energy usage calculation for home cooling
- Thread starter alarmguy
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Since you want to sleep in a cold room, shut the bedroom door. Put this Inverter in your bedroom window (Midea 12,000BTU Smart Inverter U-shaped window unit #RMW12QW-B). A new one is around $500. Midea did a recall on sold units. Walmart is selling the "restored" units for $249, free shipping, with 1 year warranty. I have watched several YouTube videos; people like it. Midea claims it uses $64 worth of electricity per year.
I would set the whole house thermostat at 77 degrees at night, too.
Sunny south facing windows; can you add curtains? or outside window awnings?
https://www.walmart.com/ip/Restored...BwRR2M0&irgwc=1&afsrc=1&sourceid=imp_19d2UF2H
I would set the whole house thermostat at 77 degrees at night, too.
Sunny south facing windows; can you add curtains? or outside window awnings?
https://www.walmart.com/ip/Restored...BwRR2M0&irgwc=1&afsrc=1&sourceid=imp_19d2UF2H
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A two ton AC hardly uses any electric anyways, your peak rate is still pretty cheap and it’s only 4 hours.
If it really bothers you, run it at 73 or whatever is comfortable til 2, bump it a few degrees til 6, then set it at 68 for sleeping.
If it really bothers you, run it at 73 or whatever is comfortable til 2, bump it a few degrees til 6, then set it at 68 for sleeping.
Doesn’t bother me at all. It was a “fun” kind of question.
Maybe could have posted it in a different way.
Impressed that the house made it through the day without the AC unit turning on and as a bonus sleeping in few degree cooler home I was curious if some math wiz could calculate if I was saving energy in this way. I knew an outside chance someone could answer but gave it a shot.
More or less the efficient home being cooled down at night when outside temperatures are coldest means the unit would run more efficiently and then the house “uses” all the stored cold energy during the hot daytime.
Just as people buy more expensive efficient appliances or heat pump water heaters I was curious if this was yet another cool idea.
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Wow!
Well at least you get the idea!
Energy is so cheap here and the new house so efficient my post was more out of curiosity.
However I agree with what you do, the thought crossed our minds being the main BR is in the back of the house I doubt we would run into an HOA issue as it wouldn’t be seen. No window or wall units are allowed.
Thanks for replying. I should have posted differently. I was just curious if what I was posting if it was more efficient cooling the house down with the unit during the cool nights that would then carry us through the day.
Seems to me like less wear and tear on the unit and a few degrees cooler while we slept as a bonus
Window and wall units not allowed in our community, however no one would see it from the street if I wanted to bother. Energy is cheap here.
I MADE A MISTAKE, house faces west which is ideal. I was thinking if I had a few solar panels the large side of our HIP roof faces south.
The phone’s ringing. It’s Jimmy Carter.
@alarmguy Unfortunately there is no way to really answer this with out some form of measurement of the energy use, be that direct or indirect. Your heat pump is a simple single stage unit so measuring the run time would closely approximate the energy use. There are multi stage and even variable speed (aka modulating) heat pumps available today that offer higher efficiencies.
Looking at this in terms of heat transfer, heat flows from areas of high temperature to areas of lower temperature and we refer to the driving force as delta T. The thermostat profile you desribe works to minimize delta T and should theoretically reduce energy consumption. Earlier @dnewton3 introduced the conept of thermal mass. Keeping the house and its contents (not just the air) cool create a form of buffer to absorb heat that enters durring the day and effectively keep the house cooler. That heat will be released when the thermostat is set lower at night.
Looking at this in terms of heat transfer, heat flows from areas of high temperature to areas of lower temperature and we refer to the driving force as delta T. The thermostat profile you desribe works to minimize delta T and should theoretically reduce energy consumption. Earlier @dnewton3 introduced the conept of thermal mass. Keeping the house and its contents (not just the air) cool create a form of buffer to absorb heat that enters durring the day and effectively keep the house cooler. That heat will be released when the thermostat is set lower at night.
The peak rate is so much higher than the non peak that it makes sense to lower your night time temperature to pre cool the house and “coast thru the day” and avoid running through the peak hours. You are definitely on the right track.
Nice, this was the intention of my post. I wonder how accurate our electricity break down is from our power company. It lists all the appliances/devices in the home and what they use every month. I THINK maybe I can even go by the day.
However, that is a great thought mentioning run times. Much easier as our Honeywell Thermostat records the run times.
I will be able to compare exact run times this year (2026) with 2025 in June, July and August etc. I can even compare by week or day but wouldnt be very accurate not knowing how much sun was shining on any particular day and the temperature. Of course the variable will be outside temperatures, still will be an interesting way to test the theory over time.
Regarding your second paragraph, exactly my thoughts but I wasnt sure my thoughts were anything but thoughts.
The home in essence can be considered a storage medium, not unlike a power wall or any other. So why not use it to its advantage?
The A/C unit running at cooler night time temperatures is more efficient all by itself because of those cooler nighttime temperatures. Using that to the homes advantage, cooling the home down to an acceptable low temperature at night will use that stored energy during the hot daytime. That cool energy is stored in all the fixtures of the home including walls, slab, ceiling, insulation. Then right about the time evening comes the unit kicks in at 6pm to a 75 degree setting and at 11pm 70 degree setting. This I suspect will be enough where the unit will not run daytime with the thermostat set at 77 degrees starting 7AM and kicking up higher to 79 degrees at 2pm to 6pm before kicking back down. (this actually worked yesterday, however the outside temperature only peaked at 87f)
My OP really didnt explain why I was posting, your answer is what I was looking for. It's not all about saving money, My wife and I do however not like to give companies money for stuff we cant use or need. Same goes for internet access. Loved our fiber 300/300 service but now we are forced into 500/500 that we cant not possibly use, yet no choice and $10 more a month.
I think what many others may not realize is the wear and tear on the HVAC system. In our low cost electric area I suspect over time that cost of wear and tear is more costly.
An example I think I posted about. Our last home, purchased new, 3000sq ft. Two builder supplied HEIL units. I forget the tonnage, grabbing at straws maybe a 2 or 2.5 ton on the main floor with NG heat pack and a 2.5 to 3 ton heat pump on the second floor. People in my community were replacing units starting around the 8 year mark. We never had issues, except for a contactor and capacitor in each unit, one fan motor in one condensing unit. I replaced them all. We sold the home at 16 years old, still working perfectly and buyers also had an HVAC inspection company inspect it (inspections only, they dont sell units). I still drive by about once a year when visiting my son as I past buy the area. At the 19 year mark they are still there. In a cheap low cost electric area not spending money on new units may be more cost effective than the electric. We lived in the Midlands of SC for 16 years, daytime summer temps exceed many places in Florida. 90+ degrees for what seemed like months at a time.
Anyway, thanks for your post
This is my run time for June 2025 so I will try this overnight cooling thing and see how things turn out. The wild card this year is we now have variable rates instead of fixed rate of 10 cents kWr. so I will also compare cost but suspect it will be lower. Prime concern to me is run time (hours) that I am putting on the unit. Last home two units, this one, more closely matched to the sq footage, also accounting for insulation type and r value and type of window glass. The good news is the house is nice and dry here at the coast but the unit does run longer and that is ok. Will be cool to see if it's reduced with the new schedule I am going to try.
There is one more thing that bothers me about the house, and I dont know if it's needed. I guess meeting the latest energy standards its a tight house. When the HVAC unit kicks on, in one of the airflow intakes is a 6 inch duct with a solenoid that opens a flap, it draws in hot outside air in the summer and cold in the winter when the unit turns on, the intake is on the roof. I do notice our CO2 levels get up to around 1000 with my wife and I when the unit doesnt run and depending how much it runs, like in winter almost constantly on brutal cold days the CO2 can go down to roughly 550 Even at 1000 it is still green though. I was thinking of disconnecting the solenoid. Or limiting how much the flap opens being this is a small house and I am sure the same set up is used in larger homes.
Ps for 20 years we have moved down south we NEVER open our windows. Not worth the extra cleaning and dust. Double that now with humidity from the ocean.
I wonder if HVAC units have a life expectancy in hours.
SO June 2025 it ran 276 hours. I will be able to check June 2026 when it is done, same goes for July 2025 at 375 hours
Appreciate your post. (yeah, I am an over thinker, its ok, hopefully will keep my brain young
)Below is 2025- looking forward to compare to this year as an experiment.
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- Joined
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I moved to Arkansas in 2017. (Close to the 1992 World Record Brown Trout) My ranch home is 1900 sqft and built 1993. The builder used 2x6 walls with R19 insulation, R30 blown installation in the attic. Peak-vent roof. Brick house with a crawlspace. I met the son of the builder and he said that building homes "energy efficient" was stressed in 1990's. My house is also wired 12-2, 20amp. And Copper water lines. This year the weather pattern has shifted. I go weeks without AC.
You could do an inverter packaged unit and hide the compressor behind a fence-wall.
I lived in a HOA community in Colorado and had the similar restrictions. I ran the lines through the garage. My master bedroom was above the garage.
My home today faces east; I'm glad because I can work in my garage during the hot/sunny afternoons. The previous owner updated the house for old people. He was 81; I'm now 75. Chair height toilets, Real Red Oak flooring and Ceramic tile in the kitchen and bathrooms. Remodeled the bathrooms; one has a large shower. And he did not install handicap handles.
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Yes, see the post I just made below yours #31
When thinking through all my insanely long posts and also @Astro_Guy post it all makes sense now. It is going to be an interesting experiment and I have the data to compare last years AC runtime to. It's not only the peak, its also the HVAC unit will be more efficient running in the cooler nighttime temperatures than at the high temperatures during the day, right now that is about a 20 degree difference and typical.
Also besides the peak time, hopefully shaving off run times (WEAR AND TEAR) of the unit. I think that may matter more than the electricity cost being it's so cheap here.
Thinking about it based on other posts too, the house is a storage medium not unlike let's say a Tesla Powerwall or any battery. Buying energy when most efficient (cool night time temperatures in addition to lower rates), storing it and using it when the temperatures are much higher and also the rate for electricity. Also @SC Maintenance made a great post about commercial building management in Post #11. I LOVE THIS stuff. Do to my post, some think all I care about is money. NO, however I dont like to give it away for nothing. No different than those with solar panels or EVs of anything in life. We live good and out home temperature is always perfect for us. We dont compromise we DO do things with efficiency in mind.
If I REALLY want to overthink it, this is one area a slab house might benefit from too. The slab and soil under the home will store the cold in addition to everything else.
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We dont open windows, not for almost 20 years now, since moving south. Pine pollen in our last home of 16 years taught us that and dust in general in our new 3 year old home with building going on in the fastest growing county in the state and top 10 of the nation.
Regarding #1 yes, I would agree however this year is a new pricing format from the utility. However in my reply to astro_guy a few posts up, he mentioned comparing run times and I can do that! I'll be able to compare 2025 run times with 2026. Very cool! Literally *LOL*
This isnt about comfort, we are always comfortable and that is why we never opened the windows for almost 20 years since moving south.
The house stays cleaner with less work.
I think you are on the right track with pre-cooling during the cheap times and just bumping up the thermostat for those 4 hrs. Some window exterior window shades to keep the direct sun out of the house in the afternoon would help too. Shade trees as well for the whole house?
My parents house has almost no direct sunlight on it, except for few hours mid-day on the roof, and they could keep the 2600 sqft bungalow quite nice with a window AC unit, even with a few days of 90s F and high humidity in a row.
They have forced air heating and now switched to a central AC unit(mostly for resale purposes) and its oversized at 2 tons (the 1 ton window unit was keeping up) so the house cools to quickly before as much humidity is removed.
My parents house has almost no direct sunlight on it, except for few hours mid-day on the roof, and they could keep the 2600 sqft bungalow quite nice with a window AC unit, even with a few days of 90s F and high humidity in a row.
They have forced air heating and now switched to a central AC unit(mostly for resale purposes) and its oversized at 2 tons (the 1 ton window unit was keeping up) so the house cools to quickly before as much humidity is removed.
Well said, I can see you understood the intention of my post if is wasnt clear, loved the commercial part. Yes, now that you mention it, big companies do this, and have for along time now.
It's about maximizing efficiency, wear and tear, cost to run with little to no disadvantage.
Love this stuff. SO the experiment begins.
As of yesterday, hit 87 degrees here at the peak.
Here is the cycle=
House started the day at 70 degrees 8AM
Thermostat kicked up to 77 at 8AM
2pm (peak time) I have the thermostat kick up to 79 degrees
6PM down to 75
11PM down to 70
For the entire cycle, house never exceeded 77 degrees. Unit never came on during the daytime.
The 2pm kick up to 79 is an experiment, house never hit 79 yet, not sure if I will leave that setting in or not. I moved south because I like the heat. Im not a typical southerner who hates the heat. In fact, only 4 people out of 60 (I misposted yesterday, thought it was 30)showed up for out pickleball match yesterday, my wife, I and another couple, windless morning, hot sun, signing out right now to repeat!
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Just curious...do these rates reflect the base kWh prices, or are they the complete cost? Here in my part of TX the base rate is around 8.5 to 9.5 cents per kWh, but with delivery charges, taxes, etc. they always seem to hover between 15 and 16 cents all-in. This is the figure I use when comparing energy providers.
I've found this approach to be very popular here on the Texas coast as well...but personally don't get it. We live about two miles from the Gulf and love the "open window" season (usually between November and March). The sea breezes are very pleasant to us, and I appreciate the accompanying $60-$80 electric bills. To us, it's somewhat funny to hear all the A/C compressors clicking on when it's 70 degrees outside in the middle of the day.
One drawback I've noticed - a lot - with this approach is that the original builder-grade windows may seize if not used for many years. When we bought our 20-year-old house in 2023, 10 out of 12 windows were completely stuck shut. Whether this was due to corrosion, foundation settling, or something else, it's a common issue here. There are many homes in my area with permanently-closed windows.
Everyone has their preferences. 1. my wife has minor allergies. 2. we like air conditioned air when in the house however we are VERY outdoor activity people. 3. the house stays pretty much dust and pollen free 4. we like the dry air, again, sitting around the house/
Choice is good! We elect not to open windows for 19 years since moving south from Long Island.
@Capt W
Our electric bills last summer. Perfectly reasonable and filtered air keeps the duct down and the humidity.
June, July and August billing periods
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