Energy efficient mini split?

I had a mini split system installed 5 weeks ago, 2 downstairs, 3 upstairs. From everything I read, they're supposed to be very energy efficient. My electric bill this month was almost double from last month. While I didn't get the system for this reason, it still surprised me. Now before, I had one 18,000 btu window unit downstairs, that I only ran during the day, and none upstairs. Still, I didn't expect this much increase. Does this sound right? Maybe I need to adjust the temps. It was really hot in August, but so was July.

 

I was always under the impression that they were efficient not only for the sake of the unit itself but also because you only used the ones that were needed in occupied rooms.

That does seem odd unless they were all on!

 

They were all on because the guy told me he didn't like turning them off and to just adjust the temperature. I'm thinking maybe I should turn off the ones I don't use or adjust the temperature a lot more than where I have them set. Appreciate any input.

 

What temp is set?

I have 2 mini-split heat pumps that are 10 years old. I very seldom use the heating capability in spring/fall. I am having a third cooling-only unit installed in a couple of weeks. This summer definitely seems much hotter than last year. My year-to-date electric costs are 8% higher than last year. My August bill is 27% higher than last year. Last year at my location there were 290 cooling degree days in August and this year 328 (a 13% increase.)

As I have posted earlier I use Cielo Eco-Breez and Alexa to schedule and control my third floor bedroom unit. If it gets above 80* in the afternoon, I start cooling so it will be 70 at 11 PM and keep it at that overnight. My second floor family room unit is controlled manually depending or temperature and occupancy. My new unit will be on the first floor in the kitchen/dining area but sized for the entire floor.

A friend of mine is coming for dinner tomorrow. He installed mini-splits last year and runs them continuously. I will ask how his electric bills are this year compared to last.

 

Well, I had them at 74 or 76 depending on how hot it was. I guess I wanted to keep the whole upstairs cooler. I decided to turn off the two in the bedrooms that aren't used since it's not so hot. Guess as long as I don't turn them on and off continuously, shouldn't matter. I'll turn the temps up higher in my bedroom during the day too and see if that makes a difference. I suppose running them all day and night, upstairs and downstairs is what made my electric bill so much higher. Still tho, didn't think it would double the price.

 

You can do a little experimenting to find out how much time is needed to get to the temperature you want. Also, you may not need an Eco-Breez if your remote control has an automatic stop/start timer. (My Mitsubishi units have that, but only for one time each every day.)

It took me a season to settle on a schedule. In summer I am away from home most weekends (Fri-Mon) so I also schedule for that.

Third floor bedroom under the roof, no attic:
Tu-Th: 8am: Off, On at 90*, cool to 85*, Off at 84*; 2pm: On at 80*, cool to 75*, 6pm: On at 75, cool to 70, off at 69. Continues until 8am.
Fr-Mon: 8am: Off, On at 90, cool to 85, Off at 84.
Mon: 12 noon, On at 80, cool to 75; 6pm: On at 75, cool to 70, off at 69. Continues until 8am.

This schedule overcomes the heat that builds up during the day and gets the temperature down to 70 for sleeping by 10:30.

 

Is it actually double the usage or double the price ?
Electric rates have gone up sharply.

You need to base your current usage vs the last years.

 

Okay, thanks. John, I guess I just have to experiment and maybe leave the rooms not used set higher or off and adjust the downstairs too. This is new to me. I'm retired and live here year round, so I'm home most of the time. My remotes have a "powerful" button, to quickly get to a lower (or higher) temp.

Pete, I'll upload a few pics of the usage/rate later. As for the past two months, the usage almost doubled, the rate was the same. I'll check the previous year.

 

The "Powerfull" function runs the unit at maximum cooling (or heating) for 15 minutes. It works well to cool the room air down quickly but is only effective if you are in the room. Latent heat stored in walls, furnishings, etc. takes a longer time to cool down. I do not schedule my family room unit for automatic operation but the latent heat is not an issue. I set that temperature to be 79 and the direct cool air flow at low fan speed is sufficient. If the room is too hot initially, I use Powerfull to start. I also have ceiling fans in both rooms that can make it feel cooler. Conventional wisdom says that a ceiling fan can make temperatures seem 3 to 4 degrees cooler.

 

So nix this question. What a dunderhead I am, lol. I was comparing the wrong two months (June and July when I still had the window unit). The newest bill (August, had it installed Aug 2) is actually slightly less than July's bill. Sorry to waste everyone's time.
Checking last and this year's, it's almost $30 more per month. That was due to a rate increase.
I should probably leave the two bedrooms not being used, off anyway. Would probably be even cheaper.

 

No to worry. We got you thinking and you discovered the problem.

 

My friend who has gas for heating, all electric for everything else (cooking, water heating heat pump, AC mini-splits, etc.) thinks his electric bills this summer are about $20 more per month than last year. HIs mini-splits were operating last year and he does not recall a noticeable difference in his electric bills then.

 

Shadeladie. I did not see any comments or specifics about how the unit was sized for the house. I did see you have 2 levels. And, you noted you have it set on "on" so continual running. So, not knowing what was installed, nor the size of the spaces you are trying to cool/heat, it's anyone guess why you bill jumped. More info would be nice. So my comments are based only on what I've seen you post in the forum -

In going from running a window unit, daytime only and not cooling the upper level, and now you're cooling both levels, you are essentially adding 2x the cooling demand.

The unit efficiency will vary and give better or worse electrical demands, and that depends on what SEER rating was installed. The other part of this equation relates to whether the installer used 1 compressors for multiple indoor blower units. If the compressor( the outdoor unit) is slightly undersized it will work harder. Hoping your installer did correct sizing on your system.

And, keep in mind ,when making these types of purchases, it's easy to want to save money and drop to min. requirements, or use lesser SEER rated units, which may reduce costs up front ,but won't provide the best efficiency during operations.

Can you post your homes square footage and the compressor unit size the installer. And, if you don't want to, then at least got look up the sizing charts for these units - it's not terribly hard to decipher.

We installed a unit in a 1970's home, which btw is a rather poorly insulated house. Using them for cooling day + night, (set at 72 degrees) reflected in an increase of near +28% on our electric bill, but we anticipated that based on the unit size and their SEER ratings.

 

SLdiy2020 I was comparing the wrong months, as I explained in post #10, however I'll probably be able to compare better this coming summer. To answer your questions, my house is 1300SF and the condenser unit is a Fujitsu 5 port 45K BTU condenser. My house is a 50's poorly insulated home also.