Guidance for selecting mini split for 24x24

[Herms21]

Hello everyone,

Been a lurker for quite some time but this is my first post here. I know this has been a heavily discussed topic and have searched plenty here and elsewhere online but would like to see if I'm on the right track somewhat. I have been going down the rabbit hole of wanting to install a mini split in my garage mainly for the cooling aspect but also for heat. I live in north central ND so it's cold in the winter and stupid hot in the summer. I currently have a mr heater 50K LP unit that i installed and have been using for the past two years and has worked fine. My intent is to install a mini split as my main heating and cooling unit and then have the LP unit as secondary heat when it gets super cold out of see how a mini split would perform and learn when to use what and at what temps. Does anyone else currently do this and how pleased are you with the results. My garage is 24x24 with 9' sidewalls and R13 batts with somewhere around R50+ in the ceiling and my 16' door is insulated as well. Currently am taping and mudding in preparation for paint. I have been looking at a 240v Della 18K unit and then purchasing the required tools to do the install myself. Is this a sound plan? Please let me know if I need to provide any other information regarding this application. I should add that I maintain 45* in the winter unless I plan to be out there but if the mini split would perform well enough and not be too costly i would maybe up that temp some also. In the summer with cooling I would only operate it as needed also.

Any input/guidance would be greatly appreciated. Thanks

 

[Mike007]

Sounds like a good plan. I have a similar garage. I'm in the NE. I cool it with an 18K BTU thru-wall unit. I probably could get away with less capacity, but I don't leave it on all the time. The extra capacity helps bring it down a little faster.

I heat it with a 15', 25k BTU tube heater. I've been able to maintain 62* when it's been 7* outside.

 

[pcmeiners]

It will be much cheaper to heat totally with an efficient minisplit then supplementing low temperature heat with an LP heater. With N Dakota winters you would likely need a low temperature minisplit, they can do 100% of rating at -26 degrees. Also for that size
garage a 12k would be more than enough.

https://www.goodlifehvac.ca/images/Fujitsu_LZ_Series.pdf

Check out this spreadsheet, exchange the spreadsheet variables with yours.....
For a very efficent minisplit, as in the above examples, use 400% efficiency 13.8 HSPF
as variables. My minisplit cost would be $8/million BTU @.11/kw, Propane $27/million

Heating Fuel Comparison Calculator​

 

[Herms21]

Sounds like a good plan. I have a similar garage. I'm in the NE. I cool it with an 18K BTU thru-wall unit. I probably could get away with less capacity, but I don't leave it on all the time. The extra capacity helps bring it down a little faster.

I heat it with a 15', 25k BTU tube heater. I've been able to maintain 62* when it's been 7* outside.

thanks for the reply. I know there is not a one size fits all cause every application is different. Just can't decide on what size of one to ultimately go with because I know bigger isn't always better in the hvac world either. But as you pointed out bigger might be better for my application also as it won't be on constantly so the recovery time would be quicker.

 

[Herms21]

It will be much cheaper to heat totally with an efficient minisplit then supplementing low temperature heat with an LP heater. With N Dakota winters you would likely need a low temperature minisplit, they can do 100% of rating at -26 degrees. Also for that size
garage a 12k would be more than enough.

https://www.goodlifehvac.ca/images/Fujitsu_LZ_Series.pdf

Check out this spreadsheet, exchange the spreadsheet variables with yours.....
For a very efficent minisplit, as in the above examples, use 400% efficiency 13.8 HSPF
as variables. My minisplit cost would be $8/million BTU @.11/kw, Propane $27/million

Heating Fuel Comparison Calculator​

you think a 12k would be sufficient enough for my application running at a constant for heat and then running as needed in the summer months? maybe they run cheap enough that i could run it in the summer months and not even think about it.

 

[pcmeiners]

In the winter and summer you would program the unit to lower the temperature at night, then bring the temperature to a more comfortable level during use hours.
If you read other posts I made, I pressently have a 12k fujitsu heating and cooling my 30 x 36 foot garage, and temporarily cooling my attached ranch home, with a small fan pushing cold air from the garage to the home area. The garage is set for 70 degrees, the home gets to 74-76 at the far end. As to heat, it got to 7 degrees this winter, the minisplit was cycling on and off occasionally so it was not even working hard at that temperature. Garage is r13 walls, roughly R20 ceiling, 2 garage doors, 2 windows, 36' common wall between garage/house.

 

[PoorUB]

you think a 12k would be sufficient enough for my application running at a constant for heat and then running as needed in the summer months? maybe they run cheap enough that i could run it in the summer months and not even think about it.

12K will definately cool it, but it might not heat it. You need to be aware of the heating specs for the units you are looking at. Some will heat to -25F, but the capacity drops of as the outdoor temp falls. You might get 12K of heat at 10F, but as the temp falls the capacity falls and it might only put out 8K at -25F. Again, you need to look at specs for what ever unit you consider. Some units will not heat below maybe 5F, some will heat much lower.

Also the 400% the other post stated is probably at 40F. Again the capacity falls off as the outdoor temp falls and at the lowest the unit will heat it is putting out 1 to 1. So if it uses 1,000 watts of electricity, it only puts out 1,000 watts or around 3,400 BTU of heat.

I am just tossing out random numbers here so real life will be different, but the concept is the same.

 

[pcmeiners]

The Fujitsu low temp units I posted above will put out 123% of rating at -20, and the 400%(COP4) was the average efficiency of the high efficiency low temp units linked.
PoorUB is correct, the true output of most manufacturers minisplits varies considerably, much of the stated specs are hyped by many manufacturers to various degrees. You need to research carefully the units you want to purchase.
Efficiency does fall at very low temperatures , especially with standard inexpensive units... you get what you pay for to a degree.

AHRI Certificate for a 12k Fujitsu unit linked above, show performance data at multiple temps.

ASHP

ashp.neep.org

 

[Herms21]

12K will definately cool it, but it might not heat it. You need to be aware of the heating specs for the units you are looking at. Some will heat to -25F, but the capacity drops of as the outdoor temp falls. You might get 12K of heat at 10F, but as the temp falls the capacity falls and it might only put out 8K at -25F. Again, you need to look at specs for what ever unit you consider. Some units will not heat below maybe 5F, some will heat much lower.

Also the 400% the other post stated is probably at 40F. Again the capacity falls off as the outdoor temp falls and at the lowest the unit will heat it is putting out 1 to 1. So if it uses 1,000 watts of electricity, it only puts out 1,000 watts or around 3,400 BTU of heat.

I am just tossing out random numbers here so real life will be different, but the concept is the same.

thanks for your reply. i still need to familiarize myself some with these no doubt but have looked at the specs as far as what their operating temps are with the understanding that there is some fall off as temp drops as well.

Pioneer Low-Ambient 18,000 BTU 1.5 Ton 19 SEER Ductless Mini Split Wall Mounted Inverter Air Conditioner with Heat Pump 208/230V WYT018GLFI19RL - The Home Depot

Cool down your space with this Low-Ambient 18,000 BTU 1.5 Ton 19 SEER Ductless Mini Split Wall Mounted Inverter Air Conditioner with Heat Pump 208/230V. It features a built-in timer, freeze protection

www.homedepot.com

that is what i’m currently leaning towards more so at the moment

 

[Herms21]

The Fujitsu low temp units I posted above will put out 123% of rating at -20, and the 400%(COP4) was the average efficiency of the high efficiency low temp units linked.
PoorUB is correct, the true output of most manufacturers minisplits varies considerably, much of the stated specs are hyped by many manufacturers to various degrees. You need to research carefully the units you want to purchase.
Efficiency does fall at very low temperatures , especially with standard inexpensive units... you get what you pay for to a degree.

AHRI Certificate for a 12k Fujitsu unit linked above, show performance data at multiple temps.

ASHP

ashp.neep.org

appreciate your reply again. if i were doing this install in my house i probably would shell out more money for a better unit. i linked in my post above the unit i'm considering the most at this time.

 

[pcmeiners]

Check the specs of my linked Fujitsu units against the Pioneer

Pioneer spec sheet....

https://images.thdstatic.com/catalog/pdfImages/7f/7fe9975b-df21-4e9e-8e95-5d6149263479.pdf

AHRI certificate....

https://www.pdhvac.com/site/downloads/certificates/certificate_WYS018GMFI20RL.pdf

The AHRI sheet shows the absolute minimum of data, AHRI certificates use data provided by manufacturers, and the data is not checked. With almost no data you need to wonder why, it is a joke to publish such little data. So with the data given you can not see what the performance is, likely rather poor at lower temps or pioneer would have been happy to publish the data.

Efficiency calculator.....Gives an idea of the energy savings with different SEER and HSPF numbers. Also since you live in ND, the SEER number is not the important rating, it is the HSPF number as the heating cost are much higher than the cooling costs in ND.

https://www.energystar.gov/sites/default/files/asset/document/ASHP_Sav_Calc.xls

 

[desmopower]

The Fujitsu low temp units I posted above will put out 123% of rating at -20, and the 400%(COP4) was the average efficiency of the high efficiency low temp units linked.
PoorUB is correct, the true output of most manufacturers minisplits varies considerably, much of the stated specs are hyped by many manufacturers to various degrees. You need to research carefully the units you want to purchase.
Efficiency does fall at very low temperatures , especially with standard inexpensive units... you get what you pay for to a degree.

AHRI Certificate for a 12k Fujitsu unit linked above, show performance data at multiple temps.

ASHP

ashp.neep.org

I thought the 18k Mitsubishi I installed was efficient. I can hardly believe the Fujitsu numbers... Wow. It's not even close.
The Mitsubishi appeared efficient but the Fujitsu is half the operating cost for heating according to the savings calc worksheet you shared.

Best I can tell the Fujitsu is also about 50% less expensive than a Mitsubishi H2i? How can it be that much better, and that much less expensive?

I am comparing the 15k Fujitsu LZB to the Mitsubishis. It looks like at least from the listings I see the 18k and up Fujitsu are not as efficient and this product line maxes out at 15k?

Completely happy with my unit but wish I had read this three years ago!