If, for example, the outside temperature was let's say around 33 degrees celsius and i would like to keep the airco. setting around 26 degrees instead of 25 how much of a difference would that make in the electricity usage for this airco. ?
Posted Jul 11, 2021, 12:59 PM UTC
That will save you somewhere around 1/8th of your aircon cost, because you are now trying to maintain a 7 degree difference instead of an 8 degree difference. But this is very approximate.
To add to your approximation, it would be greater than 1/8, BC there's diminishing returns, the first degree change will be more impactful than the second and so on.
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You're thinking backwards in 'heating mode'. OP is asking about 'cooling' where raising the setpoint decreases the delta T from indoors to outdoors.
I see , that's one way to look at it i guess.
Thanks.
I'm actuality doing the opposite, I'm trying the 'super cooling' method. This is where you run your house at a lower temp, in my case 69°F during off peak hours and 78° during peak hours. The idea is to super cool everything in your house. Of course this requires discipline to not open windows or doors longer than needed. Keep that cold air in the house and keep everything cool, under the couch, cool, back of the bed, cool, inside the closet behind the clothes, cool.
If you want to try it, find out when your energy companies peak and off peak times are and set your programmable thermostat accordingly. So far it seems to be working for lowing our summer energy costs here in Arizona.
holy shit i never realized how much cheaper electricity is at super off peak hours. in my state it's 1/3 the price of peak. 3.4c/kWh that's insane! the hours work out great too. super off peak starts at 11pm and ends at 7am. so you can crank that AC super low at night and hopefully that'll keep the house relatively cool throughout the day.
Give it a shot, it's definitely worth a try. I need better windows to keep my house more cooled but for now I have UV shades on the windows with the most sun exposure.
yeah...my windows are pretty shitty too. what's a good way to try and seal up an old house with terrible windows and doors? my house was built in '45. the insulation was fucking terrible. the windows are single pane, the doors have gaps everywhere. i just got a new AC system that's already cut my electric bill in half, but i'm sure it could be better if i could seal up some spots.
Also in Arizona, the 'peak hours' theory depends on your payment plan with the electric company. I tried your strategy with the plan where you pay less for off-peak use, but pay more for on-peak use (3-6 pm each day). After a year of this and some sweltering afternoons, I found my savings were about $1 a month. I decided to switch back to the basic plan.
Well this discussion also started with a similar idea actually. We have an airco and we also have a fan so we were trying to determine what would be the best , greener , cheaper way to cool the house . For example should we super cool it and try to make it last as long as possible while using the separate fan etc ? Thus we started making all kinds of guesses, estimations but none of us are engineers so i thought i would ask the question here.
The peak and off peak hours are definitely an issue here too and the elctricity is getting more and more expensive as well so we are trying to adapt to these changes.
For me so far the best and the most efficent method was (at least that's how it felt like to me ) to use the airco at a higher (warmer ) setting in combination with a separate fan but i dont know if this is actually more energy efficient then using only the airco with a bit lower setting (colder) or not. Thats how the discussion started and here we are :)
Edit: the fan i am using is rated at only 45 watts.
Fans use next to no energy compared to AC. I can't give you an exact figure, but setting it higher does significantly reduce electricity costs. I set mine to 28-29. It's 28.5 right now. Running a fan you can easily set it several degrees higher I think, I can go up to 30 or so with the fan comfortably. These are temperatures you get used to, take it gradually and just up it a bit, and try the fan. Don't suffer in it, but I think you'll gradually just get used to higher temperatures. I find it's much better too for when you do go outside, if you have super low AC inside all the time, the heat outside will seem oppressively hot, if you get used to a higher interior temperature it will help you adapt to the outside too.
Agreed totally. Its not only how cold the room is , temperature wise , but more about how cool it "feels like" . So i think using a fan in combination with an AC at a higher setting can save a lot of electricity too.
Where i live the humidity is rather high so even at a higher setting the AC reduces the humidity which makes it feel much more comfortable inside.
Yeah i noticed that too , that you can get used to a much higher temp. in combination with a fan. I am using it at 27 degrees setting and it feels comfy enough.
yeah that's a big one that people never think about. if you keep your home at a reasonable temp, it won't be so shockingly hot when you go outside. i don't mind it being warm in my house as long as i'm not asleep. gotta be nice and cool to get good sleep. i've tried it warmer with just a fan and i'll end up sweating in the middle of the night. that's a shitty feeling
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only way to truly know this is to run a test yourself. i dunno about where you live, but my power company shows daily Kwh usage on their website. so all you gotta do is set it to 1 degree higher for a day or 2 or maybe a week for better data. then set it back 1 degree and see how much the difference is. as long as the temperature outside is the same.
Well I am from Turkey and we dont have that here unfortunately. We only get the total usage of the whole house per month so the calculations are not that reliable . Thanks anyway.
If it's a window unit or something else with a plug, you might be able to buy something like a Kill-A-Watt -- plug the AC into this meter, plug the meter into the wall, it'll record how much energy flows through it.
No idea how you'd measure this if it's central air.
Yeah that seems like the simplest solution cause from what i am reading here from all the comments it seems like there are too many variables to calculate a reliable estimation.
Its not a central unit , i am basically just cooling a room in my house but it has a switch on the wall which i can install an energy meter i think. That's the only way we can get reliable data it seems.
Depending how it's wired, a wall switch might not be the actual power source. But yeah, I think this is the only reliable way to do it.
Short of this, best I can think of is to record the sound coming off of it, then write a program to analyze that and estimate what percentage of the time the compressor is actually on, and then you could guess 1200 BTU = 120W. But one of the steps there was "write a program", which is probably harder than installing an energy meter!
So, the way refrigeration works is very system dependent.
In industrial refrigerators, you actually save more energy by running around -13C than sitting at -1. It’s even more strange that -1 is about the same as +7. This has to do with stuff sitting at the freezing point of water is super inefficient as loads of “energy” needs to be pumped in to get it to change states.
In a home AC, I would GUESS it depends on where in the range you are, what the ambient is, humidity (a big factor for AC), the type of AC, and some other little factors like AC system insulation/damage/charge.
For room temp until about 28, and please excuse my attempt to convert my native freedom units to (and via) calculus, I would guess something like (5% + (3% times [Degrees off23c)) per each degree C off difference off of 23C.
So 23 is 100%
24 would be 92%
25 is 89% because (5 + (3 times (2)))
26 is 86% for being (5 + (9))
27 is 83%
28 is 79%
This becomes less and less accurate as it goes along because there’s no information about the system. It’s a rough guess, but might give you an idea of what we’re working with numbers wise.
Edit: thought of a better way, time how long the system runs for at one temp. Then time it at the other temp. Figure out it’s Duty Cycle as a percent of the lower temp and it should be roughly that percentage efficiancy difference.
TL;DRE 100% / (<time ON for 26c> seconds per 5 minute span) = X% / (<time ON for 27c> seconds per 5 minute span> BUT ONLY once the temp is stable after 15 minutes or more (warm up time)
So, the way refrigeration works is very system dependent.
In industrial refrigerators, you actually save more energy by running around -13C than sitting at -1. It’s even more strange that -1 is about the same as +7. This has to do with stuff sitting at the freezing point of water is super inefficient as loads of “energy” needs to be pumped in to get it to change states.
Yeah agreed but of course this is not the case for home airconditioner systems since it never goes below freezing point.
In a home AC, I would GUESS it depends on where in the range you are, what the ambient is, humidity (a big factor for AC), the type of AC, and some other little factors like AC system insulation/damage/charge.
I see, Well in the example we are assuming the ambient (outside temp) to be 33 degrees celsius and the goal is to drop the indoor temp to 25 vs 26 degrees celsius.
I didn't know that humidity would be such a big factor. Thanks for this info. I am guessing its about the cooling of the external unit and how effective the cooling might be depending on the humidity. Is cooling MORE or LESS effective when its humidity is high ? I would guess high humidity could make it more effective but i am not sure if this true per se.
The type of AC is a split unit with no inverter , if thats what you mean by the type .
I get the insulation and damage but i dont know what you mean by charge.
For room temp until about 28, and please excuse my attempt to convert my native freedom units to (and via) calculus, I would guess something like (5% + (3% times [Degrees off23c)) per each degree C off difference off of 23C.
This helps a lot . That's what i thought as well , that there would be a non linear relation with the increase in the temp difference (indoor / outdoor) and the energy requirements . I thought the difference would be bigger though so it s a bit of a surprise.
Thanks , great job. I now have a more or less idea on what to expect and that's exactly what i was asking so I will declare this post answered then .
Thanks a lot and take care.👍
Glad to help!
It’s mostly guessing but it’s likely not far off. It might be surprisingly close for a split unit like that, actually.
By “charge”, I mean the amount of coolant/refrigerant in the system. Less refrigerant tends to use more power but also tends to run MUCH colder. It’s a kind of balancing act.
Thanks again ,for these great comments and explanations. I have learned a lot from you today.
Take good care . 👍👍
home airconditioner systems
never goes below freezing point
Is that so? Even at the expansion valve?
No i meant the space they are cooling never goes below zero.
The most significant factor is heat loss of the room which is proportional with the difference in temperature as for small changes in settings we can assume the aircon operate in the same manor. Likewise we can assume the heat loss is linear due to the small chance in temperature is unlikely to change the property of the insolation in any significant way.
Under these considerations the change in temperature difference between the outside and inside changes from a delta of 8 to a delta of 7
So the AC needs to do 1/8 less work to move heat from the inside to the outside, which translate to 12.5% less power consumption.
Yeah there seems to be lots of different factors which on their own may not be so significant but when you add them all up they may have a significant impact on the outcome but sure the most important is the insulation of the room.
That's what i get from other comments as well, that its roughly around 1/8 th of a difference under "normal" conditions.
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It depends on the quality of your airco, and the size of the room/house it needs to cool. I think we're going to need some more info :)
The airco is just an average airco with energy class A . Its around 1200 BTU s. The size of the room is around 5 X 5 meters and 3,5 meters high . What other info would you need?
It doesnt have to be exact but an average amount would also be fine.
As u/cosmicosmo4 mentioned above/ below could we take it as 1/8 th decrease in electricity usage aproximately?
The heat loss of your house, in very simple terms, is proportional to the temperature difference. E.g. if you're set to 70 and it's 80 outside, you'll use twice as much energy when it's 90 outside. Because in the first case the temperature difference is 10 vs 20 in the latter case.
Yeah that's what i thought too that's why its a bit complicated to calculate it i guess. I was also thinking the amount of heat loss would also depend on the level of temp.-isolation of the room so that might also have an impact on it .
Edit: I am also thinking the way the airco works is not uniform through all various setting levels either. Basically at a lower setting there maybe more cooling and less circulation than on a higher setting (or vice versa.)???
Unless it is a really fancy unit, the compressor is on or off. Settings are the setpoint where the compressor is switched on and off, and fan speed. Maybe an econo mode to turn the fan on and of with the compressor, and maybe timers.
This is a really good question I sympathize with.
Unfortunately it's not easy to get an accurate ballpark. How thick are your walls? What insulation is inside them? What kind of windows do you have, with what surface area, and are they N/S or W/E facing? What coverings do they have? How high is your ceiling? These are all things you should know to do a load calculation (there are many calculators of varying complexity online). That BTU load is the energy (e.g. Watt-hours) required to cool the space, but even after doing a careful load calc... it's still makes a lot of assumptions, for example the max temperature difference...
My place has an E-meter so we can track usage day-to-day. That is very useful especially if you ever are traveling, to get an experimental estimate of this usage.
Yeah it sounds like a simple question but it definitely is a much more complex problem than it looks. So many variables , and so difficult to calculate them all so i guess the best thing would be , as you said it, just to get an energy meter and test it.
Thanks for the explanation.