energy usage calculation for home cooling

[alarmguy]

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.


View attachment 338504

I agree we dont post complete costs in here. I am one who does in many other threads on the subject. This was a different case and wasnt comparing rates.
The more power we use the cheaper it is, total cost. Our cost is roughly yours at the high end. We got walloped last month per kWh @ 19 cents because we used like, zero power, in-between seasons in April and the base facility charge stays the same

This was march mix of heat and cooling, below 13.5 cents kWh total cost

This below is Feb, more heat usage and an extreme kWh's 12.89 cents

Last summer ran around 800 kWh to almost 1000 kWh, June, July and August. I cant directly compare since we moved to peak usage rates now, which is between 2 and 6 summer and 6 and 9 winter.

 

[alarmguy]

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.

We are in good shape for summer sun exposure. Sun is overhead. Morning comes in from the east, over the top of the house, late afternoon the west and only effects two windows of one BR, the rest is the attached garage. As posted above our energy bills or cheap. It will be interesting to see the run times with this new cold cooling at night schedule.
BRIGHT sunshine, 88 degrees outside, 1:15pm afternoon, house is only up to 74 degrees from its 70 degree night time low. WE will make it until 6 pm before the unit kicks in and lowers us to 75 and then ultimately 70 at 11:15PM

 

[Capt W]

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
View attachment 338519 View attachment 338520

No value judgements here! In fact, us open-window people are a distinct minority around here. We simply love the sea breeze and opening up the house to let it blow through (as able). Your summer bills are awesome, BTW. That's about what we pay for a 1400 sq. ft. house in the summer.

 

[alarmguy]

No value judgements here! In fact, us open-window people are a distinct minority around here. We simply love the sea breeze and opening up the house to let it blow through (as able). Your summer bills are awesome, BTW. That's about what we pay for a 1400 sq. ft. house in the summer.

It’s all good!
We live a couple miles from the ocean and in fact was just there last night and walked 2 miles with the dog on the beach!
We also have a boat which is sitting right now, waiting to get out on the water soon!
Love the ocean

 

[jghall00]

You can monitor your HVAC and other appliance energy consumption using Home Assistant. I have Micro Air soft starts on my HVAC units. They have BLE radios integrated for use with the Micro Air app. I use an ESP32 as a bluetooth proxy to capture that data, so now I can tell when the HVAC has run, for how long, and how much power they consumed. I just added this other day because I misplaced the proxy board after the first time I attempted to set this up. But it's partially working now, except that I need it to support both HVAC units. You can add clamp monitors to the panel that will feed power consumption data to Home Assistant.

I have my HVAC configured to reduce the interior temp to 65 starting around 90 minutes before 5AM, when my free nights plan ends. It then raises the target temp to 72 degrees. The house slowly warms up, but by the time it warms enough for the HVAC to kick on, the sun is usually out and the HVAC is coming from solar. If it's cool or overcast, the house doesn't warm as quickly.

 

[alarmguy]

Ok!!
I think this is going to work nicely.

It’s 86° outside at 5:15 PM
It’s 115° in the attic (oops now 114)
The air-conditioning still has not come on since 7 AM this morning when the house was 70°f from its nighttime setback.
As described in the previous posts, it bumps up at 7AM to 77f until 2PM to 6 PM where it ticks up 2 more degrees, which is the summer peak usage rate of 21 cents a kilowatt hour for those four hours. All other hours are 7.9 cents kWh.
At 6 PM it goes down to 75 for the evening hours, then at 11 PM it lowers to 70f for sleeping and the cycle continues on the next day starting at 7AM with a nice cold 70 degree house. This is now the second day plus some more initial days of thought on it. The AC unit has not come on during the daytime at all.

These are not outdoor temperatures below. They are remote sensors.
Sensor one is in one bedroom, sensor two in another bedroom, sensor three is in the attic
Bottom temperature is the house at the display near the kitchen.

A

 

[alarmguy]

OK, 6 PM the air conditioner has not had to come on all day since 7 AM when it went from 70° setting to 77° and then at 2 PM to 79°
House never passed 77°
Now at 6 PM it will set back to 75 at 7.9 cents a kilowatt hour

 

[Skippy722]

I agree we dont post complete costs in here. I am one who does in many other threads on the subject. This was a different case and wasnt comparing rates.
The more power we use the cheaper it is, total cost. Our cost is roughly yours at the high end. We got walloped last month per kWh @ 19 cents because we used like, zero power, in-between seasons in April and the base facility charge stays the same
View attachment 338515
This was march mix of heat and cooling, below 13.5 cents kWh total cost
View attachment 338516
This below is Feb, more heat usage and an extreme kWh's 12.89 cents
View attachment 338518
Last summer ran around 800 kWh to almost 1000 kWh, June, July and August. I cant directly compare since we moved to peak usage rates now, which is between 2 and 6 summer and 6 and 9 winter.

1528kwh would cost me over $350...

 

[alarmguy]

1528kwh would cost me over $350...

Thats crazy but I believe you, Born, raised most of my life on Long Island until 20 years ago. It's crazy up there.
... and you, I thought you would have hydro up there.

 

[Skippy722]

Thats crazy but I believe you, Born, raised most of my life on Long Island until 20 years ago. It's crazy up there.
... and you, I thought you would have hydro up there.

We were primarily coal and NG.... until they decided to go full send on renewables. Now we have the highest rates for both electricity and gas delivery charges (double my actual gas cost) in the whole state and we get at least 1 24 hour minimum power outage a year. Last month it was ~30 hours.

 

[alarmguy]

We were primarily coal and NG.... until they decided to go full send on renewables. Now we have the highest rates for both electricity and gas delivery charges (double my actual gas cost) in the whole state and we get at least 1 24 hour minimum power outage a year. Last month it was ~30 hours.

Wow,
Since moving south almost 20 years ago, first in SC and now NC
The most we ever paid for electric is 10 cents a kWh. True this year we have peak times 3hrs winter, 4 summer. However it still works out to less than 15 cents most all months, including all "other" charges thrown onto the bill - meaning actual payment is on average 14 to 15 cents kWh cost. The most expensive few months per kWh are the ones where we do not use much electricity (between seasons) because the fixed costs on the bill are still the same. Over 50% of power in SC is nuclear, my new state in NC only 27%
There is a private company looking to restart the construction of 2 nuclear plants in SC after the debacle almost 10 years ago/

Ok, this is funny to my wife and I. When first moving south from Long Island almost 20 years ago. We were always thinking about getting a generator/inverter (and still am now that we are near the coast as of 3 years ago)
Anyway, you move down here like so many thinking hurricanes, tornados = power failures. WELL, living up at Lake Murray SC for 16 years, 100% true. The most we ever lost power was 4 hours. We got so excited *LOL* it was winter and I started the gas fireplace up only for the power to come back on in 4 hours.

That was it. Ok, now on the coast, true, more of a chance of a direct hurricane hit. But it you think about it, news reports never point out the strongest wind field is not typically for than 50 miles wide, yet it is made to sound like a whole coast is engulfed.
Anyway once again most all our friends and neighbors in our new communities are new here, unlike us. The come from the northeast mostly, flush with cash and first thing on many minds are power failures. Not a lot but a fair amount end up having expensive whole house generators. I think they run 15 to 20k installed. Long time residents here, mention the last time they used it was back in 2018. Big investment and annual maintenance, plus monthly automatic run times. I do sometimes think about a duel fuel small unit with 220 capability. Maybe 4 or 5000 watts. to run a window AC that we would store in the garage with the portable unit, refrigerator and our sewer system pump, plus instant LP hot water heater. Then every year goes by and I think, why?

 

[Skippy722]

Wow,
Since moving south almost 20 years ago, first in SC and now NC
The most we ever paid for electric is 10 cents a kWh. True this year we have peak times 3hrs winter, 4 summer. However it still works out to less than 15 cents most all months, including all "other" charges thrown onto the bill - meaning actual payment is on average 14 to 15 cents kWh cost. The most expensive few months per kWh are the ones where we do not use much electricity (between seasons) because the fixed costs on the bill are still the same. Over 50% of power in SC is nuclear, my new state in NC only 27%
There is a private company looking to restart the construction of 2 nuclear plants in SC after the debacle almost 10 years ago/

Ok, this is funny to my wife and I. When first moving south from Long Island almost 20 years ago. We were always thinking about getting a generator/inverter (and still am now that we are near the coast as of 3 years ago)
Anyway, you move down here like so many thinking hurricanes, tornados = power failures. WELL, living up at Lake Murray SC for 16 years, 100% true. The most we ever lost power was 4 hours. We got so excited *LOL* it was winter and I started the gas fireplace up only for the power to come back on in 4 hours.

That was it. Ok, now on the coast, true, more of a chance of a direct hurricane hit. But it you think about it, news reports never point out the strongest wind field is not typically for than 50 miles wide, yet it is made to sound like a whole coast is engulfed.
Anyway once again most all our friends and neighbors in our new communities are new here, unlike us. The come from the northeast mostly, flush with cash and first thing on many minds are power failures. Not a lot but a fair amount end up having expensive whole house generators. I think they run 15 to 20k installed. Long time residents here, mention the last time they used it was back in 2018. Big investment and annual maintenance, plus monthly automatic run times. I do sometimes think about a duel fuel small unit with 220 capability. Maybe 4 or 5000 watts. to run a window AC that we would store in the garage with the portable unit, refrigerator and our sewer system pump, plus instant LP hot water heater. Then every year goes by and I think, why?

I'm running my whole house off a 6250 watt portable generator, it even runs the AC but my central air is only 1.5 tons. It is wired into the panel with an interlock kit.

The Carolina's are gorgeous, we just recently went for the first time.

 

[jghall00]

We were primarily coal and NG.... until they decided to go full send on renewables. Now we have the highest rates for both electricity and gas delivery charges (double my actual gas cost) in the whole state and we get at least 1 24 hour minimum power outage a year. Last month it was ~30 hours.

I have free nights because of all the wind here in Texas. It's awesome. Renewables are the cheapest source of new generation.

 

[kenny91]

I know this is a long shot and maybe some day my A.D.D. will have me set the time aside to figure this out. The answer might help others too. I dont know. This is some really deep thought process in regards to energy consumption by our HVAC running in the summer.
Note, we never open windows, so it will and always be running frequently.

Structure-
New home, 2023 - 1800 sq ft., stick construction, slab, vinyl siding, one level, HIP roof, R-15 wall insulation, R-32 blown in the attic, Low E glass, slightly above builder grade LENOX 2 ton HVAC heat pump, ML17XP1-024 south facing house bakes in the sunlight all day long,

Ok, so, right now, maybe because the ground is still cool is a possibility.
We have been running the AC unit at 70 degrees from 11:15pm to 7:15AM
At 7:15AM the thermostat automatically goes up to 77 degrees
At 2PM the thermostat goes higher to 79 degrees
At 6PM the thermostat goes to 75 degrees then the cycle repeats going down to 70 degrees at 11PM

Peak rate is 21.5 cents kWh for 4 hours 2pm to 6pm, the other 20 hours the off peak rate is 7.95 cents a kWh.

I used to set the thermostat at 73 while sleeping but I have observed the following such as today. Bright sunshine, no clouds, 87 degrees at 4PM
Last night at 11:15PM the AC kicks down to 70 degrees, we love sleeping in the cold. when it kicks up to 77 degrees at 7:15 such as today, it is now 87 degrees outside at 4Pm, that is already 2 hours into the peak time and the AC unit has not turned on all day long since 7:15AM from its night time setting of 70 degrees. ON top of that, the house is still only 76 degrees. It is very possible it will not turn on by the time the peak expires at 6PM.

So the question is, is setting the night time thermostat to 70 degrees noting what I typed above saving money over setting the night time temperature like we used too at 73 degrees leaving all other settings the same?

I have another wrinkle that I think 70 degrees might be in favor. The night time setting down to 70 degrees is just that, nighttime when the night time air is MUCH cooler making the unit much more efficient. Being we live near the ocean, once night time falls and the sea breeze finishes cooling outside down it is significantly cooler. Like tonight with a high temp of 87 daytime, it will be 60/70 degrees night time. As summer goes into full swing those night time temps will be higher but still lower than daytime.

I don't expect many comments, I know this sounds insane. I think there is a thread somewhere on over thinking... but thinking is good, I think!

Honestly? we normally have our daytime temperature as it is, 77 degrees, after dinner time 75 and sleep time 73 this was last year and years before. However this is the first year of peak rates in this home.

So, I am wondering, after observing that when kicking the AC down to 70 at night, which we like. 11pm to 7am, once it bumps up to 77 degrees at 7am, then to 79 degrees 2 to 6PM the unit doesn't come on, though I do expect at times it will for the last two hours but not sure how much. I just know what is happening now.

Your logic is sound. By dropping the temp to 70 at night during off-peak hours, you are basically using your home as a thermal battery. Since the house stays cool enough to coast through the expensive peak hours without the AC turning on, you are very likely saving money. It is a smart way to game the peak-rate system!

 

[QwikKota]

That seems like a big delta for the A/C to deal with. If you can ramp it up more slowly that would be better for the unit. I am pretty frugal but even I keep it at 75 or below when we are home. My Wife would revolt at 77.

 

[QwikKota]

I have free nights because of all the wind here in Texas. It's awesome. Renewables are the cheapest source of new generation.

The free nights are a bit frustrating on my Chariot Energy plan since it is 11pm to 6am. If it were 10am to 7am to more closely match our sleep schedule, it would be awesome.

 

[alarmguy]

Your logic is sound. By dropping the temp to 70 at night during off-peak hours, you are basically using your home as a thermal battery. Since the house stays cool enough to coast through the expensive peak hours without the AC turning on, you are very likely saving money. It is a smart way to game the peak-rate system!

Yeah, right? This was my thinking, glad a few saw my point.
I like those words "thermal battery" I cant wait until the end of June 2026 to compare the HVAC run times with June 2025

I will be able to see the last two weeks of May 2026 to compare to May 2025 but two weeks isnt enough and weather very variable in May.

One thing I came to realize besides saving during that 4 hour summer peak period is that its much easier on the HVAC unit, to be running and cooling down the house when night time temperatures are a pretty standard 20 degrees cooler and no sunshine to compete with.
Thanks for your post.

Ps I want to stress, as my previous posts indicate. It's not about being cheap, we like sleeping under the covers at night. It's a win- win doing so, furthermore, we like the heat of summer and always kept our home on the warmer side meaning 75 to 78 degrees depending on time of day. SO the only change is instead of the thermostat going down to 73 or 74 degrees when sleeping it now goes down to 70 and we glide through the daytime hours right up to the start of evening at 6pm where it kicks down to 75/76 which TV and then 70 at 11PM

BTW, temps peaked at 87 the last few days, HVAC never turned on from 7:45AM to 6PM. AS we get to the heat of summer I am sure we may have days that it does and that is ok.

 

[KrisZ]

I used to do that in Canada and California with the peak and off-peak rates. If the house is well insulated it works quite well and reduces the energy consumption.
I still do this in Texas but with a lesser temp difference since the rate is constant, because we still prefer to sleep in cooler temps.

 

[Skippy722]

I have free nights because of all the wind here in Texas. It's awesome. Renewables are the cheapest source of new generation.

One flat rate all the time here, no other option except paying MORE for the utility to purchase REC's (renewable energy certificates) on your behalf. Gotta love a "regulated" monopoly.

 

[alarmguy]

That seems like a big delta for the A/C to deal with. If you can ramp it up more slowly that would be better for the unit. I am pretty frugal but even I keep it at 75 or below when we are home. My Wife would revolt at 77.

Im not sure about "delta" I guess I could look it up. Though I think I have an inkling *LOL*
A reset from 75/76 to 70 at 11PM doesnt seem too extreme being it is so much cooler at that time of night compared to daytime? By then the sea breeze has really cooled off the air outside and home temperature falls pretty quickly, in addition the unit isnt competing with the heat of the day nor the sunlight. (not that I know what I am talking about) But just seems reasonable. This in addition to the unit not turning off and on all day long.

Yeah, we like warm and glad we moved south almost 20 years ago.
If you saw my posts, we never opened our windows now for the last 19 years.

Not sure if you saw all my sometimes insane long posts and actually last evening my wife commented as we settled to watch TV it was on the cool side at 75 degrees so I programmed 76 which it the evening.

Monday thru Friday
11PM setback to 70 degrees (sleep time)
7:45 AM resets to 77 degrees (Wake up time)
2PM resets to 79 degrees
6PM resets to 75 (now 76 degrees as of last night) (evening time)

Then the cycle starts again at 11PM above.
Weekends are different and the afternoon reset goes to 81 degrees at 12 noon to 6 or 7PM because we are never home most afternoons. Other than that pretty much the same idea as Mon thru Friday, however with the 70 degree night time setting the house would never get close to a weekend 81 anymore. Though I am sure the hot summer months it may. I wont know yet.
Very much looking to compare the HVAC run times with last year as the summer wears on.