For those of you who didn’t see my article on my recent epic vacation, I had the very rare opportunity to take an entire month off and visit Vermont with my wife. My vacation rental happened to coincide with the calendar month of July, so I was away from my home from July 1 – July 31. We turned the A/C up when we were away for this extended absence, as most people would do. I just received my monthly email report from my thermostat, and the results are pretty insightful.
How Much Does Air Conditioning Contribute To Electricity Use?
The short answer is, “it depends.” But what does it depend on? In most cases, people want to know what percentage of their electrical bill is caused by air conditioning. Some of the factors include:
- How good are your insulation, windows, and doors?
- Do you have a pool? All else being equal, pool homes will naturally have a lower percentage of air conditioning use because the pool will be a big consumer of energy in total. And whether you heat your pool with electricity has a huge impact.
- What other appliances are in your home?
- What is the age, condition, and efficiency rating of your air conditioning equipment?
- What temperature do you set your air conditioner to?
That last one is the main focus of this article.
Increase Setpoint for Energy Savings
You will find all kinds of rules of thumb on the Internet that tell you how much you will save by increasing your setpoint 1º. The problem is, it’s not a linear relationship. For example, changing your setpoint from 75º to 76º will have a greater effect than changing your setpoint from 80º to 81º. There is a diminishing return.
The internet tells you that you can save 3-5% per degree. Maybe. Who knows?
There is no question that increasing your setpoint can save you substantially. The question becomes, is it worth it? After all, we have air conditioning for comfort (and sometimes safety).
A Real World Example
I mentioned that I just received my monthly energy report. A copy appears below. In the month of July, my hours of air conditioning use dropped by 271 hours, from 415 to 174! That’s a 65% decrease in air conditioning run time.
How did we achieve that? First, we normally have our setpoint at 73º. That might sound low, but who knows how accurate that really is. It might actually be 75 or 76 in the house. The point is, we are comfortable at 73º. We do not adjust the temperature on a schedule, and rarely ever manually adjust it. During our absence, I had the setpoint at 80º, which was more than adequate to provide dehumidification and keep the home fresh for our return.
Dollars and Cents
These numbers are helpful, but don’t tell the whole story in terms of percentage of bill reduction. And since Air Conditioning wasn’t the only savings when we were gone, we can’t just look at the electric bill and conclude how much this change in setpoint impacted the bill.
The rule of thumb in Southwest Florida is that air conditioning contributes 40-50% of the total annual electricity bill. That is going to vary greatly based on the factors mentioned previously. Since these are annual averages, in the summer months you can expect the percentage to be much higher – somewhere around 75% of the total bill.
Taking that into account, if we were able to reduce our air conditioning costs by 65%, and air conditioning is 75% of a typical bill, we probably reduced our total bill by almost half.
65% x 75% = 48.8%
But what is that in dollars and cents? Well, I know my air conditioner draws about 3,500W in electricity on average, so doing the math with a 271 hour reduction, that yields a savings of $128.
271 hours x 3.5 kilowatts x $0.135 electricity cost per kWh = $128
That’s a pretty good chunk of change!
Data Is Power
No pun intended, but you gain a lot of power when you are armed with data. The ultimate information would be to measure the air conditioning use directly using a datalogger. Those exist, but there is, of course, a cost associated with installing the required hardware, and it takes time to analyze the results. There are data monitors that can measure your whole home and “sense” the air conditioner usage, but they’re not perfect. Other dataloggers use current transformers to measure the air conditioning circuits directly.
Nonetheless, even having this anecdotal data from my air conditioning smart thermostat is valuable. If gives me a sense of how much energy I can save by adjusting my setpoint.
Final Thoughts On Air Conditioning Setpoints and Energy Savings
The thought of saving $128 a month is appealing, for sure. Each person will need to assess whether making changes is worth the money saved. In my case, I know that 7º is not realistic. My wife works from home, and after a long hot day outside in Southwest Florida, I want to come home to a luxuriously cool home. So it is unlikely that we will make significant changes, but it will make us more responsible with turning up the air when we are gone for any significant period of time.
And the savings are not year-round. In months where we are not using the air conditioning, there will be no savings. You can’t take this data an extrapolate it over 12 months.
While energy efficiency is important and effective, the better approach, in my opinion, is to just offset the lifestyle we have with solar energy. And that is exactly what I have done. We have solar panels that offset our total annual electricity use, netting essentially a zero dollar bill (aside from the FPL minimum bill charge). That might not be realistic for you, but anyone can install solar panels to offset a portion of their electric bill. There is no requirement to get to net zero, and often a smaller system has a better ROI.
Our next move will be replacing our air conditioner with a more efficient unit. That will further reduce our energy consumption and allow for an even better lifestyle. We can turn our house into a refrigerator, haha. But in all seriousness, solar energy can be viewed as a lifestyle improvement in addition to a money saver.
