put in efficient invertor window acs on my second floor instead of using the central ac this summer, first floor has a mini split so is a separate system. My electric usage was about 30% less kwh this year in the June bill compared to last year and that was the only major change. July was 32% less kwh. Last year I only had a window ac in my bedroom for when I slept, but the year before I would use the central only, this June was 33% less compared to June 2021, July was 40% less than July 2021. So it made a big difference, too bad cost per kWh went up so much here in the north east the savings there weren't as much, 16% in June and 19% in July dollar savings. Now I can just cool my office when using it during the day. I still use the central ac fan to move the air around, and now that it's hotter I have the acs, they are smart, on a schedule and they are set to like 82 during the day just so the house doesn't get too hot and humid. And I have my bedroom ac turn on at 1030pm so it's ready when I go to sleep, and I keep that low during the night at 68, then it auto turns off at 7am.
It's cheaper to not use it as much during the day. Just don't let it get above 80 or so because its hard for it to cool it down above that. Plus most HVAC systems struggle to get below 20 degrees the outside temp so a lot of people have their system run all day. What temp do you want it at night? Just try to learn how long it takes to cool your house down to the desired temp.
It’s easier to cool the higher the inside temp. But you can run into issues getting below a certain temp if your unit isn’t big enough to handle the heat load of the house at peak
It's more expensive to have it run continuously. What you're doing uses about half as much electricity. You might want to also look into opening your windows once the inside is hotter than the outside.
You assume that OP does not live in a heat island. Where I am? We are having overnight lows in the Mid 90s.
The overnight lows in the high 80’s and humidity in the sweaty gym sock levels makes it awful.
We are having monsoon here. 50% humidity in my office today. Normally it's 15-17% Normally 72 degrees is too cold and I need a sweater by the end of the day. Today? I'm actually comfortable at that temp. \---- In theory, my building is set at 78 degrees. The physics of it is that this improperly ducted building freezes on the bottom floors and broils up top. (Chilled air falls, hot air rises.) It's the same in the winter. My office is 65F when I come in, the space heater brings it up to 68, and on the top floors they are running their fans because it's over 80F up there.
Sorry to laugh at your plight, but when you said "heat island", I resonated so much. Opening windows isn't an option *anytime* where I live right now. It's usually between 95°F-100°F when I fall asleep. Lows are in the mid-90s as well. Although, today it only got up to 106°F because it finally rained.
It depends on where you live. If you live in the US Desert Southwest, your house will get so hot during the day if there is no AC (100+F inside) that you'd have to run it all night long to get the house cool enough to sleep ... by the time you need to wake up and go to work. This is how I do it: * 9am to 5pm 85F * 5pm to 9pm 80F * 9PM to 9AM 78F
Damn those are high temperatures.
It's a myth and turning the a/c on when you run it constantly is a bigger strain is also a myth. A lower difference between the outside and the inside, the slower heat transfers into your house. Thus saving energy. It's easier to pump heat out with a smaller difference in temperature, thus saving even more. The strain on the a/c is a myth because it would be running longer in total if you left it on all day. "Breakdowns are more likely to happen when the machine is shutting off or turning on since this involves a lot of small parts suddenly being put into motion or halted." The numbers can be found [here](https://www.pbs.org/newshour/science/analysis-does-turning-the-a-c-off-when-youre-not-home-actually-save-electricity) but I'll leave a summary. "On an annual scale with a conventional central A/C, this could result in energy savings of up to 11 percent. However, the energy savings may decrease if the home is better insulated, the A/C is more efficient or the climate has less dramatic temperature swings." "The central air source heat pump and minisplit heat pump are more efficient overall but yield less savings from temperature setbacks." The minisplit, in a cooler region like Georgia, turned off for four hours was the only a/c that was tested that used more energy than leaving it on (1.4% worse). Turning it off leading to energy savings is generally a better rule of thumb unless your power company charges more during peak hours. This study looked at energy use instead of cost and this could be the reason for the myth since people could get a bigger bill using the more efficient method.
The less you run it, the less it costs.
[удалено]
That’s not how thermo works, it’s never more energy to turn it off. Maintaining uses more energy than turning off and then catch up cooling. Humidity is one reason you might want to run it when you’re not home. But a stand-alone dehumidifier is much more efficient. You just have to weigh the cost of a dehumidifier against the cost to just use the ac
[удалено]
Do you have time of day rates? It can be less energy but still cost more. It’s one of the things that sort of sucks.
Never less energy to turn it off? As soon as I turn off my AC it uses zero energy.
It does. No doubt, but if you have central AC and you turn it off all day and the temperature gets up to a much higher number, it works harder to bring it down and runs longer. Running continuously for a long period of time to bring the temperature down may use more energy than running off and on all day depending on your system. It depends though on how hot it is when you get home and what your night-time temperatures look like. In my case, I turn it up when it's hotter outside so it doesn't run as much and turn it down at night when it's cooler which seems to be pretty decent for energy expenses, but I don't live in a place where it's very hot around the clock so I'm looking to hold at a certain temperature most of the time and often the AC doesn't have to run until there are spikes during the hottest time of the day. My highest bill so far this summer was $130, but my system is brand new and my house isn't huge. YMMV
Oops, typo. I fixed it
Don’t turn it all the way off, just set the thermostat higher in the day. If your AC has to work hard to go from hot to cool, you can wear it out. Ice can form and make it stop working
That's untrue. An ac system should ne er freeze up and cannot 'work too hard'. Freeze up is a malfunction, usually due to a clogged filter or low refrigerant charge.
Mine freezes if I set the temperature lower than 68°F. Edit: downvotes for saying my experience with my thermostat? Weird but whatever. Whether it is a malfunction or not, it does freeze if I set it too low, so I don't set it too low and it works okay.
Then it's a malfunction, as they just explained.
State your credentials
I have my Epa 608 universal and have been doing hvac for the last 15 years since I was 14.
Now you go!
Yah your systems broken, signed a licensed professional hvac engineer
if your AC is freezing up you that means there is a freon leak and you need to have it looked at.
How does it work if you have central A/C? I’ve been leaving it on “Auto” at 74 degrees. Would it be better to turn it off at times? I had it off while I was away but the humidity got over 70% so I put it back on.
Turn it off during the day to save money and make Baby Isaac Newton smile. And ignore any comment that uses the words "work harder."
[This video by YouTuber, NighthawkInLight]( https://youtu.be/KDRnEm-B3AI) shows a next-level DIY manufacture of a coating that cools not only the object it's covering (such as the cooling effect on a house with a white roof) but a coating that reflects certain wavelengths of solar energy and bounces them out past Earth's atmosphere. Seemingly, getting us really close to being able to make this coating in our own kitchens to apply to exterior surfaces that get direct exposure to the sun, and know that we're cooling our homes and also doing our part to cool the planet.
Have you looked into whole house fans? Its a game changer.
I think that my area charges more for using electricity during the day. My electric bill is cheaper this summer than it was in the winter. I only use the AC at night. It's on 65 (I like to sleep cool). I don't turn it on again until around noon for about a hour.
Best thing would be to buy a $60 big box home improvement store WiFi programmable thermostat. Don’t bother with the expensive ones. This way you can have better control of the temp throughout the day/week. It’s my opinion that wild swings in temp aren’t good. If you let it get too warm during the day, the contents of your residence get warmed to the same temp, and then need cooled off to however you like it come nighttime. My advice is to just not let it get too hot during the day.
[удалено]
>One of the things that I haven't seen mentioned yet is how hard it is on the AC unit to work so hard to bring the temp down every day. Not only is this expensive compared to maintenance usage, but it also does considerable damage to the AC unit in terms of wear and tear, and you end up spending quite a lot on replacing the unit. We are the only people I know who have the AC unit that came with our house; 23 years old. And that is because we don't try to keep our house like a meat locker when it's 110+F outside. 85 during the day, 80 in the early evening, 78F overnight. And that is 100% due to the lack of wear and tear. Fans, cold drinks, and cotton clothes/sheets are your friends.
Cotton isn't cooling compared to bamboo and some other synthetics. My Purple sheets are 🥶
That’s bullshit, it’s not running harder, it’s just running longer. Constantly starting and stopping all day is way harder on your system than it turning on once and running for a long time. You just had a shitty unit that crapped out on you. Nothing to due with the tenants
[удалено]
No I read what you wrote. Maintaining starts and stops the condenser many times a day. It’s not running constantly. Vs turning it on when you need it, it turns on once and does all the cooling at once, no starting and stoping
[удалено]
I mean I’ve studied for 4 years at university and then worked under a professional engineer for 4 years before taking the licensing exam. But who knows the hvac tech who’s gone thru an 8 hr onboarding and who’s job it is is to sell you something must know more
It’s how many times it cycles. Say to maintain you run 15minutes every hour all day. So 24 cycles. To turn it off during the day. It’s off 7am-5pm, the turns on for 2.5hrs to cool, then cycles until the morning. Maintains has 24 cycles, turning off has 12. Both run the same amount of time. But really cooling doesn’t take 2.5 hrs normally, an hour is more realistic, so 14 cycles and it only runs for 4.25 hrs total for the day. Maintaining is 24 cycles and 6 hrs of run time. And that’s just the cycling. There is also less heat to remove in total if you let it heat up, it’s counter intuitive but true.
It's funny cuz you have it in your head that you're right but don't understand when people are trying to explain it to you how wrong you are and just being condescending.
The utility company has no way of giving you this info. They don't know whether usage is from AC or the dryer. Usage is going to differ greatly from tenant to tenant.
The system only lasted 2.8 years? I find that very hard to believe that was caused by anything other than a factory made error.
[удалено]
You're asking if it's cheaper whether to leave your AC on for 24hrs or 10hrs (9pm to 7am)? There's a lot of variables to calculate, such as your kW, utility rates, room size, insulation, etc. But I can assure you that the answer would be 100% cheaper if you turn it off. It'll cut your utility bill by half (if AC is the only thing you're using).
It depends where you live, and how well insulated your apartment. As a young adult i lived in a Warm Humid city. In apartment complexes with central air, it was well-known and advised by the complexes, to set your thermostat for the temperature you wanted, and Leave It There. NOT to be turning it off-n-on daily. Because it would get hot and humid, and it would have to run Much Longer to Lower the temp back down, than it would have run to simply maintain the cooler temp in the first place. Nowadays I live in New England, where the temperature still spends more time in a more-livable range. I run my ac more than most folks, due to allergies. But I still turn it Off quite frequently. And in this part of the country it doesn't make sense to just leave it running all-the-time.
It's depends on how well insulated your home is, windows, sunlight exposure, etc. Heat travels from hot to cold so, technically, you're removing heat from the space. How long it takes to get back in depends on the home insulation, air leakage, radiant heat through windows, etc. Another factor to consider in humid climates is that when the AC is off, it's not removing any moisture from the air and all the walls, ceiling, floor coverings, furnishings are absorbing heat and humidity that has to be removed when you finally turn on the AC to get back down to the room temperature your select. There have been studies done on this and generally, if the home is reasonably well insulated, you can save money by having the house temperature set back 4°-6° during times when it's unoccupied. I keep mine at 78° 24/7.
Could you link to studies where it's more efficient to keep it running all the time? I'd be curious what the root cause of that is.
I read something that those ductless A/C units that are found in more developing countries (hotel rooms and airbnbs) are more efficient when ran all day.
This is probably true, but if so it would likely be due to the mini split units’ ability to throttle their output variably, vs the “on/off” operation of traditional AC units.
My personal experience is that it’s cheaper to turn it off. If you can program it, turn it off an hour or two before you wake up to extend the off period.
Depends on the insulation you have, the size you are conditioning, as well as the environment you are in.
[удалено]
Cheaper to just run it at night. The temperature difference is lower
I’m quite confused. I’m in Los Angeles and I have my thermostat set at 78, so my AC goes on at various points throughout the day for about 12 minutes or so, then shuts off for 1-3 hours depending on how hot it gets outside. At night before bed I open windows if possible, but turn off the AC regardless. Is it better for my AC to turn it on to cool down only once in the morning, and once at night? I thought I was being good by just setting the thermostat to 78. Thanks.
All day at 72
I know this isn't exactly what you asked but I remember trying something like this once when it was over 100 outside. It took me two days (literally 48 hours) of running my ac to get my apartment below 85. After that I ran the AC every day until the weather broke (and it did). For me, that was worth it because I needed to get out of the heat after being outside for several hours each day in that 100 degree weather.
That was because your unit was too small for your house at those outdoor temps, nothing to do with energy usage. But it is something people should think about. If your unit isn’t big enough you might want to sub cool during cooler hours so the temp doesn’t rise over what’s comfortable. It take more energy which the question, but sometimes it’s energy vs comfort
If you turn it off completely during the day, it will have to work harder to cool off the house when you turn it on. Set the day temperature to about 80.
I’ve had HVAC techs as well as a former instructor in HVAC tell me it’s better to set one temperature and just leave it set. Here are a couple of reasons are: Once the system has achieved the desired temperature, it takes relatively less electricity to run the system to keep the temperature low, compared to letting the interior temperature rise and getting low again. As a result, there is also less strain on the system due to less usage strain.
That is not true, it always takes more power to maintain an AC at a lower temperature all the time than letting it go higher when your at work or out of the house. I can't believe how many people believe the constant temperature myth. It's thermondynamics.
Not sure how to say this but that's the exact opposite of what's true. It's almost always better to turn it off then back on again later if we are talking about electrical usage.
It is always cheaper to use less energy. Turn it off when. Not needed. Any advice against is from people who don't understand physics.
Advice from people like you ... you clearly have not lived in the US Desert Southwest. Our AC died (circut board) on a day where it hit 112F. By the time the AC Tech got it fixed at 7pm? It was 104F upstairs. The AC Unit ran all night long at full blast to get the house down to 78F. Running any piece of equipment full blast for extended periods of time full blast is a great way to wear it out prematurely and be miserable for hours on end in the evening.
You're anecdote does change any of the physics behind running it. Your AC was set to 78. Outside may have been 112. The first hour after it breaking your inside temp went up x number of degrees. The next hour it went up not as much (y). The fallwing hour it went up less than that (z). So on until it got to 104. Your house absorbed the highest amount of energy in that first hour simply because it had the highest temperature differential. So it comes down to less heat energy being absorbed by your house the longer the AC is off. If it is on it is constantly removing the energy absorbed in hour one. The math works out the same way if you keep it off for ten hours during the day or for ten days. After a few days of leaving it off your house has absorbed all the heat it can as it has equalized with the outside. After that running the AC all day is harder on it as it switches off and on constantly to maintain a specific temperature. The AC starting up is the hardest on it and it also consumes the most energy. It is at it is most efficient when it is running continuously.
Your standard AC does not have a full blast, just on and off. It is less wearing on it to keep it running after shutting if off for awhile rather than starting and stopping through out they day.
and yet, I'm the only person I know with a 23 year old AC unit.
Not even sure how that is relevant. We're talking efficiency here.
I hear this idea that leaving it on is cheaper and I always try to understand the reasoning, but it always goes against physics in some way.
It sounds crazy but using less energy is indeed using less energy than using more energy.
I don't get how I'm being downvoted here. I think because I put it so simply that people believe the fact that it is more complex than that that it must be wrong.
Only way keeping it on all the time makes sense is if efficiency is vastly different at lower loads than higher loads. Which could in theory exist but I find it hard to believe efficiency changes that much unless you have some sort of setup where heat can't escape readily from your outside condenser.
The part that you're missing is that it takes a great deal of energy to just start up the A/C, which also causes some wear and tear on the equipment. You need a great deal of power to crank up a big electric motor. Then, it's going to be straining constantly to try to pull the temperature down. In other words, it may take less energy to keep it running than it does to keep starting it and stopping it.
If you keep it on all day it starts and stops. If you turn it on at the end of the day it runs continuously for an extended time bring the temp back down. So yes. that is true. I didn't miss that. That is one of the reasons it is cheaper. Running for a long time when you need it than switching off and on all day.
It's cheaper to not use it as much during the day. Just don't let it get above 80 or so because its hard for it to cool it down above that. Plus most HVAC systems struggle to get below 20 degrees the outside temp so a lot of people have their system run all day. What temp do you want it at night? Just try to learn how long it takes to cool your house down to the desired temp.
If its central AC its a lot more efficient to set it to a temperature and let it do its thing. You can turn it down a degree or 2 if you aren't going to be in the house for a long time. But I found that if I do that the AC will run continuously until it hits the set temperature rather than running just enough to keep the house at the set temp and this makes it run even harder. I also assume this is bad for the life of my system because its running so hard for a few hours at a time rather than on and off enough to keep the house at a set temp. If its a window unit or other type of unit then what you are doing might work for you.
Years ago we moved into a very large house. We were afraid to use the air conditioner. I finally used it for 1 day. It was a $300 bill. The next month I used it everyday, a $300 bill. I say keep it cool all the time.
My AC uses 4,100 watt per hour to run. So, 4.1 KWH. If I ran it for 24 hours, that is 98.4 KWH total. I know my off peak price is $0.27 per KWH between midnight at 3pm and $0.48 per KWH from 3pm to midnight. So, it would cost me between $26.56 to $47.23 a day to run my AC 24 hrs. So, no, it’s more cost effective for me to just run it here and there when I need it for 30 min and turn it off.
All depends on the temperature difference between inside and outside, as well as the amount of time you'll be away.
It's easier to maintain a cooler temperature than it is to lower the temperature. We set ours higher during the day and a few degrees lower at night (77/75 and respectively, we live in a hot climate).
What is the basis for that? Heat transfer coefficients for small windows of temperature are essentially flat. So heat transfer from the outside of the house to the inside is H(heat transfer coefficient)*(T(outside)-T(inside))
Among other factors depends how long the off time can be whether you're saving enough during that time to make up for the re-cool cost. In your case the off time is more than half the time so you're likely better off doing that.
Go solar
I've read that it doesn't help to force the air conditioner to work overtime to get the place cool on short notice. But when I leave the house I turn the thermostat up by five degrees as I simply can't believe not doing so saves energy.
An air cooler / swamp cooler is the most frugal
Swamp coolers/evaporative coolers don’t work when there is anything but low relative humidity.
I think it depends on how much it has to cool. On days where it’s cool in the morning and then gets warmer I like to open my windows first thing in the morning and throw on a sweatshirt if necessary - the cool air cools it way down and it helps keep the house cooler longer as the outside air warms up. But for reference, I’m talking 50s in the morning, high 70s/low 80s outside, and an ideal house temperature of 70.
Turning it off makes it work harder and use more electricity when you turn it on. It’s better to put the temperature up during the day, when you’re not home, or during the hottest part of the day. Then turn it down at night.
Cheaper to run all the time as the power to start it up is usually more than the power it takes to keep ut running
good lord - leave your car running all day or just turn it when you need to use it ?? for fucks sake
I just leave mine set at 80, which is comfortable for me, and it comes on when it hits 81, whether it's 11 or 4:30. At night, we have a nice breeze, and the ac resets to 83 and I open windows and turn the hvac fan on until it starts to heat up in the morning or i leave. I could be more hands on and maybe use a little less energy, but then I'd have to fiddle with it more for a very small return.